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Consequences of the Ship Rat (Rattus rattus) recent invasion on the breeding avifauna of Sainte-Anne Islets Natural Reserve (Martinique, French West Indies), established after an eradication attempt
Abstract
Since 1995, the 4 Sainte-Anne Islets were under the protected status of Natural Reserve because of the major role they play for the nesting of 2 marine bird species at the scale of the Lesser Antilles and 3 more at the scale of the Martinique Island (French West Indies). The Ship Rat (Rattus rattus) invaded these islets may be as recently as 1996 or 1997. In November 1999, an attempt to eradicate this alien species by successive trapping and poisoning was conducted by the Martinique Regional Natural Park who is in charge of the management of the natural reserve. To evaluate the impact of the management of the Ship Rat populations, breeding data for Audubon's Shearwater (Puffinus lherminieri), Brown Noddy (Anous stolidus), Bridled Tern (Sterna anaethetus), and Red-billed Tropicbird (Phaethon aethereus), were collected since 1997 solely on the Hardy Islet. A semi-quantified inventory of the herpetofauna and terrestrial carcinofauna began in 2001-02 on the same island. Controls of the eradication operation were done in January 2001 and 2002. Only the eradication of the Percé Islet Ship Rat population was verified. In 2001 and 2002, the Hardy Islet Ship Rat population size was respectively 3 and 28 % of the initial one. The decrease of the Hardy Islet Ship Rat population induced an increase of the breeding success of Audubon's Shearwater and Brown Noddy from respectively 0 and 5 % in 1999, before the eradication attempt, to 61 and 90 % in 2000 and to 63 and 85 % in 2001, after the eradication attempt. Between 1999 and 2002 the number of the terrestrial crab Gecarcinus ruricola increased from 0.85 to 1.36 for 100 traps-nights. The relationship between the increase of trapped crabs and the drop of the Ship Rat size population remains to be rigorously established by further data. The failure of the eradication of 3 island Ship Rat populations among 4 was attributed to a bad efficiency of toxic bait. A new eradication campaign took place in January 2002. Its results will not be available until 2003. The very recent diagnostic of the Ship Rat invasion and the quick decision to attempt to eradicate the rodent were the result of a peer systematic survey of these islands by scientists and wildlife rangers. Up to date quantified or half-quantified inventories of fauna and flora have to be done before eradication in order to evaluate its impact. The build-up of such inventories is clearly pointed as one of the main missions devoted to the protected areas by the French Ministry of Environment.
... In fact, these rodents have been shown to heavily impact marine bird colonies ( Atkinson, 1985;Towns et al., 2006;Jones et al., 2008). Indeed, the extent to which black rat predation can impact breeding colonies of Audubon's shearwater was recently revealed following an attempt to eradicate the rodent from the islets of Saint-Anne, Martinique ( Pascal et al., 2004). Today, Audubon's shearwater nesting grounds are for the most part located on small coastal islets ( Birdlife International, 2014;Lowrie et al., 2012;Bright et al., 2014). ...
... The case of Blanchard 2 shows the nesting area of these birds to have been larger in the past, with breeding sites found in zones other than the most inaccessible ones. The main causes that biologists assumed to underlie this reduction is the introduction of predators, such as the mongoose, but, above all, the rat ( Pascal et al., 2004;Daltry et al., 2013;Bright et al., 2014). The probable presence of the rat on Marie-Galante from the very outset of European colonisation, as well as the presence of rat bones in the upper third of the fossil deposit, suggests that this intrusive rodent did not have a sufficiently important impact, at least on the scale of several centuries, to provoke the abandonment of the nesting site. ...
In this paper we present a natural deposit in Marie-Galante island (French West Indies), Blanchard 2, where historical-period Audubon's shearwater remains dominate the vertebrate assemblage. We combined a study of sediment geometry, a taphonomic analysis of molluscs, crustaceans and vertebrate remains, and direct radiocarbon dating on bird bone to demonstrate that the cave was used as a nesting ground during the island's colonial period. This approach also allows the discussion of the causes leading to the desertion of the site by birds. Finally, we investigate hypotheses regarding the dynamics of Audubon's shearwater nesting during prehistoric and historical times and the impact of anthropogenic phenomenon on these birds.
