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Maladaptive traits in invasive species: In Australia, cane toads are more vulnerable to predatory ants than are native frogs
Functional Ecology
Abstract
Summary • If a species is translocated outside its native range, some of its traits (evolved to match conditions in the ancestral range) likely will be maladaptive. Identifying ways in which the invader are poorly suited to its new range might provide novel opportunities for biocontrol. • The spread of cane toads (Bufo marinus, native to central and South America) through tropical Australia has created major ecological problems. Although many native predators cannot deal with the toxins of the invasive toads, ‘meat ants’ (Iridomyrmex reburrus) kill and consume many metamorph toads. Might this be a mismatch between the invader and its newly invaded range, whereby the morphology, locomotor ability and/or behaviour of cane toads renders them vulnerable to a predator that poses little danger to native anurans? • To explore this possibility, we measured habitat use and activity patterns in meat ants, metamorph cane toads and metamorphs of seven native frog species (Litoria bicolor, L. caerulea, L. dahlii, L. nasuta, L. rothii, Limnodynastes convexiusculus, Opisthodon ornatus) in standardized enclosures in the laboratory. • Unlike the frogs, (1) toads selected open microhabitats and were active diurnally, thus increasing encounter rates with meat ants; (2) toads failed to detect and evade approaching ants; (3) toads exhibited poor locomotor ability (short slow hops, reflecting their small size and short limbs); and (4) toads frequently relied on an ineffective defence mechanism (crypsis) when attacked. • In combination, these traits rendered cane toad metamorphs far more susceptible to predation by meat ants than were any of the native frogs tested. That vulnerability presumably reflects lack of coevolution between cane toads and Australian ants. • The inability of invasive toads to escape predatory native ants might be exploited to reduce cane toad numbers, by manipulating ant densities and/or locations during periods of toad metamorph emergence.
... Metamorph cane toads often can be found clustered within particular hoofprints (James 1994 unpublished data), suggesting that the microhabitat provided by these might be important for toads. Also, metamorph toads in this system are vulnerable to attack by predatory meat ants [27,31,32], whose activities plausibly might be either facilitated or hindered by the presence of hoofprints. ...
... Densities of metamorph toads can exceed .100 per m 2 around water bodies in this area [31]. Because cane toads spawn primarily in ponds with open (unvegetated) ground margins, gently sloping banks, and anthropogenic disturbance [46,47], sheltered (moist, cool, safe) retreat-sites close to the water's edge can be rare (E. ...
... These species are dominant members of Australian ant communities because of their abundance, biomass, high activity rates and aggressiveness [48,49]. They overlap widely with cane toads in Australia in terms of distributional range, diel activity cycles and preferred habitats, with the species Iridomyrmex reburrus being a major predator on post-metamorphic toads at our study site [27,31,32]. Unlike many vertebrate predators, these ants are not affected by the toad's toxins [50]. ...
Many invasive species exploit the disturbed habitats created by human activities. Understanding the effects of habitat disturbance on invasion success, and how disturbance interacts with other factors (such as biotic resistance to the invaders from the native fauna) may suggest new ways to reduce invader viability. In tropical Australia, commercial livestock production can facilitate invasion by the cane toad (Rhinella marina), because hoofprints left by cattle and horses around waterbody margins provide distinctive (cool, moist) microhabitats; nevertheless the same microhabitat can inhibit the success of cane toads by increasing the risks of predation or drowning. Metamorph cane toads actively select hoofprints as retreat-sites to escape dangerous thermal and hydric conditions in the surrounding landscape. However, hoofprint geometry is important: in hoofprints with steep sides the young toads are more likely to be attacked by predatory ants (Iridomyrmex reburrus) and are more likely to drown following heavy rain. Thus, anthropogenic changes to the landscape interact with predation by native taxa to affect the ability of cane toads in this vulnerable life-history stage to thrive in the harsh abiotic conditions of tropical Australia.
... Large, highly aggressive and behaviourally dominant ants (Iridomyrmex spp.) are ubiquitous in tropical Australia, but no comparable functional group occurs in the cane toad's home range. Metamorph toads tend to ignore the approach of predatory ants, and to rely on crypsis rather than attempting to escape if seized (Ward-Fear et al. 2009; Ward-Fear, Brown & Shine 2010). As a result, metamorph toads often are consumed by ants (Clerke & Williamson 1992; Ward-Fear et al. 2009). ...
... Metamorph toads tend to ignore the approach of predatory ants, and to rely on crypsis rather than attempting to escape if seized (Ward-Fear et al. 2009; Ward-Fear, Brown & Shine 2010). As a result, metamorph toads often are consumed by ants (Clerke & Williamson 1992; Ward-Fear et al. 2009). Can we increase those rates of predation to provide an additional weapon to assist in the control of numbers of this unwelcome invasive species? ...
... Cane toads preferentially spawn in ponds surrounded by large expanses of open ground, rather than vegetation (). In combination, these factors render toad metamorphs susceptible to predatory ants (Ward-Fear et al. 2009). ...
1. Invasive species pose ecological threats in many areas, but attempts to control invaders by introducing other exotic species may cause further unanticipated problems. If we can use predators native to the introduced range to assist in control of the invader, the risks of collateral damage are lower.
2. In tropical Australia, high desiccation rates restrict newly-transformed (metamorph) cane toads Bufo marinus to the margins of waterbodies, rendering the metamorphs vulnerable to predatory ants (Iridomyrmex reburrus). By adding bait (catfood) to selected areas, we increased ant densities (and thus, toad mortality) more than fourfold.
3. Over 50% of attacks by ants in the field were immediately fatal to the metamorph toads, and most ‘escapee’ toads (88%) died of their injuries within 24 h after the attack.
4. When we increased ant densities by artificial baiting, 98% of metamorph toads were encountered, and 84% attacked, within the two-minute observation period. Collateral damage to native fauna appears to be low, but warrants closer examination.
5.Synthesis and applications. Manipulating the foraging locations of native predatory ants can substantially increase their off-take of invasive toads. More generally, vulnerabilities of invasive species to predators native to the introduced range may facilitate control of invader numbers with little collateral damage to the rest of the fauna.
... ants (Iridomyrmex reburrus), one of the few native predators that can tolerate bufotoxins (Clerke and Williamson 1992), readily consume cane toad metamorphs. Furthermore, cane toads are more vulnerable to meat ants than native species because native species have evolved behavioral responses to evade predation by meat ants (Ward-Fear et al. 2009).The probability that a cane toad metamorph will encounter and survive an attack by meat ants is dependent on metamorph body size (Ward-Fear et al. ...
... The application of these two control methods could reduce adult numbers by almost 80% in established cane toad populations. Both tadpole alarm chemicals and meat ants are not likely to have detrimental effects on populations of native species because cane toad tadpole alarm chemicals only elicit responses in cane toad tadpoles (Hagman and Shine 2008a), and meat ants are actively avoided by native species (Ward-Fear et al. 2009). In addition, meat ants and tadpole alarm chemicals are gender-neutral control strategies. ...
Background/Question/Methods
Considered one of the world’s 100 most invasive species, the cane toad (Bufo marinus) has proven to be highly adaptable and difficult to extirpate. In Australia, invasive cane toads are particularly problematic with quantified negative effects on many native species. Deterministic population models have been used to examine potential impacts of different control strategies and have generally shown that removal of adults is likely most effective. However, these models have neglected to incorporate variability in vital rates despite available cane toad life history data from both native and invasive ranges. The effect that this variability may have on cane toad population models, on the life stage(s) that should be targeted for control, and on what management strategies should be pursued to control existing populations, is unknown. A stochastic stage-based population model with density dependence at the tadpole stage was constructed using life history data from cane toad populations in Australia in order to examine the relationship between life history parameters and two metrics of successful population control: mean adult population size and extinction risk. Because the model included both stochasticity and density dependence, we used standardized coefficients of linear and logistic regression analyses as estimates of the sensitivity of population size and extinction risk, respectively, to vital rates.
Results/Conclusions
The model yielded estimates of 200-300 adults per 100 m, which is consistent with observed population estimates from Australia and the conclusions of previous modeling efforts. Results from the linear regression analysis for mean adult population size showed that control methods targeting metamorph (<30 mm) cane toads would yield the strongest decrease in the mean number of adults. Juvenile survival, metamorph survival, adult survival, and maximum tadpole survival had the greatest effect on extinction risk, indicating that control methods that reduce survival of smaller cane toads (i.e., the use of tadpole alarm pheromones in combination with lungworm parasites and meat ants) will likely prove most effective. These results contrast those of previous studies, reflecting the importance of incorporating variability into studies of population dynamics. However, uncertainty in our estimates of juvenile survival and the effects of proposed control methods warrant further examination. Future work will include the construction of a cane toad size-based population model to further investigate the population-level effect of control methods that alter cane toad body size.
... Even less is known about the other side of the coin: the impacts of 'invader versus native' interactions on the invader. Biotic resistance may be an important constraint on invasion success, with many translocated species failing to establish because of interactions with native taxa (Simberloff 1989;Ward-Fear et al. 2009). ...
... That shift may reflect avoidance of larger cannibalistic conspecifics by edibly sized metamorphs . In contrast, most native frogs are primarily nocturnal throughout their post-metamorphic life (Tyler 1994;Ward-Fear et al. 2009). Seasonality of activity varies geographically. ...
Translocated from their native range in the Americas in 1935, cane toads (Rhinella marina, Bufonidae) have now spread through much of tropical and subtropical Australia. The toad's invasion and impact have attracted detailed study. In this paper, I review information on ecological interactions between cane toads and Australian anurans. The phylogenetic relatedness and ecological similarity between frogs and toads creates opportunities for diverse interactions, ranging from predation to competition to parasite transfer, plus a host of indirect effects mediated via impacts of toads on other species, and by people's attempts to control toads. The most clear‐cut effect of toads on frogs is a positive one: reducing predator pressure by fatally poisoning anuran‐eating varanid lizards. However, toads also have a wide range of other effects on frogs, some positive (e.g. taking up parasites that would otherwise infect native frogs) and others negative (e.g. eating frogs, poisoning frogs, competing with tadpoles). Although information on such mechanisms predicts intense interactions between toads and frogs, field surveys show that cane toad invasion has negligible overall impacts on frog abundance. That counter‐intuitive result is because of a broad balancing of negative and positive impacts, coupled with stochastic (weather‐induced) fluctuations in anuran abundance that overwhelm any impacts of toads. Also, the impacts of toads on frogs differ among frog species and life‐history stages, and depend upon local environmental conditions. The impacts of native frogs on cane toads have attracted much less study, but may well be important: frogs may impose biotic resistance to cane toad colonization, especially via competition in the larval phase. Overall, the interactions between native frogs and invasive toads illustrate the diverse ways in which an invader's arrival can perturb the native fauna by both direct and indirect mechanisms, and by which the native species can curtail an invader's success. These studies also offer a cautionary tale about the difficulty of predicting the impact of an invasive species, even with a clear understanding of mechanisms of direct interaction.
... That severe ecological impact has stimulated intensive research on ways that we might reduce toad numbers. One promising area involves the discovery that toads are vulnerable to predation by several taxa of native invertebrates, including ants (Ward-Fear et al. 2009) and aquatic coleopterans and hemipterans (Cabrera-Guzmán et al. 2012). Also, the tadpoles of cane toads co-occur with those of native anurans (Crossland et al. 2008), raising the possibility that competition between toad tadpoles and frog tadpoles might suppress toad recruitment. ...
... That is, the lack of a long coevolutionary history between these two types of anurans means that there has been insufficient time for effective selection on toads to detect and avoid ponds already containing frog tadpoles. In the same way, cane toads do not recognize and avoid large carnivorous ants that feed heavily upon metamorph toads in Australia (but not within the toads' native range; Ward-Fear et al. 2009), and adult toads are readily attracted to a wriggling caudal lure of a predatory Australian snake ). ...
The cane toad (Rhinella marina) is one of the most successful invasive species worldwide, and has caused significant negative impacts on Australian fauna. Experimental work in the laboratory and in mesocosms has shown that tadpoles of native frogs can affect survival, size at metamorphosis and duration of larval period of cane toad tadpoles. To test if these effects occur in nature, we conducted a field experiment using two temporary ponds where we set up enclosures with tadpoles of native green tree frogs (Litoria caerulea) and cane toads in treatments with a range of densities and combinations. The presence of green tree frog tadpoles significantly decreased the growth rate of toad tadpoles and increased the duration of their larval period in both ponds; in one pond, frog tadpoles also significantly reduced the body length and mass of metamorph toads. Toad tadpoles did not have any significant negative effects on green tree frog tadpoles, but there was strong intraspecific competition within the latter species: increased frog tadpole density resulted in increased larval period and reduced survival, growth rate and size at metamorphosis for frogs at one or both ponds. Our results are encouraging for the possibility of using native frogs as one component of an integrated approach to the biological control of cane toads.
