Functional diversity of mammalian predators and extinction in island birds

The probability of a bird species going extinct on oceanic islands in the period since European colonization is predicted by the number of introduced predatory mammal species, but the exact mechanism driving this relationship is unknown. One possibility is that larger exotic predator communities include a wider array of predator functional types. These predator communities may target native bird species with a wider range of behavioral or life history characteristics. We explored the hypothesis that the functional diversity of the exotic predators drives bird species extinctions. We also tested how different combinations of functionally important traits of the predators explain variation in extinction probability. Our results suggest a unique impact of each introduced mammal species on native bird populations, as opposed to a situation where predators exhibit functional redundancy. Further, the impact of each additional predator may be facilitated by those already present, suggesting the possibility of "invasional meltdown."