... For this purpose we monitored attempts to eradicate the ship rat (Rattus rattus) from the four islets of the Sainte Anne archipelago (Martinique, French Caribbean). This rodent was introduced in the seventeenth century to the French Caribbean (Lorvelec et al. 2001), but it was observed on the Sainte Anne islets only since 1995 (Pascal et al. 2004). Despite this very recent invasion, rats significantly threaten five marine bird species. ...
... In 1999 a campaign to eradicate the rat was conducted. Nevertheless, rats were observed on three of the four islets in 2001 and 2002 (Pascal et al. 2004; Lorvelec & Pascal 2005). The genetic study of the 1999 and 2002 Sainte Anne rat populations and population samples from the Martinique main island (MMI) coast was initiated (1) to make an a posteriori evaluation of the eradication unit chosen for the eradication attempt (i.e., the four islets) and (2) to evaluate whether the individuals observed in 2002 descended from survivors of the eradication attempt or resulted from a new invasion. ...
Determining the causes of a failed eradication of a pest species is important because it enables an argued adjustment of the methodologies used and the improvement of the protocols for future attempts. We examined how molecular monitoring can help distinguish between the two main reasons for an eradication failure (i.e., survival of some individuals vs. recolonization after eradication). We investigated genetic variation in seven microsatellite loci in ship rat (Rattus rattus) populations from four islets off the Martinique coast (French Caribbean). In 1999 an eradication attempt was conducted on the four islets. Three years later rats were observed again on two of them. We compared the genetic signatures of the populations before and after the eradication attempt. On one of the islands, the new rat population was likely a subset of the pre-eradication population. A weak genetic differentiation was found between them, with almost no new alleles observed in the new population and moderate FST values (0.15). Moreover, assignment procedures clustered the two populations together. In contrast, on the other islet, many new alleles were observed after the eradication attempt, resulting in an increase in genetic diversity (from 2.57 to 3.57 mean number of alleles per locus) and strong FST values (0.39). Moreover, genetic clustering clearly separated the two samples (i.e., before and after the eradication attempt) in two different populations. Thus, to achieve long-term eradication on these islets, it seems necessary to redevelop the eradication procedure to avoid individuals surviving and to prevent reinvasion, probably from the mainland, by installing permanent trapping and poisoning devices and conducting regular monitoring. We strongly encourage wildlife managers conducting eradication campaigns to integrate molecular biological tools in their protocols, which can be done easily for most common invasive species.
... La taille des rongeurs évoquée par Fernández de Oviedo est compatible avec celle du Rat noir. Quant aux robes, blanche (ou crème ?) et brune ou rousse, elles ont été observées au sein des populations de R. rattus des îlets de Sainte Anne en Martinique à l'occasion d'une opération d'éradication (Pascal et al., 2004a). Reste à déterminer si les dates d'apparition du Rat noir sur les côtes pacifiques de l'Amérique Centrale ou de l'Amérique du Sud sont compatibles avec l'observation de l'espèce sur l'île à une date antérieure à 1556. ...
History and modalities of alien species introductions are major information sources for scientists and managers that have in charge ecological restoration programmes. The present paper synthesizes the evolution of the Coco Island vertebrate fauna since its discovery by Europeans, between 1531 and 1542. Restricted to species that reproduced there, this synthesis was elaborated with the aim of contributing to a comprehensive, long-term strategy for introduced species management in this island. Presently, among the 26 vertebrate species hosted by the island, 7 are allochthonous (27%). Among the 21 species that were introduced during the last half millennium (11 mammals and 10 birds), 7 (6 mammals and one bird) are always present and reproduce, that is to say 33% of the total. This percentage is more then three times higher than the percentage given by the empirical 10% rule. Among all the allochthonous species, only the two Rattus were non-intentionally introduced. The insular autochthonous vertebrate fauna is totally deprived of mammals and encompasses 42% of endemic species. Available data do not allow the conclusion that autochthonous species may have disappeared since the discovery of the island by Europeans. During the last half millennium, man has dramatically and deliberately modified the Coco Island vertebrate fauna in spite of its geographical isolation, far from the main trading routes and without any harbour and perennial human settlements.
... Most information on the effect of rats on invertebrates comes from work in temperate climates, although due to the prevalence of terrestrial crabs in the tropics there is some data to suggest that rats suppress crab populations, often severely. Observations suggest that even large crabs like Gecarcinus ruricola in the Caribbean and G. planatus on Clipperton Island are depredated by rats (Pascal et al., 2004;Pitman et al., 2005). Other observations, like a substantial increase in the numbers of fiddler crabs (Uca spp.) on Palmyra Atoll within 18 months of a rat eradication (G. ...