... ants (Iridomyrmex reburrus), one of the few native predators that can tolerate bufotoxins (Clerke and Williamson 1992), readily consume cane toad metamorphs. Furthermore, cane toads are more vulnerable to meat ants than native species because native species have evolved behavioral responses to evade predation by meat ants (Ward-Fear et al. 2009).The probability that a cane toad metamorph will encounter and survive an attack by meat ants is dependent on metamorph body size ( Ward-Fear et al. 2010): ...
... The application of these two control methods could reduce adult numbers by almost 80% in established cane toad populations. Both tadpole alarm chemicals and meat ants are not likely to have detrimental effects on populations of native species because cane toad tadpole alarm chemicals only elicit responses in cane toad tadpoles (Hagman and Shine 2008a), and meat ants are actively avoided by native species (Ward-Fear et al. 2009). In addition, meat ants and tadpole alarm chemicals are gender-neutral control strategies. ...
Invasive species are costly and difficult to control. In order to gain a mechanistic understanding of potential control measures, individual-based models uniquely parameterized to reflect the salient life-history characteristics of invasive species are useful. Using invasive Australian Rhinella marina as a case study, we constructed a cohort- and individual-based population simulation that incorporates growth and body size of terrestrial stages. We used this allometric approach to examine the efficacy of nontraditional control methods (i.e., tadpole alarm chemicals and native meat ants) that may have indirect effects on population dynamics mediated by effects on body size. We compared population estimates resulting from these control methods with traditional hand removal. We also conducted a sensitivity analysis to investigate the effect that model parameters, specifically those associated with growth and body size, had on adult population estimates. Incremental increases in hand removal of adults and juveniles caused nonlinear decreases in adult population estimates, suggesting less return with increased investment in hand-removal efforts. Applying tadpole alarm chemicals or meat ants decreased adult population estimates on the same level as removing 15-25% of adults and juveniles by hand. The combined application of tadpole alarm chemicals and meat ants resulted in approximately 80% decrease in adult abundance, the largest of any applied control method. In further support of the nontraditional control methods, which greatly affected the metamorph stage, our model was most sensitive to changes in metamorph survival, juvenile survival, metamorph growth rate, and adult survival. Our results highlight the use and insights that can be gained from individual-based models that incorporate growth and body size and the potential success that nontraditional control methods could have in controlling established, invasive Rhinella marina populations.
... For example, invasive cane toads in Australia have had both positive and negative consequences for native fauna (Shine 2010). Introduced to northeastern Australia in 1935 to control insect pests of commercial agriculture , the cane toad (Bufo marinus) is one of the world's most infamous invasive species (Lever 2001; Tyler 1999). This highly toxic anuran from South and Central America now occupies more than 1 million square kilometers of tropical and subtropical Australia (Lever 2001). ...
... Avian scavengers are not the only native Australian species to benefit from the arrival of cane toads. As noted above, the toads also are consumed by keelback snakes (Llewelyn et al. 2010a) and by native carnivorous ants (Ward-Fear et al. 2009, b). Most other ''benefits'' of cane toad invasion likely reflect indirect effects, mediated by the toads' negative impact on interacting species. ...
Although interest in the ecological impacts of invasive species has largely focused on negative effects, some native taxa may benefit from invader arrival. In tropical Australia, invasive cane toads (Bufo marinus) have fatally poisoned many native predators (e.g., marsupials, crocodiles, lizards) that attempt to ingest the toxic anurans, but birds appear to be more resistant to toad toxins. We quantified offtake of dead (road-killed) cane toads by raptors (black kites (Milvus
migrans) and whistling kites (Haliastur
sphenurus)) at a site near Darwin, in the Australian wet-dry tropics. Raptors readily took dead toads, especially small ones, although native frogs were preferred to toads if available. More carcasses were removed in the dry season than the wet season, perhaps reflecting seasonal availability of alternative prey. Raptors appeared to recognize and avoid bufotoxins, and typically removed and consumed only the toads’ tongues (thereby minimizing toxin uptake). The invasion of cane toads thus constitutes a novel prey type for scavenging raptors, rather than (as is the case for many other native predators) a threat to population viability.
... These tests provide mixed support for the ERH, and evidence for the ISH is rare [6,12,14,16]. Few studies have examined predation pressures of native enemies on exotic species in the exotic species' new range [18]. Recent theories emphasize the ability of the naı¨veténaı¨veté of exotic species or native enemies to influence the establishment and proliferation of exotic species, and the links between naı¨veténaı¨veté and ERH and ISH in predator-prey systems [6,8,13,19]. ...
... These results suggest that Japanese frogs might have effective defenses against red-banded snakes and experience lower predation pressures than bullfrogs. Higher predation pressures of red banded snake on bullfrogs than native anurans on Daishan Island was consistent with interactions among 'meat ant', invasive cane toads and native anurans in Australia [18]. Cane toad metamorphs were more susceptible to predation by native enemy 'meat ants' than were seven native anuran species due to the cane toads' ineffective defense response when attacked. ...
Although native enemies in an exotic species' new range are considered to affect its ability to invade, few studies have evaluated predation pressures from native enemies on exotic species in their new range. The exotic prey naiveté hypothesis (EPNH) states that exotic species may be at a disadvantage because of its naïveté towards native enemies and, therefore, may suffer higher predation pressures from the enemy than native prey species. Corollaries of this hypothesis include the native enemy preferring exotic species over native species and the diet of the enemy being influenced by the abundance of the exotic species. We comprehensively tested this hypothesis using introduced North American bullfrogs (Lithobates catesbeianus, referred to as bullfrog), a native red-banded snake (Dinodon rufozonatum, the enemy) and four native anuran species in permanent still water bodies as a model system in Daishan, China. We investigated reciprocal recognition between snakes and anuran species (bullfrogs and three common native species) and the diet preference of the snakes for bullfrogs and the three species in laboratory experiments, and the diet preference and bullfrog density in the wild. Bullfrogs are naive to the snakes, but the native anurans are not. However, the snakes can identify bullfrogs as prey, and in fact, prefer bullfrogs over the native anurans in manipulative experiments with and without a control for body size and in the wild, indicating that bullfrogs are subjected to higher predation pressures from the snakes than the native species. The proportion of bullfrogs in the snakes' diet is positively correlated with the abundance of bullfrogs in the wild. Our results provide strong evidence for the EPNH. The results highlight the biological resistance of native enemies to naïve exotic species.
... As such, a spatio-temporal mismatch of predator and prey in Lake Michigan may hinder the use of natural predators as a control mechanism. The use of native predators as a form of biocontrol on Rusty Crayfish could conceivably be achieved, however, through the use of enclosures to manipulate foraging locations and behaviors (Ward-Fear et al. 2009. ...
Unlabelled:
The goal of most invasive species suppression programs is to achieve long-term sustained reductions in population abundance, yet removal programs can be stymied by density-dependent population responses. We tested a harvest removal strategy for invasive Rusty Crayfish (Faxonius rusticus) at two nearshore native fish spawning habitats in northern Lake Michigan. Changes in average Rusty Crayfish densities were evaluated with a before-after reference-impact study design. We removed 3182 Rusty Crayfish, primarily adults (> 20 mm carapace length), at two sites over two harvest seasons, expending 17,825 trap days in effort. Generalized linear modeling results suggested a statistically significant reduction in Rusty Crayfish densities was achieved at one reef, Little Traverse Bay (LTB Crib). Reduced densities were sustained over the egg maturation period for native fish and into the following year after removal ceased. By late summer/early fall, between consecutive suppression efforts in 2018 and 2019, we observed a threefold increase in pre-removal densities. Size-frequency histograms from diver quadrat surveys showed higher abundances of juvenile (< 20 mm carapace length) size classes the following spring and summer at LTB Crib compared to its paired reference site. Stock-recruit curves fit to count data, pooled across all sites, provided further evidence of density-dependence. With a proviso that we only conducted two seasons of consecutive suppression, this study highlights an important aspect of invasive species management and raises questions about the efficacy of adult-only crayfish removal strategies.
Supplementary information:
The online version contains supplementary material available at 10.1007/s10530-023-03076-6.
... As such, a spatio-temporal mismatch of predator and prey in Lake Michigan may hinder the use of natural predators as a control mechanism. The use of native predators as a form of biocontrol on Rusty Cray sh could conceivably be achieved, however, through the use of enclosures to manipulate foraging locations and behaviors(Ward-Fear et al. 2009. ...
The goal of a harvest removal program to control invasive species is usually to achieve sustained reductions in population abundance. Yet removal efforts may be counteracted by density-dependent processes by increasing available resources and reducing stage-specific mortality. We tested a harvest removal strategy for invasive Rusty Crayfish ( Faxonius rusticus ) focused on nearshore cobble reefs, used by several native fishes as spawning habitats, in Lake Michigan with a before-after control-impact (BACI) study design. We removed 3182 Rusty Crayfish, primarily adults (> 20 mm carapace length), at two sites over two harvest seasons, expending 17,825 trap days in effort. While the BACI analysis results suggested that a statistically significant reduction in Rusty Crayfish densities assessed from diver quadrat surveys was achieved on one reef (Little Traverse Bay Crib), suppression effects were highly variable across sites. In addition, reduced densities were sustained over the egg maturation period for native fish and into the following year after removal ceased. However, by late summer/early fall between consecutive suppression efforts in 2018 and 2019 we observed a threefold increase in pre-removal densities. Size-frequency histograms from diver quadrat surveys showed higher abundance of juvenile size classes over the following spring and summer at Little Traverse Bay Crib compared to its paired reference site, suggesting a compensatory response. Evidence of compensation was corroborated by stock-recruitment analysis and a coincident increase in ovarian egg counts at Little Traverse Bay Crib between 2018 and 2019. With a proviso that we only conducted two seasons of consecutive suppression, our results emphasizes the effects of density-dependent processes in invasive species management and raises questions about efficacy of adult-only removal strategies.
... The displacement of native species by resource competition (Johnson, Germain, Tarwater, Reid, & Arcese, 2018) and the extinction of native species by increasing the number of predators (Noonburg & Byers, 2005) are examples of effects caused by invasive species. The interactions between native and exotic species do not always result in the advancement of the exotic species (Green, Lake, & O'Dowd, 2004;Paini, Funderburk, & Reitz, 2008;Radville, Gonda-King, G omez, Kaplan, & Preisser, 2014;Simberloff, Relva, & Nuñez, 2002;Ward-Fear, Brown, Greenlees, & Shine, 2009) or have harmful effects on the ecosystem (Ewel & Putz, 2004;Hoddle, 2004;Schlaepfer, Sax, & Olden, 2011). ...
Every year exotic species are introduced into the environment worldwide; some species succeed, and others do not manage to establish themselves in the new environment. The introduction of exotic organisms affects ecological relationships, mainly by acting as potential competitors with native species. In 2004, an exotic mite from America, Raoiella indica, was detected and has consequently experienced rapid territorial expansion having a high population density. To understand the effects of the introduction of R. indica on the native mites, we selected the native mite web producing mite Oligonychus pratensis and evaluated the competition between exotic (R. indica) and native mites (O. pratensis). Four experiments were conducted to evaluate the effect of competition on oviposition rate, intrinsic growth rate, behavioural choice of colonisation site and distributional behaviour on plants. The presence of the heterospecific mites had a negative effect on both species, reducing the oviposition rate. R. indica preferred sites previously colonised by O. pratensis, but O. pratensis did not prefer sites with or without R. indica colonisation. R. indica exhibited a higher growth rate with some interactions with O. pratensis. The species altered its distribution pattern on plants when in the presence of the heterospecific mite. In our study, R. indica appeared to benefit from previous colonisation by O. pratensis, which could contribute to its territorial expansion.
... V arious arthropod taxa, including arachnids, aquatic hemipterans, beetles, and ants, are known predators of both juvenile and adult amphibians (e.g., McCormick and Polis 1982;Hinshaw and Sullivan 1990;Haddad and Bastos 1997;Freed and Neitman. 1998;Jung et al. 2000;Zuffi 2001;Toledo 2005;Dehling 2007;Ward-Fear et al. 2009). Carabid beetles frequently feed on live or dead amphibians (Littlejohn and Wainer 1978;Ovaska and Smith 1988;Robertson 1989) and carabid beetle larvae in the genus Epomis feed entirely on amphibians and use a unique luring behavior to attract their prey (Barve and Chaboo 2011;Wizen and Gasith 2011;Wizen et al. 2017). ...
... The toads themselves propagate via the emergence of adults from water to land and via the dispersal of adults as they invade new waterbodies. Cane toad metamorphs (i.e., earliest terrestrial life stage) are small upon leaving water and most susceptible to predation by arthropods including ants (Ward-Fear et al. 2009). When consumption of juvenile or adult cane toads by native nest predators (i.e., predators that eat eggs in a nest) increases the mortality of such predators, cane toads can indirectly enhance hatching success of other native semiaquatic and terrestrial species including tree snakes (Dendrelaphis punctulatus), herbivorous pig-nosed turtles (Carettochelys insculpta), predatory freshwater crocodiles (Crocodylus johnstoni), and predatory Gilbert's dragons (Amphibolurus gilberti) (Doody et al. 2009;Webb and Manolis 2010). ...
