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Variation in the per capita strength of competition between two desert annuals.
Kilpatrick, Auston1, Ives, Anthony1, Brown, James2, 1 2
ABSTRACT- How variable are competitive interactions across space, through time, and in the presence and absence of shared predators? We used multivariate time-series analysis to compare the per capita strength of competition between two desert annuals, Bouteloua aristidoides and Eriogonum abertianum in fourteen plots where two classes of seed predators (granivorous rodents and granivorous ants) were either present or absent. In addition, we also asked whether the strength of intra- and interspecific competition varied spatially and/or temporally with the density of the annuals. We found that the presence of shared predators had only minor effects on the per capita strength of competition. In contrast, there was a significant positive relationship between the strength of competition and the density of the competitor; specifically, the per capita strength of interspecific competition increases with increasing density. We discuss several mechanisms that could produce this relationship. These mechanisms may be common to a wide range of plant communities, which suggests that the per capita strength of competition may often be stronger in more productive habitats, as has been previously suggested.
KEY WORDS: competition, time series analysis, spatial variability, temporal variability