The three most invasive rat species, black or ship rat Rattus rattus, brown or Norway rats, R. norvegicus and Pacific rat, R. exulans have been incrementally introduced to islands as humans have explored the world’s oceans. They have caused serious deleterious effects through predation and competition, and extinction of many species on tropical islands, many of which are biodiversity hotspots. All three rat species are found in virtually all habitat types, including mangrove and arid shrub land. Black rats tend to dominate the literature but despite this the population biology of invasive rats, particularly Norway rats, is poorly researched on tropical islands. Pacific rats can often exceed population densities of well over 100 rats ha−1 and black rats can attain densities of 119 rats ha−1, which is much higher than recorded on most temperate islands. High densities are possibly due to high recruitment of young although the data to support this are limited. The generally aseasonally warm climate can lead to year-round breeding but can be restricted by either density-dependent effects interacting with resource constraints often due to aridity. Apparent adverse impacts on birds have been well recorded and almost all tropical seabirds and land birds can be affected by rats. On the Pacific islands, black rats have added to declines and extinctions of land birds caused initially by Pacific rats. Rats have likely caused unrecorded extinctions of native species on tropical islands. Further research required on invasive rats on tropical islands includes the drivers of population growth and carrying capacities that result in high densities and how these differ to temperate islands, habitat use of rats in tropical vegetation types and interactions with other tropical species, particularly the reptiles and invertebrates, including crustaceans.
... For a long time it was considered to be the only Gymnophthalmus in Martinique (Schwartz and Henderson, 1991). For example, Pascal et al. (2004) saw a Gymnophthalmus sp. on Hardy islet in Sainte-Anne (south Martinique) and thought that this species was G. pleii. I made a herpetological inventory of these islets before them in 2001 and identified G. pleii, but G. underwoodi was also present on the nearby shore. ...
I present an up-to-date annotated list of the herpetofauna of Martinique, and try to explain the causes responsible for the eradication of species such as Leptodactylus fallax, Boa sp. and Leiocephalus herminieri. Mabuya mabouya and Liophis cursor have not been seen for decades and may have been extirpated. It cannot be established that the mongoose was responsible; Didelphis marsupialis, of recent introduction, may have played an important role. Introduced and invasive species are numerous in Martinique: Chaunus marinus, Scinax ruber, Eleutherodactylus johnstonei, Gymnophthalmus underwoodi, Iguana iguana, Gekko gecko, Hemidactylus mabouia, without considering escaped pets and the dubious case of Allobates chalcopis as an endemic species. I also present the restoration plan for Iguana delicatissima in the French West Indies and the conservation work for this species in Martinique; increase of nesting areas, translocation, creation of numerous protected areas, and control of I. iguana. Of a total of 13 endemic and indigenous species from Martinique, three are definitely and a further two are probably eradicated. Including Guadeloupe, the French West Indies have the highest loss of herpetological biodiversity among all the islands in the West Indies.
... The first one was carried out in 2001 on Herpestes auropunctatus in the 115 ha Îlet Fajou off Guadeloupe (Lorvelec et al., 2004a). The second one occurred in 2002 and concerned Rattus rattus in the 5.7 ha Îlets de Sainte-Anne off Martinique (Pascal et al., 2004). After the eradications, terrestrial crab and bird populations increased, and in the case of Îlet Fajou, the systematic destruction of the marine turtle Eretmochelys imbricata eggs was stopped. ...
At least five marine turtles and 49 terrestrial or freshwater amphibians and reptiles have been listed from the French West Indies since the beginning of human settlement. Among terrestrial or freshwater species, two groups may be distinguished. The first group comprises 35 native species, of which seven are currently extinct or vanished. These species are often endemic to a bank and make up the initial herpetofauna of the French West Indies. Disregarding two species impossible to rule on due to lack of data, the second group includes twelve species that were introduced. Except for marine turtles and some terrestrial species for which the decline was due to human predation, the extinctions primarily involved ground living reptiles of average size and round section body shape. Habitat degradation and mammalian predator introductions have probably contributed to the extinction of these species, in addition to a possible direct impact of man. To better understand the threats to species, we suggest studying the interactions between native herpetofauna and introduced competitors or predators, taking into account the habitat structure. This would help to give the necessary information for successful management measures for conservation or restoration. As an example, the conservation of the Petite Terre (Guadeloupe) Iguana delicatissima population requires identifying both the mechanisms that regulate its population and their relationships to catastrophic climatic events.