Pervasive environmental degradation has altered biodiversity at a global scale. At smaller scales, species extirpations, invasions, and replacements have greatly influenced how ecosystems function and interact by affecting the exchanges of energy, materials, and organisms. In this chapter, we examine how a variety of environmental stressors, and associated species losses and gains, change the exchange of resources (materials or organisms) within and among ecosystems. We specifically consider how changes that occur within an ecosystem may trigger effects that reverberate (e.g., directly, indirectly, and via feedbacks) back and forth across ecological boundaries and propagate to other ecosystems connected via exchanges of materials and organisms. Our synthesis provides cursory overviews of ecosystem “openness” as it has been addressed by community ecologists and the conceptual development of ecological frameworks used to examine resource exchanges between ecosystems. We then describe four case studies and examine how species losses and gains affect food web structure via resource exchanges between ecosystems, with particular emphasis on effects spanning land-water boundaries. Finally, we discuss the need for more complex conceptual treatment of the interconnectedness of food webs among ecosystems.
... Evidence for the presence of ecological traps has grown considerably since the term was first coined in the 1970s (Dwernychuk & Boag, 1972;Hale & Swearer, 2016). Although much of the initial work focused on birds, the increasing interest in, and importance of, ecological traps has led to evidence of their impact on insects (Horvath et al., 2007), amphibians (Ward-Fear et al., 2009), mammals (Balme, Slotow & Hunter, 2010;van der Meer et al., 2014) and reptiles (Hawlena et al., 2010;Rotem et al., 2013). Multiple anthropogenic activities have now been implicated in the formation of ecological traps, such as agriculture (Gilroy et al., 2011), ecological restoration ) pollution (Boda et al., 2014, harvesting and climate change (Sherley et al., 2017). ...
The speed and scale at which humans are altering natural systems creates novel
challenges for many species. Some species can cope with human-induced rapid
environmental change by exhibiting adaptive behavioural or phenotypic plasticity.
Many others, however, respond maladaptively in ways that can impact individual
fitness. When rapid environmental change triggers mismatches between perceived and
actual habitat quality, animals can prefer inferior habitats, that are known as ecological
traps. Using a meta-analysis, I show that ecological traps are an unexplored but
potentially important conservation risk to animals within wetland habitats (Chapter 2).
Focusing on urbanisation and stormwater wetlands as a case study, I assess how
anthropogenic environmental change affects frogs, in terms of the environmental
variables influencing species occurrence (Chapter 3), the capacity of individuals to
make adaptive habitat selection decisions (Chapter 4), and the fitness and behavioural
consequences of these decisions (Chapter 4 and 5). I show that frogs occupied wetlands
across a broad spectrum of pollution levels, including even the most contaminated, and
that pollution exposure reduced survival and impaired predator avoidance behaviours.
Breeding frogs did not avoid wetlands where these fitness reductions occurred,
demonstrating that stormwater wetlands can function as ecological traps. Collectively,
my results highlight that we need to a greater focus on individual-level metrics (e.g.
fitness and habitat preferences) in addition to the more commonly measured populationand
community-level metrics (e.g. richness and abundance). Based on my research, I
propose three key recommendations to maximise biodiversity at wetlands within urban
landscapes. Firstly, appreciate that poor water quality at stormwater wetlands may
impact resident wildlife, and attempt to reduce the causal factors. Second, despite this,
do not ignore the potential value of stormwater wetlands in providing habitat and
enhancing connectivity amongst aquatic habitats, particularly when they are
appropriately designed and managed. Finally, it is important to design and construct
wetlands for wildlife that are not connected to stormwater networks, with their
placement within the landscape carefully considered.
... Furthermore, nonnative prey species can benefit from na¨ıve native predators (''enemy release hypothesis''; Keane and Crawley, 2002). Finally, although less reported, invaders can also suffer from na¨ıveté (''increased susceptibility hypothesis' ' Colautti et al., 2004;Ward-Fear et al., 2009;Sih et al., 2010;Li et al., 2011), and even highly successful invaders may be limited at local scales via top-down control from native enemies (Jones et al., 2009). When there is reciprocal na¨ıveté between predator and prey, predicting the outcome of such novel interactions becomes especially difficult. ...
Long-term interactions often shape predator-prey relationships in the form of a co-evolutionary "arms race." The arrival of nonnative species may disrupt these relationships by introducing novel behaviors that shift interactions in favor of one of the participants. Here we investigated the response of an imperiled native predator, the Eastern Hellbender (Cryptobranchus alleganiensis), to nonnative and native crayfish prey. Crayfish constitute an important prey item for hellbenders, and in the northern portion of its range where this research was conducted, the nonnative Rusty Crayfish (Orconectes rusticus) has become the dominant crayfish. The objective of this study was to determine prey choice and feeding success of hellbenders presented with native (Allegheny Crayfish; Orconectes obscurus) and nonnative (Rusty Crayfish) crayfish prey. We tested hellbender chemoreception in discriminating between the native and nonnative prey, analyzed behavioral interactions between hellbenders and crayfish during video-recorded trials, and assessed hellbender selectivity of crayfish during overnight feeding trials. Hellbenders were able to discriminate crayfish odor from controls, showed a preference for the scent of native crayfish over nonnative crayfish, and were more likely to strike at native crayfish than at nonnative crayfish; however, more nonnative crayfish were consumed during overnight feeding trials. This discrepancy apparently resulted from differences in avoidance behavior between the prey species; native crayfish engaged more in predator-avoidance tail-flip responses and climbing retreats than the nonnatives, who tended to "stand their ground." Accordingly, during biotic invasions, food preferences of native predators may be superseded by antipredator prey behavior.
... Thus, we can suppress toad larval survival by encouraging native frogs to breed in the ponds used by toads, or by introducing eggs or tadpoles of native frogs directly (Cabrera-Guzmán et al. 2011, 2013bShine 2011). Similarly, many native invertebrates are voracious predators of toad tadpoles (e.g., water beetles and dragonfly larvae) or metamorph toads (ants), and we might be able to increase densities of such predators by manipulating habitat attributes (Ward-Fear et al. 2009Cabrera-Guzmán et al. 2012, 2013a, 2015b. Additionally, dense growth of vegetation around waterbody edges discourages toad breeding, such that replanting these areas might curtail toad recruitment (Hagman and Shine 2006;Semeniuk et al. 2007). ...
Our best hope of developing innovative methods to combat invasive species is likely to come from the
study of high-profile invaders that have attracted intensive research not only into control, but also basic
biology. Here we illustrate that point by reviewing current thinking about novel ways to control one of
the world’s most well-studied invasions: that of the cane toad in Australia. Recently developed methods
for population suppression include more effective traps based on the toad’s acoustic and pheromonal
biology. New tools for containing spread include surveillance technologies (e.g., eDNA sampling and
automated call detectors), as well as landscape-level barriers that exploit the toad’s vulnerability to desiccation—
a strategy that could be significantly enhanced through the introduction of sedentary, rangecore
genotypes ahead of the invasion front. New methods to reduce the ecological impacts of toads include
conditioned taste aversion in free-ranging predators, gene banking, and targeted gene flow. Lastly,
recent advances in gene editing and gene drive technology hold the promise of modifying toad phenotypes
in ways that may facilitate control or buffer impact. Synergies between these approaches hold great
promise for novel and more effective means to combat the toad invasion and its consequent impacts on
biodiversity.
... Large, highly aggressive, and behavioral dominants ants (Iridomyrmex spp.) are ubiquitous in tropical Australia and can prey on cane toad metamorphs. Ants of this group occur across most continental Australia (Andersen 1995) and have the potential to contribute to cane toad control over a broad area (Ward-Fear et al. 2009. ...
... Many potentially vulnerable predators (such as small marsupials, fishes and frogs) rapidly learnt to avoid the toxic newcomer O'Donnell et al., 2010;Shine, 2010) (as originally predicted by Froggatt). Many invertebrates (ants, water-beetles, water-bugs) and vertebrates (rodents, birds) can tolerate the toad's toxins, and thus consume them without ill-effect (Beckmann and Shine, 2009;Ward-Fear et al., 2009;Cabrera-Guzmán et al., 2012). Even for most snakeswhich are vulnerable to toad toxin, and seem to be slow to learn aversionnumbers often have increased rather than decreased since the arrival of toads (Brown et al., 2011). ...
The history of biological invasions, and of attempts to combat them, is dominated by stories of futility. Especially in the case of invasive species that have a high public profile, like the cane toad (Rhinella marina) in Australia, the voices of scientists often have been drowned out in the roar of populist political debate. There have been many failures by science as well, beginning with the initial importation of toads for biocontrol, and extending through failed attempts to predict future patterns of toad colonisation and impact, or to devise practical means to ameliorate that impact. In our (highly biased) opinion, progress in understanding such issues and in developing effective means of toad control emerged only from detailed ecological research on toad biology, rather than enthusiastic but poorly informed attempts to find better ways to slaughter toads. The story of cane toad science in Australia is a cautionary tale for our ability to predict the future, because, to date, we have done an abysmal job of doing so. ‘In the biological control of insect pests, … perhaps more than in any other [field], the path to successful achievement is strewn with the remains of optimistic attempts which have ended in abject failure. … Such a project is not to be embarked upon lightheartedly, but only after the most mature consideration, since a false step may have most disastrous … consequences through the upsetting of the whole biological balance.’ R. W. Mungomery (1934, p.5), written the year before he brought cane toads to Australia.
... Nymphs of the dragonflies Pantala flavescens and Anax (Hemianax) papuensis have been previously reported to prey upon Cane Toads (Hearnden 1991;Alford et al. 1995;Crossland and Alford 1998;Alford 1999). Of the terrestrial arthropods, meat ants (Iridomyrmex spp.) have been frequently reported as active predators of Cane Toad metamorphs (Clerke and Williamson 1992;Cohen and Alford 1993;Ward-Fear et al. 2009, 2010a, but the three other ant species that we report here had not been previously recorded as Cane Toad predators. ...
The successful spread of invasive Cane Toads (Rhinella marina) across tropical Australia has been attributed to a lack of biotic resistance, based upon the inability of most anuran-eating vertebrate predators to tolerate the powerful chemical defenses of the toads. However, despite their high species richness, invertebrates have been much less studied than vertebrates as predators of Cane Toads. Our field and laboratory studies show that toads are killed and consumed by a phylogenetically diverse array of arthropod taxa. No arthropod predators consumed toad eggs in our laboratory experiments, but fishing spiders, water beetles, water scorpions, and dragonfly nymphs killed toad tadpoles, and ants and fishing spiders killed metamorph toads. Published accounts report predation on toads by crustaceans and hemipterans also. In our experiments, no predators showed any overt ill effects from consuming toad tissue. Dragonfly nymphs (Pantala flavescens) and fishing spiders (Dolomedes facetus) selectively took Cane Toad tadpoles at higher rates than some simultaneously offered native frog tadpoles. In combination with published data, our experiments suggest that the tadpoles and metamorphs of Cane Toads face high predation rates from the diverse and abundant invertebrate fauna of aquatic and riparian habitats in tropical Australia. The invasion of Cane Toads can potentially have positive effects on populations of many native animal species.
... Populations may be confronted with new patterns of selection by various processes, including large-scale habitat change in their existing environment (e.g., Haas et al. 2010), climate change (Crozier and Hutchings 2014), interactions with invasive species (e.g., Green and Coˆte´2014) or transplantation to new environments (Hutchings 2014). Under unfamiliar conditions a mismatch between phenotype and the environment causes some previously advantageous traits to be maladaptive, resulting in a competitive disadvantage, reduced fitness, or extinction of the population (e.g., Ward-Fear et al. 2009, and references therein). On the other hand, if the phenotype matches the new environment the species may thrive and this is the case with many successful invasive species (Iba´n˜ez et al. 2014). ...
Life history traits reflect interactions between evolutionary lineage and environmental conditions. Translocations of populations to new environments, and changes in their natal environment, provide insights into the factors controlling life history. For example, the trade-off between egg size and egg number is a well-studied adaptation in fishes, and especially salmon and trout. We used existing and new data on this tradeoff in anadromous sockeye salmon, Oncorhynchus nerka, and the non-anadromous form of the species (kokanee), to investigate the likely origin of a population of uncertain ancestry, land-locked for a century above an impassable dam. Native kokanee have smaller eggs than do the larger-bodied anadromous sockeye salmon. However, the land-locked population in Lake Sutherland, in the Elwha River system, Washington, USA had much larger eggs for their body size than any other kokanee population, similar only to the land-locked descendants of anadromous sockeye salmon in New Zealand. After evaluating and rejecting a series of competing explanations for the unusually large eggs, we infer that the population was mostly likely of anadromous origin, retaining the ancestral tendency to produce large eggs, despite the sacrifice in fecundity that is necessitated by the limited female energy resources. This study revealed the utility of life history traits for studying the ancestral origins of a population for which molecular genetic tools were not informative. Worldwide, many populations have been transplanted or exposed to new conditions, affording similar opportunities to investigate phenotypic plasticity and evolutionary adaptations.
