More species, fewer specialists: 100 years of changes in community composition in an island biogeographical study
2009
Christian, Kerbiriou | Isabelle, Le Viol | Frédéric, Jiguet | Vincent, Devictor
We measured the changes in an island avifauna over more than 100 years (1898-2006), using community indices accounting for difference in expected species sensitivity to land-use and climate changes. Ouessant Island, France, Great Britain. We assessed the temporal trend of the relative proportion of generalist species breeding on Ouessant island and whether high-temperature tolerant species have replaced less tolerant species over this time period. We further tested the relationship between the observed change in the avifauna composition, and long-term population species' trends measured independently in potential source regions of colonist species (France and Great Britain). During the whole study period, Ouessant island has experienced a strong increase in species richness (+41%), but a severe decline in specialist species. In contrast, we found no change in species composition in terms of their temperature-tolerance. The observed trend was highly correlated with species trends measured in the Great Britain. Our results revealed an ongoing biotic homogenization process towards more generalist species, coupled with a strong local increase in species richness. The observed trend was most likely driven by a strong habitat change in the island occurring during the period considered, favouring the colonization of generalist species. Our results show that an increase in species richness can be misinterpreted as a sign of conservation improvement and that assessing change in community composition using species-specific ecological traits provides more accurate insights for conservation planning purposes.
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