... Reinvasion is a serious threat to all pest control programs, because it is the most likely cause of failure to achieve protection of core values (Pascal et al. 2004;Abdelkrim et al. 2007;Russell et al. 2010). The sink effect, induced by eradication of local populations connected by gene flow to a wider meta-population (Russell et al. 2009b), makes reinvasion inevitable. ...
Reinvasions provide prime examples of source-sink population dynamics, and are a major reason for failure of eradications
of invasive rats from protected areas. Yet little is known about the origins and population structure of the replacement population
compared with the original one. We eradicated eight populations of ship rats from separate podocarp-broadleaved forest fragments
surrounded by open grassland (averaging 5.3ha, scattered across 20,000ha) in rural landscapes of Waikato, New Zealand, and
monitored the- re-establishment of new populations. Rats were kill-trapped to extinction during January to April 2008, and
then again after reinvasion in April–May (total n=517). Rats carrying Rhodamine B dye (n=94), available only in baits
placed 1–2months in advance in adjacent source areas located 170–380m (average 228m edge to edge) away, appeared in 7 of
the 8 fragments from the first day of the first eradication. The distribution of age groups, genders and proportions of reproductively
mature adults (more immature juvenile males and fewer fully mature old females) was different among marked rats compared with
all other rats (P=0.001, n=509); in all rats caught on days 7+ of the first eradication compared with on days 1–6 (P=0.000); and in the total sample collected in fragments by trapping to and after local extinction compared with in brief,
fixed-schedule sampling of populations in continuous forests (P=0.000). Genotyping of 493 carcases found no significant population-level differentiation among the 8 fragments, confirming
that the rats in all fragments belonged to a single dynamic metapopulation. Marked rats of both genders travelled up to 600m
in a few days. Conservation of forest fragments is compromised by the problem that ship rats cannot be prevented from rapidly
reinvading any cleared area after eradication.
KeywordsInvasive predators–Reinvasion–Roof rat–Black rat–Forest fragment–Genetic differentiation–Eradication units
In this paper, we review and analyse how three species of invasive rat (Rattus rattus, R. norvegicus and R. exulans) disperse to and invade New Zealand offshore islands. We also discuss the methods used to detect and prevent the arrival of rats on islands. All species of invasive rat can be transported by ship. However, rats can also swim to islands. Swimming ability varies greatly between individual rats, and is probably a learned trait; it is unlikely to be affected by variation in sea temperature in this region. Norway rats (R. norvegicus) are the best swimmers and regularly swim up to 1 km. Therefore, to prevent recurrent swimming invasions of islands, source populations may need to be controlled. Since islands differ in their attributes and individual rats differ in their behaviours, multiple devices need to be used to detect and prevent the invasion of islands, including poisons, traps, passive detection devices and trained dogs. In New Zealand, 85% of rat incursions have been successfully intercepted using traps and/or poisons. Any response should cover at least a 1-km radius around the point of incursion. If trapping, it is recommended that jaw traps are used. If using poison, it is recommended that hand-spread, short-life, highly palatable bait of the maximum permissible toxin concentration in small pellet form is used; if bait stations are used, large wooden tunnels that have a line of sight through them are recommended. To intercept invasions early, it is recommended that island surveillance is undertaken at least annually (preferably every 6 months).
