Coexistence theory in the Cape Floristic Region: revisiting an example of leaf niches in the Proteaceae

Competition in plant communities is often a contentious issue because the mechanisms of competitive interactions are not obvious.We sought evidence that Proteaceae communities are competing along two leaf niche axes as observed in a previous study.Two functional characters,leaf size and leaf shape were measured on numerous individuals per species per plot of six communities from two different regions. Patterns of overdispersion along these leaf trait axes between species were observed, similar to the earlier study.The observed results were compared with the patterns expected under a null model using standard and novel indices to test the significance of trait dispersion between species within a plot. Competition and niche differentiation in the observed plots were not supported as the observed trait overlaps were not significantly different from the null expectation. Our results do not support the theory that Proteaceae communities compete along the two proposed functional leaf traits.