Temporal changes in bird functional diversity across the United States
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Global changes are modifying the structure of species assemblages, but the generality of resulting diversity patterns and of their drivers is poorly understood. Any such changes can be detected and explained by comparing temporal trends in taxonomic and functional diversity over broad spatial extents. In this study, we addressed three complementary questions: How did bird taxonomic and functional diversity change over the past 40 years in the conterminous United States? Are these trends non-linear? Can temporal variations in functional diversity be explained by broad-scale changes in climate and vegetation productivity? We quantified changes in taxonomic and functional diversity for 807 bird assemblages over the past four decades (1970–2011) considering a suite of 16 ecological traits for 435 species. We found increases in local bird species richness and taxonomic equitability that plateaued in the early 2000’s while total abundance declined over the whole period. Functional richness, the total range of traits in an assemblage, increased due to the rising prevalence of species with atypical life-history strategies and under-represented habitat or trophic preferences. However, these species did not trigger major changes in the functional composition of bird assemblages. Inter-annual variations in climate and primary productivity explained the richness of bird life-history traits in local assemblages, suggesting that these traits are influenced by broad-scale environmental factors, while others respond more to more local drivers. Our results highlight that a comparative analysis of the multiple facets of functional diversity can raise novel insights on processes underlying temporal trends in biodiversity.
KeywordsBreeding bird survey Climate Community dynamics Ecological traits NDVI Non-linear trends
This study is a contribution by the Center for Informatics Research on Complexity in Ecology (CIRCE), funded by the Aarhus University Research Foundation under the AU Ideas program. JCS additionally considers this work a contribution to his VILLUM Investigator project “Biodiversity Dynamics in a Changing World” (BIOCHANGE) funded by VILLUM FONDEN. We wish to thank the Patuxent Wildlife Research Center for granting public access to the breeding bird survey data. We also thank Vincent Devictor and Olivier Gimenez for statistical advice and discussions on a previous version of the manuscript, and the Associate Editor and referees for constructive comments that improved substantially our work.
Author contribution statement
J.-Y. B. and J.-C. S. conceived the ideas; J.-Y. B. and K.P. collected the data; B. Z. reviewed the trait database; J.-Y. B. and P.G analyzed the data; J.-Y. B., P. G. and B. Z. interpreted the results; all the authors contributed substantially to the writing.
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