Available online: http://www.ieep.eu/assets/448/ias_assessments.pdf
The lack of biological knowledge of many invasive species remains as one of the greatest impediments to their management. Here I detail targeted research into the biology of the yellow crazy ant
Anoplolepis gracilipes
within northern Australia and detail how such knowledge can be used to improve the management outcomes for this species. I quantified nest location and density in three habitats, worker activity over 24 h, infestation expansion rate, seasonal variation of worker abundance and the timing of production of sexuals. Nests were predominantly (up to 68%) located at the bases of large trees, indicating that search efforts should focus around tree bases. Nest density was one nest per 22, 7.1 and 6.3 m
2
in the three habitats, respectively. These data form the baselines for quantifying treatment efficacy and set sampling densities for post-treatment assessments. Most (60%) nests were underground, predominantly (89%) occurring in an open area rather than underneath a rock or log. Some seasonality was evident for nests within leaf litter, with most (83%) occurring during the ‘wet season’ (October–March). Of the underground nests, most were shallow, with 44% being less than 10 cm deep, and 67% being less than 20 cm deep. Such nest location and density information serves many management purposes, for improving detection, mapping and post-treatment assessments, and also provided strong evidence that carbohydrate supply was a major driver of
A. gracilipes
populations. Just over half of the nests (56%) contained queens. Of the 62 underground nests containing queens, most queens (80%) were located at the deepest chamber. When queens were present, most often (38%) only one queen was present, the most being 16. Queen number per nest was the lowest in July and August just prior to the emergence of virgin queens in September, with queen numbers then remaining steadily high until April. Nothing is known for any ant species about how the queen number per nest/colony affects treatment efficacy, but further research would no doubt yield important breakthroughs for treating ants. Activity occurred predominantly nocturnally, ceasing during mid-day. These activity data determined the critical threshold above which work must be conducted to be considered reliable, and also suggests that treatments are best applied in the afternoon. Total brood production peaked in February and was the lowest around August and September. These abundance data form the baselines for quantifying treatment efficacy, and may have implications for treatment efficacy. Males were found every month, predominantly between August and November. Queen pupae were found in September. The reproductive timing of sexuals determines the treatment schedule. Targeted, site-specific research such as that described here should be an integral part of any eradication program for invasive species to design knowledge-based treatment protocols and determine assessment benchmarks.
Many European politicians, managers, and scientists believe that non-indigenous species cannot be eradicated and that attempts to do so are hazardous because of frequent undesirable results. This notion seems to be based on the view that successful eradications undertaken in many other parts of the world cannot be generalised. To allow reasoned consideration of this argument, the eradication of non-indigenous vertebrate species performed in the French territories (European and overseas) and their recorded consequences on native fauna and flora are synthesised. Nineteen vertebrate eradication attempts were recorded, with seven mammal species as the targets. Of these attempts four failed for technical reasons and one for reasons undetermined as yet. These operations took place on islands of four biogeographical areas (West-European, Mediterranean, West Indies and Indian Ocean subantarctic) except a continental one (West-European continent). Among these 19 attempts, 13 were conducted according to a global strategy that provided data on the impact of the disappearance of the non-indigenous species on several native species. This impact, never detrimental, was determined for 14 species (one mammal, nine birds, one marine turtle, one crab, one beetle, one plant). Unexpected consequences of the disappearance of the invader were recorded for four native species (29%). This result highlights the poverty of natural historical information for several taxa and the flimsiness of the empty niche concept that is often used to argue for the delay of or to prevent any action again a non-indigenous species. If French territories can be taken as an example, eradications of non-indigenous species are not impossible; a good risk assessment prevents undesirable long-term consequences for native species and several native species benefited from the disappearance of the invader. Furthermore, eradication constitutes a powerful experimental tool for ecology and natural history studies if conceived as both a management and research operation.
The Lesser Antilles is a biodiversity hot spot but unfortunately human disturbance has taken its toll, causing dramatic population declines and even extinction of numerous endemic species. Nevertheless, today the rediscovery of previously thought extinct species is not uncommon. Often, old museum specimens and their original descriptions are the only information available for such species. The application of molecular phylogenetic relationships to extant species can help to elucidate pivotal information on their ecology and conservation. Erythrolamprus cursor is possibly an extinct colubrid racer from Martinique, currently classified as critically endangered on the International Union for Conservation of Nature Red List. Mitochondrial deoxyribonucleic acid sequences were obtained from four E. cursor specimens from the Muséum national d'Histoire naturelle (Paris) collections. All sequences recovered the same haplotype and the level of divergence between E. cursor and E. juliae, from the nearby island of Dominica, was lower than between other intraspecific distances within other Erythrolamprus. Furthermore, phylogenetic analyses confirm that these two species are sister taxa and share most recent common ancestry. We discuss that published ecological data available for the sister species (E. juliae) may help to elucidate information on this species' natural history, ultimately having important implications for a future conservation management program if E. cursor is to be found. We emphasize the urgent need to conduct an exhaustive survey on the supposed last population of E. cursor at Diamond Rock to establish the survival of this species there, to understand how it may have adapted to such an ecosystem, especially in sympatry of several introduced rodent species.
