Alternative designs lead to similar performance when traits and performance vary on different axes

Abstract

Variation in plant traits related to size and architecture, water relations, and resource uptake reflect important dimensions of plant function that may explain how different species are adapted to their local environments. Within a local community, variation in many of these traits may promote coexistence of competing species through niche partitioning. If differences in traits are associated with differences in performance, and there is substantial trait variation within local communities, we might expect competitive asymmetries that would lead to competitive exclusion. Alternatively, if combinations of trait differences converge on similar performance trait differences associated with niche partitioning may lead to phenotypically diverse species that exhibit similar performance. Here we develop a model showing that when the major axes of trait covariation do not align with the axis of performance variation, species that differ in structural traits, i.e., species having alternative designs, may achieve similar performance. We apply this model to data from commonly co-occurring Protea species in the Cape Floristic Region, South Africa and demonstrate that despite large differences in traits that are related to performance, trait covariation leads to minimal performance differences among species.