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Competition in an invaded rodent community reveals black rats as a threat to native bush rats in littoral rainforest of south‐eastern Australia
Journal of Applied Ecology
Abstract
1. Interspecific competition is a recognized but under-studied mechanism by which invasive species affect native fauna.
2. We experimentally reduced populations of the introduced black rat Rattus rattus in relatively undisturbed littoral rainforest in south-eastern Australia to test its competitive impact on populations of the native bush rat Rattus fuscipes.
3. Removal of R. rattus resulted in significant and sustained increases in populations of the native rodent due to immigration, juvenile recruitment and increases in residency of females. Native juveniles were particularly vulnerable to R. rattus, being largely absent from untreated populations despite indications of breeding in females, but responding rapidly to their removal.
4. The absence of changes in body condition and reproduction of adult R. fuscipes with long-term removal of R. rattus suggests that direct interference by R. rattus rather than competition for resources best explains the low densities and poor juvenile recruitment of R. fuscipes.
5. The behavioural dominance of R. rattus was not due to an inherent competitive ability because they did not re-establish post-removal as expected if competition was asymmetrical. Instead, competitive dominance seemingly shifted to R. fuscipes with changes in residency status of populations. Improved survivorship among native females reveals that they were particularly important in establishing resident populations following removal of R. rattus.
6.Synthesis and applications. These findings identify R. rattus as a significant competitive threat to native R. fuscipes. Removal of invasive rodents and active conservation of common native species is recommended to forest managers based on the potential for R. fuscipes to prevent re-invasion subsequent to pest control efforts and maintain invasion resistance.
... Although Chiew Larn is technically within the native range of R. tiomanicus, 24 in this context, the species is behaviorally characterized as invasive. Its habitat preferences include urban areas, selectively logged forest, oil palm plantations, and other areas of intermediate land-use intensity, [25][26][27] whereas the original vegetation found in Chiew Larn prior to insularization was primary, undisturbed lowland evergreen forest. This renders R. tiomanicus as a prime beneficiary of the post-isolation conditions at Chiew Larn. ...
... 40 Interference competition has often been observed between Rattus spp. and native rodents, 26,41 with dominance through direct physical contest and aggression often favoring larger-bodied species. 12 This may in part explain the continued, although declining, presence of Mü ller's rat Sundamys muelleri detected on two Chiew Larn islands in 2020, down from 6 islands in 1994, whereas all other smaller bodied species had been extirpated. ...
... The key management recommendation to suppress Rattus populations would be to prevent landscape fragmentation in the first place as these rodents are human-commensals and are less likely to proliferate within large tracts of undisturbed primary forest. [25][26][27] Previous studies in other archipelagic landscapes also suggest that retaining forest patches larger than 475 ha can support species-rich vertebrate communities containing R80% of the local fauna. 62 Maintaining >40% forest cover at the landscape scale and a high-quality matrix between patches would further ensure a nearly full complement of species. ...
As tropical forests are becoming increasingly fragmented, understanding the magnitude and time frame of biodiversity declines is vital for 21st century sustainability goals. Over three decades, we monitored post-isolation changes in small mammal species richness and abundance within a forest landscape fragmented by the construction of a dam in Thailand.¹,² We observed the near-complete collapse of species richness within 33 years, with no evidence of a recolonization effect across repeatedly sampled islands. Our results further revealed a decline in species richness as island size decreased and isolation time increased, accelerated by the increasing dominance of the ubiquitous Malayan field rat, Rattus tiomanicus. This species was already hyper-abundant on smaller islands in the initial surveys (1992–1994, 66% of individuals) but became monodominant on all islands, regardless of island size, by the most recent survey (2020, 97%). Our results suggest that insular forest fragments are highly susceptible to rapid species loss, particularly due to the competitive nature of Rattus accelerating the rate at which extinction debts are paid. To mitigate these impacts, reducing the extent of habitat degradation, as triggered by fragmentation and exacerbated by isolation time, can help to sustain native biodiversity while averting Rattus hyper-abundance.
... Black Rat numbers were reduced by 90% on two 1-ha trapping grids in the northern section of the reserve between April and November. However, there was no corresponding increase in Bush Rats, unlike a similar study at Jervis Bay (Stokes et al. 2009), where a 70% reduction in Black Rat numbers on identical trapping grids resulted in a large increase in Bush Rat numbers and a shift in competitive dominance to Bush Rats, preventing Black Rats from re-establishing. ...
... Each grid was rectangular and consisted of 30 (5 x 6) trappoints 18 m apart. The grids are similar to those used in another study of Bush Rat/Black Rat interaction at Jervis Bay (Stokes et al. 2009), allowing specific comparisons to be made between the two studies. The southern end of the south-eastern grid was the site of the definite Bush Rat hair record in February 2013 (Smith and Smith 2013). ...
... In a similar study of interaction between introduced Black Rats (Rattus rattus) and native Bush Rats (Rattus fuscipes) in littoral rainforest at Jervis Bay, Stokes et al. (2009) reduced Black Rat numbers by 70% on five 1-ha trapping grids and compared the results with five untreated trapping grids. Removal of Black Rats resulted in significant and sustained increases in Bush Rat populations on the removal grids, with no corresponding increase on the untreated grids. ...
Small to medium-sized native ground-dwelling mammals are now extremely rare on the Cumberland Plain of Western Sydney. Following a hair tube record of the native Bush Rat (Rattus fuscipes) in Nurragingy Reserve in February 2013, we have been engaged by Blacktown City Council to undertake a Bush Rat recovery project in the reserve from January to December 2015. Council obtained funding for the project from Greater Sydney Local Land Services, through the Commonwealth Biodiversity Fund. The project involved: live-trapping and hair-tubing for Bush Rats to confirm their presence and to determine their distribution in the reserve; trapping and removal of introduced Black Rats (Rattus rattus) in the northern section of the reserve (competition and interference from Black Rats is known to be a major factor in depressing Bush Rat populations); and monitoring of introduced Red Fox (Vulpes vulpes) activity and diet in the reserve to assess how much of a threat they pose to Bush Rats.
The only Bush Rat records obtained during the study were tentative identifications from two hair-tube samples in April 2015. Despite a large live-trapping effort (2730 trap-nights over four seasons), we were unable to catch any Bush Rats to positively confirm their presence in the reserve. Black Rat numbers were reduced by 90% on two 1-ha trapping grids in the northern section of the reserve between April and November. However, there was no corresponding increase in Bush Rats, unlike a similar study at Jervis Bay (Stokes et al. 2009), where a 70% reduction in Black Rat numbers on identical trapping grids resulted in a large increase in Bush Rat numbers and a shift in competitive dominance to Bush Rats, preventing Black Rats from re-establishing.
There are two possible explanations for the failure of Bush Rats to respond to culling of Black Rats at Nurragingy: there is, in fact, no Bush Rat population in the reserve (the hair identifications were in error or the population has since died out); or else the population is so small that it was unable to respond as rapidly and effectively as the Bush Rats at Jervis Bay. Bush Rats were much more numerous at Jervis Bay than at Nurragingy, even before removal of Black Rats, occurring at densities of 2-4 animals per 1-ha grid in the year before Black Rats were culled, whereas no Bush Rats were caught at Nurragingy at any stage during the study. If there is still a Bush Rat population at Nurragingy, it is tiny, making it hard to detect even with intensive trapping. The hair-tube success rate for Bush Rats was only 0.07%. Assuming that this is also the success rate for live-trapping Bush Rats in the reserve, it would mean that 4277 trap-nights would be required for a 95% probability of catching a Bush Rat, and 6576 trap-nights for a 99% probability. Thus, with such a small population, our live-trapping effort of 2730 trap-nights was still not enough to confidently conclude that there are no Bush Rats in the reserve.
Regarding methodology, the Nurragingy study showed that bandicoot-size cage traps are far more effective at catching Black Rats than standard Elliott traps. The trap-night success rate for Black Rats was more than 14 times greater for cage traps than for Elliott traps (4.3% versus 0.3%). However, Elliott traps are highly effective for Bush Rats, as shown in many studies elsewhere by ourselves and others. Elliott traps can therefore be used for targeted trapping of Bush Rats without the problem of too many captures of Black Rats rendering the traps unavailable for Bush Rats.
The study also provided data on Red Foxes (Vulpes vulpes) in Nurragingy Reserve and how much of a threat they pose to any Bush Rat population in the reserve. Foxes were regularly active at night in the northern section of the reserve, being recorded there on at least 82% of nights during the study. The potential hunting pressure from foxes is high. However, the diet of the local foxes, from analysis of their scat contents, was found to be very mixed, including large quantities of seeds and other plant material and many invertebrates, as well as reptiles, birds and a variety of mammals, including mice, rats, rabbits, possums and deer (presumably feeding on carrion as well as taking live prey). The foxes were preying on rats, but probably opportunistically rather than specifically targeting them, since rats were represented in only 14% of the fox scats analysed. Rabbits were the most common mammalian prey (26% of scats) rather than rats. Predation by foxes, together with cats and dogs (both of which appear to be hunting in the reserve to some extent), poses a threat to any Bush Rat population in the reserve, particularly as the loss of just one or two animals could be critical for such a small population. However, Black Rats pose a greater threat, as indicated by the Stokes et al. (2009) study at Jervis Bay, and should be the management priority in any Bush Rat recovery program.
Following on from this study, the next stage for Bush Rat recovery in Nurragingy Reserve should be to confirm that there is still a Bush Rat population in the reserve. This study has demonstrated that bandicoot-size cage traps are an effective method of reducing Black Rat numbers. Fox control is also highly desirable, but for Bush Rat recovery it is secondary to control of Black Rats. The fox control method would be baiting rather than shooting, since Blacktown Police are unwilling to allow shooting in the reserve. If foxes are successfully controlled there may be an increase in the rabbit population and so rabbit control may need to be undertaken in conjunction with fox control. However, before undertaking further recovery actions, it is necessary to confirm that there is a Bush Rat population to recover, and to determine its distribution in the reserve. Since the population, if present, is very small, it will require intensive trapping before it can be concluded with 95% probability (1547 more trap-nights in addition to this study) or 99% probability (3846 more trap-nights) that Bush Rats are not present. Trapping should be carried out using standard Elliott traps since these are effective for Bush Rats but are avoided by Black Rats.
... Despite a long and close association with human built environments, black rats can exploit naturally vegetated areas (Cox et al. 2000), often becoming a significant invasive species (Banks and Smith 2015). In ecosystems containing native rodent species, however, black rats can be competitively excluded (Stokes et al. 2009) and thus restricted to human built environments. Therefore, it remains unclear how R. rattus (and commensals more generally) would assort when given a free choice between urban and native habitats. ...
... Despite the preference for bushland evidenced in this study, R. rattus is generally uncommon in large natural areas in Australia. It is highly likely that their invasion of bushland beyond cities is severely restricted by competition with native Rattus species such as R. fuscipes (Stokes et al. 2009), which is notably absent from the peri-urban forests used in the present study (Banks et al. 2011). This is likely an example of incumbent replacement (Rosenzweig and McCord 1991), where the local extinction of a well-adapted competitor has left vacant niche space able to be easily occupied by the invasive R. rattus. ...
Human commensal species are thought to depend so closely on resources provided by humans that they are effectively ‘natives' of urban environments. However, while their adaptations to urban existence are well understood, their ecology and habitat choices have not been closely examined. This study investigated the habitat preferences of the archetypal commensal species, the invasive black rat Rattus rattus, at the urban–bushland interface in Sydney, Australia, and modelled the results using isodar analysis. Unexpectedly, we found evidence that rats perceived bushland as a more resource‐rich habitat compared to urban areas, resulting in higher rat abundance in bushland areas. Resultant spillover of commensal species into native vegetation may pose acute ecological risks in the future, yet management of commensal pests remains focused on urban areas. Ultimately, these findings highlight the complex nature of commensal ecology, suggesting that adaptation to human coexistence does not necessarily lead to a preference for human‐modified landscapes. We suggest that inter‐specific interactions with competitors, or the lack thereof, likely modulate the habitat preferences of commensals.
... Therefore, selective lethal trapping may be considered as a more ecologically-friendly option, and in areas where the use of rodenticides is unlawful or not accepted by local communities, the only viable management approach (Ogden and Gilbert 2008). While control by trapping has proven successful to suppress rodent numbers to low densities in a short-term commitment (Stokes et al. 2009;King et al. 2011;Pender et al. 2013), we believe that there is a scope for optimise rodent trapping strategies in order to enhance project sustainability and achieve long-term ecological outcomes. ...
... superba released from rat predation pressure (Pender et al. 2013). In Australia, a rat removal experiment conducted with live traps (first intensively for two months; then with three-days-long capture sessions every 4-8 weeks) maintained black rat densities 3.3 times lower (3.7 ind.ha -1 ) than untreated sites, and was associated with a substantial increase in the populations of native rat R. fuscipes (Stokes et al. 2009). These examples, with many others, show that rat control operations can be highly beneficial for native biodiversity (Duron et al. 2017), although the optimal level of management required to ensure the long-term persistence of vulnerable prey is often not known. ...
On large inhabited islands where complete eradication of alien invasive rodents through the use of poison delivery is often not practical or acceptable, mechanical trapping may represent the only viable option to reduce their impact in areas of high biodiversity value. However, the feasibility of sustained rodent control by trapping remains uncertain under realistic operational constraints. This study aimed to assess the effectiveness of non-toxic rat control strategies through a combination of lethal and live-trapping experiments, and scenario modelling, using the example of a remote montane rainforest of New Cal-edonia. Rat densities, estimated with spatially-explicit capture-recapture models, fluctuated seasonally (9.5-33.6 ind.ha-1). Capture probability (.01-.25) and home range sizes (HR 95 , .23-.75 ha) varied greatly according to trapping session, age class, sex and species. Controlling rats through the use of lethal trapping allowed maintaining rat densities at ca. 8 ind.ha-1 over a seven-month period in a 5.5-ha montane forest. Simulation models based on field parameter estimates over a 200-ha pilot management area indicated that without any financial and social constraints, trapping grids with the finest mesh sizes achieved cumulative capture probabilities > .90 after 15 trapping days, but were difficult to implement and sustain with the local workforce. We evaluated the costs and effectiveness of alternative trapping strategies taking into account the prevailing set of local constraints, and identified those that were likely to be successful. Scenario modelling, informed by trapping experiments, is a flexible tool for informing the design of sustainable control programs of island-invasive rodent populations, under idiosyncratic local circumstances.
... Human development has long been associated with biodiversity loss on islands (Brooks, Pimm & Collar, 1997;Sodhi et al., 2008). Given the inherently limited area of islands and their proximity to the sea, conservation of island biodiversity now must also consider habitat loss related to rising sea level (Fordham & Brook, 2010;Maschinski et al., 2011). ...
... If invasive species on islands are more resilient than native wildlife to environmental stressors, then anthropogenic global change is likely to exacerbate their detrimental effects on native wildlife (Holmes et al., 2019). In addition to causing direct mortality via predation (Altizer, Foufopoulos & Gager, 2001;Medina et al., 2011), invasive species may spread diseases or outcompete native species for the same resources (Stokes et al., 2009). In the latter case, an understanding of how animals use their environment across multiple scales, is requisite to understand potential competition between native and invasive island wildlife (Lindenmayer et al., 2008). ...
Wildlife is increasingly threatened by a suite of anthropogenic factors including climate change, habitat loss from human development, and invasive species. These threats are particularly pronounced on islands where species are more likely to go extinct. To better understand how native and invasive species on islands might respond to these threats, we compared habitat use between the endangered silver rice rat (SRR) Oryzomys palustris natator and invasive black rat Rattus rattus across multiple scales. We used a specialized camera trap design to survey rodents across the Lower Florida Keys, USA, a region vulnerable to emerging threats, such as rising sea level, and persistent threats, such as human development. Additionally, we used a novel modeling approach to investigate temporal variation in rodent activity as a function of lunar tides. Silver rice rat occurrence was greatest in regularly inundated mangroves that could potentially increase in extent as sea level rises. Black rats were widespread and often co‐occurred with SRR, but we observed temporal resource partitioning between these species, which suggests competition may be limited. Of the stressors we investigated, we conclude that contjaceinued urban development is the most substantial threat to SRR, and potentially other island species. Our results highlight island species’ disparate responses to different aspects of global change and the potential conservation opportunities that may result.
