Site invasibility by exotic birds and mammals

Abstract

Eradication of exotic species has been proposed to protect the integrity of nature reserves, but this can be a futile attack on symptoms without curing the causes of site invasibility—the susceptibility of a site to invasion by exotic species. More exotic bird and mammal species are found in California nature reserves that are surrounded by agriculture and human settlement, and that have suffered reduced richness of native mammal species. The chaparral ecotope contains 37 of the 41 exotic bird and mammal species in California, many of which are confined to large urban centers or residences. Farmland and settlements in the grassland ecotope support 17 of the wider-ranging exotic species. Site invasibility did not decrease with habitat area, but habitat fragmentation might lower biotic resistance in reserves by reducing mammal species richness and abundance after restricting dispersal. Reserve integrity can be best protected by landscape management that promotes native mammal species richness in and around reserves.