... Adding to this complexity, invaders can induce shifts in behaviour or life-history traits in the native fauna (Blanchet et al. 2007;Greenlees et al. 2007;Hoare et al. 2007), so that impacts are mediated by such reaction norms (Strauss et al. 2006;Carroll 2007) and finally, mechanisms of impact, and the fitness consequences of interactions, may differ between life-history stages. For example, Cane Toads Rhinella marina are preyed upon by a native taxon (Meat Ants Iridomyrmex reburrus) during the metamorph phase, compete with Meat Ants during the sub-adult phase, and eat Meat Ants during the adult phase (Lever 2001;Greenlees et al. 2006;Pizzatto and Shine 2008;Ward-Fear et al. 2009). In species with multi-phasic life histories, such ontogenetic shifts in mechanisms and outcome of impact are most likely where ecological and morphological divergences between larvae and adults are profound (Wilbur and Collins 1973;Wilbur 1980). ...
The viability of a metamorph anuran can be influenced by its body size and the time it has taken to complete larval development In a laboratory experiment, we show that the presence of tadpoles of the invasive Cane Toad Rhinella marina causes tadpoles of a native frog (Marbled Frog Limnodynastes convexiusculus) to metamorphose later and at smaller sizes.These effects may render frog metamorphs more vulnerable to desiccation and predation, but render them less vulnerable to Cane Toads. Marbled Frogs prey upon other anurans, including the highly toxic Cane Toad metamorphs. Small, late-emerging metamorph frogs are unlikely to encounter metamorph toads small enough to ingest; and hence, are less likely to be fatally poisoned by consuming the toxic invader. Developing in the presence of larval Cane Toads thus increases the native taxon's ability to survive the presence of toads post-metamorphosis. Predicting the ecological impacts of an invasive species on native taxa with biphasic life histories (such as most anurans) thus requires information on interactions in both aquatic and terrestrial environments.The expression of phenotypic plasticity in one phase may influence fitness in a subsequent phase, in complex and non-intuitive ways.
... Toad arrival will have both direct and indirect effects on food availability for rats. In terms of direct effects (rats eating toads), the biomass of these slow-moving easily-captured prey can be very high (Ward-Fear et al. 2009), especially in the years immediately following toad arrival at a site (Freeland 1986). Indirect effects may well be even greater. ...
The success of an invasive species can be reduced by biotic resistance from the native fauna. For example, an invader that is eaten by native predators is less likely to thrive than one that is invulnerable. The ability of invasive cane toads (Rhinella marina) to spread through Australia has been attributed to the toad’s potent defensive chemicals that can be fatal if ingested by native snakes, lizards, marsupials and crocodiles. However, several taxa of native insects and birds are resistant to cane toad toxins. If native rodents are also capable of eating toads (as suggested by anecdotal reports), these large, abundant and voracious predators might reduce toad numbers. Our field observations and laboratory trials confirm that native rodents (Melomys burtoni, Rattus colletti and Rattus tunneyi) readily kill and consume cane toads (especially small toads), and are not overtly affected by toad toxins. Captive rodents did not decrease their consumption of toads over successive trials, and ate toads even when alternative food types were available. In combination with anecdotal reports, our data suggest that rodents (both native and invasive) are predators of cane toads in Australia. Despite concerns about the decline of rodents following the invasion of toads, our data suggest that the species we studied are not threatened by toads as toxic prey, and no specific conservation actions are required to ensure their persistence.
... Many aquatic and terrestrial invertebrates are known predators of juvenile and adult amphibians (Mccormick andPolis 1982, Toledo 2005). Among the most important terrestrial predators are spiders (Moura and Azevedo 2011), ants (Ward-Fear et al. 2009) and adult beetles (Mccormick and Polis 1982). The tiger beetles genus Tetracha Hope, 1838 (Coleoptera: Cicindelidae) has its greatest diversity in the southern Amazonian region, Bolivia and Brazil. ...
Here we report two cases of predation on newly-metamorphosed frogs by the tiger beetle, Tetracha brasiliensis
brasiliensis, in southern Brazil.
... Their ancestors never had to deal with such large, predatory ants, so the escape behavior has not evolved. Thus the toadlets often provide a nutritious morsel for the ants, and these predators successfully reduce the young toad population (up to 90%) (Ward-Fear et al. 2009). Develop a simulation that contains a grid with water, land, toadlets, and meat ants. ...
... In general, interactions between non-native prey species and native predators have rarely been addressed (Bulte and Blouin-Demers 2008;Carlsson et al. 2009;Ward-Fear et al. 2009;Li et al. 2011;Robbins et al. 2013). The notable exceptions have been studies regarding the influence of introduced toads to indigenous snake species in Australia (e.g., Shine 2012 and references therein). ...
In aquatic and surrounding terrestrial ecosystems, snakes of the genus Natrix are among the top predators,
feeding predominantly on fishes and amphibians, but also on other reptiles and small mammals. In the diets of Natrix natrix and N. tessellata, preferred food items vary geographically and during ontogeny. To understand these variations, we collected data on their diet composition in several habitats (river, wetlands, and two types of lakes), some of which are under severe anthropogenic pressures. Both Natrix species were able to quickly adapt to changes in available prey, and to feed even on non-indigenous, invasive, and potentially hazardous fish. Disturbed ecosystems are particularly susceptible to invasions. Therefore, if alien fishes become dominant, they may threaten populations of native snakes. On the other hand, semi-aquatic snakes can contribute to natural regulation of alien fish species abundance. The preliminary results presented herein emphasize the urgent need for integrative studies of natricine snakes and their prey ecology under various and/or dynamic circumstances. Better understanding of the functioning of different aquatic ecosystems may enable proper conservation and restoration for these snake species and their habitats.
... For example, Paini et al. (2008) suggested that the exotic thrips Frankliniella tritici cannot reach high densities on the east coast of the United States because it is competitively inferior to the native thrips F. occidentalis. Exotic species may be at a competitive disadvantage whenever they are maladapted to the novel ecosystem (Ward-Fear et al. 2009). Despite the large number of studies addressing interspecific herbivore competition for a given pair of species, we lack an overarching sense of whether a species' native/exotic status and coevolutionary history with its host plant affects the outcome of interspecific herbivore competition. ...
Competition plays an important role in structuring the community dynamics of phytophagous insects. As the number and impact of biological invasions increase, it has become increasingly important to determine whether competitive differences exist between native and exotic insects. We conducted a meta-analysis to test the hypothesis that native/ exotic status affects the outcome of herbivore competition. Specifically, we used data from 160 published studies to assess plant-mediated competition in phytophagous insects. For each pair of competing herbivores, we determined the native range and coevolutionary history of each herbivore and host plant. Plant-mediated competition occurred frequently, but neither native nor exotic insects were consistently better competitors. Spatial separation reduced competition in native insects but showed little effect on exotics. Temporal separation negatively impacted native insects but did not affect competition in exotics. Insects that coevolved with their host plant were more affected by interspecific competition than herbivores that lacked a coevolutionary history. Insects that have not coevolved with their host plant may be at a competitive advantage if they overcome plant defenses. As native/exotic status does not consistently predict outcomes of competitive interactions, plant-insect coevolutionary history should be considered in studies of competition.
... The most important determinants of the cane toad tadpoles' vulnerability to D. rusticus and C. godeffroyi may be their small size, their low locomotor ability, and their lack of a long coevolutionary history with Australian predators. The same factors render postmetamorphic cane toads very vulnerable to Australian predatory ants (Ward-Fear et al., 2009, 2010b. ...
An invasive species is less likely to flourish if it is vulnerable to the predators it encounters in its newly-colonised range. The success of cane toads (Rhinella marina) in invading Australia has been attributed to the toads’ powerful chemical defences, which render this toxic invader invulnerable to most vertebrate predators. However, invertebrate predators have been largely ignored. Our laboratory studies show that at least three invertebrate species (one coleopteran, two hemipterans) are unaffected by the toads’ bufadienolide defences, and consume aquatic stages of the cane toad life history. The water beetle Cybister godeffroyi consumed eggs, hatchlings and tadpoles of R. marina, whereas the water bugs Diplonychus rusticus and Lethocerus insulanus consumed toad tadpoles but not eggs. In choice tests, C. godeffroyi and D. rusticus preferred cane toad tadpoles to simultaneously available native tadpoles or fish, possibly reflecting the smaller size and/or slower swimming speeds of larval cane toads. Rates of predation on cane toad tadpoles were high (e.g., a single water beetle often consumed five tadpoles per day in a complex environment). These abundant, voracious invertebrate predators could reduce cane toad recruitment success in some tropical waterbodies. Future research could usefully examine whether densities of water beetles and water bugs increase after toad invasion (potentially explaining why toad numbers often decline post-colonisation).
... For example, Paini et al. (2008) suggested that the exotic thrips Frankliniella tritici cannot reach high densities on the east coast of the United States because it is competitively inferior to the native thrips F. occidentalis. Exotic species may be at a competitive disadvantage whenever they are maladapted to the novel ecosystem (Ward-Fear et al. 2009). Despite the large number of studies addressing interspecific herbivore competition for a given pair of species, we lack an overarching sense of whether a species' native/exotic status and coevolutionary history with its host plant affects the outcome of interspecific herbivore competition. ...
Research investigating interactions between aboveground (AG) and below-ground (BG) herbivores has been central to characterizing AG-BG linkages in terrestrial ecosystems, with many of these interactions forming the basis of complex food webs spanning the two subsystems. Despite the growing literature on the effects of AG and BG herbivores on each other, underlying patterns have been difficult to identify due to a high degree of context dependency. In this study, we present the first quantitative meta-analysis of AG and BG herbivore interactions. Previous global predictions, specifically that BG herbivores normally promoted AG herbivore performance and AG herbivores normally reduced BG herbivore performance, were not supported. Instead, the meta-analysis identified four factors that determined the outcome of AG-BG interactions. (1) Sequence of herbivore arrival on host plants was important, with BG herbivores promoting AG herbivore performance only when introduced to the plant simultaneously, whereas AG herbivores had negative effects on BG herbivores only when introduced first. (2) AG herbivores negatively affected BG herbivore survival but tended to increase population growth rates. (3) AG herbivores negatively affected BG herbivore performance on annual plants, but not on perennials, and these effects were observed more consistently in laboratory than field studies. (4) The type of herbivore was also important, with BG insect herbivores belonging to the order Diptera (i.e., true flies) having the strongest negative effects on AG herbivores. Coleoptera (i.e., beetles) species were the most widely investigated BG herbivores and had positive impacts on AG Homoptera (e.g., aphids), but negative effects on AG Hymenoptera (e.g., sawflies). The strongest negative outcomes for BG herbivores were seen when the AG herbivore was a Coleoptera species. We found no evidence for publication bias in AG-BG herbivore interaction literature and conclude that several biological and experimental factors are important for predicting the outcome of AG-BG herbivore interactions. The sequence of herbivore arrival on the host plant was among the most influential.
... Importantly, much of that early mortality is due to factors that act most strongly against smaller-than-average metamorph toads. Size-dependence in vulnerability has been documented in response to predation (Ward-Fear et al. 2009), cannibalism (Pizzatto & Shine 2008), parasitism (Kelehear, Webb & Shine 2009) and desiccation (Child et al. 2008a). Thus, any competition-induced reduction in toad viability that results from larval interactions may persist into the terrestrial phase of the toad's life-history, when density-dependent effects are weaker. ...
1. Native to the Americas, cane toads Bufo marinus are an invasive species causing substantial ecological impacts in Australia. We need ways to control invasive species such as cane toads without collateral damage to native fauna.
2. We explored the feasibility of suppressing survival and growth of cane toad tadpoles via competition with the tadpoles of native frogs. Compared to the invasive toads, many native frogs breed earlier in the season and their tadpoles grow larger and have longer larval periods. Hence, adding spawn or tadpoles of native frogs to toad-breeding sites might increase tadpole competition, and thereby reduce toad recruitment.
3. Our laboratory trials using tadpoles of eight native frog species gave significant results: the presence of six of these species (Cyclorana australis, C. longipes, Litoria caerulea, L. dahlii, L. rothii and L. splendida) reduced toad tadpole survival and/or size at metamorphosis. Litoria caerulea also increased the duration of the larval period of cane toad tadpoles. Tadpoles of the other two frog species (Litoria rubella and Litoria tornieri) did not affect survival or growth of larval cane toads any more than did an equivalent number of additional toad tadpoles. Native frog species with larger tadpoles exerted greater negative effects on toad tadpoles than did native species with smaller tadpoles.
4. Synthesis and applications. Encouraging the general public to construct and restore waterbodies in peri-urban areas to build up populations of native frogs – especially the much-loved green tree frog Litoria caerulea– could help to reduce recruitment rates of invasive cane toads in Australia.
... People involved in volunteer-based activities to cull feral pests talk of ''waging a war" on the invasive pest (e.g., Bright, 1998;Mack et al., 2000;Baskin, 2002;Chew and Laubichler, 2003;Larson, 2005). Accordingly, invasive-species control often relies upon military concepts such as targeting the enemy's weak points (Hagman et al., 2009;Ward-Fear et al., 2009). Inevitably, some of the problems that beset military strategists also bedevil invasivespecies control. ...