... Although the negative impacts of black rats in mainland Australian systems have, until recently, been poorly understood compared to elsewhere (Banks and Hughes 2012), we now understand that they compete with native rodents (Stokes et al. 2009), have negative predatory effects on bird nests (Smith et al. 2016) and act as hosts of diseases (Banks and Hughes 2012). On the other hand, there is some evidence that black rats can act as pollinators. ...
... Furthermore, black rats can show aggression towards smaller mammals in competitive interactions (Harris and Macdonald 2007;Stokes et al. 2009). Therefore, it is also possible that interference competition at inflorescences between black rats and small native species will limit the natives' ability to pollinate. ...
Alien species are a major cause of species extinctions globally and the effects of introductions can become substantial, especially once aliens become entrenched and impossible to eradicate. Some entrenched aliens may assume niches of extinct native species that are functionally similar, but the capacity of an alien to perform specialised ecological processes is unknown. Here we examine the potential for the alien black rat (Rattus rattus) to effectively pollinate native Banksia ericifolia in heath at North Head, Sydney where endemic mammalian pollinators such as brown antechinus (Antechinus stuartii) and eastern pygmy-possums (Cercartetus nanus) had been locally extinct prior to recent reintroductions. Using artificial inflorescences, we compared the use of inflorescences, visit frequency and duration of alien black rats to reintroduced natives according to the stem diameter of the inflorescence. Black rats were the most frequent visitor and they spent similar or more time at artificial inflorescences as natives, but they also spent more time visiting inflorescences with thicker stem diameters. In contrast, the native mammals visited artificial inflorescences regardless of the stem thickness. We suggest that, as black rats are heavier than the native mammals, this could limit their capacity as substitute pollinators of B. ericifolia. This finding shows the importance of understanding the extent of the benefits of aliens before relying on them as functional replacements for extinct natives.
... Also, on Pearl Island (New Zealand), Harper (2006) found that the adults (64%) were more surveyed than the other age classes. Stokes et al. (2009) found a marked capture of adults than the other classes during the four seasons. By contrast, Tobin et al. (1994) found that the sub-adults accounted for 31% of the capture. ...
... 1 individuals / month) and females (1.3 ± 1 individuals / month). Subsequently, a decrease was noted until December 2016 (♂ = 1 ± 0.8, ♀ = 0.3 ± 0.5). Just after, an increase in captures was observed until August 2017 for males (11.3 ± 3.8) and September for females (8.3 ± 2.8). These results were different with those recorded by different authors.Stokes et al. (2009), reported the importance of males in October and November. On the other hand, ...
The counting and characterization of the black rat population in 4 stations (2 palm groves and 2 storage sites) located in the region of Touggourt (southern Algeria) were studied by comprehensive trappings, following the use of BTS traps. These allowed the capture of 492 individuals through a trapping effort of 936 trap nights. The palm groves (n = 301) were more infested than the storage sites (n = 191). So for the densities, the latter are more infested (0.49 and 0.97 ind./m2) than the palm groves (0.04 ind./m2). On the other hand, June (16.3 ± 7.3), July (17 ± 7.0), August (18 ± 7.5) and September (18.5 ± 5.8) were characterized by the highest captures. The sex ratio showed a predominance of males in both palm groves (185♂ / 116♀) and storage sites (115♂ / 76♀). The adults (33.5%) and the sub-adults (28.6%) were the most important in the black rat.
... Interactions between native Rattus species and the introduced black rat in peri-urban settings suggest that the former are competitively superior in essentially 'natural' habitats but that the latter win out when habitat modification becomes more extreme (Stokes et al. 2009;Banks and Hughes 2012). Similarly, as discussed under Hypothesis 2, the house mouse appears to competitively superior to similar-sized native rodents such as Pseudomys novaehollandiae only under early successional stages after heavy disturbance, and to lose that advantage as native vegetation re-establishes. ...
... Other opportunities to test this hypothesis abound in Australia, including many situations where the introduced house mouse competes with other similar-sized Pseudomys species in both mesic and xeric environments; and others where the black rat competes with native Rattus (e.g. R. fuscipes; Stokes et al. 2009). Among the native rodents, New Guinea presents numerous opportunities to study the interaction among closely related pairs or sets of species that occur in altitudinal replacement series, often with bands of sympatric co-occurrence and direct competition. ...
Many conservationists argue that invasive species form one of the most important threats to ecosystems the world over, often spreading quickly through their new environments and jeopardising the conservation of native species. As such, it is important that reliable predictions can be made regarding the effects of new species on particular habitats. This book provides a critical appraisal of ecosystem theory using case studies of biological invasions in Australasia. Each chapter is built around a set of 11 central hypotheses from community ecology, which were mainly developed in North American or European contexts. The authors examine the hypotheses in the light of evidence from their particular species, testing their power in explaining the success or failure of invasion and accepting or rejecting each hypothesis as appropriate. The conclusions have far-reaching consequences for the utility of community ecology, suggesting a rejection of its predictive powers and a positive reappraisal of natural history.
... Black rats are larger than both of these Tasmanian endemic small mammals, and have occurred in Tasmania for at least 200 years (Menkhorst and Knight 2001). They negatively affect native fauna (especially small mammals) in other ecosystems in Australia (Stokes et al. 2009) and worldwide (King 1984, Banks andHughes 2012). ...
... Removal methods are a potential option for addressing some of the above questions. For example, in a different system, the abundance of native bush rats Rattus fuscipes increased following the removal of black rats, and black rats were unable to re-establish following increases in the abundance of bush rats (Stokes et al. 2009). ...
Effective conservation management requires an understanding of the source and direction of
the many interactions that occur within ecological communities. Without this understanding, management
interventions such as control or eradication of introduced species can have unexpected and undesirable
outcomes. One of the challenges for wildlife managers is to garner relevant information for their site of
management. In this paper we describe how images of mammals captured on remote cameras can be used
to uncover behavioral interactions that can in turn help to identify and prioritize areas for more explicit
research or management. Our cameras were set repeatedly at four sites over three years in Tasmania,
Australia, and we used a series of generalized linear mixed models to interpret relative changes in count
data of three species of small mammals: the introduced black rat Rattus rattus, and the native long-tailed
mouse Pseudomys higginsi and swamp rat Rattus lutreolus velutinus. We also included two potential
predators, the introduced feral cat Felis catus and the native Tasmanian devil Sarcophilus harrisii. We found
that counts of the two species of native small mammals were correlated positively with each other, that
swamp rats had a negative effect on black rats, and that black rats had a negative effect on the long-tailed
mouse. Devils were important effects in most small mammal models. Despite their effect probably being
underestimated by the remote camera survey method, feral cats were included in models for the long-tailed
mouse. On the basis of the inclusion of native and both species of introduced mammals in long-tailed
mouse models, we propose that the long-tailed mouse is a priority for further research. This research
should clarify the competitive dominance and predatory pressure exerted by the black rat and feral cat,
respectively, on this species, and also the potential for management of either introduced species to increase
the impact of the other. We conclude that remote cameras can help to uncover cryptic or unsuspected
interactions within ecological communities, and hence provide an informed basis for developing targeted
research questions to increase the effectiveness of wildlife management.
... In fact, abundance increased inversely with farm cattle food and mosaic of crop covers in the landscape, indicating that this species likely avoids sites with higher abundance of commensal species such as R. norvegicus that could prey on it. In this respect, the more dominant behavior of commensal species could severely affect the abundance of native rodent species (Harris 2009;Stokes et al. 2009;Feng and Himsworth 2014). Moreover, some studies indicate that this species selects patches of herbaceous vegetation in agroecosystems (Busch et al. 1997;Busch 2006, 2010;Lovera et al. 2019)-however, those studies were conducted at the microhabitat scale, indicating that the response patterns of A. azarae could be "scale-dependent" (Turner 1989) and that, at the farm scale, the proportion of area occupied by medium or tall herbaceous vegetation may not be decisive for this species. ...
Natural processes and patterns are altered by human activity at different spatial and temporal scales, affecting species assemblages and population traits, modifying mechanisms or regulating dynamics at different scales. However, little is known about the influence of landscape structure on small mammal assemblages and populations on farms. Thus, in this work, we aimed to study the effect of landscape and environmental characteristics at the farm scale on the assemblage and populations of native and introduced small mammals in pig and dairy farms located in Buenos Aires province, Argentina. Our results showed that farms in contexts of higher environmental diversity at the landscape scale have higher species richness. Our results also showed that variations in assemblage composition were associated with the quantity of water body surfaces, cattle food, small mammal refugia, and impervious surfaces at the farm scale—and with woodland, grassland, and natural vegetation cover at the landscape scale. The abundance of commensal murids was higher on farms near towns, with higher vegetation cover at the farm scale and/or in landscape contexts with fewer crops. The abundance of Akodon azarae was higher on farms with a lower amount of cattle food at the farm scale and crop patches in the landscape. The abundance of Didelphis albiventris was higher during spring on farms with a low proportion of bare ground, while that of Lutreolina crassicaudata was higher on farms with high vegetation cover and a lower number of water body surfaces. These results show the relevance of multiscale determinants in the development of ecologically based management strategies to control pest small mammals.
... If at a landscape scale, the habitat is managed so that it is favorable to R. everetti, then perhaps the rate of growth of R. tanezumi populations may be substantially reduced. These results complement the findings of studies in eastern Australia, indicating that the native bush rat, Rattus fuscipes, can outcompete the introduced black rat, Rattus rattus, in a littoral rainforest (Stokes et al., 2009). These findings form the basis of a study to reintroduce bush rats in urban Sydney to examine the interaction between these two species at an urban bushland boundary (Banks and Smith, 2015). ...
... Here, removal of boneseed may have imparted increased predation risk, which resulted in a reduction in the use of these sites by mice (Arthur et al. 2004). The role of retained structure supporting small mammals is likely to apply to native species (Rendall et al. 2019;Chadwick et al. 2022;White et al. 2022), and where native species overlap with house mice, they are likely to outcompete them (Stokes et al. 2009;Rendall et al. 2019). House mouse was the only small mammal species captured throughout the study, with no native species observed. ...
Weed management often involves active measures to minimize or prevent negative impacts on local wildlife. Approaches include retention of weed structure, altered timing of management to avoid wildlife breeding seasons, and/or the gradual removal of weeds in conjunction with revegetation of native plants. We assess the short-term impacts of retaining some structural complexity offered by weeds post management to birds and a small mammal in two ecosystems. One ecosystem involves a wetland with an emergent weed, the other a woodland with a sub-canopy weed. Before-After-Reference-Control-Impact experiments revealed that assemblage and activity of birds and an invasive small mammal-the only captured in numbers during our study-were minimally altered by weed management. In some instances, we observed the activity of native bird species favoring the use of weeds. Evidence also suggested the weedy sites supported different species assemblages compared to reference sites without weeds. This study indicates that, in the short-term, retention of weed structure can sustain birds and an exotic mammal that use weeds.
... Invasive rodents have numerous detrimental impacts on invaded ecosystems, resulting from both direct (e.g., competition, predation, destruction through digging and gnawing) and indirect (e.g., transmission of diseases, reductions in pollination efficiency or nutrient recycling) mechanisms (e.g., Stokes et al., 2009;Wardle et al., 2012;Diagne et al., 2016;Russell et al., 2020). These rodents have been implicated in the decline and extinction of native biota on numerous islands worldwide (e.g., Jones et al., 2008;St Clair, 2011;Sainsbury et al., 2020). ...
Background
Rodents are among the most notorious invasive alien species worldwide. These invaders have substantially impacted native ecosystems, food production and storage, local infrastructures, human health and well-being. However, the lack of standardized and understandable estimation of their impacts is a serious barrier to raising societal awareness, and hampers effective management interventions at relevant scales.
Methods
Here, we assessed the economic costs of invasive alien rodents globally in order to help overcome these obstacles. For this purpose, we combined and analysed economic cost data from the InvaCost database—the most up-to-date and comprehensive synthesis of reported invasion costs—and specific complementary searches within and beyond the published literature.
Results
Our conservative analysis showed that reported costs of rodent invasions reached a conservative total of US$ 3.6 billion between 1930 and 2022 (annually US$ 87.5 million between 1980 and 2022), and were significantly increasing through time. The highest cost reported was for muskrat Ondatra zibethicus (US$ 377.5 million), then unspecified Rattus spp. (US$ 327.8 million), followed by Rattus norvegicus specifically (US$ 156.6 million) and Castor canadensis (US$ 150.4 million). Of the total costs, 87% were damage-related, principally impacting agriculture and predominantly reported in Asia (60%), Europe (19%) and North America (9%). Our study evidenced obvious cost underreporting with only 99 documents gathered globally, clear taxonomic gaps, reliability issues for cost assessment, and skewed breakdowns of costs among regions, sectors and contexts. As a consequence, these reported costs represent only a very small fraction of the expected true cost of rodent invasions ( e.g. , using a less conservative analytic approach would have led to a global amount more than 80-times higher than estimated here).
Conclusions
These findings strongly suggest that available information represents a substantial underestimation of the global costs incurred. We offer recommendations for improving estimates of costs to fill these knowledge gaps including: systematic distinction between native and invasive rodents’ impacts; monetizing indirect impacts on human health; and greater integrative and concerted research effort between scientists and stakeholders. Finally, we discuss why and how this approach will stimulate and provide support for proactive and sustainable management strategies in the context of alien rodent invasions, for which biosecurity measures should be amplified globally.
... Prey responses to predator cues may also depend on the evolutionary history of the predator-prey relationship. Invasive species pose severe risks to their native counterparts due to the absence of heritable experiences in the form of biological interactions, which include competition and predation (Dickman 1996;Stokes et al. 2009). For instance, native prey may lack adequate antipredator defenses to introduced predators (Kovacs et al. 2012;Jolly et al. 2018). ...
Prey behavioral responses to predation risk cues may vary between species; moreover, the strength of these behaviors may differ depending on risk cue. In northwestern Taiwan, we used the giving up density (GUD) framework supported with camera trap observations to test how two wild murid rodents that differ by up to fivefold in body size (striped field mouse, Apodemus agrarius, and lesser rice-field rat, Rattus losea) altered their foraging behavior depending on microhabitat characteristics (indirect predator cues) and exposure to predator odors (direct predator cues) of three felids: the native leopard cat (Prionailurus bengalensis), the introduced domestic cat (Felis catus), and the exotic bobcat (Lynx rufus). GUD was not affected by predator odors but rather by microhabitat type; rodents removed more seeds under the cover of vegetation compared to exposed food stations, which may reflect a proactive approach to avoiding high-risk areas in a heterogeneous environment. The smaller mouse, A. agrarius, spent more time foraging in experimental food patches compared to the larger rat, R. losea, irrespective of predator odor. Conversely, R. losea spent more time investigating stations and exhibiting vigilance compared to A. agrarius. Species-level differences are consistent with behavioral phenomenon that smaller, “faster” species confer more boldness compared to larger, “slower” species, which reinforces the connection between behavior and pace of life, and further elucidates how the behavior of different prey species may not be interchangeable in contexts of risk.
Significance statement
In the wild, animals eat while trying not to be eaten. Therefore, preys often change their behavior in response to risk cues, but the intricacies of these behavioral shifts can be complex and vary between species. With the use of camera trap monitoring and experimental food patches, we were able to examine fine-scale species-specific behaviors and test for dissimilarities. Two species of wild rodents did not change their foraging behavior to the addition of predator odors, but we did observe an interspecific behavioral variation. The smaller, “faster” rodent species spent more time foraging, while the larger, “slower” species spent more time vigilant with more thorough investigation. These interspecific behavioral differences likely indicate the smaller species demonstrated more boldness, whereas the larger rodent was more cautious, which is consistent with the association between pace of life (POL) and behavior.
... Most studies have focused on islands, showing R. rattus as a dominant competitor in rodent assemblages in New Zealand and Hawaii [85,86]. In addition, Stokes et al. [87] in Australia and Harris and Macdonald [88] in Galapagos have shown that R. rattus competes with the Australian bush rat (Rattus fuscipes) and the Santiago Galapagos mouse (Nesoryzomys swarthi) respectively, mainly through interference rather than resource competition. Our findings revealed that the interactions of R. rattus with native rodents are primarily aggressive. ...
