From pets to pest : Cat impact on island biodiversity. A global perspective and a focus on the tropical Pacific area

Transcription

1 From pets to pest : Cat impact on island biodiversity. A global perspective and a focus on the tropical Pacific area Elsa Bonnaud, Eric Vidal, Felix Medina, Manuel Nogales Josh Donlan, Brad Keitt, Bernie R. Tershy, Erika Zavaleta, Matthieu Le Corre, Mike Fitzgerald & Lucie Faulquier UC SANTA CRUZ

2 Island ecosystems and biodiversity loss currently : 6th crisis of biodiversity loss species extinctions have more frequently occurred on islands than in other biogeographical regions Group Islands Continents Oceans Total % Insular Mammals Birds Reptiles Molluscs Insects Plants Total species extinction in the world from 16th century a large part of the recently extinct species were strictly island species

3 Island ecosystems and biodiversity loss Bird group : Maurice Réunion Guam New-Zelande Hawaii Invasive species Exploitation 50% of species extinctions caused by cats and rats! Habitat loss/degradation Unknown Natural disasters Persecutions Change in species dynamics Others Number of extinctions Causes of bird extinctions on islands

4 Some biological characteristics of islands Islands particularly sensitive to introduced species Species traits Low species diversity High rate of endemism Species are less competitive (naive species) Ecological traits Simple trophic webs Broadening trophic niches Broadening habitats numerous species facing imminent extinction!

5 Introduced mammals : cats as a striking case Domestic cat (Felis silvestris catus) : one of the predator the most spread on islands worldwide Domesticated very early Most ancient evidence of domestication and insular introduction : years B.P. Science, 2004 Great ability to catch rodents

6 Characteristics of Feral cats Feral cat (domestic cat returned to wild stage and feeding on wild prey) Great ability to spread Efficient predator Plasticity of feeding behavior Promiscuous mating system High fecundity success to establish feral cat populations Insertion in insular food webs Cats are one of the most detrimental introduced predator for the viability of insular species (small mammals, reptiles, and terrestrial and marine birds)

7 Two reviews are being conducted Feral cats on islands: global patterns in the diet of an invasive predator A review of the impacts of Feral Cat on insular endangered species

8 The diet of feral cats on islands Feral cats on islands: global patterns in the diet of an invasive predator E. Bonnaud, F.M. Medina, E. Vidal, M. Nogales, E. Zavaleta, J. Donlan, B. Tershy, B. Keitt, M. Le Corre & M. Fitzgerald Aim: to describe in detail the diet of feral cats on islands

9 Study sites 38 islands where the feral cat diet was investigated (59 contributions) 68 diet studies

10 General diet studies (%) /68 67/68 39/68 57/68 Mammals and birds are present in almost 100% of studies and the percentage of invertebrates and reptiles are relatively high too 20 8/68 0 mammals birds reptiles fishes prey categories invertebrates However, part of the information is rather limited because some studies did not give the frequency of occurrence of main prey categories 0 mammals birds reptiles fishes frequecy of occurence (%) /67 41/67 15/67 6/67 17/67 invertebrates prey categories

11 Number of species preyed on by feral cats Total of species preyed on: 217! (Number under-estimated because some studies did not distinguish prey at species level) 54 Invertebrates Birds Landbirds Fishes 2 Reptiles Mamm Seabirds 62 Birds were the category with most species eaten Among mammals, 17 were introduced species Number of reptile species was relatively high and were mainly natives Most invertebrates were insects and usually the largest ones

12 Biogeographical & biological factors on main prey categories Latitude Distance from mainland Area * Elevation Rat Mouse Rabbit Mammals ns ns ns * (+) ns ns Birds ns *** (+) ns ns ns *(-) Reptiles * (-) ns ns ns ns ns Rabbits could mitigate the frequencies of occurrences of birds in cat diet

13 Biogeographical & biological factors on diet diversity Latitude Distance from mainland Area * Elevation Rat Mouse Rabbit Levins-std * (-) * (+) ns ** (+) ns ns Shannon-std * (-) * (+) ns *** (+) ns ns Cats in rat presence caught rats but many other prey species too

14 A review of the impact of feral cats on insular endangered species A review of the impact of Feral Cat on insular endangered species F. M. Medina, E. Bonnaud, M. Nogales, E. Vidal, J. Donlan, B. Keitt, B. Tershy, M. Le Corre, E. Zavaleta & M. Fitzgerald Aim: to assess the impact on globally threatened species preyed by feral cats (the five most critical IUCN categories: EX, EW, CR, EN, VU)

15 Feral cat s effect and evaluation Data only include those cases where the pernicious effect of feral cats was clearly demonstrated and nowadays the prey species is threatened Reptiles Birds Mammals 20 0 complex strong extinction

16 Geographical distribution of impact on main prey groups Reptiles Birds Mammals

17 Number of taxa affected EX EW CR EN VU Taxa Species Reptiles Birds Mammals Total Amblyrhynchus cristatus Zoothera terrestris Nesoryzomys darwini

18 Geographical distribution of impact on islands Number of islands Cyclura spp. Branta sandwichensis Peromyscus spp Pacific Caribbean Atlantic Indian Sub-Antarctic Mediterranean Oceans Reptiles Birds Mammals

19 Details of prey listed in the IUCN categories EX EW CR EN VU 30 Number of islands Number of islands Pacific Caribbean Atlantic Indian Sub-Antarctic Mediterranean Mammals 0 Pacific Caribbean Atlantic Indian Sub-Antarctic Mediterranean Birds Number of islands Pacific Caribbean Atlantic Indian Sub-Antarctic Mediterranean Reptiles Mammal and bird species highly predated on many islands (especially in the Pacific ocean) Reptiles are less predated but the impact on these species is largely spread over oceans

20 Main conclusions of these two reviews 1. Mammals and birds are present in practically all diet studies. Invertebrates and reptiles are also relatively frequent 2. More than 200 of species were identified as prey for feral cats. Half of them were birds 3. While predation was on mainly native birds and reptiles, half of the mammals were introduced species 4. At least 167species (20 reptiles, 118 birds and 29 mammals), on 123 islands, are threatened and included in the five most critical categories of the IUCN 5. A total of 32 extinct taxa have been recorded (21 birds, 9 mammals and 2 reptiles) 6. The impact on birds is widespread but acute on Pacific islands. Mammals and reptiles were more locally affected (Pacific, Caribbean and Atlantic areas)

21 Number of species threatened by feral cats 50 number of species diet review (this study) impact review (Medina et al., in prep.) 0 EX EW CR EN VU EX EW CR EN VU EX EW CR EN VU mammals birds reptiles globally threatened species are underrepresented in diet analyses for most threatened species : which part in the diet? magnitude of cat impact? French Polynesia : need of detailed cat studies due to high number of threatened species

22 Manuel Nogales Lucie Faulqiuer Mike Fitzgerald Félix M. Medina Eric Vidal Josh Donlan Erika Zavaleta Elsa Bonnaud Matthieu Le Corre Bernie Tershy Brad Keitt