Members of the general public interact with wildlife in many ways, and an inability to distinguish between species can have significant implications for conservation. For example, attempts by environmentally-concerned private citizens to control invasive species may cause collateral damage unless people can reliably distinguish native fauna from the invader. We tested the Australian public’s ability to distinguish invasive cane toads (Bufo marinus) from native frogs at egg, tadpole, subadult and adult life-history stages. Errors were common, especially for eggs and tadpoles (27–31% error rates) and less so for subadult and adult toads and frogs (5–43% error rates). Accuracy of identification was higher in people living in areas where toads occur (compared to other parts of Australia or overseas), and similar in men and women (but with a decrease in older men). Ability to identify anurans was increased by toad-identification awareness programs and membership of “toad-busting” community groups, but direct killing of cane toads by the general public may inflict substantial “friendly fire” on native frogs. In the absence of any clear evidence for ecological benefits from toad-killing, we suggest that such collecting activities should be conducted only in areas where toads are known to occur, and under the supervision of trained personnel (to identify any anuran before it is killed), rather than as an ad hoc activity pursued independently by local residents. More generally, conservation activities that involve public participation should carefully evaluate the potential rates and consequences of species misidentification by well-intentioned but untrained people.
... Toledo 2005) as the main arthropod predators. A few studies report predation by ants (Freed and Neitman 1988; Zuffi 2001; Ward-Fear et al. 2009) and by adult beetles (McCormick and Polis 1982; Hinshaw and Sullivan 1990; Jung et al. 2000). The latter involves mostly carabid beetles (Littlejohn and Wainer 1978; Ovaska and Smith 1988; Robertson 1989). ...
The genus Epomis is represented in Israel by two species: Epomis dejeani and Epomis circumscriptus. In the central coastal plain these species are sympatric but do not occur in the same sites. The objective of this study was to record and describe trophic interactions between the adult beetles and amphibian species occurring in the central coastal plain of Israel. Day and night surveys at three sites, as well as controlled laboratory experiments were conducted for studying beetle-amphibian trophic interaction. In the field we recorded three cases of Epomis dejeani preying upon amphibian metamorphs and also found that Epomis adults share shelters with amphibians. Laboratory experiments supported the observations that both Epomis species can prey on amphibians. Predation of the three anuran species (Bufo viridis, Hyla savignyi and Rana bedriagae) and two urodele species (Triturus vittatus and Salamandra salamandra infraimmaculata) is described. Only Epomis dejeani consumed Triturus vittatus. Therefore, we conclude that the two species display a partial overlap in food habit.
... For example, meat ants of the genus Iridomyrmex take many metamorph toads (Clerke and Williamson 1992; Ward-Fear et al. 2009a,b,c). Laboratory and field studies show that cane toad metamorphs are more vulnerable to ant attack than are the metamorphs of native frog species (Ward-Fear et al. 2009a). That vulnerability reflects the facts that toad metamorphs are smaller and slower than frog metamorphs, are primarily diurnal in their activity (an adaptation to reduce vulnerability to intraspecific cannibalism:), and lack effective antipredator responses to ants (Ward-Fear et al. 2009a,b). ...
Although invasive species are viewed as major threats to ecosystems worldwide, few such species have been studied in enough detail to identify the pathways, magnitudes, and timescales of their impact on native fauna. One of the most intensively studied invasive taxa in this respect is the cane toad (Bufo marinus), which was introduced to Australia in 1935. A review of these studies suggests that a single pathway-lethal toxic ingestion of toads by frog-eating predators-is the major mechanism of impact, but that the magnitude of impact varies dramatically among predator taxa, as well as through space and time. Populations of large predators (e.g., varanid and scincid lizards, elapid snakes, freshwater crocodiles, and dasyurid marsupials) may be imperilled by toad invasion, but impacts vary spatially even within the same predator species. Some of the taxa severely impacted by toad invasion recover within a few decades, via aversion learning and longer-term adaptive changes. No native species have gone extinct as a result of toad invasion, and many native taxa widely imagined to be at risk are not affected, largely as a result of their physiological ability to tolerate toad toxins (e.g., as found in many birds and rodents), as well as the reluctance of many native anuran-eating predators to consume toads, either innately or as a learned response. Indirect effects of cane toads as mediated through trophic webs are likely as important as direct effects, but they are more difficult to study. Overall, some Australian native species (mostly large predators) have declined due to cane toads; others, especially species formerly consumed by those predators, have benefited. For yet others, effects have been minor or have been mediated indirectly rather than through direct interactions with the invasive toads. Factors that increase a predator's vulnerability to toad invasion include habitat overlap with toads, anurophagy, large body size, inability to develop rapid behavioral aversion to toads as prey items, and physiological vulnerability to bufotoxins as a result of a lack of coevolutionary history of exposure to other bufonid taxa.
How does behaviour affect biological invasions? Can it explain why some animals are such successful invaders? With contributions from experts in the field, and covering a broad range of animals, this book examines the role of behaviour in biological invasions from the point of view of both invaders and native species. The chapters cover theoretical aspects, particularly relevant behaviours and well-documented case studies, showing that behaviour is critical to the success, and ecological and socio-economic impact, of invasive species. Its insights suggest methods to prevent and mitigate those impacts, and offer unique opportunities to understand the adaptive role of behaviour. Offering a comprehensive overview of current understanding on the subject, the book is intended for biological invasion researchers and behavioural ecologists as well as ecologists and evolutionary biologists interested in how organisms deal with anthropogenic environmental changes such as climate change and habitat loss.
During the Anthropocene, Earth has experienced unprecedented habitat loss, native species decline, and global climate change. Concurrently, greater globalisation is facilitating species movement, increasing the likelihood of alien species establishment and propagation. There is a great need to understand what influences a species’ ability to persist or perish within a new or changing environment. Examining genes that may be associated with a species’ invasion success or persistence informs invasive species management, assists with native species preservation, and sheds light on important evolutionary mechanisms that occur in novel environments. This approach can be aided by coupling spatial and temporal investigations of evolutionary processes. Here we use the common starling, Sturnus vulgaris, to identify parallel and divergent evolutionary change between contemporary native and invasive range samples and their common ancestral population. To do this, we use reduced-representation sequencing of native samples collected recently in north-western Europe and invasive samples from Australia, together with museum specimens sampled in the UK during the mid-19th Century. We found evidence of parallel selection on both continents, possibly resulting from common global selective forces such as exposure to pollutants. We also identified divergent selection in these populations, which might be related to adaptive changes in response to the novel environment encountered in the introduced Australian range. Interestingly, signatures of selection are equally as common within both invasive and native range contemporary samples. Our results demonstrate the value of including historical samples in genetic studies of invasion and highlight the ongoing and occasionally parallel role of adaptation in both native and invasive ranges.
Invasive species have a massive impact on their environment and predicting geographical zones at risk of invasion is paramount to the control of further invasions. Invasive anurans are particularly detrimental to native amphibian species, other vertebrates, and even aquaculture through competition, predation, disease transmission, toxicity, or a combination of these. Four species have been designated as the worst anuran invaders worldwide: Duttaphrynus melanostictus, Rhinella marina, Lithobates catesbeianus and Xenopus laevis. In this study, we modelled global habitat suitability for all four species using ecological niche factor analysis (ENFA) to predict the most susceptible areas to invasion. Models showed suitable climatic conditions for all four species expanded beyond their current native and invasive ranges. Tropical, subtropical, and island biomes around the world were among the areas with the highest ENFA suitability for all four species. Further, marginality statistics indicate niche expansion in D. melanostictus, and generalism in the three other species. As only climatic variables were used in the modelling, these results show the ultimate distributions if all landscape conditions are met without significant barriers to invasion.
Invasive and introduced species can pose major ecological challenges to vulnerable
native wildlife. Biodiversity hotspots, in particular, require protection from this
significant cause of species loss. One hotspot, Madagascar, is experiencing the
accidental introduction of a potentially ecologically damaging species – the toxin
carrying bufonid toad, Duttaphyrnus melanostictus. The presence of these toxic
invaders drives fears that if such a species gains a foothold widespread poisoning of
Malagasy predators could occur, mirroring the invasion of Australia by Rhinella
marina. This includes numerous endemic and endangered species. The mechanism
by which the toxin acts upon organisms has been previously identified via the study
of toxin resistant versus toxin non-resistant taxa. Specific amino acid substitutions
are required on the organism’s Na+/K+–ATPase for them to be resistant to bufonid
toxin. This solution to combat the toxin is widely consistent across taxa providing a
method to discover and predict toxin resistance or vulnerability. Here I investigate
the Na+/K+–ATPase gene to detect vulnerability of a selection of Malagasy fauna to
the toxics of Duttaphrynus melanostictus. It is discovered that no tested species on
Madagascar have the capacity to survive ingestion of the novel toxin. The
vulnerability is found in all examined species, including snakes, frogs, lizards, lemurs
and tenrecs. The results suggest that the invasive Duttaphrynus melanostictus is
liable to have significant impact on Malagasy fauna.
Ecological traps occur when a species makes maladaptive habitat-selection decisions. Human-modified environments including deforested riparian habitats can change how organisms respond to environmental cues. Stream amphibians alter their habitat selection in response to abiotic cues associated with riparian clearing, but little research exists to determine if behavioral shifts to abiotic cues may make them more susceptible to predation. To evaluate if deforested habitats create ecological traps, we studied habitat-selection behavior of larval Black-bellied Salamander (Desmognathus quadramaculatus (Holbrook, 1840)) when given conflicting environmental cues. We also evaluated the potential for learning or adaptation to cues in deforested reaches by evaluating individuals from forested and deforested reaches. We anticipated that individuals from deforested reaches would make adaptive antipredator choices when presented with well-lit habitat, whereas individuals from forested reaches would select shaded habitat closer to a predator. We found that habitat origin, light, and predator presence all interacted to influence habitat selection. Although individuals from forested habitats selected shaded environments, all observed individuals adaptively avoided a predator. Individuals from deforested reaches were more willing to enter well-lit habitat to avoid the predator. Despite documented declines of salamanders associated with forest removal, it appears that individuals are capable of making adaptive antipredator decisions in degraded habitats.
Human-induced rapid environmental change (HIREC; e.g., climate change or exotic species) has caused global species declines. Although behavioral plasticity has buff-ered some species against HIREC, maladaptive behav-ioral scenarios called 'evolutionary traps' are increasingly common, threatening the persistence of affected species. Here, we review examples of evolution-ary traps to identify their anthropogenic causes, behav-ioral mechanisms, and evolutionary bases, and to better forecast forms of HIREC liable to trigger traps. We sum-marize a conceptual framework for explaining the sus-ceptibility of animals to traps that integrates the cost– benefit approach of standard behavioral ecology with an evolutionary approach (reaction norms) to understand-ing cue–response systems (signal detection). Finally, we suggest that a significant revision of conceptual thinking in wildlife conservation and management is needed to effectively eliminate and mitigate evolutionary traps. Why evolutionary traps? In making decisions, organisms commonly rely upon envi-ronmental cues to assess the current or future state of their environment. HIREC (see Glossary; [1]) can increase the mismatch between environmental cues and the conditions that they have historically been associated with, such that animals are unable to accurately assess the fitness value of habitats, mates, food items, or other resources that affect their fitness. In this way, HIREC can cause animals to preferentially exploit resources associated with the lowest fitness rewards ('evolutionary traps'; Figure 1) [2,3], or to avoid and, thus, fail to capitalize on, resources that would enhance their fitness ('undervalued resources') [4]. Evolu-tionary traps are capable of causing rapid population declines that threaten species persistence [5,6] and, thus, have become an emerging conservation concern. The last review of the topic in 2006 [7] found only a few good examples of evolutionary traps supported by data, suggesting that traps are a rare and relatively unimpor-tant phenomenon. However, the intervening years have witnessed an explosion of interest in the topic from researchers and, accordingly, an increase in the number
Human-induced rapid environmental change (HIREC; e.g., climate change or exotic species) has caused global species declines. Although behavioral plasticity has buffered some species against HIREC, maladaptive behavioral scenarios called 'evolutionary traps' are increasingly common, threatening the persistence of affected species. Here, we review examples of evolutionary traps to identify their anthropogenic causes, behavioral mechanisms, and evolutionary bases, and to better forecast forms of HIREC liable to trigger traps. We summarize a conceptual framework for explaining the susceptibility of animals to traps that integrates the cost-benefit approach of standard behavioral ecology with an evolutionary approach (reaction norms) to understanding cue-response systems (signal detection). Finally, we suggest that a significant revision of conceptual thinking in wildlife conservation and management is needed to effectively eliminate and mitigate evolutionary traps.
Experimental evidence on the determinants of prey vulnerability is scarce, especially for vertebrates in the field. Invasive species offer robust opportunities to explore prey vulnerability, because the intensity of predation on or by such animals has not been eroded by coevolution. Around waterbodies in tropical Australia, native meat ants (Iridomyrmex reburrus) consume many metamorph cane toads (Bufo marinus, an invasive anuran). We document the determinants of toad vulnerability, especially the roles of toad body size and ant density. Larger metamorphs were attacked sooner (because they attracted more ants), but escaped more often. Overall, smaller toads were more likely to be killed. Ant densities influenced toad responses, as well as attack rate and success. Data on the immediate outcomes of attacks underestimate mortality: more than 73% of apparent ‘escapees’ died within 24 h. Because mortality during this period was independent of toad size, predation was less size selective than suggested by immediate outcomes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 738–751.