The degree of temporal overlap between sympatric wild hosts species and their behavioral interac‐
tions can be highly relevant to the transmission of pathogens. However, this topic has been scantly addressed.
Furthermore, temporal overlap and interactions within an assemblage of wild rodents composed of native and intro‐
duced species have been rarely discussed worldwide. We assessed the nocturnal activity patterns and interactions
between rodent taxa of an assemblage consisting of native species (Oligoryzomys longicaudatus, Abrothrix hirta, and
Abrothrix olivaceus) and the introduced black rat (Rattus rattus) in a temperate forest from southern Chile. All rodent
species in this study are known hosts for various zoonotic pathogens.
... Interspecific associations within small mammal communities remain poorly understood. Black rats are known to negatively impact woodland bird communities (Towns et al., 2006) and compete with native species such as bush rats (Rattus fuscipes, Stokes et al., 2009). Bush rats are absent from the Gariwerd landscape, yet similar interspecific interaction could be occurring with swamp rats with unknown impacts on their persistence. ...
Refugia within landscapes are increasingly important as climate change intensifies, yet identifying refugia, and how they respond to climatic perturbations remains understudied. We use Normalized Difference Vegetation Index (NDVI) developed during extreme drought to identify drought refugia. We then utilise camera trapping to understand the ecological role and importance of these refugia under fluctuating rainfall conditions. Ground foraging mammals and birds were surveyed annually from 2016 to 2019 whereby 171 remote-sensing cameras were deployed in the southern section of the Grampians, Australia. NDVI values were calculated during Australia's millennium drought, allowing the assessment of how NDVI calculated during extreme drought predicts drought refugia and the response of biodiversity to NDVI under rainfall fluctuations. Site occupancy of bird and mammal assemblages were dependent on NDVI, with areas of high NDVI during drought exhibiting characteristics consistent with refugia. Rainfall pulses increased site occupancy at all sites with colonisation probability initially associated with higher NDVI sites. Extinction probabilities were greatest at low NDVI sites when rainfall declined. Within mesic systems, remotely sensed NDVI can identify areas of the landscape that act as drought refugia enabling landscape management to prioritise species conservation within these areas. The protection and persistence of refugia is crucial in ensuring landscapes and their species communities therein are resilient to a range of climate change scenarios.
... We observed no evidence of resilience to the effects of pythons among native mammal populations within areas of prolonged exposure. However, the black rat, a globally distributed invasive species (Borroto-Páez, 2009;Courchamp et al., 2003;Harper and Bunbury, 2015;Stokes et al., 2009) was the only mammal to increase in occurrence within the invasion core over the 5-year period. ...
Invasive predators have caused catastrophic declines in native wildlife across the globe. Though research has focused on the initial establishment, rapid growth, and spread of invasive predators, our understanding of prey resilience to established invasive predators remains limited. As a direct result of invasive Burmese pythons (Python molurus bivittatus), medium- to large-bodied native mammals decreased drastically across much of southern Florida as early as 2003. By 2014, most of these mammal species were exceedingly rare within the core invasion area, while pythons expanded outward to newly invaded areas. We used python observations to delineate the core python invasion area from the more recently invaded invasion front, and we compared changes in mammal occurrence from 2014 to 2019 between these two areas. We surveyed mammal communities using camera traps and scat surveys and used these observations to quantify the changes in occurrence among mammal species. As expected, occurrence of medium- and large-bodied mammals declined within the invasion front. However, contrary to our expectation, we observed little evidence of resilience among mammals within the invasion core. Of the 15 species detected in 2019, invasive black rats were the only species to increase in occurrence within the invasion core. Additionally, we observed declines in occurrence among native rodents within the invasion core, which were previously thought to be resistant to the effects of pythons. The continued presence of invasive pythons appears to be shifting the diverse mammal communities of southern Florida to one primarily composed of invasive species.
... In south-eastern Australia, an experimental reduction in R. rattus numbers in littoral rainforest resulted in significant and sustained increases in populations of the bush rat R. fuscipes (Stokes et al. 2009). Juvenile bush rats appeared particularly vulnerable, being largely absent from control untreated sites despite breeding in females, but responding rapidly to the removal of R. rattus via juvenile recruitment, immigration and increases in residency of females. ...
ContextThe pale field-rat (Rattus tunneyi) is a small native rat that formerly had a wide distribution throughout Australia. It has suffered substantial range contraction since European settlement and is now largely absent from arid and semiarid Australia. In this biome, it was known to persist only at two Western Australian locations: Edel Land, on the south-western shore of Shark Bay, and islands off the Pilbara coast. AimsWe aimed to establish the extent of the species range at Edel Land, its habitat preference, the temporal stability of its populations with respect to rainfall, and threats to its persistence. Methods
We trapped at 54 sites to establish distribution and habitat preference, and re-trapped four of these sites at which R. tunneyi was present in each season for 2.5 years to establish trends in abundance. Key resultsTrapping resulted in the capture of 45 R. tunneyi individuals across 17 of 54 sites (4104 trap-nights; 1.1% capture success). Rattus tunneyi typically occupied localised areas of dense shrubland, often in habitats with free water or near-surface moisture from drainage from high dunes allowing denser and taller vegetation and, at some sites, year-round growth of grasses or rushes. Regular re-trapping of four sites in each season (2002 – 2004) suggested a declining population, probably owing to a sequence of dry years. Key conclusionsRattus tunneyi at Shark Bay occurred only in localised mesic refuges, apparently dependent on seepage from high dunes generated by major inputs of rainfall from infrequent cyclones or sequences of high-rainfall years. ImplicationsThis isolated population is likely to be threatened by browsing by feral goats, opening up otherwise densely vegetated habitats of refuge areas, and their trampling of R. tunneyi burrows; by the depletion of grasses from herbivory by European rabbits; and by the long-term impact of a drying climate. It is unlikely to persist without effective on-going management, particularly of the goat population.
... Rattus rattus is an urban exploiter and human commensal that is considered a highly invasive pest species globally. As an opportunistic omnivore with habitat preferences that range from forests to urban areas, R. rattus has frequently been cited as contributing to the local extinction of other wildlife (Towns et al. 2006, Stokes et al. 2009, Shields et al. 2014, Wells et al. 2014, Cusack et al. 2015. Critically, this species is also a known reservoir of a range of important zoonotic pathogens, including Leptospira spp., Bartonella spp., and hepatitis E virus (Meerburg et al. 2009, Himsworth et al. 2013, Mulyanto et al. 2013, Strand & Lundkvist 2019. ...
Urbanization is rapidly transforming much of Southeast Asia, altering the structure and function of the landscape, as well as the frequency and intensity of the interactions between people, animals, and the environment. In this study, we began to explore the impact of urbanization on zoonotic disease risk by simultaneously characterizing changes in the abundance and diversity of reservoir hosts (rodents), ectoparasite vectors (ticks), and microbial pathogens across a gradient of urbanization in Malaysian Borneo. We found that although rodent species diversity decreased with increasing urbanization, two species appeared to thrive in anthropogenic environments: the invasive urban exploiter, Rattus rattus and the native urban adapter, Sundamys muelleri. R. rattus was strongly associated with the presence of built infrastructure across the gradient and dominated the urban rodent community where it was associated with high microbial diversity and multi-host zoonoses capable of environmental transmission, including Leptospira spp., and Toxoplasma gondii. In contrast, S. muelleri was restricted to sites with a significant vegetative component where it was found at high densities in the urban location. This species was strongly associated with the presence of ticks, including the medically important genera Ambylomma, Haemaphysalis, and Ixodes. Overall, our results demonstrate that the response to urbanization varies by species at all levels: host, ectoparasite, and microbe. This may lead to increased zoonotic disease risk in a subset of environments across urban and urbanizing landscapes that can be reduced through improved pest management and public health messaging.
... Our analysis highlights the potential for reducing the impacts of invasive species through the reestablishment of native species communities. Studies have demonstrated the ability of native bush rats (Rattus fuscipes) to outcompete black rats in coastal woodlands (Stokes et al. 2009). Similarly house mice abundance has been observed to be restricted by native small mammals (Rendall et al. 2019) or decline in response to native small mammal recovery after fire (Hale et al. 2016). ...
Managing ecosystems in the face of complex species interactions, and the associated uncertainty, presents a considerable ecological challenge. Altering those interactions via actions such as invasive species management or conservation translocations can result in unintended consequences, supporting the need to be able to make more informed decisions in the face of this uncertainty. We demonstrate the utility of ecosystem models to reduce uncertainty and inform future ecosystem management. We use Phillip Island, Australia, as a case study to investigate the impacts of two invasive species management options and consider whether a critically endangered mammal is likely to establish a population in the presence of invasive species. Qualitative models are used to determine the effects of apex predator removal (feral cats) and invasive prey removal (rabbits, rats, and mice). We extend this approach using Ensemble Ecosystem Models to consider how suppression, rather than eradication influences the species community; and consider whether an introduction of the critically endangered eastern barred bandicoot is likely to be successful in the presence of invasive species. Our analysis revealed the potential for unintended outcomes associated with feral cat control operations, with rats and rabbits expected to increase in abundance. A strategy based on managing prey species appeared to have the most ecosystem‐wide benefits, with rodent control showing more favorable responses than a rabbit control strategy. Eastern barred bandicoots were predicted to persist under all feral cat control levels (including no control). Managing ecosystems is a complex and imprecise process. However, qualitative modeling and ensemble ecosystem modeling address uncertainty and are capable of improving and optimizing management practices. Our analysis shows that the best conservation outcomes may not always be associated with the top‐down control of apex predators, and land managers should think more broadly in relation to managing bottom‐up processes as well. Challenges faced in continuing to conserve biodiversity mean new, bolder, conservation actions are needed. We suggest that endangered species are capable of surviving in the presence of feral cats, potentially opening the door for more conservation translocations.
... Coexistence with ship rats had a negative effect on skull size and weight of Pacific rats on Rakiura/Stewart Island and other Pacific islands, but the mechanism of competition remained unknown (Yom-Tov et al. 1999). Harper et al. (2005) have shown that dominant ship rats have displaced Pacific rats from habitats on Stewart Island and interference by aggressive encounter has been identified as the mechanism of interspecific competition between invasive ship rats and native rats in the Galapagos Islands (Harris and Macdonald 2007) and Australia (Stokes et al. 2009). Russell et al. (2014) found interference competition as the cause for ship rat domination over Pacific rats on a tropical island where exploitative competition could be excluded. ...
On Aotea/Great Barrier Island, New Zealand, two invasive rat species (Pacific rats and ship rats) pose risks to the ecosystems and challenge the management in two sanctuaries. At Glenfern Sanctuary (83 ha) an eradication has successfully removed ship rats and a predator-proof fence prevents reinvasion. However, Pacific rats persist in low abundance. At Windy Hill Sanctuary (770 ha) intensive rodent control maintains both species at low abundance despite ongoing reinvasion. A capture-mark-recapture study was conducted between February and April in 2016 and repeated between July and September 2017 to determine population densities, confirm species composition, and analyse the effects of time, population density, and interspecific competition on rat behaviour. Live traps were monitored with camera traps to analyse behaviour of rats around traps. Population density and detection probability of Pacific rats varied between times reflecting seasonality in food abundance and rat reproduction. The detection probability of Pacific rats also differed between sites, being higher at Glenfern Sanctuary than at Windy Hill Sanctuary, presumably due to interspecific competition with ship rats. Where Pacific rats were the sole species they were captured in traps in the first night. However, in coexistence with ship rats, Pacific rat detection was delayed by at least ten days. Population density influenced the number of trap encounters and interactions but did not significantly influence the capture rate. Interspecific competition was identified as problematic for monitoring, controlling, and eradicating Pacific rats.
... However, the sex ratio in this study was not equilibrated (81 males to 155 females) and was different from the findings of Ben Faleh et al. [14]. The reduction in the number of male black rat caught in this study may be due to competition and their territorial behavior [15]. ...
Aims: This study assessed the morphology and the bait preference of black rat (Rattus rattus) in Obafemi Awolowo University student hostel with the aim of controlling the population of black rat in the students' hostels. Place and Duration of the Study: The study was carried out at Obafemi Awolowo University which is situated in Ile-Ife, an ancient city in the Southwestern Nigeria and lies between latitudes 7°28′N and 7.467°N and longitudes 4°34′E and 4.567°Ewith a landmass of 5,506 hectares between December 2017 and February 2018 Methodology: Locally made metal traps (cage traps) (Plate 1) contains baits were placed fortnightly in various sampling locations (Awolowo, Fajuyi, Angola, Akintola, Mozambique and Moremi halls of residence) for a period of 3 months between the months of December 2017 to February 2018. The traps were set around the dark corners of the sites in the evening and Original Research Article 2 collected the following morning (6.00am). Results: A total of 236 black rats (Rattus rattus) were caught (81 male & 155 female), with the female having the highest weight (238.30 g). Among the baits used, fried fish caught the highest number of the black rat (58%) followed by beans cake (akara) (28%) and the locust bean (14%). There was a positive correlation in the morphology of the black rat caught in all the hostels. Conclusion: The black rats in the University student hall of residence were of the same family and genus, and fried fish is the best-preferred bait.
... It is well known that species intrinsic factors (body mass, range size, life history, trophic level, habitat specialization, and phylogeny/lineage age) determine the susceptibility of vertebrates to extrinsic disturbances that are responsible for declines and extinction (Fisher et al., 2003;Stokes et al., 2009;Brown and Roff, 2019). For example, large species that have slow life history and occupy small areas are more likely to experience population decline than small species that have fast life history and occupy large areas. ...
... Invasive species can significantly impact native communities through competition for resources (Koenig, 2003;Russell, Sataruddin, & Heard, 2014;Stokes, Banks, Pech, & Spratt, 2009;van Riel, van der Velde, & bij de Vaate, 2009). Competition in the form of direct interactions (aggression) or indirect interactions (e.g. more efficient exploitation of resources) is important to quantify at a community level as such interactions have important consequences for invasion dynamics (i.e. ...
Interaction networks among native and invasive species in a community can inform both invasion impacts and applied management of invasive species. The intensity of aggressive interactions may be related to the overlap in species’ ecological niche and functional traits, especially in cavity‐breeding species, that often compete for limited nesting sites. Australia is home to over 100 native and introduced cavity‐nesting species, including several invasive species that are widespread globally, such as the common myna Acridotheres tristis. Here, we aimed to test the extent to which shared functional traits inform the intensity of aggression between cavity‐nesting birds.
We quantified the outcomes of aggressive interactions between birds in large hollow‐bearing trees in SE Queensland, Australia. We examined whether more similarly sized birds interacted more frequently, whether larger species won aggressive interactions more often, and whether cavity‐breeding species with similar preferences for nesting sites (breeding‐niche space) interacted more frequently.
We recorded a total of 410 aggressive interactions and 48 interacting bird species around tree hollows, including 20 cavity‐nesting bird species. These interactions were dominated by the invasive common myna, the native noisy miner (a non‐cavity‐breeder) and the native rainbow lorikeet Trichoglossus moluccanus, but the common myna won the largest total number of interspecific interactions. On average, larger birds won aggressive interactions more frequently, yet there were some important exceptions to this finding; the common myna (113 ± 30 g) won 26 of the 29 interactions against the larger native rainbow lorikeet (126 ± 44 g). Importantly, species with more similar nest‐site preferences were observed aggressively interacting more frequently.
Synthesis and applications. The impact of the invasive common myna was higher‐site preferences. Control efforts for the myna should focus on birds that nest in natural tree hollows. An analysis of shared traits by managers could be used to help identify how many local species would benefit from common myna control in a given area and test if further behavioural studies of common myna are warranted.
... Alternatively, the latecomer may only be able to invade the area in case of an extirpation of the founder (Fraser et al., 2015). The question also remains whether substantial niche shifts (including shifts in the fundamental niche) are more prevalent in the founder, such as niche expansions often documented in invasive species (Stokes, Banks, Pech, & Spratt, 2009). ...
Aim: I assess the impact of interspecific competition on species' post-glacial range expansions into previously glaciated areas. I hypothesize that expansion of one species (the founder) after the last glacial maximum (LGM) into areas that were glaciated has hindered expansion of its competitor (the latecomer). If true, I predict that range and niche sizes of two congeners are more disproportionate within the previously glaciated areas (i.e. the areas of post-glacial expansion) than within areas that were not glaciated. I also predict that niche partitioning is reduced within previously glaci-ated areas. If true, range and climatic niche overlap of two congeners is smaller in the previously glaciated areas than in non-glaciated areas.
