Data from: The biotic interactions hypothesis partially explains bird species turnover along a lowland Neotropical precipitation gradient

Aim: We evaluated the influence of climate in determining bird communities
along precipitation gradients. We argue that mechanisms responsible for
community turnover along precipitation gradients are similar to mechanisms
operating along temperature and latitudinal gradients. We test the
hypothesis that environmental conditions affect community composition in
dry forests, whereas biotic interactions affect community composition in
wet forests. Location: Low-elevation forests along a precipitation
gradient in Colombia where precipitation ranges from 700 – 4000 mm
annually but elevation and temperature remain constant. Time period:
Present day Major Taxa Studied: Tropical Forest Birds. Methods: We
performed 291 bird counts in nine study areas across the ~3000 mm
precipitation range. In each locality we obtained climatic
characteristics, and a phylogenetic, morphological and physiological proxy
data set to test predictions about the evolutionary relationships and
distribution of traits. Results: Bird communities changed abruptly along
the precipitation gradient and could be divided into dry and wet forest
communities. Analyses of phylogenetic relationships, trait space, and
observations at nests suggested that environmental filtering is more
important in dry forest, especially for breeding. In contrast, we found
little evidence that competition was more important in wet forest. Nest
predation or competition for nest space, however, may be more critical in
wetter forests. Conclusions: The two distinct bird communities we
documented suggest that lowland precipitation gradients, where temperature
is constant, can be as important as temperature gradients in generating
high beta diversity. We conclude that the breeding process in bird
communities might be crucial for determining community assembly along
environmental gradients. Given that recent population declines in tropical
birds have been attributed to changes in precipitation, by understanding
the mechanisms underlying community assembly along precipitation gradients
our study may improve our ability to understand those declines and predict
the effects of climate change on neotropical avifauna.