Nonnormal distributions of competitive ability reflect selection for facultative metamorphosis.
Waterbodies in diverse habitats throughout Venezuela were sampled for biotic and abiotic characteristics that might influence breeding site choice in Bufo marinus. Sites where breeding by B. marinus was present differed in many respects from sites where breeding was absent, and these differences varied between habitat types. The combination of variables that best explained the difference between breeding sites and nonbreeding sites across all habitats was the transparency and pH of the water, the density of the vegetation surrounding the waterbody, and whether the waterbody was temporary or permanent. The size and abundance of fish apparently was not important in breeding site choice.
Introduced into Australia in 1935, the cane toad (Chaunus [ Bufo] marinus) threatens native vertebrate predators. However, there have been few rigorous quantitative studies on species threatened by this toxic invasive species. This study examines the changes in abundance and proportion of sites occupied by Merten's water monitor (Varanus mertensi) at a site in the Northern Territory following invasion by cane toads. The study was located at Manton Dam Recreation Area, 70 km south of Darwin, and ran for 18 months. Cane toads were first detected at the study site in February 2005, three months after the first survey, and their abundance remained low until February 2006, when an increase was observed. The abundance of V. mertensi declined substantially 8 months after the arrival of cane toads and remained low. The probability of detection of V. mertensi varied considerably within and among surveys, and was higher in the wet season surveys. The proportion of sites occupied by V. mertensi at the start of the study was 0.95 +/- 0.03. Site occupancy remained high for 6 months after the arrival of cane toads, but declined gradually to a low of 0.15 +/- 0.16 within 12 months. There has been demonstrable change in the abundance and proportion of sites occupied by V. mertensi following the colonisation of cane toads, but the population has been able to persist. Monitoring of populations impacted by cane toads may provide unique opportunities to understand processes underlying local extinction and colonisation of native predators following the impact of invasive species.
Previous research on cane toads (Bufo marinus) has documented non-random selection of breeding sites by this invasive species. In the wet-dry tropics of the Northern Territory, toads selected spawning sites in open areas with gently sloping banks and shallow water. If consistent, such biases may present opportunities for toad control via waterbody manipulation - but first we need to know whether such criteria for spawning-site selection (1) are consistent across other parts of the toad's extensive Australian range, and (2) differ from those of native anurans breeding at the same waterbodies. We quantified the attributes of potential and actual spawning-sites in north-eastern New South Wales, in temperate-zone habitat where cane toads have been present for many decades; our study area thus differs in many ways from the previously studied tropical site. We compared habitat and water chemistry variables between 23 cane toad breeding sites and 23 nearby unused sites. To examine habitat use at an even finer scale, we conducted nocturnal surveys of microhabitat use by calling male toads and native anurans. Our results revealed that cane toads in this region were highly selective in their choice of breeding sites, and that the criteria they used in this respect were similar to those used by toads in the Northern Territory. Calling male cane toads also used microhabitats non-randomly within each pond, apparently based on similar criteria to those used when selecting among ponds. Toads differed significantly from native anurans in these respects, suggesting that it may be feasible to manipulate waterbody attributes to impact on invasive toads without disrupting reproduction by native anurans.
The reproductive success of ducks nesting in association with gulls on islands in Miquelon Lake, Alberta, was studied over a period of 3 years. Gulls protected nesting ducks by preventing other egg-eating birds from foraging on the islands. Pilfering of duck eggs by gulls was correlated with the point in incubation when ducks were trapped and handled. Without trapping, we estimated hatching success would exceed 90%. However, duckling mortality, concentrated in the 1st week posthatching, was positively correlated with the numbers of associated gulls. The survival of ducklings declined to zero when the number of nesting gulls approached 500 pairs. The origin and maintenance of this ecologically unstable relationship is discussed.
Invasive species control is now a conservation priority in many parts of the world. Demographic modeling using population matrix models is a useful tool in the design of these control efforts as it identifies the life stages with the strongest influence on pop-ulation dynamics. As a case in point, American bullfrogs (Rana catesbeiana) have been introduced around the world and have negative effects on native fauna. We studied de-mography of four populations on southern Vancouver Island, Canada, using field obser-vations and capture–mark–recapture methods to estimate survival, growth, and fecundity. The life cycle of these introduced bullfrogs progressed in yearly increments through the following stages: eggs/small tadpoles, first-year tadpoles, second-year tadpoles, meta-morphs/juveniles, and adults. Some bullfrog tadpoles were able to skip the second-year tadpole stage and metamorphosed one year after hatching. With tadpole survival estimates from the literature and field estimates of the remaining parameters we constructed a matrix population model. Prospective demographic perturbation analysis showed that bullfrog population growth rate () was most influenced by the proportion of tadpoles metamor-phosing early (tadpole development rate), and by early postmetamorphic survival rates. Most current control efforts for bullfrogs have focused on removing tadpoles and breeding adults, and our modeling suggests that these efforts may not be optimal. Partial removal of tadpoles may lead to higher tadpole survival and development rates and higher postmeta-morphic survival due to decreased density-dependent competition. Removal of adults leads to higher survival of early metamorphic stages through reduced cannibalism. Our modeling suggests that culling of metamorphs in fall is the most effective method of decreasing bullfrog population growth rate. Our study shows how demographic information can be used to maximize the efficacy of control efforts, and our results are likely directly applicable to other invasive species with complex life cycles.
In the last decade there has been increasing evidence of amphibian declines from relatively pristine areas. Some declines are hypothesized to be the result of egg mortality caused by factors such as elevated solar UV-B irradiation, chemical pollutants, pathogenic fungi, and climate change. However, the population-level consequences of egg mortality have not been examined explicitly, and may be complicated by density dependence in intervening life-history stages. Here we develop a demographic model for two amphibians with contrasting life-history strategies, Bufo boreas and Ambystoma macrodactylum. We then use the complementary approaches of elasticity and limitation to examine the relationships among stage-specific survival rates, larval-stage density dependence and amphibian population dynamics. Elasticity analyses showed that for a range of density dependence scenarios both species were more sensitive to changes in post-embryonic survival parameters, particularly juvenile survival, than to egg survival, suggesting that mortality of later stages may play an important role in driving declines. Limitation analyses revealed that larval density dependence can dramatically alter the consequences of early mortality, reducing or even reversing the expected population-level effects of egg mortality. Thus, greater focus on later life stages and density dependence is called for to accurately assess how stressors are likely to affect amphibian populations of conservation concern.
Laboratory studies show that predatory cane toads (Bufo marinus) exhibit specialized toe-luring behavior that attracts smaller conspecifics, but field surveys of toad diet rarely record
cannibalism. Our data resolve this paradox, showing that cannibalism is common under specific ecological conditions. In the
wet–dry tropics of Australia, desiccation risk constrains recently metamorphosed toads to the edges of the natal pond. Juvenile
toads large enough to consume their smaller conspecifics switch to a primarily cannibalistic diet (67% of prey biomass in
stomachs of larger toads). Cannibalistic attack was triggered by prey movement, and (perhaps as an adaptive response to this
threat) small (edible-sized) toads were virtually immobile at night (when cannibals were active). Smaller metamorphs were
consumed more frequently than were larger conspecifics. The switch from insectivory to cannibalism reflects the high dry season
densities of small conspecifics (in turn, due to desiccation-imposed constraints to dispersal) and the scarcity of alternative
(insect) prey during dry weather. Our study pond (102m in circumference) supported >400 juvenile toads, which consumed many
metamorphs over the course of our study. Toads appear to be low-quality food items for other toads; in laboratory trials,
juvenile toads that fed only on conspecifics grew less rapidly than those that ate an equivalent mass of insects. This effect
was not due to parotoid gland toxins per se. Thus, cane toads switch to intensive cannibalism only when seasonal precipitation
regimes increase encounter rates between large and small toads, while simultaneously reducing the availability of alternative
prey.
We examined factors affecting the growth and survival of postmetamorphic Bufo marinus using sampling and experiments. Bufo metamorphs, defined as newly emerged terrestrial toads of 9-29 mm snout-ischium length (SIL), were classified into four stages on the basis of colour and size. Stage 1 were uniformly black and about 9-12 mm SIL, stage 2 were mottled with orange spots and about 12-16 mm SL, stage 3 had a white mid-dorsal line and were about 16-25 mm SIL, and stage 4 had enlarged parotoid glands and were about 25-29 mm SIL. We determined the density of each stage at three distances (0-1, 2-3, 4-5 m) from their larval habitat using 1 x 1-m quadrat samples. The mean densities of all metamorphs within 1 m of water were 2.6 m-2 and 2.1 m-2 for the wet and early dry seasons, respectively. The mean densities of all metamorphs during both seasons at 2-3 m and 4-5 m from water were 0.8 m-2 and 0.6 m-2, respectively. Stage 2 metamorphs were most common in samples. Most stage 1 metamorphs occurred within 1 m of the water in both seasons (98% wet; 95% dry). Increasing percentages of stage 2, 3 and 4 metamorphs occurred in samples 2-3 and 4-5 m from water (38, 49 and 80%, respectively, averaged over both seasons). Three experiments examined the response of metamorph growth and survival rates to density in open-topped flyscreen enclosures. Stage 1 or 2 metamorphs were established at initial densities of 3.3, 6.7 and 16.7 m-2. Metamorphs in the lower-density enclosures grew more rapidly than metamorphs in the higher-density enclosures. A profile analysis showed that daily survival rate was not density-dependent. Correlation analyses showed that daily metamorph survival was influenced by daily maximum and minimum temperatures. Metamorphs at lower densities attain juvenile size (30 mm) more rapidly; because they survive at the same daily rates as metamorphs at higher densities they experience lower cumulative mortality as metamorphs.
Why are some animals active by day and others by night? The selective forces that favor diurnal versus nocturnal activity may be evaluated by comparing age classes within a species that exhibits intraspecific (ontogenetic) variation in activity times. In many species of toads, adults are nocturnally active but postmetamorphic animals are primarily diurnal. The small body sizes of these animals render them vulnerable to desiccation and overheating--so why are they active by day? To answer this question, we studied an invasive population of cane toads (Bufo marinus) in tropical Australia. In the field, these small toads often encounter cannibalistic conspecifics because desiccation risk concentrates toads around the moist margins of the natal pond. We manipulated factors that differ between day and night (time of day, illumination, presence of cannibalistic conspecifics, scent, or visual cues from cannibalistic conspecifics) to identify the proximate cues and fitness advantages associated with diurnal versus nocturnal activity. Activity levels, response to disturbance, and feeding rates of metamorph toads were enhanced by light but suppressed by the presence of a larger conspecific. Metamorphs used both visual and scent cues to detect larger toads. An endogenous diel rhythm in activity was present also but weaker in metamorph toads than in larger (cannibal sized) individuals. The risk of cannibalism was high only at night and only in dark conditions. Thus, the diurnal activity of metamorph toads enables these vulnerable animals to avoid conspecific predators. Copyright 2008, Oxford University Press.
Invasive species are widely viewed as unmitigated ecological catastrophes, but the reality is more complex. Theoretically, invasive species could have negligible or even positive effects if they sufficiently reduce the intensity of processes regulating native populations. Understanding such mechanisms is crucial to predicting ultimate ecological impacts. We used a mesocosm experiment to quantify the impact of eggs and larvae of the introduced cane toad (Bufo marinus) on fitness-related traits (number, size and time of emergence of metamorphs) of a native Australian frog species (Opisthodon ornatus). The results depended upon the timing of oviposition of the two taxa, and hence the life-history stages that came into contact. Growth and survival of O. ornatus tadpoles were enhanced when they preceded B. marinus tadpoles into ponds, and reduced when they followed B. marinus tadpoles into ponds, relative to when tadpoles of both species were added to ponds simultaneously. The dominant tadpole-tadpole interaction is competition, and the results are consistent with competitive priority effects. However, these priority effects were reduced or reversed when O. ornatus tadpoles encountered B. marinus eggs. Predation on toxic toad eggs reduced the survival of O. ornatus and B. marinus. The consequent reduction in tadpole densities allowed the remaining O. ornatus tadpoles to grow more rapidly and to metamorphose at larger body sizes (>60% disparity in mean mass). Thus, exposure to B. marinus eggs reduced the number of O. ornatus metamorphs, but increased their body sizes. If the increased size at metamorphosis more than compensates for the reduced survival, the effective reproductive output of native anurans may be increased rather than decreased by the invasive toad. Minor interspecific differences in the seasonal timing of oviposition thus have the potential to massively alter the impact of invasive cane toads on native anurans.