Location: North America.
Taxon: Non-volant mammals.
Methods: I calculate species range size for 87 congeneric species pairs and climatic niche hypervolume for 71 pairs, separately for areas that were and were not glaciated during the LGM. I then compare (a) range and climatic niche size ratio and (b) range and climatic niche overlap for each species pair between areas that were and were not glaciated using a paired t test.
Results: Congeneric species pairs exhibit more disproportionate range areas and climatic niche hypervolumes, and smaller range and climatic niche overlap within previously glaciated areas, in comparison with areas that were not glaciated during the LGM.
Main conclusions: Interspecific competition has likely hindered post-glacial range expansion of some species into deglaciated areas. Similarly to the founder effect documented on the intraspecific level, the founder species may hinder the expansion of the latecomer. Consequently, one species may expand over very large areas whereas its competitor may expand very little or not at all. Additionally, niche partitioning within the deglaciated areas may be reduced as the founder expands and fills biotopes that would otherwise be utilized by its competitor.
... However, the sex ratio in this study was not equilibrated (81 males to 155 females) and was different from the findings of Ben Faleh et al. [14]. The reduction in the number of male black rat caught in this study may be due to competition and their territorial behavior [15]. ...
Aims: This study assessed the morphology and the bait preference of black rat (Rattus rattus) in Obafemi Awolowo University student hostel with the aim of controlling the population of black rat in the students’ hostels. Place and Duration of the Study: The study was carried out at Obafemi Awolowo University which is situated in Ile-Ife, an ancient city in the Southwestern Nigeria and lies between latitudes 7°28′N and 7.467°N and longitudes 4°34′E and 4.567°Ewith a landmass of 5,506 hectares between December 2017 and February 2018 Methodology: Locally made metal traps (cage traps) (Plate 1) contains baits were placed fortnightly in various sampling locations (Awolowo, Fajuyi, Angola, Akintola, Mozambique and Moremi halls of residence) for a period of 3 months between the months of December 2017 to February 2018. The traps were set around the dark corners of the sites in the evening and collected the following morning (6.00am). Results: A total of 236 black rats (Rattus rattus) were caught (81 male & 155 female), with the female having the highest weight (238.30 g). Among the baits used, fried fish caught the highest number of the black rat (58%) followed by beans cake (akara) (28%) and the locust bean (14%). There was a positive correlation in the morphology of the black rat caught in all the hostels. Conclusion: The black rats in the University student hall of residence were of the same family and genus, and fried fish is the best-preferred bait.
... Rattus rattus were present also at Venus Bay, although direct spatial and temporal overlap with stick-nest rats was not confirmed. Black rats were regarded also as a significant competitive threat to native R. fuscipes in forest habitat in south-eastern Australia (Stokes et al. 2009). Juvenile R. fuscipes were largely absent from sites where R. rattus were abundant, and direct predation of native juveniles was considered as one possible mechanism. ...
Greater stick-nest rats were widely distributed across southern Australia in pre-European times, but only survived as a single population on the Franklin Islands in South Australia. Conservation efforts since 1983 have included survey of the remaining population, establishment of a captive colony and subsequent translocations to both island and mainland sites. Translocations have met with mixed success, with four of 10 (three islands and one mainland site) successful and extant for 19–28 years, five unsuccessful (one island and four mainland sites) and one as yet indeterminate. Overall, the increase in number of populations, area of occupancy and extent of occurrence has been positive, and has resulted in a down-listing of conservation status. There are numerous plausible explanations for the lack of success at some sites, but few data to differentiate among them. These plausible explanations include: the release of stick-nest rats to habitats of poor quality; high levels of predation (perhaps hyperpredation) by native predators (chiefly monitors and predatory birds) in combination, at some sites, with predation by feral cats or foxes; and ineffective release protocols. Most extant populations have undergone substantial fluctuations over time, and some show apparent long-term declines in abundance, likely increasing their probability of local extinction over time. There is a need for regular ongoing monitoring – of stick-nest rats themselves, their habitat and their suite of potential predators – to aid interpretation of outcomes. A more experimental approach to future releases is required to adjudicate among competing explanations for such declines.
... Competitive interactions between the 2 species may also be occurring because peak activity levels for each species were recorded at different distances inside the reserve. Competition between rodent species has caused spatial shifts in activity in other ecosystems (Monamy & Fox 1998;Maitz & Dickman 2001;Stokes et al. 2009). ...
Spillover effects are an expansion of conservation benefits beyond protected areas through dispersal of species that reside within. They have been well documented in marine but not terrestrial systems. To understand the effects on wildlife created by conservation fences, we explored the internal and external gradients of activity in mammal, reptile, and bird species at a conservation reserve in arid Australia that is fenced to exclude invasive rabbits (Oryctolagus cuniculus), cats (Felis catus), and foxes (Vulpes vulpes). Two methods were used: counts of animal tracks along transects on sand dunes and captures at pitfall‐trapping sites. In both cases, sites were spaced at different distances from the reserve fenceline inside and outside the reserve. We recorded a range of spillover, source‐sink, step, and barrier effects that combined to create a zone within and around the reserve with fence‐induced species‐specific wildlife gradients. Two endemic rodents but none of the 4 mammal species reintroduced to the reserve showed positive spillover effects. Barrier effects, where activity was highest close to the fence, were recorded for the feral cat and native bettong (Bettongia lesueur), species that could not breach the fence. In comparison, some reptiles and native mammal species that could permeate the fence displayed source‐sink effects; that is, their activity levels were reduced close to the fence likely due to constant emigration to the side with lower density. Activity of some reptiles was lowest at sites inside the reserve and gradually increased at outside sites with distance from the fence, a gradient likely related to trophic cascades triggered by predator exclusion. Our result shows that fenced reserves can create overlapping layers of species‐specific gradients related to each species’ ability to permeate the fence and its varying susceptibility to threats. Managers should be aware that these gradients may extend for several kilometers either side of the fence and that not all contained species will increase in abundance. Creating wider conservation benefits may require increased fence permeability and threat reduction outside the fence.
... The rats that repopulate a treated area may come from residual individuals that were not removed during the initial intervention. Hastening this internal rebound of rats is the fact that the initial campaign reduces competition for resources among the remaining rats, increasing reproductive rates and juvenile recruitment (Smith, 1963;Stokes et al., 2009;Vadell et al., 2010). Alternatively, rats may re-colonize the targeted area from nearby, untargeted areas. ...
Rats thrive in human-dominated landscapes and have expanded to a near global distribution. Norway rats (Rattus norvegicus) contaminate food, damage infrastructure, and are reservoirs for zoonotic pathogens that cause human diseases. To limit these negative impacts, entities around the world implement intervention and control strategies designed to quickly and drastically reduce the number of rats in a population. While the primary goal of these interventions is to reduce rat numbers and their detrimental activities, there are important, yet unexplored, population genetic implications for these rapid population declines. Here, we compare the population genetics of R. norvegicus before, immediately after, and several months following a rodenticide-based eradication campaign targeting rats in an urban slum of Salvador, Brazil. This slum has been the focus of long-term research designed to understand and reduce the risk of leptospirosis for people in this area. We also look for a clear source of rats contributing to population recovery, by either rebounding through breeding of local survivors, or by immigration/reinvasion of the site. We found evidence of severe genetic bottlenecks, with the effective population size dropping 85–91% after eradication, consistent with declines in population sizes. These rapid declines also led to a strong shift in the genetic structure of rats before and after the eradication campaign. Relatedness increased in two of the three study areas after eradication, suggesting reduced population sizes and an uneven impact of the campaign across colonies within the population. Lastly, dozens of low-frequency alleles (mean frequency of 0.037) observed before the campaign were undetected after the campaign, potentially lost from the population via drift or selection. We discuss the public health and ecological implications of these rapid genetic impacts of urban control efforts. Our data suggests that targeting the genetic viability of rat populations may be another important component for integrated pest management (IPM) strategies, designed to reduce urban rats.
... R. rattus is amongst the most omnipresent rodents in the world, and has a strong potential to displace other (native) rodent species [86,87]. In Australian ecosystems, it was shown that the invasive R. rattus was dominant over the native R. fuscipes [88,89]. On Madagascar, R. rattus competes for resources with the native rodents and replaces native rodent species [90]. ...
Worldwide, Leptospira infection poses an increasing public health problem. In 2008, leptospirosis was recognised as a re-emerging zoonosis of global importance with South-East Asia being one of the most significant centres of the disease. Rodents are thought to be the most important host for a variety of Leptospira serovars. Because Bangladesh offers a suitable humid climate for the survival of these pathogenic bacteria, the presence of rodents could be a serious risk for human infection, especially in peri-urban areas or locations where food is stored. In order to gain more understanding of the multi-host epidemiology, a prevalence study was conducted in Comilla, Bangladesh to determine the presence of pathogenic Leptospira species in rodents. Real-time Polymerase Chain Reaction (qPCR) and sequencing showed that 13.1% (61/465) of the trapped rodents were infected with pathogenic Leptospira. Sequencing of the qPCR products identified the presence of three species: Leptospira interrogans, Leptospira borgpetersenii, and Leptospira kirschneri. Rodents of the genus, Bandicota, were significantly more likely to be positive than those of the genus, Rattus and Mus. Our results confirm the importance of rodents as hosts of pathogenic Leptospira and indicate that human exposure to pathogenic Leptospira may be considerable, also in places where food (rice) is stored for longer times. This study emphasizes the need to improve rodent management at such locations and to further quantify the public health impacts of this neglected emerging zoonosis in Bangladesh.
... A fascinating variation of EBRM is understanding the ecology and behavior of the pest species and determining whether a native, non-pest species could competitively exclude the pest species. The black rat, Rattus rattus, is a major pest species globally (see Banks and Hughes 2012, for review) and in southern temperate Australia, a native bush rat, R. fuscipes, was able to minimize the recolonization of the black rat after the density of the black rat population was substantially reduced (Stokes et al. 2009). This led to the development of a biotic resistance hypothesis, and a large-scale experiment is underway to see whether the removal of the black rat followed by the reintroduction of the bush rat into urban and peri-urban areas of Sydney harbour can prevent the black rat from re-establishing (Peter Banks, pers. ...
... Changes in the abundance of intraspecific competitors relative to that in the original invasion may also prevent establishment of a reinvader (Efford et al. 2000) and provide an opportunity to exploit Allee effects to control it (Tobin et al. 2011). Similarly, the reestablished presence of indigenous competitors may suppress reinvasion (Stokes et al. 2009). Such competitive interactions may be managed in a metapopulation context in order to reduce the probability of reinvasion among patches. ...
Biological invasions are a major driver of global environmental change, and there is well-developed theory for predicting invasion success. Managing the impacts of established invasive species is expensive and hugely problematic, but this ongoing challenge is largely about managing reinvasion—defined here as the reestablishment of a nonindigenous species in a location after control. We review conceptual and theoretical frameworks developed to understand initial invasions and identify how reinvasion differs because of three factors: (1) changes in the invader, (2) changes in the invaded environment, and (3) interactions among invaders and with local taxa. We find a distinct lack of theory about the processes involved in reinvasion, but theory is needed to develop systematic research to optimally manage reinvaders. We detail the circumstances under which reinvasion is fundamentally different from initial invasion, address management issues specific to understanding and managing reinvasion, and highlight promising opportunities for future research. © The Author(s) 2018. Published by Oxford University Press on behalf of the American Institute of Biological Sciences. All rights reserved.
... Hypothesis B: If risk effects from highly abundant ship rats limit mice, mice will not use feeders when they are supplied, but they will have lower body weights indicating apparent food shortage (Eccard and Ylönen 2002;Harris and Macdonald 2007;Stokes et al. 2009). ...
When the abundance of ship rats (Rattus rattus) is reduced, sympatric house mice (Mus musculus) are released from constraints of food shortage, intimidation or predation. As a result, mice may become either more abundant or more active and detectable. To distinguish between these effects, we monitored mice at eight sites within Pureora Forest Park during periods of rat removal and non-removal, and supplemented food in mouse-specific feeders to half of the sites. We used live-trapping to estimate mouse relative abundance, and tracking tunnels to detect activity. Mouse relative abundance increased when rats were removed, which correlated with increased mouse activity in tracking tunnels. Analysis of mouse capture probability showed that although rat population levels predominantly influenced mouse relative abundance, mouse detectability was also affected at a subtler level. Fluctuations in mouse relative abundance were driven by immigration, and there was evidence that mice were food-limited in the presence of abundant rats. However, this effect was not offset by supplementing food, so it is unlikely that exploitation competition alone limits mice in the presence of rats. Instead, when ship rats were abundant the danger to mice was likely to have limited their foraging opportunities. Evidence of direct predation of mice by ship rats was observed, but it is unclear what role direct predation plays in determining mouse abundance relative to risk effects.
... Black rats have been linked to extinctions and declines of native bird populations both worldwide and in Australia (e.g. Banks and Hughes 2012;Blackburn et al. 2004;Doherty et al. 2016), and there is mounting evidence that they compete with Australian native rodents in bush habitats (Stokes et al. 2009(Stokes et al. , 2012. Black rats share a coexistence history of thousands of years with dogs, foxes, and cats in Europe and the United Kingdom, several hundreds of years in North America, and many tens of thousands of years in Asia (Long 2003). ...
Alien species experience both costs and benefits in invaded environments, through naiveté of potential prey species, but also predation pressure from native predators. The question of whether alien prey recognise and respond to native predators has been relatively understudied, despite the hypothesised potential for native predators to provide biotic resistance to invasion. There are two main hypotheses about whether exotic prey should recognise native and exotic predators in their new ranges: (1) naiveté—predicting recognition of evolutionarily familiar predators only, and (2) pre-adaptation—predicting recognition of all predators through a generalist recognition template. With regards to antipredator responses, (3) naïveté theory presumes that exotic prey will respond to the predators they recognise, but we suggest that (4) a bold behavioural syndrome, and/or a high marginal value of food in invaded environments might result in weak or absent responses, even to recognised predators. Here we combine the giving-up density framework with behavioural analysis of remote camera footage to experimentally test these ideas in a disturbed, peri-urban, Australian ecosystem, where alien black rats are predated on by alien dogs, foxes, cats, and native quolls. Black rats recognised dogs and foxes, but appear naïve towards quolls. However, they showed no antipredator responses at all, consistent with a bold behavioural syndrome, elevated predation risk, and/or a high marginal value of food in invaded environments.
... Ultimately, dominant invasive species can exclude native species through competition leading to their local extinction (Komdeur, 1996). Behavioural dominance of an invasive species over natives seems widespread in nature, being recorded in several animal taxa (reptiles: Case et al., 1994;birds: Freed & Cann, 2009;insects: Holway, 1999; fishes: Marchetti, 1999; mammals: Stokes et al., 2009). ...
Behavioural dominance and aggressiveness may be crucial traits facilitating the establishment of invasive species. Few studies considered agonistic interactions between exotic and native bird species in feeding contexts, particularly when the exotic has social habits. We aimed to know if individuals of a social invasive species, the red-billed leiothrix Leiothrix lutea, are: more aggressive; the initiators of the first interaction; and dominant (i.e., won most interactions) over native opponents in a feeding context. We performed an experiment in a closed environment forcing dyadic interactions between an individual of a native species facing a leiothrix individual. We found that the leiothrix was the initiator in most experiments, being apparently dominant over natives. However, the invader was not more aggressive than natives. This can increase the risk of injury for natives because the leiothrix has a relatively larger body size. We discuss possible negative impacts of the leiothrix on native species.
... Second, the specified endpoint can include foreign species if they do not radically alter ecosystem integrity and function (e.g., European starlings (Sturnus vulgaris) in North America; Koenig 2003). However, invasive species that impede restoration and distort trophic structures need to be removed beforehand, as seen in fenced ecosanctuaries on mainland New Zealand (Innes et al. 2012) or in Australia where competing exotic black rats (Rattus rattus) must be removed to allow recolonization of native bush rats (Rattus fuscipes; Stokes et al. 2009). ...