The introduction of mammal predators to islands often results in rapid declines in the number and range of seabirds. On Ascension Island the introduction of cats in 1815 resulted in extirpation of large seabird colonies from the main island, with relict populations of most species persisting only in cat-inaccessible locations. We describe the eradication of feral cats from this large and populated island. The campaign had to minimize risk to humans and maintain domestic animals in a state that prevented them re-establishing a feral population. Feral cat numbers declined rapidly in response to the strategic deployment of poisoning and live trapping, and cats were eradicated from the island within 2 years. During the project 38% of domestic cats were killed accidentally, which caused public consternation; we make recommendations for reducing such problems in future eradications. Since the completion of the eradication campaign cat predation of adult seabirds has ceased and five seabird species have recolonized the mainland in small but increasing numbers. Breeding success of seabirds at Ascension was low compared to that of conspecifics elsewhere, and the roles of food availability, inexperience of parent birds and black rat predation in causing this warrant further investigation. It is likely that the low breeding success will result in the rate of increase in seabird populations being slow.
Invasive species are a global problem but most studies have focused on their direct rather than indirect ecological effects. We studied litter and soil-inhabiting invertebrate communities on 18 islands off northern New Zealand, to better understand the indirect ecological consequences of rat (Rattus) invasion. Nine islands host high densities of burrowing procellariid seabirds that transport large amounts of nutrients from the ocean to the land. The other nine have been invaded over the past 50–150 years by rat species that have severely reduced the density of seabirds by preying on eggs and chicks. Invaded islands had lower densities of seabird burrows but deeper forest litter than did the uninvaded islands, indicative of rats reducing disturbance effects of seabirds. However, despite deeper litter on the invaded islands, eight of the 19 orders of invertebrates that we measured were significantly less abundant on invaded islands. Furthermore, three soil-inhabiting micro-invertebrate groups that we measured were significantly less abundant on invaded islands. These differences probably result from rats thwarting transfer of resources by seabirds from the ocean to the land. We also investigated community-level properties of each of three test groups of invertebrates (minute land snails, spiders and soil nematodes) to illustrate this process. Spiders were equally abundant on both groups of islands, but showed lower species richness on the invaded islands. The other two groups showed no difference in species richness with island invasion status, but were more abundant on uninvaded islands. Reduced abundance of soil nematodes on invaded islands provides strong evidence of indirect consequences of seabird reduction by rats, because nematodes are unavailable to rats as prey. We predict that if rats are eradicated from islands, components of below-ground invertebrate dependent on seabird-mediated soil conditions may take considerable time to recover because they require subsequent seabird recolonisation.
Many European politicians, managers, and scientists believe that non-indigenous species cannot be eradicated and that attempts to do so are hazardous because of frequent undesirable results. This notion seems to be based on the view that successful eradications undertaken in many other parts of the world cannot be generalised. To allow reasoned consideration of this argument, the eradication of non-indigenous vertebrate species performed in the French territories (European and overseas) and their recorded consequences on native fauna and flora are synthesised. Nineteen vertebrate eradication attempts were recorded, with seven mammal species as the targets. Of these attempts four failed for technical reasons and one for reasons undetermined as yet. These operations took place on islands of four biogeographical areas (West-European, Mediterranean, West Indies and Indian Ocean subantarctic) except a continental one (West-European continent). Among these 19 attempts, 13 were conducted according to a global strategy that provided data on the impact of the disappearance of the non-indigenous species on several native species. This impact, never detrimental, was determined for 14 species (one mammal, nine birds, one marine turtle, one crab, one beetle, one plant). Unexpected consequences of the disappearance of the invader were recorded for four native species (29%). This result highlights the poverty of natural historical information for several taxa and the flimsiness of the empty niche concept that is often used to argue for the delay of or to prevent any action again a non-indigenous species. If French territories can be taken as an example, eradications of non-indigenous species are not impossible; a good risk assessment prevents undesirable long-term consequences for native species and several native species benefited from the disappearance of the invader. Furthermore, eradication constitutes a powerful experimental tool for ecology and natural history studies if conceived as both a management and research operation.
Introduced rats are now being eradicated from many islands. Increasingly, these eradications are contested by activists claiming
moral, legal, cultural, historic or scientific reasons and poorly documented evidence of effects. We reviewed the global literature
on the effects of rats on island flora and fauna. We then used New Zealand as a case study because of its four-decade history
of rat eradications and many detailed and innovative studies of how rats affect native species. These include use of exclosures,
local manipulations of rat populations, video surveillance, and measurements of responses following eradications. The most
intensive studies have been on the Pacific rat (Rattus exulans), a small South-East Asian species spread by Polynesians throughout the Pacific. These and the more recently introduced Norway
rat (R. norvegicus) and ship (roof) rat (R. rattus) suppress some forest plants, and are associated with extinctions or declines of flightless invertebrates, ground-dwelling
reptiles, land birds, and burrowing seabirds. On islands off France, Norway rats are also implicated in declines of shrews.
