9318096 Brown This study will investigate spatial variation in the abundance of a species over its geographic range. Most of the research will involve analysis of data from the Breeding Bird Survey (BBS), standardized censuses of hundreds of species of breeding birds at approximately 2000 local sites in North America, some of which have been conducted annually for 25 years. Statistical analysis of these data using a Geographic Information System (GIS) and other methods will quantify: 1) the frequency distribution of abundace among sites where a species occurs, 2) spatial patterns of variation in abundance, especially with respect with distance from the center and boundaries of the range, and 3) temporal variation in the spatial distribution of abundance, including shifts in range boundaries. These analyses will enable the investigators to distinguish among hypotheses to explain the observed patterns, including both null hypotheses of random variation and alternative hypotheses based on the mechanistic ecological processes that affect local abundance. The empirical patterns will also be compared to patterns predicted by computer simulation models of multidimensional niches. %%% Results of this research will contribute to the unification of ecology and biogeography by addressing basic questions about the relationship between local abundance and geographic distribution. The results will also enhance our ability to understand, and therefore ultimately predict, changes in the geographic distributions and local abundances of species that are occurring in response to human activities. ***
