A search for stability gradients in North American breeding bird communities.

Abstract

Stability is defined as year-to-year persistence in species composition and distribution of species abundances. From the census data for 174 study plots, 9 indices were derived that estimate annual variability of species composition, species abundance distribution, diversity, and breeding density. The resulting matrix of study plot by stability indices was used to estimate the correlation structure of the stability indices. The correlation matrix was in turn subjected to a principal components analysis to derive synthetic gradients of variation. Three independent principal component axes reproduced most of the variation in the initial data and were interpreted as gradients of variation in species turnover, diversity, and breeding abundance. Thus, the annual stability of community structure apparently responds independently to species and abundance variation. Few patterns emerged when the plots were ordinated by either habitat or geographic location. In general, grasslands showed greater annual variation in diversity than forested habitats, and, for some habitats, northern communities were less stable than more southern communities. -from Authors