Globally, ship rats were associated with declines or extinctions of the largest number of indigenous vertebrate species (60),
including small mammals such as deer mice and bats. Effects of rats on forest trees and seabird populations are sufficiently
pervasive to affect ecosystem structure and function. However, the data are patchy. Deficiencies in our knowledge would be
reduced by documenting distribution and abundance of indigenous species before and after eradications. Comprehensive measurements
of the responses of indigenous species to rat eradications would enable the development of testable models of rat invasion
effects.
Invasive predators pose a significant risk to bird populations worldwide. Humans have a long history of removing predators
from ecosystems; current island restoration actions typically focus on the removal of invasive predators, such as non-native
rodents, from seabird breeding islands. While not overly abundant, the results of predator removal studies provide valuable
information on the demographic response of birds, and can assist conservation practitioners with prioritizing invasive predator
removal projects. We review such studies focusing on observed demographic responses of bird populations to predator removal
campaigns and whether ecological factors are useful in predicting those responses. From the 800+ predator removal programs
indentified, a small fraction (n=112) reported demographic responses of bird populations. Change in productivity was the most commonly reported response,
which on average increased by 25.3% (2.5 SE) with predator removal. The best supported model for predicting the change in
productivity from predator removal incorporated bird body mass, egg mass, predator type, nest type and an interaction term
for body mass and nest type (AICc weight=0.457). The predicted percent increase in productivity resulting from hypothetical predator removal ranged from
16.9 to 63.0% (mean=45.0, 5.6 SE), and was lowest for large, surface nesting birds such as albatrosses. The predicted increase
in productivity resulting from predator removal alone was insufficient to reverse the predicted population decline for 30–67%
of bird species considered, suggesting that in many cases, removal of predators must be performed in combination with other
conservation actions in order to ensure a stable or increasing population.
KeywordsEradication benefits-Island restoration-Invasive predator-Population recovery-Predator control
The widespread invasive rodents Rattus norvegicus, R. rattus, R. exulans and Mus musculus have been implicated in the decline and extinction of hundreds of island endemic vertebrates, but their effects on island invertebrates are less well-known. Here I present the first global review of the subject, which confirms that large-bodied invertebrates are most at risk from these rodents, and that although a disproportionate number of studies (69%) are from New Zealand, rodent-invertebrate impacts are geographically widespread. Mechanisms of impact are both direct (mediated by predation) and indirect (involving intermediary species). Some studies also suggest knock-on effects on ecosystem properties, and given the diverse ecological functions of invertebrates (as detritivores, primary consumers, predators, prey and pollinators), I suggest that an understanding of the interactions between invasive rodents and invertebrates in island ecosystems is essential for effective conservation management. Currently many reported impacts are unquantified, come from uncontrolled and unreplicated designs, or rely on time-series with inadequate baseline data. In addition to basic improvements in study design, this review highlights a need for studies which investigate mechanisms of impact, or impacts across trophic levels.
Consideration of definitions of 'biological invasion' and 'biodiversity' shows why invasions have recently generated great interest among conservationists. Many studies show that invasion numbers have increased drastically over the last five centuries, that this exponential increase is not levelling off, and that human activities are the only reason for the phenomenon. Many mechanisms are portrayed in an evolutionary framework and their consequences for biodiversity are described at three levels of life--gene, species and ecosystem. Examples from islands show that insular ecosystems are especially prone to damage from invasions; they also serve as 'laboratories' to elucidate the nature of invasion impacts. An important management approach--eradication--is discussed. Eradicating invaders not only aids understanding of their impacts on native species but also in understanding how ecosystems function. In fact, biological invasions can be seen as 'experiments', providing a rare opportunity to help answer certain fundamental scientific questions.
Since the beginning of the 70's, some engineers and nature conservationists have increased the experiments of ecosystems rehabilitation and creation to limit the disastrous effects of human activities characterized by a high ecological impact.
In its infancy, the scientists have neglected this field judged too "technical". The reversal of situation dates of the 80's with the emergence of a new disciplinary trend called the restoration ecology, that is conceived as a mean to connect the applied and basic scope of ecology. Then the experimental nature of these programs was emphasized.
