Different responses of taxonomic and functional bird diversity to forest fragmentation across an elevational gradient
Many studies have investigated how habitat fragmentation affects the taxonomic and functional diversity of species assemblages. However, the joint effects of habitat fragmentation and environmental conditions on taxonomic and functional diversity, for instance across elevational gradients, have largely been neglected so far. In this study, we compare whether taxonomic and functional indicators show similar or distinct responses to forest fragmentation across an elevational gradient. We based our analysis on a comprehensive data set of species-rich bird assemblages from tropical montane forest in the Southern Andes of Ecuador. We monitored birds over 2 years in two habitat types (continuous and fragmented forest) at three elevations (i.e., 1000, 2000, and 3000 m a.s.l) and measured nine morphological traits for each bird species on museum specimens. Bird species richness and abundance were significantly higher in fragmented compared to continuous forests and decreased towards high elevations. In contrast, functional diversity was significantly reduced in fragmented compared to continuous forests at low elevations, but fragmentation effects on functional diversity tended to be reversed at high elevations. Our results demonstrate that taxonomic and functional indicators can show decoupled responses to forest fragmentation and that these effects are highly variable across elevations. Our findings reveal that functional homogenization in bird communities in response to fragmentation can be masked by apparent increases in taxonomic diversity, particularly in diverse communities at low elevations.
KeywordsEcuador Monitoring Traits Richness Abundance Functional diversity
We thank the German Research Foundation (DFG) for funding our projects in the framework of the Research Bundle 823–825 “Platform for Biodiversity and Ecosystem Monitoring and Research in South Ecuador” (PAK 825/1) and the Research Unit FOR2730 “Environmental changes in biodiversity hotspot ecosystems of South Ecuador: RESPonse and feedback effECTs”. The Ecuadorian Ministry of the Environment (MAE) kindly provided permission to conduct research. We are grateful to Agustín Carrasco and Patricio Estrella, for their help in fieldwork. We thank Nature and Culture International (NCI), Felix Matt, Jörg Zeilinger, Mathias Templin, and Catherine Vits for logistic support. Two anonymous reviewers provided the helpful comments on an earlier version of this manuscript.
Author contribution statement
VS, MQ, KBG, MS and ELN conceived and designed this study. VS and MQ conducted fieldwork. VS analysed the data. VS, ELN, and MS wrote the manuscript. KBG, BT, and EZ provided editorial advice.
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