Ants are one of the most important faunal groups in Australia and are widely used as bioindicators in land monitoring and assessment programs. The Ants of Northern Australia will help in the identification of the 1500 or more ant species occurring in monsoonal Australia, an area which encompasses most of the northern third of the continent. Until now, no book has described the northern Australian ant fauna below genus level. Such a treatment is required to support and promote the numerous ecological studies involving ants, especially in the context of their use as bioindicators. The Ants of Northern Australia features original analyses of genera at the species-group level, and so has relevance throughout Australia. It treats all major species that have been described, as well as numerous others that remain undescribed.
An adaptationist programme has dominated evolutionary thought in England and the United States during the past 40 years. It is based on faith in the power of natural selection as an optimizing agent. It proceeds by breaking an oragnism into unitary 'traits' and proposing an adaptive story for each considered separately. Trade-offs among competing selective demands exert the only brake upon perfection; non-optimality is thereby rendered as a result of adaptation as well. We criticize this approach and attempt to reassert a competing notion (long popular in continental Europe) that organisms must be analysed as integrated wholes, with Baupläne so constrained by phyletic heritage, pathways of development and general architecture that the constraints themselves become more interesting and more important in delimiting pathways of change than the selective force that may mediate change when it occurs. We fault the adaptationist programme for its failure to distinguish current utility from reasons for origin (male tyrannosaurs may have used their diminutive front legs to titillate female partners, but this will not explain why they got so small); for its unwillingness to consider alternatives to adaptive stories; for its reliance upon plausibility alone as a criterion for accepting speculative tales; and for its failure to consider adequately such competing themes as random fixation of alleles, production of non-adaptive structures by developmental correlation with selected features (allometry, pleiotropy, material compensation, mechanically forced correlation), the separability of adaptation and selection, multiple adaptive peaks, and current utility as an epiphenomenon of non-adaptive structures. We support Darwin's own pluralistic approach to identifying the agents of evolutionary change.
Conservation tillage fields may consititue 'ecological traps' for nesting birds because these fields appear to provide more suitable nesting cover than more heavily tilled fields but nest disturbance may still be frequent enough to cause poor nesting success. -from Author
1. Introduction 2. Estimation 3. Hypothesis testing 4. Graphical exploration of data 5. Correlation and regression 6. Multiple regression and correlation 7. Design and power analysis 8. Comparing groups or treatments - analysis of variance 9. Multifactor analysis of variance 10. Randomized blocks and simple repeated measures: unreplicated two-factor designs 11. Split plot and repeated measures designs: partly nested anovas 12. Analysis of covariance 13. Generalized linear models and logistic regression 14. Analyzing frequencies 15. Introduction to multivariate analyses 16. Multivariate analysis of variance and discriminant analysis 17. Principal components and correspondence analysis 18. Multidimensional scaling and cluster analysis 19. Presentation of results.
The temperature preference of Bufo marinus larvae was determined at six stages of development. At stage 37 the temperature preference of the larvae was also determined at each of three acclimation temperatures. Preferred temperature generally increased as larval development progressed. This trend was compared with the thermal tolerance at different stages of development. There was no significant correlation between temperature tolerance and temperature preference. The temperatures experienced by tadpoles in nature as they select different microhabitats at different stages of development showed a trend similar to the temperature preferences. Different acclimation temperatures at stage 37 had no effect on temperature preference.
Recently metamorphosed Bufo marinus exhibit patterns of activity and habitat use that vary in relation
to changes in weather and moisture availability. Activity adjacent to water is greatest on moist substrates
at high daytime temperatures in windy weather. Conditions that inhibit evaporative cooling (no
wind, dry substrates, high humidity), or are likely to lead to low body temperatures (cool temperatures
at night under windy conditions) restrict activity. Activity in habitats away from permanent water is
dependent on metamorphlings having grown large enough to allow night-time activity on dry substrates.
Growth leads to a change in activity from diurnal as metarnorphlings, to nocturnal and diurnal as
juveniles (30-70 mm SVL), and to nocturnal as adulthood approaches. Size-dependent changes in patterns
of activity and habitat use are accompanied by changes in pelvic patch morphology and body pigmentation.
The morphological changes may have resulted from selection acting to minimise time spent
in the smaller size classes which are vulnerable to predators, competitors and the environment, and
size-dependent optimisation of chemical defences.
Abstract Spawning sites are a critical and often scarce resource for aquatic-breeding amphibians, including invasive species such as the cane toad (Bufo marinus). If toads select spawning sites based on habitat characteristics, we can potentially manipulate those characteristics to either enhance or reduce their suitability as breeding sites. We surveyed 25 spawning sites used by cane toads, and 25 adjacent unused sites, in an area of tropical Australia recently invaded by these feral anurans. Water chemistry (pH, conductivity, salinity, turbidity) was virtually identical between the two sets of waterbodies, but habitat characteristics were very different. Toads selectively oviposited in shallow pools with gradual rather than steep slopes, and with open (unvegetated) gradually sloping muddy banks. They avoided flowing water, and pools with steep surrounds. In these respects, cane toads broadly resemble previously studied toad species in other parts of the world, as well as conspecifics within their natural range in South America.
The foraging activity of the meat ant Iridomyrmex purpureus form viridiaeneus is closely correlated with temperature in an arid environment. The ants feed on a wide range of plant and animal material, travelling up to 100 m to gather food.
Results of a mark-release study of Rattus sordidus colletti (Gould) on sub-coastal, treeless plains in the monsoonal north of the Northern Territory of Australia are given for 5 years. R. s. colletti is the dominant component of the small mammal fauna of these plains, with only small numbers of Melomys spp. and Planigale maculata also occurring. Two classes of peak densities were observed. Localized peaks resulted from non-breeding adult R. s. colletti refuging onto the marginally higher levees during flooding of the plains, and also from refuging into a lower-lying area at the end of a dry-season drought. Generalized peak densities resulted from peaks in reproductive effort. In 1972 and 1974, reproduction was confined to the period immediately following the monsoons, but in 1973 breeding continued throughout the dry season, following unseasonal rain in June. Thus, generalized peak densities were observed in one year at the beginning of the dry season, and in another at its end. The relatively shallower flooding and mildness of the 1972–3 wet season resulted in commencement of breeding earlier in 1973 than in 1974, while rapid severe flooding of the plains in December 1974 resulted in mass mortality and failure of the refuging populations of adults to recolonize the lower plains in 1975. R. s. colletti remained extremely rare until November 1976, when the study was terminated.
Of two native Australian fishes naïve to the introduced toad Bufo marinus most barramundi Lates calcarifer rapidly learned to avoid B. marinus tadpoles, while sooty grunter Hephaestus fuliginosus exhibited considerable intraspecific variation in their learning ability. Some sooty grunter learned to avoid tadpoles after only a few attacks, while other individuals continued to attack and reject tadpoles throughout the entire laboratory trials. Individuals of both species recognized and avoided tadpoles 1 day after their previous encounter. None of the fishes died during the trials. The observed variation in behavioural responses of fishes to B. marinus may be due to differences in (1) learning ability, (2) fish hunger levels, and or (3) tadpole palatability and toxicity. The results demonstrate that most barramundi and sooty grunter learn to avoid B. marinus tadpoles with minimal trauma. Consequently, it is anticipated that the toads are unlikely to have a significant negative impact on wild populations of these fishes through direct toxic effects.
Abstract Cane toads (Bufo marinus) have invaded large areas of Australia, killing many native predators as they have done so. The metamorph stage of the life cycle – the first terrestrial phase, immediately after transformation from the tadpole – is critical for ecological impact (because these animals are small enough to be prey for many native predators) and for potential control of toad populations (because small body size renders metamorphs vulnerable to desiccation). To quantify the spatial and temporal distribution of metamorph toads, and the biotic and abiotic factors that might affect their distributions, we surveyed toad breeding sites in Australia's wet-dry tropics (Adelaide River floodplain, NT) in both the wet season and the dry season. Metamorphs were concentrated close to the water's edge during the dry season, especially at midday when desiccation rates were highest. During the wet season, metamorphs were widely dispersed through the landscape. Our surveys indicate that abiotic factors (risk of desiccation) are most favourable for metamorph toads close to the pond edge, but biotic factors (food supply, and risk of competition and cannibalism) are most favourable away from the water. Operative temperatures were spatially homogeneous and sublethal, and so are unlikely to influence metamorph distribution. Desiccation risk fluctuated on a diel cycle as well as seasonally. We predict that metamorph toads benefit from dispersing as soon as desiccation risk allows them to do so, and hence the distribution of metamorph toads will shift dynamically in response to weather-mediated changes in rates of evaporative water loss.
Capybaras, Hydrochaeris hydrochaeris, live in groups of varying size averaging 10 adults of both sexes. Vigilant behaviour was studied in capybaras under natural conditions, using focal-animal sampling on individual females, dominant males and subordinate males from groups of different sizes. There was a significant negative correlation between group size and individual alert rate, and a positive correlation with total group alert rate. Although the reduction in individual rates of vigilance levelled off at group sizes of 9-10, total alert rate continued to increase. The behaviour of the females accounted for most of the variation in individual alert rate and the behaviour of subordinate males accounted for most of the variation in total alert rate. These results suggest that females benefit the most from being in larger groups due to reduced vigilance required, while subordinate males 'pay' for their group membership by the vigilance they perform.
Despite the considerable research that has focused on the evolutionary relationships and biogeography of the genus Bufo, an evolutionary synthesis of the entire group has not yet emerged. In the present study, almost 4 kb of DNA sequence data from mitochondrial (12S, tRNA Val , and 16S) and nuclear (POMC; Rag-1) genes, and 83 characters from morphology were analysed to infer a phylogeny of South American toads. Phylogenies were reconstructed with par-simony and maximum likelihood and Bayesian model-based methods. The results of the analysis of morphological data support the hypothesis that within Bufo , some skull characters (e.g. frontoparietal width), correlated with the amount of cranial ossification, are prone to homoplasy. Unique and unreversed morphological synapomorphies are presented that can be used to diagnose recognized species groups of South American toads. The results of all phylo-genetic analyses support the monophyly of most species groups of South American Bufo . In most DNA-only and combined analyses, the South American (minus the B. guttatus and part of the ' B. spinulosus ' groups), North Amer-ican, Central American, and African lineages form generally well-supported clades: ((((((((South America) (North America + Central America)) Eurasia) Africa) Eurasia) South America) West Indies) South America). This result con-firms and extends prior studies recovering South American Bufo as polyphyletic. The biogeographical results indi-cate that: (1) The origin of Bufo predates the fragmentation of Gondwana; (2) Central and North American species compose the sister group to a large, 'derived' clade of South American Bufo ; and (3) Eurasian species form the sister group to the New World clade.
1. Many arthropods are predators of vertebrates: four orders of the class arachnida, six orders of insecta, five orders of crustacea and one order of chilopoda include species that have been reported to eat vertebrates. At the population level, some arthropods are responsible for significant mortality among some vertebrates.
2. Arthropods are well equipped for this type of predation; many are larger than vertebrates (approximately 20% of the vertebrate fauna of eastern North America is less than 10 cm in length), they may hunt in social groups and many have toxins or other adaptations that increase predatory efficiency.
3. Several arthropod predators and vertebrates may be involved in cross predation, the species eating each other. The switch in the role of predator and prey occurs during ‘ontogenetic reversal’ as the vertebrate grows from small and vulnerable to large and predaceous. Cross predation decreases the future risk for one's self or offspring.
4. The opportunity for arthropod predation on vertebrates exists in many communities, but a review of some food webs catalogued by Cohen (1978) indicates that this particular link may be easily overlooked. Some arthropods should be investigated as potential predators of vertebrates.
5. The information available from the analysis of feeding interactions in a community should be an important link between field and theoretical ecology; however, most food webs are probably underestimates of the complexity that is commonplace.
Cane toads (Bufo marinus) are large, highly toxic anurans that were introduced into Australia in 1937. Anecdotal reports suggest that the invasion of toads into an area is followed by dramatic declines in the abundance of terrestrial native frog-eating predators, but quantitative studies have been restricted to nonpredator taxa or aquatic predators and have generally reported minimal impacts. Will toads substantially affect Australian snakes? Based on geographic distributions and dietary composition, we identified 49 snake taxa as potentially at risk from toads. The impact of these feral prey also depends on the snakes' ability to survive after ingesting toad toxins. Based on decrements in locomotor (swimming) performance after ingesting toxin, we estimate the LD50 of toad toxins for 10 of the at-risk snake species. Most species exhibited a similar low ability to tolerate toad toxins. Based on head widths relative to sizes of toads, we calculate that 7 of the 10 taxa could easily ingest a fatal dose of toxin in a single meal. The exceptions were two colubrid taxa (keelbacks [ Tropidonophis mairii] and slatey-grey snakes [ Stegonotus cucullatus]) with much higher resistance to toad toxins (up to 85-fold) and one elapid (swamp snakes [ Hemiaspis signata]) with low resistance but a small relative head size and thus low maximum prey size. Overall, our analysis suggests that cane toads threaten populations of approximately 30% of terrestrial Australian snake species.