Today, the debates between supporters and opponents of the restoration ecology are as intense as ever and deal with crucial concepts and principles in conservation biology : the key-species or perturbations roles, the relevant scale for the analysis and action, the methodology for the assessment and the monitoring, etc. These programs cause also some deontological problems dealing with the choice of the priorities and the reference systems, with the risk to be used as an alibi for destruction.
Five species of tern breed on Aldabra Atoll (09° 24′ S; 46° 20′ E). The Caspian tern Sterna caspia and Crested tern S. bergii feed exclusively in very shallow reef/lagoon water, the Fairy tern Gygis alba and Brown noddy Anous stolidus feed out at sea, and the Black-naped tern Sterna sumatrana is intermediate in its foraging. Both of the shallow-water species lay during the south-east monsoon season, the Caspian tern from April to August and the Crested tern from June to August, but the Crested tern also lays in December and January. The remaining three species have extended laying periods largely circumscribed by the north-west monsoon season from November to March. Breeding population size of the Caspian tern is in the low tens and of the Brown noddy in the low thousands, with the other species each numbering in the hundreds. The distribution and abundance of the nine species of tern breeding within the Seychelles (sensu lato) vary on the different island groups in a manner interpretable in terms of depth of the surrounding waters. Systematic differences between the central Seychelles and Aldabra groups in timing of breeding by terns which feed out at sea may be associated with seasonal latitudinal movement of the divergence zone between the South Equatorial Current and the Equatorial Counter-current, acting via correlated latitudinal shifts of prey species and game-fish abundance.
During the last five centuries, along with the reduction of biogeographic barriers, a great number of alien species were introduced by men, intentionally or not, in nearly all ecosystems throughout the world. Most of these introductions failed and a majority of the others didn't raise any problem. But some of them led to major economic losses and/or biological diversity reduction. The insular vegetal and animal communities are little diversified, often disharmonic, and characterized by an important rate of endemic species when compared with those of continental ecosystems. These communities are therefore particularly vulnerable to alien species. For these reasons and because of the small size of islands which allows experimental studies, most operations of eradication took place in this type of ecosystems since the 1960s, mammal species being the main target. This paper offers an approach to improve the decision and the technical implementation in view of the eradication of alien mammals on islands. These recommendations are founded on the experiences of brown rat eradication from ten Brittany Islands (1994-1996) and those of rabbit eradication from three islands of the Kerguelen Archipelago (1992-1999).
This paper deals with the built up of an eradication method of the Norway rat (Rattus norvegicus) from eight islands belonging to two archipelagoes off the Brittany Channel coast (Sept-Îles, 36,1 ha and Cancale Archipelago, 2,7 ha). The eradication took place in September-October 1994 and long term control started in the same season in 1995. The eradication was carried out in less than 17 days within one month. The use of trapping and poison (clorophacinone) successively permitted the reduction by 76 % of the input of poison into the food web and reduced by the same percentage the secondary poisoning hazard. There was no evidence of impact on the native mammals (shrews) but 31 birds belonging to 4 passerine species died in traps.
We have studied brown noddies Anous stolidus breeding on Cayo Noroeste in the Culebra National Wildlife Refuge for the past five years (1985–1989). Daily visits during our residence there each year permitted collection of precise data on arrival chronology, egg-laying and incubation patterns, egg morphometries, chick growth rates, food delivered to chicks and breeding success. Over 150 adults are now individually colour-banded, and each annual chick cohort has been uniquely marked. Some features of the breeding biology of Culebran brown noddies were similar to those reported for pairs at Atlantic and Pacific Ocean colonies; these included duration of egg development, mass of newly hatched chicks, chick growth rates and fledging periods. Other features appear unique to Culebra. These include a tightly synchronous arrival (range of first egg dates: 29 April-4 May) and short egg-laying period (about six weeks), a consistently high breeding success each year (average 84% hatching success, 88% chicks fledged from eggs hatched, 0.79 chicks fledged per pair), and an unusually narrow range of food items (two fish species) taken by adults for their own needs and those of chicks. Observations of the direction taken by adults departing the colony suggest a predictable and productive foraging area along a prominent east-west shelf-break located c. 20 km to the north. We conclude that during these five years, brown noddies on Cayo Noroeste were not limited by food during the breeding season.