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Stanley, Falkland Islands

Tabak M.A.,University of Wyoming | Poncet S.,Beaver Island LandCare | Passfield K.,Beaver Island LandCare | Martinez Del Rio C.,University of Wyoming
Biological Invasions | Year: 2014

Invasive species pose significant threats to biodiversity, especially on islands. They cause extinctions and population declines, yet little is known about their consequences on the emergent, metacommunity-level patterns of native species in island assemblages. We investigated differences in species-area relationships, nestedness, and occupancy of 9 species of native land birds between island assemblages with and without invasive Norway rats (Rattus norvegicus) in the Falkland Archipelago. We found that species-area curves, nestedness, and individual species' occurrences differed between island assemblages with and without rats. Rat-free islands had, on average, 2.1 more land bird species than rat-infested islands of similar size. Passerine bird communities on islands with and without rats were significantly nested, but nestedness was significantly higher on rat-free islands than on rat-infested islands. The presence of rats was associated with differences in the incidence of many, but not all bird species. On rat free islands the occurrence of all species increased with island area. The occurrence of most, albeit not all, bird species was lower on islands with than on islands without rats. Two species of conservation concern, Troglodytes aedon cobbi and Cinclodes antarcticus, were abundant on rat-free islands, but absent or found at very low frequencies on islands with rats. The occurrence of three species was not associated with the presence of rats. The patterns presented here can be used to evaluate the consequences of ongoing rat eradications for passerine diversity, distribution, and abundance. © 2013 Springer Science+Business Media Dordrecht. Source


Tabak M.A.,University of Wyoming | Poncet S.,Beaver Island LandCare | Passfield K.,Beaver Island LandCare | Goheen J.R.,University of Wyoming | Martinez del Rio C.,University of Wyoming
Journal of Animal Ecology | Year: 2015

Norway rats (Rattus norvegicus) were introduced to the Falkland Islands and are detrimental to native passerines. Rat eradication programmes are being used to help protect the avifauna. This study assesses the effectiveness of eradication programmes while using this conservation practice as a natural experiment to explore the ecological resistance, resilience and homeostasis of bird communities. We conducted bird surveys on 230 islands: 85 in the presence of rats, 108 that were historically free of rats and 37 from which rats had been eradicated. Bird detection data were used to build occupancy models for each species and estimate species-area relationships. Count data were used to estimate relative abundance and community structure. Islands with invasive rats had reduced species richness of passerines and a different community structure than islands on which rats were historically absent. Although the species richness of native passerines was remarkably similar on eradicated and historically rat-free islands, community structure on eradicated islands was more similar to that of rat-infested islands than to historically rat-free islands. The results suggest that in the Falkland Islands, species richness of passerines is not resistant to invasive rats, but seems to be resilient following their removal. In contrast, community structure seems to be neither resistant nor resilient. From a conservation perspective, rat eradication programmes in the Falkland Islands appear to be effective at restoring native species richness, but they are not necessarily beneficial for species of conservation concern. For species that do not recolonize, translocations following eradications may be necessary. © 2014 The Authors. Source


Tabak M.A.,University of Wyoming | Poncet S.,Beaver Island LandCare | Passfield K.,Beaver Island LandCare | Martinez Del Rio C.,University of Wyoming
NeoBiota | Year: 2015

Non-native rats (Rattus spp.) threaten native island species worldwide. Efforts to eradicate them from islands have increased in frequency and become more ambitious in recent years. However, the long-term success of some eradication efforts has been compromised by the ability of rats, particularly Norway rats (Rattus norvegicus) which are good swimmers, to recolonize islands following eradications. In the Falkland Islands, an archipelago in the South Atlantic Ocean, the distance of 250 m between islands (once suggested as the minimum separation distance for an effective barrier to recolonization) has shown to be insufficient. Norway rats are present on about half of the 503 islands in the Falklands. Bird diversity is lower on islands with rats and two vulnerable passerine species, Troglodytes cobbi (the only endemic Falkland Islands passerine) and Cinclodes antarcticus, have greatly reduced abundances and/or are absent on islands with rats. We used logistic regression models to investigate the potential factors that may determine the presence of Norway rats on 158 islands in the Falkland Islands. Our models included island area, distance to the nearest rat-infested island, island location, and the history of island use by humans as driving variables. Models best supported by data included only distance to the nearest potential source of rats and island area, but the relative magnitude of the effect of distance and area on the presence of rats varied depending on whether islands were in the eastern or western sector of the archipelago. The human use of an island was not a significant parameter in any models. A very large fraction (72%) of islands within 500 m of the nearest potential rat source had rats, but 97% of islands farther than 1,000 m away from potential rat sources were free of rats. © Michael A. Tabak et al. Source


Tabak M.A.,University of Wyoming | Poncet S.,Beaver Island LandCare | Passfield K.,Beaver Island LandCare | Carling M.D.,University of Wyoming | Martinez del Rio C.,University of Wyoming
Conservation Genetics | Year: 2014

Norway rats (Rattus norvegicus) have been either introduced to or have invaded a large number of the world’s islands. Rats have caused population declines and the extinction of island endemics. Their eradication is often a major conservation success as it leads to recovery of affected species and even ecosystem processes. However, eradication efforts can be hampered by the ability of rats to re-colonize eradicated islands. Here we present the results of genetic analyses that inform migration rates and population structure of Norway rats from 14 sampling locations in the Falkland Islands, where rat eradication efforts are taking place. We used 12 microsatellite markers and population genetic tools to estimate rat migration patterns between 12 islands that were separated by distances ranging from 230 m to 112 km. We found evidence of significant migration rates, and hence presumably of rat movements between islands up to 830 m away from each other. Norway rats seem capable of swimming this distance even in the cold waters of the Falkland Islands. Our results can inform managers about strategies of rat eradication in the Falklands including minimal distances that reduce recolonization and the choice of island clusters for eradication. © 2014, Springer Science+Business Media Dordrecht. Source

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