Restoration of degraded landscapes has become necessary to reverse the pervasive threats from human exploitation. Restoration requires first the monitoring of progress towards any chosen goals to determine their resilience and persistence, and second to conduct in a comparable adjacent area but with less human impact the restoration of trophic structures and ecosystem processes to act as reference systems (controls) with which we compare the viability of the chosen goal. We present here the rationale and a method for predicting the trajectory of restoration and assessing its progress towards a pre-determined state, the endpoint, using a restoration index. This assessment of restoration requires that we know when a predetermined endpoint has been achieved and whether the envisioned community of species and their interactions can be restored. The restoration index can use species’ presence or density, and the rate of change of ecosystem processes. The index applies to trophic levels, functional groups, successional stages, alternative states and novel ecosystems. Also our method allows measurement of the resilience of ecosystems to disturbance, a desired property for conservation and management. We provide global examples to illustrate these points. This article is protected by copyright. All rights reserved
... Habitat destruction is one of the factors leading to the decline and/or extinction of species. Introduced species outcompete native flora by either overexploiting resources required by native species for survival or by aggressively excluding native species from space and/or resources (Dickman, 2006;Stokes et al., 2009). ...
Biological invasion is defined as the introduction (intentional or non-intentional), successful establishment, and potential spread of species outside their native range of habitat, and recognized as a threat to the economy, environment and biodiversity globally. Together, such species are regarded as 'invasive alien species'. Liberalization of global trade, increase in transport, travel and tourism are the root causes of invasions by alien species that pose a serious threat to biodiversity of different ecosystems, food security, human and animal health. In the recent past, the implications of climate change for biodiversity have been widely recognized, however, the ill effects of invasive alien species on global biodiversity have received little attention. Climate change is itself a major factor responsible for the complete shift of native flora diversity, which may further complicate the puzzle of biological invasions. It has been generally visualized that predicted changes in climatic factors will also modify interaction scenarios between crops and weeds that will make weed management more difficult. And, if this happens, invasive alien weed species will dominate the other flora due to their superior adaptability to new environments. An attempt has been made to review the available literature on invasive alien weed species and their significant impact on different ecosystems, including forestry, agro-forestry, cropped and non-cropped lands in India and elsewhere
... In an experimental test of biotic resistance in rainforest in south eastern Australia, Stokes et al. (2009) showed that resident populations of indigenous bush rats (Rattus fuscipes) can block invasion by functionally equivalent, similar-sized invasive black rats. In the northern Philippines, an island ecosystem with a very high level of mammalian endemism, endemic small mammals were resistant to invasion by nonindigenous species, especially in areas least disturbed by humans (Rickart et al. 2011). ...
Populations of invasive wild mammals have contributed significantly to the total unwanted impacts of biological invasions. They are known to impact forest ecosystems globally, but reviews summarizing this information are currently lacking. Here we (1) review the ecological characteristics of mammal invasions in forests; (2) characterize the range of ecological impacts on forest communities and the economic consequences of those impacts; (3) review what is known about interactions between the impacts of invasive mammals and other drivers of global change; and (4) consider the complex ecological and socio-economic challenges of simultaneously managing multiple invasive mammals and native biota affected by them. The unwanted impacts of invasive herbivores and predators are intensifying in many parts of the world and the need to manage their impacts to prevent further loss of indigenous biodiversity and damage to productive assets is greater than ever. However, management needs to be conducted within appropriate social, cultural, ethical, and animal welfare frameworks. Achieving effective management of populations of mammals invasive in forest ecosystems will require the filling of many knowledge gaps, including: better understanding their impacts; strategic options and tactical solutions for managing them; and achieving social licence to operate.
... My finding that alien black rats recognised but showed no response to the odours of dogs, foxes and cats (Chapter 5) proposes the interesting possibility that this highly successful invasive alien species (Long 2003) exhibits a form of behavioural 'invasion syndrome' (as proposed by Chapple et al. 2012) consisting of increased aggression and boldness in response to predation risk. Successful acquisition of resources in the face of predation risk may give alien black rats a competitive advantage over native bush rats in areas where they coexist (Stokes et al. 2009a, Stokes et al. 2009b, Stokes et al. 2012. ...
Alien predators have devastating impacts on native prey in invaded ecosystems worldwide, a fact commonly attributed to ecological naiveté or the failure of native prey to defend themselves against a novel predator due to a lack of experience. Despite this, few studies have convincingly demonstrated naiveté in native prey. Ecological naiveté is of particular relevance in Australia, where eighteen endemic mammal species have gone extinct, and many more are in decline, since the introduction of alien placental dogs (Canis lupus dingo and Canis lupus familiaris), red foxes (Vulpes vulpes) and feral cats (Felis catus). The role of naiveté in the vulnerability of Australia’s native mammal species remains unresolved. More generally, the naiveté of native species towards novel enemies in all types of antagonistic interactions is an important predictor of the outcomes of future introductions and conservation efforts in invaded ecosystems.
In this thesis, I used theoretical, experimental and chemical approaches to investigate ecological naiveté in Australian predator-prey interactions and its implications for the persistence of native prey. I reviewed classic predator-prey theory to show how alien species disrupt predator-prey interactions at every stage of the predation sequence, from detection, to capture, and escape or consumption. Rather than adopting the longheld view of naiveté as an all-or-nothing status, I expand upon and argue the recent theory that naiveté is best viewed as a process through which native prey can progress towards predator wariness.
Using a broad-scale survey approach, I demonstrated that native vulnerable marsupial bandicoots recognise and avoid pet dogs, but not cats, when choosing where to forage. I attributed this finding to the approximately 4000 years’ experience that bandicoots have with dingoes, which are very closely related to dogs. I extended this line of reasoning to argue that naiveté of local native prey provides an objective criterion for determining the native status of an introduced predator with a long history in a particular ecosystem.
I developed a two-pronged experimental approach to test for naiveté in small to medium size free-living mammals, by combining giving-up density (GUD) methodology with remote-sensing night vision cameras to enable direct observation of behavioural changes in response to predator odours. Despite the prevalent use of scats or urine to represent risk in previous studies of olfactory predator recognition, here I used ‘whole animal’ body odour because it represents imminent danger through proximity or likely revisitation of the predator at a den site or resting place. GUDs revealed that native bush rats (Rattus fuscipes) recognise and respond strongly to dog odour, while subtle changes in vigilance behaviour detected by the analysis of camera footage showed that they also increased vigilance in the presence of cat, fox and native quoll (Dasyurus maculatus) odour. In contrast, the same experimental methodology showed that alien black rats (Rattus rattus) increased investigation of alien predator odours over controls or native quoll odour, but did not respond with increased GUDs or vigilance. This highly successful invasive species may exhibit a behavioural invasion syndrome that makes it bolder to forage under predation risk and potentially more aggressive.
Native bush rats left low GUDs in the presence of cat odour, and since rats are an intermediate host of the parasite Toxoplasma gondii that has been shown to reduce riskaversion and increase attraction to cat odours in rats (increasing their vulnerability to cat predation so that T. gondii can return to its definitive host) I tested for the presence of T. gondii in the population. Seroprevalence of immune response to T. gondii was found to be relatively low (at 4.10 %), but the role of parasites and pathogens in increasing vulnerability of native species to alien predators deserves further research attention. This is because they may effectively ‘override’ the native species’ preadaptations or any progress made due to learning or adaptation.
Using solid phase micro-extraction and gas chromatography-mass spectrometry (SPME GC-MS), I then showed significant differences in the chemical composition of scats, urine and body odours from marsupial and placental predators. The odours of individual predator species also differed from one another with the following exceptions: the compositions of placental body odours overlapped, and the scats, urine and body odours of dingoes and dogs were chemically indistinguishable. If differentiation of social cues has been a major cause of vertebrate evolutionary divergence, the importance of olfaction in social communication between mammals predicts that this difference between species and higher taxonomic groups should occur. The chemical similarity of dog and dingo odour confirms that these two closely related predators probably smell very similar when encountered by native prey, and supports my conclusion that native prey species recognise and respond to dogs due to their considerable experience with dingoes.
In Australia, where native mammalian predators are almost exclusively marsupial and alien predators eutherian, differences in odour cues of these two taxonomic groups may have resulted in native prey failing to recognise foxes and cats when they first arrived. This probably played a very important role in Australia’s recent mammal extinctions. Nevertheless, it is clear from this research that native species that survive today, including bush rats and bandicoots, are currently not entirely naïve towards introduced predators. Whether this is due to preadaptations or experience, it has positive implications for their continued persistence.
... Exotic black rats are physically similar to their native Australian counterpart, the bush rat, although black rats appear to fare better in human-modified landscapes whereas bush rats hold their ground in natural habitat [33,34]. In eastern Australia bush rats and black rats are competitively symmetrical (i.e. both species are able to defend territory and resources from the other) where they co-occur [35,36], but in the Sydney region historical events and habitat fragmentation have led to local extinctions of bush rats and other native small mammals. Now black rats dominate most of the urban remnants of Sydney's foreshore [37]. ...
Exotic predators are a major threat to native wildlife in many parts of the world. Developing and implementing effective strategies to mitigate their effects requires robust quantitative data so that management can be evidence-based, yet in many ecosystems this is missing. Birds in particular have been severely impacted by exotic mammalian predators, and a plethora of studies on islands record predation of bird eggs, fledglings and adults by exotic species such as rodents, stoats and cats. By comparison, few studies have examined nest predation around mainland urban centres which often act as dispersal hubs, especially for commensal species such as rodents. Here, we experimentally examine nest predation rates in habitat patches with varying black rat (Rattus rattus) densities in Sydney, Australia and test whether these exotic rats have the effects expected of exotic predators using effect size benchmarks. In the case where black rats have replaced native Rattus spp., we expected that black rats, being more arboreal than native Rattus spp., would be a significant source of predation on birds because they can readily access the arboreal niche where many birds nest. We tested this idea using above-ground artificial nests to represent those of typical small bird species such as the New Holland honeyeater (Phylidonyris novaehollandiae). We found that fewer eggs were depredated by rodents on sites where we removed black rats compared to unmanipulated sites, and that the effect size calculated from the total number of eggs surviving beyond the typical incubation period was similar to that expected for an exotic predator. Our results suggest that, although Australian birds have co-evolved with native Rattus species, in the case where black rats have replaced native Rattus species, exotic black rats appear to pose an additive source of predation on birds in remnant habitats, most likely due to their ability to climb more efficiently than their native counterparts. Management of these commensal rodents may be necessary to retain urban birdlife.
... The scarcity of direct observations is not surprising given that most rat-small mammal predation would occur hidden from human view. In some cases, for example in rat removal studies, we might also presume only competitive interactions when predation may have contributed to a decline in numbers of native animals (Goodman 1995, Stokes et al. 2009). In spite of the dramatic impact on seabirds and some other animals, the effects of rat predation on small mammals may be overlooked because it is poorly known, diffi cult to document, and has not been the focus of research. ...
Few previous studies document Rattus predation as a mechanism of impact on native small mammals. In a mixed Araucaria araucana (Molina) Koch -Nothofagus forest in Parque Nacional Lanín in southwestern Neuquén Province, Argentina, we discovered the remains of long-clawed mice, Chelemys macronyx Thomas, cached in a burrow of Rattus norvegicus Berkenhout. We discuss this evidence of predation in light of Rattus biology and invasion ecology. Predation on native small mammals by invasive rats is easily underestimated or overlooked and deserves more careful attention.
Rodents are a notorious group of invaders worldwide. Their invasions have substantially impacted native ecosystems, local infrastructure, and human health and well-being. However, a lack of synthesized estimation of their economic impacts hampers effective management interventions at relevant scales. Here, we used the InvaCost database – the most up-to-date and comprehensive synthesis of reported monetary invasion costs – to assess the economic costs of invasive rodents globally. Our conservative analysis showed that reported costs of rodent invasions reached at least US$ 3.28 billion between 1930 and 2018, and were significantly increasing through time. The highest species-specific costs were reported from Ondatra zibethicus , Rattus norvegicus and Castor canadensis , with over 90% of the total costs damage-related, principally impacting agriculture, and predominantly reported in Asia (65%) and Europe (20%). Although minimal compared to damages, the majority of management investments were made on islands, with post-invasion spending always dominant. Importantly, managements expenditures to prevent rodent invasions were entirely absent from mainland areas. However, only approximately one quarter of the 48 known invasive alien rodents had reported costs, highlighting clear taxonomic biases. Obvious cost reporting gaps were also evidenced across different areas, sectors and contexts, suggesting a great underestimation of the costs incurred by invasive rodents globally. Greater and integrative research effort on the direct and indirect costs of rodent invaders – particularly the distinction between native rodent pests and invasive rodents’ impacts, or from indirect impacts on human health – would be crucial for bridging these gaps. Ultimately, this would support proactive and sustainable management strategies.
The swamp rat (Rattus lutreolus) is one of the few Australian terrestrial mammals that is commonly active between dawn and dusk. The species has typically been considered cathemeral (active throughout the diel cycle) with variation in circadian activity dependant on proximate factors such as the risk of predation or competition with closely related taxa. Data from camera trapping over 8 years and across 79 sites in South Central Victoria confirmed the species was effectively diurnal throughout the region and that night activity was relatively uncommon. Activity generally tracked daily temperature cycles; lowest in the period prior to dawn and highest in the middle of the afternoon and is consistent with an energy conservation strategy linked to the species’ unusual diet. Other rodent taxa, including two widespread exotic species were strictly nocturnal yet there was little evidence to suggest that R. lutreolus activity was influenced by the presence or absence of other murids or the risk of predation.
Les rats introduits (Rattus spp.) sont des espèces invasives majeures menaçant la biodiversité sur la plupart des îles de la Planète. Deux espèces, le rat noir (R. rattus) et le rat du Pacifique (R. exulans) vivent en sympatrie au sein des forêts de Nouvelle-Calédonie, où la question de la faisabilité et de l' intérêt de leur contrôle (i.e. limitation locale de leur 'abondance)pour la conservation de la biodiversité native est posée. En raison d'un manque de cadre conceptuel des projets de contrôle,nous avons d'abord réalisé une synthèse et une analyse des opérations de contrôle de rats invasifs dans les milieux naturels des îles du monde. Puis, nous avons cherché à caractériser et à comprendre la dynamique des populations de ces deux espèces de rats sympatriques ainsi que leurs interactions avec la biodiversité native en forêt dense humide du massif du Mont Panié.Des opérations de piégeage létal et de capture-marquage-recapture ont montré que les rats noirs étaient plus abondants que les rats du Pacifique. Les analyses de leur régime alimentaire ont révélé que les deux espèces ont à la fois des proies communes et des proies qui leur sont propres impliquant un renforcement ainsi qu'un élargissement de leurs impacts sur la biodiversité native. Les rats consomment une grande majorité de fruits et de graines, d'invertébrés et de Squamates mais les oiseaux, qui justifient souvent la mise en place de projets de gestion de rats, ne semblent pas ici être une de leur proie préférentielle. De potentiels effets positifs des rats sur la dispersion des graines ont également été mis en évidence au travers d'une comparaison du potentiel germinatif de graines après passage par leur tractus digestif et celui de frugivores natifs. Enfin, nous avons proposer des stratégies de piégeage létal afin de contrôler efficacement les populations de rats invasifs. Une meilleure compréhension des impacts des rats en situation de sympatrie ainsi qu' une meilleure connaissance du lien entre densité de rats et intensité des effets sur la biodiversité permettraient d'optimiser les stratégies de contrôle de rats invasifs lorsque l'éradication n'est pas envisageable.
Phylogeography and zooarchaeology are largely separate disciplines, yet each interrogates relationships between humans and commensal species. Knowledge gained about human history from studies of four commensal rats (Rattus rattus, R. tanezumi, R. exulans, and R. norvegicus) is outlined, and open questions about their spread alongside humans are identified. Limitations of phylogeographic and zooarchaeological studies are highlighted, then how integration would increase understanding of species’ demographic histories and resultant inferences about human societies is discussed. How rat expansions have informed the understanding of human migration, urban settlements, trade networks, and intra‐ and interspecific competition is reviewed. Since each rat species is associated with different human societies, they identify unique ecological and historical/cultural conditions that influenced their expansion. Finally, priority research areas including nuclear genome based phylogeographies are identified using archaeological evidence to understand R. norvegicus expansion across China, multi‐wave colonization of R. rattus across Europe, and competition between R. rattus and R. norvegicus. By combining phylogeography and zooarchaeology, the spatial distribution and temporal dynamics of within species lineages can be reconstructed. Both approaches should be used with four rat species (black, Asian house, Pacific, and brown) to understand the minimum dates of commensalism, urbanization dynamics, and connections among human societies.
