Relationships between phenotypes, the environment, and demographic outcomes are complex, but high-dimensional trait-based trade-offs have been hypothesized as being important for promoting species co-existence and maintaining community diversity. However, research addressing these relationships often focuses on interspecific variation, whereas limited investigation has taken place into these relationships intraspecifically, despite its known importance in generating and maintaining species and functional diversity. Here, we determined if intraspecific relationships between phenotypes and the environment promote differential demography and species coexistence by modeling and comparing species specific growth performance landscapes and species co-occurrence patterns that span a multidimensional trait space along environmental gradients. We asked three main questions: 1) Where are species located in growth performance landscapes based on their phenotype?, 2) Are phenotypes for resource acquisition more or less similar within species than between species?, and 3) What drives the similarities or differences in phenotypes for resource acquisition? We utilized individual-level leaf, stem and root trait data combined with growth data from 24 species in a hyper-diverse Chinese tropical rainforest along soil nutrient and light gradients.
Results/Conclusions
We did not find evidence of alternative designs within species. In particular, a population does not occupy multiple growth performance peaks in phenotypic landscapes. Rather, populations occupy areas of trait space that are distinct from those occupied by populations of other species in the community. We did find that species shared to varying degrees which traits and/or environmental variables most influenced their relative growth rate and that co-occurring species were more dissimilar in their resource acquisition strategies for growth, suggesting that similar species spatially segregate to decrease competition for resources. All of these findings suggests that individuals within species are more phenotypically similar to each other than to other species, which should lead to increased intraspecific competition for resources over interspecific competition, promoting coexistence. These results expand our understanding of what generates and maintains species and functional diversity in tropical forest seedling communities and how so many species can coexist there.