INTRA-GUILD COMPENSATION REGULATES SPECIES RICHNESS IN DESERT RODENTS: COMMENT

Abstract

Goheen et al. (2005) noted that species richness of local communities frequently remains relatively constant despite substantial changes in species composition, and that identification of the processes that produce such constancy represents an important step in understanding community dynamics. Brown et al. (2001) suggested that regulation of species richness within communities should occur if two conditions are met: (1) fluctuations in one or more environmental conditions, despite relatively constant resource availability, and (2) a feedback mechanism between the regional pool and local com munity, such that the probability of colonization increases when local richness falls below the long-term mean, and the probability of extinction increases when local richness exceeds the long-term mean. Goheen et al. (2005) thus used data from a long-studied desert rodent community to test proposed condition (2) of compensa tory changes in probabilities of colonization and extinction. Goheen et al. (2005) used species richness data from eight plots at 52 sampling periods, each period consist ing of six monthly samples. The species pool included 21 species, and mean richness was about 10 species. They developed a simulation approach designed to determine if observed dynamics of species richness differed from those expected based on random colonization and extinction. This approach involved initializing each simulation with the mean number of 10 species. For each subsequent sampling period, they "randomly drew an integer value for the net number of colonizations and extinctions (i.e., the net change in species richness) with