Zonation is a dominant feature of coastal ecologies, yet comparatively few studies are available on zonation of ecological assemblages in coastal dunes. Studies of zonation often focus on invertebrate macrofauna in the sub or inter-tidal regions; rarely has zonation of small mammal communities been considered in dunes. In this study we use 10 years of mammal trapping data and show that a diverse small mammal community was present within a coastal dune system. Nine species were captured within the dune, only one of which was introduced. The invasive house mouse was limited to a narrow band above the beach/dune interface, while the native small mammal assemblage dominated in the rest of the dune field. This clear zonation may result from habitat preference, interspecific competition, predation, species-specific predator risk tolerances, marine or beach subsidies or a combination of these influences. We demonstrate the conservation value of dune systems and highlight the presence of zonation within a mobile small mammal community.
Rodent communities have multiple functions including comprising a majority of the mammalian diversity within an ecosystem, providing a significant portion of the available biomass consumed by predators, and contributing to ecosystem services. Despite the importance of rodent communities, few investigations have explored the effects of increasing anthropogenic modifications to the landscape on rodents. Throughout the western United States, the construction of artificial water developments to benefit game species is commonplace. While benefits for certain species have been documented, several researchers recently hypothesized that these developments may cause unintentional negative effects to desert-adapted species and communities. To test this idea, we sampled rodents near to and distant from wildlife water developments over 4 consecutive summers. We employed an asymmetrical before-after-control-impact (BACI) design with sampling over 4 summers to determine if water developments influenced total rodent abundance. We performed an additional exploratory analysis to determine if factors other than free water influenced rodent abundance. We found no evidence that water developments impacted rodent abundance. Rodent abundance was primarily driven by vegetation type and year of sampling. Our findings suggested that water developments on our study area do not represent a significant disturbance to rodent abundance and that rodent abundance was influenced by the vegetative community and temporal factors linked to precipitation and primary plant production. Our findings represent one of the 1st efforts to determine the effects of an anthropogenic activity on the rodent community utilizing a manipulation design.
Mimosoideae are a dominant plant clade in Australia with more than 1000 taxa recognised. Most species belong to genus Acacia s.s. Mill. and evolved in Australia during the post-Gondwanan isolation. Very few species (<20) belong to genera that evolved outside Australia (Vachellia Wight & Arn., Senegalia Raf.; until quite recently both included under Acacia s.l.) and have subsequently invaded into Australia (Chapter 2). Most of these are descended from individuals that immigrated into Australia and New Guinea prior to European migrations (hereafter pre-colonial species), while a few were either accidentally or deliberately introduced by Europeans (hereafter colonial species). The relative abundance and distribution of the species varies significantly between early and later invaders: the later colonial invaders show wider or rapidly expanding distributions and superior dominance status in the communities where they are found (Table 3.1; Australian Biological Resources Study 2001; Kriticos et al. 2003). The early colonial species range from being (more usually) abundant to locally dominant, in some instances (Table 3.1). This suggests that either trait differences between the species have affected their relative performance under modern, post-colonial systems of native vegetation management, or that human activities have particularly favoured the spread of post-colonial species.
Apex predators are important in protecting biodiversity through top-down influence on food webs. Their loss is linked with competitive release of invasive mesopredators and species extinctions. The Tasmanian devil (Sarcophilus harrisii) has experienced severe declines over a 15-yr period as a novel transmissible cancer has spread across its current geographic range. We surveyed the mammalian community, using hair traps, across the spatial extent of the devil's progressive population decline. We found increased activity of alien invasive species (feral cats, black rats), and reduced small and medium-sized native prey species in response to the timing of the decline. In areas of long-term devil decline, invasive species comprised a significantly larger proportion of the community. The results provide evidence that the devil plays a keystone role in Tasmania's ecosystem with their decline linked to a shift toward an invasive state and biodiversity loss in one of Australia's most intact faunal communities.
Experimental removal was conducted to test interspecific competition between the wood mouse Apodemus sylvaticus (Linnaeus, 1758) and the bank vole Clethrionomys glareolus (Schreber, 1780) that dominate the rodent communities in the forested biotopes through most of central Europe. Population density, body mass, reproductive condition, and habitat use were compared among two experimental sites (where one of the species had been removed) and one control site. The 5-year-study included pre-removal, removal, and post-removal periods. Reproductive condition was not affected by the density of the competitor or the conspecifics. Also, we did not detected any habitat shift that could be related to competitive release. However, the removal of wood mice strongly affected the population density of bank voles, but the removal of bank voles affected density of wood mice only slightly. Thus, we conclude that the competitive effect was asymmetrical.
Populations of introduced black rats (Rattus rattus) were studied by removal trapping in five nonagricultural habitats in the Galapagos Islands; montane forest, montane scrub, tropical deciduous woodland, thorn scrub, and savannah. Density of rats ranged from 0.4 to 18.9/ha, and both density and biomass of rats were significantly correlated with an index of vegetation biomass. The estimated quantity of vegetation per individual and per unit biomass decreased with increasing rat density. These results suggest that rat poplations were food-limited. A 2-mo drought significantly lowered condition (mass/length) of montane forest and montane scrub rats. Analysis of size and reproductive classification of resident and immigrant rats showed significant heterogeneity among subgroups bases on sex and period of capture. Rats from the two habitats of lowest rat density appeared to have more specific microhabitat requirements than rats from denser populations. Breeding was confined to the hot and early cool seasons (January through July) in all habitats. Mean and minimum body lengths in all populations were positively correlated with time since arrival of arid zone rains, while the coefficients of variation of these quantities were negatively correlated. Sex ratio varied seasonally; the percentage of males increased significantly during the nonbreeding season. Intraisland pelage differentiation was observed. Compared to other tropical rodents, Galapagos Rattus rattus have been very successful in range of habitats occupied and in biomass maintained.
Diet selection by the oimnivorous black rat (Rattus rattus) was examined by detailed analysis of stomach contents of individuals from seven wild populations in the Galápagos Islands. High within-meal diversity of foods was found: nearly all stomachs contained at least four foods, and many contained eight or more. Although 77% of the rats had eaten at least one potentially filling food,no individual (N = 173) had only one food in its stomach. Meals tended to be dominated by one food; these dominant foods included a variety of plant and animal materials, but were rarely leaves. Nearly all stomachs contained at least one food present in a trace amount (
We used a food-supplementation experiment to test the hypothesis that small-mammal populations are food-limited during winter in southeastern Australia. We trapped small mammals along 120- to 150-m transects at 12 creek and 12 ridgetop sites (representing high- and low-quality habitats) for 2 months prior to winter and 2 months during winter. High-quality food (peanut butter, honey, oats, and dried cat food) was provided ad libitum for 7 weeks during winter at four sites in each habitat. Eight sites were provided with empty feeding tubes and eight were untreated. Seven weeks of food supplementation caused numerical increases of 4.0- and 5.0-fold for the rodents Rattus fuscipes and Rattus lutreolus, respectively. Increases were due largely to immigration, and were only observed in the high-quality creek habitats (R. lutreolus were exclusively captured at creek sites). Food supplementation also led to an increase in body mass and reversed the hiatus in winter breeding for rodents. These results suggest that populations of both species are limited by winter food availability. However, survival rates (indexed from recapture rates) were not affected by food supplementation. Mean body mass of the marsupial Antechinus stuartii also increased with food supplementation, but other demographic parameters showed no response; numbers declined at creek sites after additional food was provided. Trapping-revealed measures of interspecific association showed that A. stuartii avoided areas of high rat numbers after additional food was provided. It is thus likely that interference competition from the much larger and more abundant rodents forced A. stuartii out of the food-supplemented creek sites, hence mediating the direct effects of food supplementation on this species.
The distributions of the introduced nematode parasite, Angiostrongylus cantonensis, and the native Angiostrongylus mackerrasae in Australia are poorly understood. We sampled rodents and/or their faeces, and intermediate gastropod hosts for the presence of Angiostrongylus species in coastal forests surrounding Jervis Bay in south-eastern Australia. We found A. cantonensis in populations of introduced Rattus rattus in forests to the north of Jervis Bay, and A. mackerrasae in native Rattus fuscipes in forests to the south of Jervis Bay. The apparent geographical separation of these lungworm species may be a consequence of host specificity and negative associations between R. rattus and R. fuscipes that results from interspecific competition. A. cantonensis was regularly found in R. rattus or their faeces across 9 of 12 study sites north of Jervis Bay, and three species of snail common to the area were suitable intermediate hosts. This has potential negative implications for native wildlife and human visitors to these forests, because A. cantonensis infection causes zoonotic disease (neuro-angiostrongyliasis) in humans and a wide range of bird and mammal hosts. Management of pest rodents in the study area is warranted.
We used a food-supplementation experiment to test the hypothesis that small-mammal populations are food-limited during winter in southeastern Australia. We trapped small mammals along 120- to 150-m transects at 12 creek and 12 ridgetop sites (representing high- and low-quality habitats) for 2 months prior to winter and 2 months during winter. High-quality food (peanut butter, honey, oats, and dried cat food) was provided ad libitum for 7 weeks during winter at four sites in each habitat. Eight sites were provided with empty feeding tubes and eight were untreated. Seven weeks of food supplementation caused numerical increases of 4.0- and 5.0-fold for the rodents Rattus fuscipes and Rattus lutreolus, respectively. Increases were due largely to immigration, and were only observed in the high-quality creek habitats (R. lutreolus were exclusively captured at creek sites). Food supplementation also led to an increase in body mass and reversed the hiatus in winter breeding for rodents. These results suggest that populations of both species are limited by winter food availability. However, survival rates (indexed from recapture rates) were not affected by food supplementation. Mean body mass of the marsupial Antechinus stuartii also increased with food supplementation, but other demographic parameters showed no response; numbers declined at creek sites after additional food was provided. Trapping-revealed measures of interspecific association showed that A. stuartii avoided areas of high rat numbers after additional food was provided. It is thus likely that interference competition from the much larger and more abundant rodents forced A. stuartii out of the food-supplemented creek sites, hence mediating the direct effects of food supplementation on this species.
This study aimed to quantify changes in rat abundance and population structure before, during, and after a rimu (Dacrydium cupressinum) mast seed event in lowland forest on Stewart Island, New Zealand. Rats, primarily ship rats (Rattus rattus), were trapped in low numbers throughout the study period (March 2000‐March 2003), except when they erupted to very high abundance in spring 2002, shortly after heavy rimu seed fall. In the immediate post‐peak phase, scavenging of trapped rats increased substantially; rats were seen and trapped in daylight; and weights of adult female rats were low in relation to their size, which suggests that food shortage was the cause of the subsequent steep decline in abundance. Rat eruptions have been observed on Stewart Island after heavy rimu seed fall several times over the past 40 years. Eruptions of rats caused by heavy rimu seed‐fall may have triggered the invasion of nearby islands by rats, and caused the extinction of several native species on Stewart Island.
1. We extend a predator-prey model previously parameterized for voles and weasels to two prey species, a 'Microtus' (field vole) type which is competitively superior to but more vulnerable to predation than a 'Clethrionomys' (bank vole) type. 2. The model explains four patterns in the dynamics of multispecies rodent assemblages in Fennoscandia: a predictable shift in the relative abundances of different prey species during one multiannual population cycle; long-term (supracyclic) variation in relative prey abundances; an association between the amplitude of population oscillations and the type of the numerically dominant prey species; and increasing rodent species number with increasing latitude. 3. The model results illustrate the complex and often unexpected behaviour of strongly connected multispecies assemblages, of which the Fennoscandian rodent-predator community is a prime example. 4. Since the mid 1980s, rodent oscillations in many, though not all, parts of northern Fennoscandia have become distinctly less regular (non-cyclic), a change which is reflected in the entire animal community linked to the keystone species, the arvicoline rodents. We demonstrate that such long-term changes in the amplitude and regularity of rodent oscillations are not unexpected in multispecies prey-predator assemblages.
We studied the effect of a dominant species, Gerbillus pyramidum (Egyptian sand gerbil), on the patch use of its subordinate competitor, G. andersoni allenbyi (Allenby's gerbil), to better understand interspecific competition between the two species. We used manipulated resource patches (seed trays) covered with cages with two adjustable species-specific gates (either opened or closed to the bigger-dominant species, but always opened to the subordinate one). We recorded species tracks around and on the seed trays and giving-up densities (GUDs) of seeds in the trays after each night of foraging. G. a. allenbyi depleted seed patches to a lower level whenever G. pyramidum was given the opportunity to forage on the seed trays (i.e., present on the grid). This result held regardless of whether G. pyramidum was actually present at a particular station. We suggest that competition from G. pyramidum occurs both directly by interference, in which G. a. allenbyi is forced to be active in the late part of the night, and indirectly by exploitation via resource depletion by G. pyramidum in the early part of the night. The results suggest that interspecific competition from G. pyramidum reduces seed availability and the richness of the environment for G. a. allenbyi enough to affect the marginal value of energy for G. a. allenbyi individuals and cause them to experience lower costs of predation and manifest lower GUDs.
We studied habitat preferences and intra and interspecific density-dependent effects on habitat selection by Akodon azarae and Calomys laucha between maize fields and their adjacent borders, during different developmental stages of the crop. Akodon azarae detected quantitative differences between habitats, using preferentially borders throughout the year, while C. laucha perceived borders and cropfields as quantitatively similar during spring and summer and it detected borders as quantitatively
better at the high density period (autumn and winter). These results support the prediction of differential habitat preferences
as a model of community organisation at the low density period, while they are consistent with shared habitat preferences
during autumn and winter when both species apparently coexist in the better habitat (border). Akodon azarae showed intraspecific density-dependent habitat selection throughout the year, except in spring, while habitat selection by
C. laucha was density-dependent in spring, autumn and winter. The effect of interspecific density on habitat selection was detected
in both habitats and changed seasonally. The effect of A. azarae over C. laucha by resources exploitation was detected in borders, while competitive effects of C. laucha over A. azarae was observed within cropfields. Both species were more affected by exploitation competition than interference, which was
more common in borders than in maize fields. We conclude that seasonally have a profound effect in habitat selection of these
species because it changes the intensity of intra and interspecific competition and affects different habitat preferences
and basic suitability of habitats.
The role of interspecific competition in shaping animal and plant communities has formed one of the major issues in ecology for decades. Small mammals, mainly rodents, have been among the model systems used for research on interspecific competition. Most studies within small mammal systems in the past have examined effects of competition on population attributes such as on population size, habitat use, or population dynamics. Population-level responses are the cumulative effects of individual responses, however, the influence of competition on individual life-history traits has rarely been studied. Research on life-histories may bridge gaps between population biology and effects of competition on individual behaviour. In this paper, we review recent research approaches to interspecific competition in rodents based on census data and species assemblages, that use regression analysis, time series analysis, removal and exclusion experiments, and showcase our own experimental research on the effects of interspecific competition on individual life-history traits in boreal voles.
Interactions between the invasive Argentine ant, Linepithema humile, and native ant species were studied in a 450-ha biological reserve in northern California. Along the edges of the invasion, the presence of Argentine ants significantly reduced the foraging success of native ant species, and vice versa. Argentine ants were consistently better than native ants at exploiting food sources: Argentine ants found and recruited to bait more consistently and in higher numbers than native ant species, and they foraged for longer periods throughout the day. Native ants and Argentine ants frequently fought when they recruited to the same bait, and native ant species were displaced from bait during 60% of these encounters. In introduction experiments, Argentine ants interfered with the foraging of native ant species, and prevented the establishment of new colonies of native ant species by preying upon winged native ant queens. The Argentine ants' range within the preserve expanded by 12 ha between May 1993 and May 1994, and 13 between September 1993 and September 1994, with a corresponding reduction of the range of native ant species. Although some native ants persist locally at the edges of the invasion of Argentine ants, most eventually disappear from invaded areas. Both interference and exploitation competition appear to be important in the displacement of native ant species from areas invaded by Argentine ants.
