Table 2 Interactions between covariates, hypotheses, inclusion in or exclusion from model and model results.
Interac tion | Hypothesis* | Interactions included in final model | Model result |
|---|---|---|---|
Area* Invasive mammal type | Invasive mammals expected to cause more extinctions on small islands due to smaller native populations, fewer alternative resources for invasive mammals and fewer refuges from invasive mammal impacts8 Invasive mammal groups differ in ability to successfully colonize small islands, depending on dietary flexibility and total resource needs7 | Rat*area | Invasive rats increase extirpation probability for all native groups, with a stronger effect on smaller islands |
Temperature or precipitation* Invasive mammal type | Invasive mammal impacts may be stronger on resource-poor islands, which may correlate with low precipitation and extreme high or low temperatures70 Invasive mammal groups differ in the ability to successfully invade environments with different climates18,34 | None | NA |
Area* Native class/volancy | Native vertebrate groups may differ in their ability to disperse to and diversify on islands of different sizes, due to differences in dispersal ability, body size and home range size36,37 These differences may influence the vulnerability of different native groups to anthropogenic impacts on islands of different sizes | Area* Native class/volancy | Non-volant mammals and volant birds have higher extirpation risk on smaller islands; amphibians, bats, reptiles and non-volant birds have higher extirpation risk on larger islands† |
Temperature or precipitation* Native class/volancy | Native vertebrate groups differ in susceptibility to anthropogenic impacts in different climates depending on life history traits (for example, endotherm versus ectotherm, home range size, flight ability)10 | Precipitation* Native class/volancy | Reptiles, non-volant mammals and bats have higher extirpation risk on drier islands; non-volant birds and amphibians have higher extirpation risk on wetter islands; precipitation has no effect on extirpation risk for volant birds† |
Native class/volancy* Invasive mammal type | Native vertebrate groups differ in vulnerability to different invasive mammal groups depending on ecological overlap and predator/prey or competition relationships between native species and invasive mammals7 | Native class/volancy* Pig Native class/volancy*cat | Invasive pigs increase extirpation probability for amphibians, bats, non-volant mammals, non-volant birds and volant birds; Invasive cats increase extirpation probability for non-volant birds, amphibians, reptiles and non-volant mammals† |
Native species body mass* Native class/volancy | Different-sized species within each native group differ in life history traits that influence their vulnerability to anthropogenic impacts33 | None | NA |
Native species body mass* Invasive mammal type | Native vertebrates of different sizes vary in susceptibility to invasive mammal impacts including predation (predators and omnivores) and habitat modification (omnivores and herbivores)33 | None | NA |
