Patterns of consequences of interspecific competition in natural communities: a review of field experiments with plants

We present a quantitative literature review to assess the extent to which field experiments with plants have addressed questions about patterns of competition over time and space, consequences of competition for community structure, and comparisons of competitive ability among species. We outline the necessary treatment comparisons and statistical analyses to answer each question and then describe the number of experiments that meet these criteria and their results. Although we found a total of 101 experiments in 89 studies, 63% of these experiments only addressed whether competition significantly affected some component of individual fitness of a single species at a single time and site. Despite the limited data base to address more complex questions about competitive interactions, we did find consistent results for a few of the questions we reviewed. Where tested, competition always had significant effects on distribution patterns (five experiments), on relative abundances (two experiments), and on diversity (four experiments), consistent with the notion that competition has strong effects on community structure. On the other hand, intraspecific competition was not usually stronger than interspecific competition for either competitive effect (four experiments) or response (three experiments), which suggests that resource partitioning may not be an important mechanism of coexistence in plants.