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Variation in bird diversity and composition between elevations and human land-use types in a seasonally dry tropical forest

Abstract:

Climate seasonality and human land-use are major pressures shaping biodiversity in tropical dry regions and both are expected to intensify in the near future. Therefore, understanding the interplay of these factors is crucial for mitigating biodiversity loss in these rapidly changing ecosystems. We examined the effects of seasonality (i.e., wet and dry seasons) and human land-use types (i.e., natural forests and silvopastures) on taxonomic and functional diversity, and community composition of birds in a seasonally dry tropical forest in southern Ecuador. We repeatedly recorded birds in 12 1-ha plots across natural forests and silvopastures at two elevations (600 and 1200 m a.s.l.) using point counts, and classified the bird community into primary (i.e., nectarivores, frugivores, granivores and omnivores) and secondary (i.e., invertivores) consumers. Functional bird diversity based on four morphological traits was not affected by human land-use type or seasonality, while taxonomic diversity of the overall community and of secondary consumers increased with elevation. The taxonomic diversity of primary consumers was higher in silvopastures compared to natural forests. The composition of the overall bird community and that of primary and secondary consumers differed between elevations. Seasonality had no effect on diversity nor on composition. Our study shows that elevation is a major driver of bird diversity and community composition in seasonally dry tropical forests, indicating that even short elevational gradients shape bird communities in these ecosystems. Protecting continuous elevational transects of dry tropical forests is therefore essential to maintain their high bird diversity under current and future conditions.