Determinants of the diversity of plants, birds and mammals of coastal islands of the Humboldt current systems: implications for conservation

摘要

Sound conservation plans for islands require understanding the processes underlying to the patterns of species richness and composition. Larger islands are often the targets of conservation assuming that the island area mainly determines species richness, and that species composition is nested across islands. However, in small-island these patterns could be altered because of stochastic processes, and species assemblages could be disharmonious. In addition, human impact could further modify the distribution pattern and diversity. Here we use the case of seven islands from the coastal system of Coquimbo as a model to address the role of environmental variables and human impacts on species richness and assembly rules of plants, birds, and mammals. We hypothesize (a) the existence of a small-island effect, and the prevalence of habitat diversity and anthropogenic impacts as main drivers of species richness, and (b) the existence of disharmonious assemblages, characterized by a low degree of nestedness and random patterns of species co-occurrence. Our results showed that (a) species richness is mainly correlated with habitat diversity, and only weakly related to island area supporting the ‘small-island effect’ and (b) species composition is highly structured, but that such structure may be the result of anthropogenic activities. Nestedness was observed in plants and landbirds, while co-occurrence patterns were only detected in plants. Assemblages in small-islands departed from the nestedness pattern and maintain rare species. Currently, only three of the seven islands are protected by national regulations, excluding the smaller ones that are subjected to human disturbance and invasive mammals. Our study suggests that it necessary to include all the islands in a major protected area to preserve both richness and species composition of a number of representative islands of the Humboldt current systems. We showed that conservation plans solely based on island area might not be robust.