Hyper abundant mesopredators and bird extinction in an Atlantic forest island

Mauro Galetti,Marcos Rodrigues,Ariane D Alvarez,Carlos O A Gussoni,Kaiser Alves,Paulo R Guimarães Jr,Ricardo S Bovendorp,Rodrigo F Fadini

doi:10.1590/s1984-46702009000200011

Abstract

Islands can serve as model systems for understanding how biological invasions affect native species. Here we examine the negative effects of mesopredator mammals on bird richness at Anchieta Island, an 826 ha offshore island in the coast of Brazil. Anchieta Island has the highest density of mammals of the entire Atlantic forest, especially nest predators such as marmosets and coatis, introduced more than 20 years ago. This indiscriminate introduction of mammals may have affected directly the bird community, nowadays represented by 100 species comprised mainly by water-crossing birds, being 73 forest-dwelling species. A small component of these remnant bird species nests in tree holes and on the forest floor, null model analysis suggest that birds within these two nest types are under-represented on Anchieta Island. All guilds were affected negatively, but "opportunist insectivorous/omnivorous". Experiments using artificial nests showed a predation of 73% of nests on the floor while only 26% on the mainland. Camera traps recorded predation by coatis, agoutis, and opossums. The restoration of the bird community on this island is highly constrained by the high density of hyper abundant nest predators.

Highlights

Islands can serve as model systems for understanding how biological invasions affect native species
In 1983, the São Paulo Zoo introduced in this island 100 mammals from 15 species which originally occurred in the mainland of the Atlantic forest or in Brazilian savannas (Cerrado) such as agoutis, coatis, and marmosets (BOVENDORP & GALETTI 2007)
We investigated if guild and nest category affect the extinction of birds at Anchieta Island using a null model approach (GOTELLI & GRAVES 1996)

Summary

Introduction

Islands can serve as model systems for understanding how biological invasions affect native species. Anchieta Island has the highest density of mammals of the entire Atlantic forest, especially nest predators such as marmosets and coatis, introduced more than 20 years ago. This indiscriminate introduction of mammals may have affected directly the bird community, nowadays represented by 100 species comprised mainly by watercrossing birds, being 73 forest-dwelling species. Islands are the most disturbed components of the entire Atlantic forest ecosystem because they have long history of human occupation and because they are more susceptible to human impact (OLMOS 1996, NAKA et al 2002) Anchieta Island represents an excellent opportunity to study the impact of introduced mammals on avian extinction at the Atlantic forest

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Conclusion