This study investigates patterns of habitat use and competition in sympatric populations of the bush rat, Rattus fuscipes, and swamp rat, R. lutreolus, in the Blue Mountains National Park, New South Wales, Australia. Radiotracking showed that the home ranges of R. fuscipes tended to occupy woodland more than those of R. lutreolus, whereas use of heath and sedgeland by both species was equal. Home range overlaps were less between the two species than between individuals of R. lutreolus. Trap-captures showed that both species used structurally complex microhabitats, but also that R. fuscipes occupied relatively drier sites with denser leaf litter and taller canopy than R. lutreolus. In a field enclosure containing equal parts dense sedge and woodland, both species spent most time in the sedge. R. lutreolus frequently initiated agonistic behaviour and dominated its smaller congener; subordinate individuals fled or vocalized loudly. To test whether the observed patterns of habitat use of R. fuscipes resulted from habitat selection or competition with R. lutreolus, a field experiment was carried out in which the latter species was removed from two study sites but maintained in two controls. Following removal, the capture rate of R. fuscipes increased some 6.5-fold in sedgeland habitat that had been occupied formerly by R. lutreolus, while capture rates in sedge in the control sites remained unchanged. The rapidity of the habitat shift implicates current or intense competition, mediated by interference. Although interference is a costly process, it may benefit the dominant R. lutreolus by allowing priority of access to preferred moist habitats containing important food or shelter resources. Conversely, R. fuscipes may tolerate interference if it benefits from even temporary access to moist habitats, can reliably detect and avoid R. lutreolus prior to encounters, or has access to drier woodland areas under-used by the dominant species. We suggest finally that extensive gene flow in R. fuscipes may preclude adaptive shifts in habitat preferences in local populations that are sympatric with R. lutreolus, thus reducing the importance of competition but maintaining its intensity over time.
A population of Rattus fuscipes, in Sherbrooke Forest, Victoria, had a well defined breeding season. Mating occurred between November and January and the young were born between December and February. Juveniles were first captured in late February at approximately 1.5 months of age. The subadult age class displaced the parental age class in the population by the following August, so that almost all animals breeding in a season belonged to a single age class. The degree of home range overlap changed seasonally and could be related to changes in the proportion of amicable and agonistic behaviour judged from a series of contrived laboratory encounters. Diet consisted of both plant and insect material and changes in the proportion of these two components correlated with changes in survival. Measurements of 15 physiological parameters and organ weights, drawn at montly intervals indicated three periods during the life cycle when R. fuscipes exhibited heightened adreno-cortical activity. It is suggested that the development of territoriality in subadults during late autumn and possibly the decrease in abundance and quality of food in early winter, largely determine the size of the breeding population in late spring.
Swamp rat Rattus lutreolus and eastern chestnut mouse Pseudomys gracilicaudatus occupy the same coastal wet heath habitat in E Australia. Previous experimental removals have demonstrated asymmetric interspecific competition with the larger R. lutreolus excluding the smaller P. gracilicaudatus from preferred habitat and reducing its abundance. Using a reciprocal manipulation experiment in summer, with the abundance of the smaller P. gracilicaudatus being depressed by removals over a 40 d period, the abundance of R. lutreolus increased more rapidly than on control sites. Body size difference provides the mechanism which facilitates asymmetric competition and determines access to better habitat. The authors analyse the response by R. lutreolus for two size classes separately, large (animals heavier than the largest P. gracilicaudatus) and small (lighter individuals). Interspecific competition in summer can be attributed to the small R. lutreolus size class alone but in winter neither size class exhibits competitive release. Normal growth of juveniles between summer and winter reduces the number of small R. lutreolus and also the intensity of competition with P. gracilicaudatus. Only small R. lutreolus are vulnerable to competition with P. gracilicaudatus and large individuals remain unaffected. The different outcomes of such competition are determined by the size class structure of the larger species, thus producing seasonally variable interspecific competition. -from Authors
Competitive interactions among three common rodent species (Apodemus flavicollis, A. agrarius and Clethrionomys glareolus) were investigated. In order to determine how the rodent community affects the population of A. agrarius, a field experiment was performed consisting of the removal of C. glareolus and A. flavicollis from an experimental plot leaving only A. agrarius. The dynamics of this experimental population was compared to that of the species living as part of the whole community on a control plot. It was found that on the control plot the density of A. agrarius and the size of the area available to them were strongly limited by the other species; also the rate of mortality (or emigration) of A. agrarius was much higher than that of the two other species. Comparison of population parameters for A. agrarius on the control and the experimental plot revealed differences in the survival of offspring, in the mortality (or emigration) of older individuals and in the reproduction. The hypothesis has been advanced that the negative interactions within the community are caused by competition for food, especially in the midsummer period. /// Исследованы конкурентные взаимообношения между тремя обычными видами грызунов (Apodemus flavicollis, A. agrarius, Clethrionomys glareolus). Для определения влияния населения грызунов на популяцию A. agrarius проведены полевые опыты с удалением C. glareolus и A. flavicollis с опытных участков, где оставались толско A. agrarius. Динамика численности этой зкспериментальной популяции A. agrarius сравнивали с популяцией того же вида, обитающей вместе с друтими видами грызунов на контрольном участке. Установлено, что на контрольном участке плотность A. agrarius и размеры территории, доступной для них, четко лимитированы другими видами. Уровень смертности (или змиграции) A. agrarius так же был значительно выше, чем у других двух видов. Сравнения популяционных колебаний у A. agarius в контрольных и опытных участах показали различия в выживаемости рождающихся особей, в уровне смертности (или змиграции) у более старших особей и в скорсти размножения. Выдвинута гипотеза, чсо отрицательные взаимодействия среди грызунов вызваны конкуренцией за пишу, особенно в середине лета.
The silver rice rat (Oryzomys argentatus) a rare endemic rodent, and the black rat (Rattus rattus), an exotic species, have coexisted for <500 years in the Florida Keys. Determination of fine-scale movements and behavior, by use of neck-attached fluorescent dust dispensers, revealed the degree of overlap in use of space, and some food resources, in free-ranging animals. Food selection tests were conducted in the laboratory. Significant differences in vegetation association, behavior, arboreality, and diet were found. From estimates of spatial niche overlap based on four indices I suggested the differences were biologically insignificant; the average value of four estimators on the habitat-choice resource axis was 89%, higher than reported for 47 of 48 pair-wise comparisons of native rodent species. I suggest that silver rice rat populations may be jeopardized by the presence of black rats whose invasion was reported to have caused oryzomine extinctions in the Galapagos and Antilles islands.
(1) Microtus sp. were removed from two grassland areas south of Vancouver, British Columbia, over three years in order to test the hypothesis that Microtus sp. competitively exclude Peromyscus maniculatus from grasslands. Social organization of Microtus on a third area was disrupted for two years and the demographic fate of P. maniculatus on these manipulated areas was compared. (2) Peromyscus populations increased dramatically to sixty-one mice/ha within two years of the continuous removal of Microtus from one grassland area. Peromyscus populations also increased dramatically to thirty-four mice/ha in an area where the social organization of the resident Microtus townsendii was disrupted by manipulation of the sex-ratio of Microtus toward a shortage of females. Virtually no Peromyscus lives on the control area which had a normal Microtus population. (3) In the absence of Microtus the trappability of male Peromyscus was 9% higher than in the presence of Microtus. (4) Survival of Peromyscus was remarkably high on all study areas, especially in winter and spring. There were no indications of a decline in survival rates with the onset of breeding. (5) Reproduction of Peromyscus appeared to start earlier in the year and last later in autumn in the absence of Microtus. (6) When Microtus were allowed to recolonize an experimental grid, the number of Peromyscus dropped dramatically within six weeks. The cause of the decline in the number of Peromyscus was traced to an almost complete exclusion by Microtus of newly recruiting Peromyscus and an increase in mortality or dispersal in adult Peromyscus.
To determine if dispersing prairie voles, Microtus ochrogaster, are prevented from establishing home ranges in habitat already occupied by conspecifics or potentially competitive species, voles were introduced into enclosed populations of: the same species; southern bog lemmings, Synaptomys cooperi; cotton rats, Sigmodon hispidus; or an empty enclosure. The results indicated that colonization by dispersing voles was negatively affected by resident conspecifics. Introduced females were more strongly affected than males during the vegetative growing season but not during the nongrowing season when reproductive activity is typically low. Resident bog lemmings also negatively affected colonization by dispersing voles. However, both sexes of introduced voles were similarly affected in both seasons. There was no evidence of postcolonization competitive effects, suggesting that interspecific competition does not occur between established resident individuals. Cotton rats, which have only recently become part of the small mammal community in Kansas, did not adversely affect colonization by dispersing voles or have adverse post-colonization effects on their survival and reproduction. The ability of residents to inhibit colonization by another species may facilitate the coexistence of M. ochrogaster and Synaptomys cooperi by retarding the competitive exclusion of either species until annual fluctuations in reproduction and density create an abundance of suitable but unoccupied space. This type of coexistence is similar to the storage effect in lottery models of competitive coexistence.
The changes in surface structure and bonding of PET films has been monitored as a function of temperature by means of ESCA. By monitoring both the C1s and O1s core levels it is shown that at remarkably low temperatures there is a reduction in oxygen functionality. This contrasts with the results in the literature relating to bulk techniques for monitoring thermal degradation.
Ancestrally continental forest species of the tribe Oryzomyini, the endemic cricetid rodents of the Galápagos, have had to adapt to the harsh tropical desert of the Islands. Following the recent rediscovery of the Santiago nesoryzomys (Nesoryzomys swarthi) endemic to Isla Santiago, Galápagos, we conducted the 1st autecological study of this species. Our 3-year study revealed mean annual survival of 23.2% and maximum survival of 812 days. Reproductive activity was restricted to the wet season with a stable annual proportion of breeding females and a consistent peak in pregnancy in April. The likelihood of postpartum breeding increased with rainfall when 2 litters were produced. The growth and development of juveniles was slow and they did not reproduce in their natal year. Positive correlations between rainfall and mean adult body weight and between vegetation density (particularly prickly pear cactus [Opuntia galapageia]) and population levels supported a hypothesis of food limitation. Comparisons with the Galápagos oryzomys (Oryzomys bauri), endemic to Isla Santa Fe, and a review of continental members of the tribe Oryzomyini suggest that the ephemeral, unpredictable environment of the Galápagos arid zone has selected for a strategy of relatively high survival and low reproduction in N. swarthi and O. bauri that is more typically found among the desert Heteromyidae than other members of the Oryzomyini. We also present data on sex ratio, home range, and philopatry that together indicate a promiscuous or polygynous mating system. Our findings may help to guide future conservation strategies for this endangered rodent species.
Quantitative data were collected on population size and structure, mortality,
growth, movements, and activity during a 3-yr live-trapping study. Both species maintained
relatively stable population levels with seasonal peaks related to the duration
of the breeding season. R. fuscipes commenced breeding in November, M. cervinipes
in September each year. In both species the breeding season was of variable duration
from year to year. The average litter size for R. fuscipes was 4.4, and for M. cevvinipes
1.8. A few individuals of each sex in both species survived to a second breeding season.
Both species were strictly nocturnal. R. fuscipes rarely left the forest floor, but M.
cevvinipes showed considerable arboreal activity. Movements and ranges of male
R, ~ K S C @ ~ S were larger than those of females; there was little difference between the
sexes in M, cevvinipes. There appeared to be some nomadic movements in the adult
R. fuscipes population. The M. cevvinipes population appeared to be relatively sedentary.
R. lutreolus was predominantly herbivorous; in heath it selected the basal stems of certain cyperaceous herbs, and in forest ate non-sclerophyllous grasses. Fungi were an important dietary component and seed might be eaten in some quantity for a short time in spring and early summer. R. fuscipes showed little dietary overlap with R. lutreolus; in forest it was reliant on fungi and fibrous plant material from particular grasses; in heath it relied on particular cyperaceous species in winter, and ate primarily fleshy fruit, seed and arthropods in summer. Both species are selective; this selectivity changes with season.-from Author
Faeces were studied during 1 to 3 years for rodents live-trapped in 7 areas of Victoria. Diet changed with season for all 6 species studied. In general the staple diet of Rattus lutreolus was basal stem and young rhizome of monocotyledons, probably sedge, and of R. rattus was fungus. Fungus was a main food item for most species and places, especially in winter. Some was basidiomycete but by far the most, especially for R. rattus on coastal heath, was an underground phycomycete tentatively identified as Endogone incrassata. R. fuscipes ate various foods, mainly seeds, insects, fungus and fibrous plant material, whatever was seasonally abundant. Mus musculus ate mostly insects for most of the year, though it is usually considered granivorous and seed was available in summer. Only in June and July were insects less than half the value of food eaten. Pseudomys novaehollandiae ate many foods and almost no insects, but the sample of mice was too small to allow a general conslusion. P. shortridgei ate grass and fungus in autumn and winter but more variety in spring and summer, including flowers, seeds and insects.
We surveyed ground-dwelling small mammals in twenty-four rainforest remnants which were virtual islands surrounded by farmland on a plateau on the east coast of Australia. We investigated the effect of island size, level of disturbance, isolation and microhabitat on the abundance and species richness of the mammals. The remnants ranged from 0.3 to 29 ha, resulting from fragmentation during 175 years of European occupation. Two rodent species (Rattus fuscipes[Waterhouse, 1839] and R. rattus[Linnaeus, 1758] ) and one marsupial insectivore (Antechinus stuartii Macleay, 1841) were trapped in these remnants, with an additional species (A. swainsonii[Waterhouse, 1840] ) several kilometres away in rainforest on the escarpment of the plateau. Small-mammal species richness was low, but the native species (R. fuscipes and A. stuartii) were abundant. Three-way analyses of variance demonstrated that species richness and abundance decreased significantly with decreasing remnant size and increasing disturbance, but showed no distance effect. The abundance and richness of native species responded even more significantly. The interaction between the first two effects is important. Small remnants are affected most detrimentally by increasing disturbance, large remnants are less affected, and medium sized remnants show intermediate effects. The introduced R. rattus which was least abundant in large remnants, but more abundant in distant than near remnants, was also more abundant in those with major disturbance. The single most important variable in step-wise, multiple linear regression analyses was the logarithm of remnant area not influenced by edge effects, explaining 39% of the variance in species richness, 57% for native species richness and 46% for A. stuartii abundance. Disturbance related variables additionally contributed from 12 to 30% of the variance in dependent variables, while habitat variables explained between 22 and 48% of the variance, and accounted for two thirds of the explainable variance in R. fuscipes abundance. The implications of our results for wildlife conservation on the plateau are discussed.
The Lincoln-Petersen model (Chapter 2) and closed population models (Chapter 3) are presented briefly. The Jolly-Seber open population model is covered in detail in Chapter 4. In Chapter 5, the authors consider the "enumeration' or "calendar of captures' approach, which is widely used by mammalogists and other vertebrate ecologists, and recommend that it be abandoned in favor of analyses based on the Jolly-Seber model. One restricted version of the Jolly-Seber model, which allows losses (mortality or emigration) but not additions (births or immigration), is likely to be useful in practice. Another series of restrictive models requires the assumptions of a constant survival rate or a constant survival rate and a constant capture rate for the duration of the study. In Chapter 5, the authors consider 2 generalizations of the Jolly-Seber model. The temporary trap response model allows newly marked animals to have different survival and capture rates for 1 period. The other generalization is the cohort Jolly-Seber model. Ideally all animals would be marked as young, and age effects considered by using the Jolly-Seber model on each cohort separately. Chapter 6 presents a detailed description of an age-dependent Jolly-Seber model, which can be used when ≥2 identifiable age classes are marked. Detailed description of the "robust' design is given in Chapter 7, in which each primary period contains several secondary sampling periods. Chapter 8 gives detailed discussion of the design of capture-recapture studies. A new program has been written to accompany the material on the Jolly-Seber model (Chapter 4) and its extensions (Chapter 5). Another new program has been written for a special case of the age-dependent model (Chapter 6) where there are only 2 age classes. In Chapter 9 a description of the different versions of the 2 programs is given. Chapter 10 gives a description of some alternative approaches that were not considered in this monograph. -from Authors
A native asexual gecko, Lepidodactylus lugubris, declines numerically when the sexual gecko Hemidactylus frenatus invades urban/suburban habitats throughout the Pacific. Previous studies showed that the competitive displacement occurs rapidly and is facilitated by clumped insect resources. Five lines of evidence suggest that the mechanism of displacement is primarily due to differences in the ability of each species to exploit insect resources. (1) These species show nearly complete diet overlap. (2) Insects are a limiting resource for both geckos as evidenced by positive demographic effects with increased insect abundance. (3) Hemidactylus frenatus depletes insect resources to lower levels than L. lugubris, which results in reduced rates of resource acquisition in L. lugubris. (4) This reduced resource acquisition translates into significant reductions in the body condition, fecundity, and survivorship of L. lugubris individuals. (5) Evidence for interference (and other) mechanisms does not account for these negative demographic effects on L. lugubris. Interspecific competition is stronger than intraspecific competition for L. lugubris, with increasing L. lugubris density having negligible effect on H. frenatus, mirroring the asymmetry of the large-scale displacement. The superior harvesting ability of H. frenatus is most pronounced when insects are clumped spatially and temporally, and is attributable to a variety of species-specific traits such as their larger body size, faster running speed, and reduced intraspecific interference while foraging. We conclude that clumped resources can increase interspecific exploitation competition, and this mechanism may contribute to species turnover when human environmental alterations redistribute resources.
