Comparisons of intermediately ranked species in avian rank-abundance distributions from four California forests

Biodiversity indices, such as those that measure species richness or evenness, provide limited information about ecological communities. The species abundance distributions from which these indices are derived contain greater detail about community structure. For this reason conservation planners and land managers would benefit from methods that allow more informative comparisons of these distributions than offered by traditional indices. We used bird survey data from four research forests in California to construct rank-abundance distributions. Using bootstrap re-sampling, we created uncertainty bands associated with the empirical shapes of these curves, allowing identification of significant (P<0.05) differences between distributions over a portion of their ranks. We found higher abundances of intermediately ranked species on two of the forests, and ascribe this result to differences in forest productivity and habitat complexity leading to greater niche partitioning of resources. Diversity indices derived from these data were less informative.