A Shared Niche? The Case of the Species Pair Protea obtusifolia-Leucadendron meridianum

Abstract

We tested the hypothesis that there is niche separation between Protea obtusifolia and Leucadendron meridianum, which are obligately co-occurring species in potholes in limestone bedrock in Cape fynbos. We compared canopy volumes of individuals with a conspecific pothole neighbour to those of individuals with a contraspecific pothole neighbour, and found that a null hypothesis of substantial difference should be rejected, in at least some cases. This implies that these species are equivalent with respect to resource utilisation. Since they are spatially constrained to using the same resources by the microsites in which they grow, and temporally constrained to sharing these resources by germinating after the same fires and having the same growth and reproductive phenology, we suggest that they constitute a pair of coexisting species occupying the same niche with respect to resources and phenology. We were furthermore unable to demonstrate any significant differences in seedling establishment and growth pattern of the two species, which suggests that they share the same regeneration niche (though partition is considered). The alternative to niche theory is some stochastic theory. We consider the application of a lottery model, and confirm that in this case a predicted pattern of abundance indeed occurs.