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Keywords:

  • Establishment;
  • introduction;
  • islands;
  • null model;
  • species–area;
  • species–isolation

ABSTRACT

Aim  A recent upsurge of interest in the island biogeography of exotic species has followed from the argument that they may provide valuable information on the natural processes structuring island biotas. Here, we use data on the occurrence of exotic bird species across oceanic islands worldwide to demonstrate an alternative and previously untested hypothesis that these distributional patterns are a simple consequence of where humans have released such species, and hence of the number of species released.

Location  Islands around the world.

Methods  Statistical analysis of published information on the numbers of exotic bird species introduced to, and established on, islands around the world.

Results  Established exotic birds showed very similar species–area relationships to native species, but different species–isolation relationships. However, in both cases the relationship for established exotics simply mimicked that for the number of exotic bird species introduced. Exotic bird introductions scaled positively with human population size and island isolation, and islands that had seen more native species extinctions had had more exotic species released.

Main conclusion  The island biogeography of exotic birds is primarily a consequence of human, rather than natural, processes.