Distributions of the three nominal forms of the meat ant Iridomyrmex purpureus (Smith), I. viridiaeneus Viehmeyer and J. sanguineus Forel have been studied. Each ranges widely, and seems characteristically to be developed in areas within prescribed limits of rainfall and vegetation. The most common form, purpureus, is found over one third of the Australian mainland; it is sometimes found in association with the other two forms and in places it appears to occupy a buffer zone between areas where viridiaeneus or sanguineus are common. Examples of apparent character displacement are given, with discussion of how the variation in nest structure could enable colonies to survive extreme conditions. Evidence suggesting effects of soil, altitude, rainfall and vegetation in limiting the distribution of each form is discussed.
Aim To assemble a continental‐scale data set of all available anuran records and investigate trends in endemism and species richness for the Anura.
Location Continental Australia.
Methods 97,338 records were assembled, covering 75% of the continent. A neighbourhood analysis was applied to recorded locations for each species to measure richness and endemism for each half‐degree grid square ( c. 50 km) in the continent. This analysis was performed for all anurans, and also for each of the three main anuran families found in Australia. A Monte Carlo simulation was used to test a null hypothesis that observed centres of endemism could result simply from an unstructured overlapping of species ranges of different sizes.
Results Eleven main centres of anuran endemism were identified, the most important being the Wet Tropics and the south‐west near Bunbury‐Augusta and near Walpole. With the exception of south‐western Australia, all of the identified significant endemic centres are in the northern half of the continent. The regions identified as significant for endemism differed from those identified for species richness and are more localized. Species richness is greatest in the Wet Tropics and the Border Ranges. High species richness also occurs in several areas not previously identified along the east and northern coasts.
Main conclusions Weighted endemism provides a new approach for determining significant areas for anuran conservation in Australia and areas can be identified that could be targeted for beneficial conservation gains. Patterns in endemism were found to vary markedly between the three main anuran families, and south‐eastern Australia was found to be far less significant than indicated by previous studies. The need for further survey work in inland Australia is highlighted and several priority areas suggested. Our results for species richness remain broadly consistent with trends previously observed for the Australian Anura.
In sexually cannibalistic species, selection is thought to have favoured the evolution of male approaching behaviour that reduces the probability that the female will kill the male. However, investigations of behaviours that could reduce the probability of sexual cannibalism are few. We examine the hypothesis that male wolf spiders, Lycosa tarantula (L.) (Araneae, Lycosidae), decides to approach females in periods when they are less dangerous. Males of this species approach females for mating during the daytime only. While attending females, males stay farther from the female's burrow at night than during the daytime. In field experiments, we offered a grasshopper (typical prey) or a male L. tarantula to females at night and during the day, and our findings show that the diel changes in the male's approaching behaviour matches diurnal changes in the female's tendency to attack both the grasshopper and the male spider. These findings support our hypothesis that a diel change in female responsiveness to prey has been a selection pressure influencing the evolution of male approach behaviour in a sexually cannibalistic species.
Larvae of five Nearctic Pieris butterflies accept a wide range of native and naturalized crucifers under laboratory test conditions. Preferences among crucifers are usually statistical rather than absolute. Caterpillars do not necessarily reject plants that do not support larval growth in favor of those that do. Preferences are not significantly altered by larval development or prior experience with specific foodplant species. Progeny of different females do not exhibit significantly different preferences. Retention of behavioral flexibility by Pieris may enable older larvae to exploit alternative resources not suitable for young larvae.
The mortality risk from hunting/predation should increase animals' vigilance and modify their selection of feeding sites. This risk may thus be costly if vigilance interferes with feeding and/or if animals select poorer but safer feeding sites. We observed the vigilance behaviour of roe deer, Capreolus capreolus, feeding in a fragmented landscape during and outside the hunting season and compared food availability and local landscape features at these feeding sites with random paired sites. Roe deer spent more time vigilant during the hunting season than outside it. During the hunting season, vigilance decreased as the woodland extent within an 800 m radius increased, but this was not the case outside the hunting season. Vigilance decreased with increasing distance to houses, both during and outside the hunting season. When food is abundant, interference with feeding may be low because animals can simultaneously process food (chewing) and be vigilant. During the hunting season, the total time spent vigilant while chewing increased with increasing food abundance to a lesser extent than outside the hunting season, suggesting a higher level of costly exclusive vigilance during the hunting season. Outside the hunting season animals selected feeding sites that provided more food, but during the hunting season, as risk (proximity to houses) was positively correlated with food availability, animals no longer selected feeding sites on the basis of food availability. Taken together, our results indicate that roe deer trade off risk avoidance for food availability in hunted populations.
Organisms often rely on environmental cues to make behavioral and life-history decisions. However, in environments that have been altered suddenly by humans, formerly reliable cues might no longer be associated with adaptive outcomes. In such cases, organisms can become ‘trapped’ by their evolutionary responses to the cues and experience reduced survival or reproduction. Ecological traps occur when organisms make poor habitat choices based on cues that correlated formerly with habitat quality. Ecological traps are part of a broader phenomenon, evolutionary traps, involving a dissociation between cues that organisms use to make any behavioral or life-history decision and outcomes normally associated with that decision. A trap can lead to extinction if a population falls below a critical size threshold before adaptation to the novel environment occurs. Conservation and management protocols must be designed in light of, rather than in spite of, the behavioral mechanisms and evolutionary history of populations and species to avoid ‘trapping’ them.
Observations of 21 species of open-nesting passerines breeding in contiguous field and forest habitats at Rose Lake Wildlife Research Area, Michigan, were made during 1974 and 1975. Data were collected on nest dispersion, clutch-size, and fledging success in relation to the field-forest edge. Losses of eggs or nestlings were attributed to predation, inclement weather, Brown-headed Cowbird (Molothrus ater) parasitism, nest desertion, hatching failure, and adult death. Each bird species seemed to have a preferred distance from the habitat discontinuity that was used as a nest site. Furthermore, nests were not uniformly distributed on the area. Over one-half of the nests were found within ?15 m of the habitat discontinuity. Seventy-five percent of the nests belonged to birds characteristic of mixed breeding habitats, i.e., birds requiring an open overstory canopy with elevated singing and observation perches and dense cover near the ground for nesting and feeding. These mixed-habitat species also accounted for the increase in avian species nesting near edges. Based on Kendall rank and partial rank correlation tests, increasing numbers of nests and the percentage of total clutches ^3 eggs were found to be negatively correlated with increasing distance from the habitat discontinuity. Correlation between fledging success and increasing distance from the edge was positive and highly significant. Of the several mortality factors investigated, predation and cowbird parasitism were found to be the most important. The increased predation rate with decreased distance from the edge was attributed primarily to a functional response to higher numbers of nests and a greater activity of potential nest predators in the vicinity of the habitat discontinuities. Our results indicate that habitat suitability decreases with increasing numbers of nests toward the narrow field-forest edges. Although such abrupt habitat discontinuities did attract a variety and abundance of birds characteristic of habitats with mixed life-form, these discontinuities seemed to function as "ecological traps" by concentrating nests and thereby increasing density-dependent mor? tality. Ironically, the cowbird was also a victim of the increased predation rate. As these man-made forest edges are of recent origin, they are perhaps unrepresentative of the ecological niche in which these species evolved, and thus they may be poorly adapted to cope with the increased nest predation.
Ant distribution and behavioural dominance is examined at nine sites along an elevational gradient (1400–2600 m) in south eastern Arizona, in order to classify North American species according to a functional group scheme used extensively in Australia. The functional groups are then used as a basis for determining patterns of community structure along the environmental gradient, and for comparing community structure between Australia and North America. Quantitative information on species com- position was obtained from pitfall traps, and patterns of ant abundance at tuna baits were used to determine relative behavioural dominance among taxa. A total of eighty-three species from twenty-eight genera was recorded along the elevational gradient, with site species richness ranging from four (high elevation Douglas fir forest) to thirty-three (mid elevation oak–juniper woodland). There was a strong correlation between ant abundance and richness, which was not an artefact of sampling intensity. The most common ants were species of Forelius, Monomorium, Crematogaster and Pheidole at the three desert sites, species of Formica, Pheidole and Crematogaster at the three woodland sites, and species of Prenolepis and Formica at one forest site. No species were abundant at two other forest sites. The most common species in traps also tended to be the most common species at baits. In terms of behavioural dominance, highly competitive ants included species of Solenopsis, Forelius, Monomorium and Liometopum. Species of Pheidole and Crematogaster tended to be moderately competitive, whereas species of Dory- myrmex, Myrmica, Camponotus and Formica (fusca gp) had low competitive ability. On the basis of these results and on published records of other taxa, North American ants were assigned to functional groups as follows (major taxa only given here): Dominant Dolichoderinae—Forelius, Liome- topum; Subordinate Camponotini—Camponotus; Hot Climate Specialists—Pogonomyrmex, Myrmecocystus; Cold Climate Specialists—Formica (rufa, exsecta and microgyna groups), Leptothorax, Stenamma, Lasius, Prenolepis; Cryptic Species—Smithistruma, Solenopsis (subgenus Diplorhop- trum), Acanthomyops; Opportunists—Formica (fusca group), Myrmica, Paratrechina, Dorymyrmex; Generalized Myr- micinae—Pheidole, Crematogaster, Monomorium; Specialist Predators—no major taxa. Functional group composition varied systematically along the elevation gradient: Dominant Dolichoderinae, Generalized MyrÃmicinae and Hot Climate Specialists were predominant at desert sites; Generalized Myrmicinae and Opportunists were predominant at woodland sites; and Opportunists and Cold Climate Specialists were predominant at forest sites. These patterns are consistent with published studies from elsewhere in North America. Almost all North American taxa can be matched with what appear to be ecologically equivalent taxa in Australia, and biogeographic patterns of functional group composition are broadly similar across the two continents. The major differences are that Australian ant communities are far richer in species, and are almost always dominated by dolichoderines, particularly species of Iridomyrmex. Generalized myrmicines are subdominant to dolichoderines in Australia, but are the behaviourally dominant ants throughout the warmer parts of North America. In cool-temperate North America, species of Formica (especially rufa and exsecta groups) are behaviourally dominant, as they are throughout the Palearctic. Some major features of the North American fauna can be linked to its poor representation of Dominant Dolichoderinae, including (1) the relatively low degree of physiological, morphological and behavioural specialization of Hot Climate Specialists; (2) behavioural dominance by formicines in cool-temperate habitats; and (3) the susceptibility to invasion by behaviourally dominant species such as the imported fire ant Solenopsis invicta and the Argentine ant Linepithema humile.
• In considering the Origin of Species, it is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration. Naturalists continually refer to external conditions, such as climate, food, &c, as the only possible cause of variation. In one very limited sense, as we shall hereafter see, this may be true; but it is preposterous to attribute to mere external conditions, the structure, for instance, of the woodpecker, with its feet, tail, beak, and tongue, so admirably adapted to catch insects under the bark of trees. In the case of the misseltoe, which draws its nourishment from certain trees, which has seeds that must be transported by certain birds, and which has flowers with separate sexes absolutely requiring the agency of certain insects to bring pollen from one flower to the other, it is equally preposterous to account for the structure of this parasite, with its relations to several distinct organic beings, by the effects of external conditions, or of habit, or of the volition of the plant itself. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
• In considering the Origin of Species, it is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration. Naturalists continually refer to external conditions, such as climate, food, &c, as the only possible cause of variation. In one very limited sense, as we shall hereafter see, this may be true; but it is preposterous to attribute to mere external conditions, the structure, for instance, of the woodpecker, with its feet, tail, beak, and tongue, so admirably adapted to catch insects under the bark of trees. In the case of the misseltoe, which draws its nourishment from certain trees, which has seeds that must be transported by certain birds, and which has flowers with separate sexes absolutely requiring the agency of certain insects to bring pollen from one flower to the other, it is equally preposterous to account for the structure of this parasite, with its relations to several distinct organic beings, by the effects of external conditions, or of habit, or of the volition of the plant itself. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
An adaptationist programme has dominated evolutionary thought in England and the United States during the past 40 years. It is based on faith in the power of natural selection as an optimizing agent. It proceeds by breaking an oragnism into unitary 'traits' and proposing an adaptive story for each considered separately. Trade-offs among competing selective demands exert the only brake upon perfection; non-optimality is thereby rendered as a result of adaptation as well. We criticize this approach and attempt to reassert a competing notion (long popular in continental Europe) that organisms must be analysed as integrated wholes, with Baupläne so constrained by phyletic heritage, pathways of development and general architecture that the constraints themselves become more interesting and more important in delimiting pathways of change than the selective force that may mediate change when it occurs. We fault the adaptationist programme for its failure to distinguish current utility from reasons for origin (male tyrannosaurs may have used their diminutive front legs to titillate female partners, but this will not explain why they got so small); for its unwillingness to consider alternatives to adaptive stories; for its reliance upon plausibility alone as a criterion for accepting speculative tales; and for its failure to consider adequately such competing themes as random fixation of alleles, production of non-adaptive structures by developmental correlation with selected features (allometry, pleiotropy, material compensation, mechanically forced correlation), the separability of adaptation and selection, multiple adaptive peaks, and current utility as an epiphenomenon of non-adaptive structures. We support Darwin's own pluralistic approach to identifying the agents of evolutionary change.