We sought to assess the effects of forest fragmentation, introduced Rattus
rattus, exotic tree plantations and secondary vegetation on the endemic rodent Eliurus
webbi (Nesomyinae) and the lemur Microcebus
murinus in the littoral forests of southern Madagascar. For E.
webbi the number of individuals caught, the body mass of males and the percentage of females in the population were positively correlated with the size of the forest fragments. Capture rates and population characteristics of the other two species were uncorrelated with fragment size. None of the endemic species was caught outside the native forest while R.
rattus inhabited all vegetation formations except for a newly planted corridor of tree saplings. Capture rates of both endemic species were uncorrelated with the number of R.
rattus caught at the same site and thus did not indicate replacement of native species by R.
rattus. The study demonstrated negative effects of fragmentation on capture rates of E.
webbi and changes in their population characteristics. Exotic tree plantations or secondary vegetation seem to represent unsuitable or marginal habitats for the endemic species.
Abstract We examined faecal samples of the eastern chestnut mouse (Pseudomys gracilicaudatus) that were collected during a removal experiment conducted in a coastal heathland at Myall Lakes National Park to see whether removal of the swamp rat (Rattus lutreolus) had any effects on food resource use by P. gracilicaudatus. The results showed that, at the young successional stage of vegetation (1. 5 years since last fire), the diet of P. gracilicaudatus changed significantly after the number of R. lutreolus was significantly reduced on the experimental sites. Two months after the removal treatment was terminated there were no significant differences between the control and experimental sites. Factor analysis showed that seasonal change was significant for all three food factors on the control sites, whereas on experimental sites the change was significant only for factor 1. At the middle successional stage (3.5 years since last fire), P. gracilicaudatus showed relatively small seasonal changes on both control and experimental sites, and significant differences between the control and experimental sites did not occur until after the removal manipulation was completed, showing a delayed response. Comparisons of the young and the middle successional stages on both control and experimental sites showed that P. gracilicaudatus used proportionally different food when R. lutreolus was present, but consumed similar food when R. lutreolus was removed. These results suggest that R. lutreolus might have restricted the access of P. gracilicaudatus to better microhabitats, and hence to a better food supply. The ecological implication of these results is that the interpretation of observed population and community patterns must take into account the direct effects of species interactions.
Abstract A competitive interaction between two species of sympatric native rodents was demonstrated experimentally in Myall Lakes National Park (NSW, Australia). The previously documented replacement of Pseudomys gracilicaudatus by Rattus lutreolus in areas of wet heath in this region implied that competition may be the mechanism facilitating this succession. We present experimental evidence to support this suggestion. Removal of the larger R. lutreolus caused a significant increase in abundance of P. gracilicaudatus on five experimental sites in comparison to five unmanipulated control sites. The sites used in this experiment were chosen from three ages of wet heath regenerating after fire. These three ages represent key stages in the replacement of P. gracilicaudatus by R. lutreolus and the occurrence of competition in each of these ages indicates that competition plays an important role in this succession. In the initial stages of the experiment when R. lutreolus were removed they were replaced by new R. lutreolus individuals. This has been interpreted as evidence of strong intraspecific competition. After removal of R. lutreolus, P. gracilicaudatus expanded its habitat range into microhabitats that had formerly been occupied by R. lutreolus and reduced its range in microhabitats previously occupied by P. gracilicaudatus. This leads us to believe that P. gracilicaudatus was occupying inferior microhabitat before the removal of R. lutreolus, which had excluded it from more preferable microhabitat.
This paper tests the hypothesis that Pseudomys novaehollandiae shows competitive superiority over Mus musculus. Experimental removals of P. novaehollandiae on four I ha treatment plots and additions on a further four I ha plots show significant effects of interspecific competition when compared to two I ha unmanipulated control plots. Significant effects of P. novachollandiae populations on the abundance of M. musculus populations were observed for number of captures/day, abundance/trapping session and for the recruitment of new individuals over the post‐removal period, thus allowing rejection of the null hypothesis in each case. There was an apparent ceiling on the total rodent abundance which is indicative of a resource limitation. The resource in short supply appears to be space, but it is not clear if the competition is for food or shelter resources contained within such space or for the space per se , but the latter seems less likely.
The confirmation of this interspecific competition supports the inferences drawn from a considerable amount of indirect evidence, largely descriptive, obtained from previous studies in the Myall Lakes National Park. This study also shows that competition is one of the mechanisms controlling the replacement of species in the succession following disturbance and lends support to the habitat accommodation model proposed for such succession. These points support previous statements on the importance of interspecific competition as a determinant of the structure of these small‐mammal communities.
Habitat preferences of five species of small mammals were studied on a 6.6 ha trapping grid in heathland on an undulating, deep, sandy podzol at Cranbourne, Victoria. The 120 sites were sorted into groups using a polythetic, agglomerative, non-hierarchical clustering procedure with (i) floristic and (ii) structural data. The dispersion of 4051 trap captures over 28 months was studied in relation to these groupings. Rattus lutreolus showed no preference for any of the structural groups, but good differentiation was obtained with the floristic groups. Dispersion of R. lutreolus was related to a sedge-food index, and seasonal change in R. lutreolus dispersion was related to change in rainfall. The preference of R. rattus for areas of wet heath of high structural complexity was best revealed using the structural classification. The results for the other species tended to favour the floristic rather than structural groups. Pseudomys novaehollandiae and Isoodon obesulus preferred dry heath of a younger successional stage. Mus musculus captures showed a preference for the dry heath generally. This preference was most pronounced in spring when the population was declining.The wet community species (R. lutreolus, R. rattus) tended to be food specialists and habitat generalists and the dry community species P. novaehollandiae, I. obesulus, M. musculus), exhibited converse traits.
Habitat selection by seven species of small mammals was investigated in three areas of heathland in Victoria. A total of 12 120 trapnights over 22 months was used to assess preference for different vegetation groups formed by clustering trap sites on (a) floristic and (b) structural criteria.Rattus lutreolus proved to have both floristic and structural requirements. Seasonal changes in distribution in relation to rainfall appeared to be dependent on soil type. Greatest movement occurred on sandy podzol soils. Pseudomys shortridgei selected the most diverse vegetation types. Rattus fuscipes preferred wet, structurally complex vegetation. Mus musculus appeared to fill the niche of Antechinus minimus and partially replace A. stuartii and A. flavipes when Antechinus spp. were absent. M. musculus seems to commonly fill three niches in these heathlands: fossorial insectivore, scansorial insectivore and immediate post-fire omnivore.A small mammal community structure of five major food niches may be common to both heathland and forest communities of south-eastern Australia.
The black rat, Rattus rattus, is an alien rodent in Australian ecosystems where niche overlap with native small mammals may lead to competition for resources and displacement of native species. In coastal habitats surrounding Jervis Bay in south-eastern Australia, R. rattus co-occurs with the native bush rat, Rattus fuscipes, and brown antechinus, Antechinus stuartii. Relative distributions and abundances, and fine-scale space use suggest invasive and native rodents compete for use of space and habitat. Such competitive interactions were not evident between R. rattus and native A. stuartii, which was negatively influenced more by disturbance to habitat. Differences in rodent communities between spatially separate forests forming the northern and southern peninsulas of Jervis Bay potentially reflect symmetrical competition and differences in competitive outcomes. In southern forests, R. rattus was largely restricted to patches of disturbed forest associated with campgrounds. Competitive interference by native rodent populations inhabiting surrounding intact forests may have so far limited R. rattus colonization of these areas. In northern forests, R. rattus was the predominant rodent irrespective of disturbance, while populations of R. fuscipes were unusually low seemingly due to poor juvenile recruitment. Native individuals avoided areas frequented by adult R. rattus and given that species did not partition use of microhabitats, R. rattus most likely precluded R. fuscipes from suitable habitat and in doing so limited native populations. We discuss how natural disturbance of habitat and human activity have potentially facilitated successful invasion by R. rattus of the northern forests. Studies that manipulate rodent populations are required to support these interpretations of observed patterns.
Studies on the effects of nonindigenous invasive species and habitat fragmentation on native ecosystems have become priorities for conservation biologists. This is relevant particularly for islands with high degrees of endemism. In the present paper the role of fragmentation and possible effects of introduced Rattus rattus on endemic rodents (Macrotarsomys bastardi and Eliurus spp.) and the gray mouse lemur (Microcebus murinus) were assessed for dry deciduous forests in Madagascar. Capture rates of endemic rodents declined significantly with declining fragment size. Macrotarsomys bastardi was never caught in primary forest fragments < 600 ha or outside the primary forest but captures of M. bastardi were correlated to changes in vegetation structure associated with fragmentation rather than to fragment size per se. Eliurus spp. were also found in small primary-forest fragments and in secondary forests close to primary forests, suggesting that secondary forests can serve as buffer zones or corridors for this species. The lemur M. murinus was caught in all types of primary and secondary forest. This species did not seem to respond to fragmentation of primary forests. Even though it was found in most secondary-forests, capture rates declined as these secondary forest formations increased in size. This indicates that secondary forests are suboptimal habitats for M. murinus. Rattus rattus were caught in all vegetation formations except for the open savanna. Their capture rates increased as forest fragments became smaller, indicating that mosaics of different habitat types are beneficial for introduced rats. There was no significant relation between capture rates of R. rattus and the endemic species. In conclusion, these results suggest that (1) native Malagasy rodents of the dry deciduous forest are more sensitive towards forest disturbance than M. murinus; (2) there is no indication for negative interactions between introduced rats and the native small-mammal fauna.
Understanding the recovery of populations after disturbance is critical to many aspects of applied population management, ranging from the development of conservation strategies to pest control. We used a controlled and replicated field experiment linked to a genetic study to examine the rate and mechanism of population recovery of the Australian bush rat after severe experimental population reduction.
The main factors examined were perturbation treatment (removal of animals, removal followed by restocking, no removal), patch size and patch isolation. Although large numbers of animals were removed from many patches, on average populations recovered to pretreatment levels within 2 years. Populations rebounded to levels that appeared to approximate patch carrying capacity. Initially small populations recovered to a small size and those that were large were also large 24 months later. No significant relationships between population recovery and patch size and isolation were identified.
There was an effect of initial population size on proportional trapping success: a higher proportion of initially large populations was trapped than smaller ones.
Genetic analyses revealed a significant genetic change following experimental perturbation. Rapid population recovery was mostly via residual animals (and their offspring) that escaped capture, rather than colonization from neighbouring populations.
Synthesis and applications . This study has implications for vegetation and habitat management in fragmented landscapes where disturbances such as fire occur. Parts of a habitat fragment that escape disturbance, or are partially disturbed, may continue to support suitable habitat and be a source of animals, thereby facilitating population recovery. Post‐disturbance human activities (e.g. salvage harvesting of fire‐damaged trees) can modify refugial habitats and, in turn, impair population recovery and species persistence in fragmented landscapes. These activities require careful management to ensure biota are not negatively impacted.
Information theory and log-likelihood models - a basis for model selection and inference practical use of the information theoretic approach model selection uncertainty with examples Monte Carlo insights and extended examples statistical theory.
Summary • Introduced predators are a major threat to native island populations, yet direct evidence of predation is often lacking, especially when it is difficult to detect by traditional dietary methods. • Historical declines of nesting seabirds on the Shiant Islands, Outer Hebrides, roughly coincided with the accidental introduction of ship rats Rattus rattus in c. 1900. Rats have been implicated in declines of seabirds, but the Shiant population is one of two remaining naturalized R. rattus populations in Britain, prompting calls for their protection. • Live-trapping studies with stable isotopes and gut content analysis were used to investigate whether ship rats prey on Shiant Islands seabirds. Another aim of this study was to determine whether marine-derived foods subsidize rat populations, permitting higher densities, greater productivity and larger body size than expected from terrestrial resources alone. • Comparisons of stable carbon and nitrogen isotopic signatures of rat tissues with those of seabirds, marine invertebrates, marine algae and land-based foods revealed that seabirds and other marine prey were the primary source of protein for rats living in colonies or near the shore. These results were corroborated by gut content analysis, and suggest a greater role for active predation of seabirds by rats than has previously been apparent at this locality. • Seabird colonies and especially coastal areas supported higher numbers of rats than more inland habitats. Coastal and colony-dwelling rats were more active reproductively and were larger than those living inland. • Although rats are capable of surviving solely on terrestrial foods, their ability to use marine prey may buffer populations during lean times, i.e. outside the seabird nesting season, and may in part explain their success and status as pests on islands world-wide. Overall, this work reveals the value of stable isotopes in identifying predation by exotic species, but also underscores potential uncertainties inherent in all diet-based methods in distinguishing predation from scavenging.
Throughout much of Britain, Ireland and north Italy, red squirrels ( Sciurus vulgaris L.) have been replaced by alien grey squirrels ( S. carolinensis Gmelin) introduced from North America. We have studied squirrels in two mixed woodlands in north Italy and two conifer forests in north England. In each country, one site was occupied by red squirrels and one site by both species.
We have previously considered interference competition and exploitation competition for food and space between red and grey squirrels and have showed that grey squirrels caused reduced body growth in juvenile and subadult red squirrels, and compete for tree seeds cached by adult red squirrels in spring. Here we report on the effects of grey squirrels on three fitness components in red squirrels that have consequence at the population level: fecundity, residency and recruitment.
Litter production peaked in the spring and summer, but fewer females bred in the summer with grey squirrels present. In addition, fewer individual red squirrel females produced two litters per year in the sites with grey squirrels. Moreover, red squirrel recruitment rate and, in the mixed broadleaf sites, red squirrel juvenile residency, decreased with increasing grey squirrel density.
Fecundity of individual female red squirrels was lower in red–grey than in red‐only sites because they had a lower body mass in sites with grey squirrels.
Overall, there was no significant effect of grey squirrels on residency of adult red squirrels or on population turnover rate. However, the presence of grey squirrels resulted in a reduction in red squirrel fitness which was evident by lower population summer breeding and a lower recruitment. Over time, this will result in a decline in population size and eventually population extinction.
Studies on competing mammalian species in the past have focused mainly on the competitive exclusion of one species from the preferred habitat of the other. Investigations on effects of competition and coexistence on individual fitness are rare. In this study we were able to measure effects of interspecific competition on major fitness components, using a system with two vole species in asymmetric competition. Survival, reproduction and space use of bank vole Clethrionomys glareolus females were monitored in 32 enclosed populations over four replicates of eight parallel run enclosures. Into half of the enclosures we introduced an additional number of field voles Microtus agrestis, a dominant competitor.
Survival of bank vole females was lower under competitive conditions. Total number of breeding females was lower in populations coexisting with competitors. Territory size of bank vole females decreased. Females body weight and litter size bank vole litters conceived during the experiment were not affected by interspecific competition. These characteristics should respond to differences in food resources, and territory size should increase if food was scarce, thus we found no indication of direct exploitation competition between the two species. Space use was overlapping between the species, but individuals of both species were never caught together in the same trap, indicating avoidance behaviour.
We conclude that adult bank vole females do suffer fitness consequences through interference competition with field voles, probably basing on increased number of aggressive encounters in the presence of the dominant species. Our results suggest, that direct interference rather than indirect exploitation competition may be the cause for observed fitness decrease in bank vole females.
