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Testing hypotheses in spatio-temporal plant competition using measures of interaction strength.
Chesson, Peter1, Sears, Anna1, 1
ABSTRACT- Measures of interaction strength, such as the intensity of competition, are commonly used in the study of plant and animal communities to understand the dependence of interactions on such factors as stress, productivity, density and biomass. The potential connectedness of communities at different localities by dispersal, or connectedness through time by community persistence, are rarely considerations. Various measures of interaction intensity, closely related to those commonly used in empirical studies, have important roles in spatio-temporal competition theory and its extensions to consider apparent competition. Of major importance in this theory, however, is the nature of the variation in interaction strength between communities that are connected by dispersal or community persistence. This variation is quantified by 1) standard statistical covariances between an interaction strength measure and environmental factors or densities, and 2) by variances of these quantities. Such covariances and variances help quantify spatio-temporal coexistence mechanisms such as the storage effect and relative nonlinearity of competition. Each of these mechanisms leads to predictions about patterns of variances and covariances that can be tested using the same methods in common use in the study of interaction strength. For example, coexistence by the storage effect predicts stronger intraspecific covariance between environment and competition than interspecific covariance between environment and competition, which distinguishes the storage effect from other mechanisms. In this way, these spatio-temporal mechanisms may be tested by modification of standard methodology currently used for different purposes.
KEY WORDS: intensity of competition, storage effect, spatio-temporal variation, environmental heterogeneity