Foundation (dominant or matrix) species play a key role in structuring plant communities, and influence processes from population to ecosystem scales. However, the effects of genetic diversity of foundation species on these processes have not been adequately assessed. We modified the classical filter model of community assembly to include genetic diversity as part of the biotic filter, and propose scenarios that show how genetic diversity of foundation species may result in contrasting levels of species diversity during community assembly. We suggest that the proportion of fit genotypes (i.e., competitively superior and dominant) affects niche space availability for subordinate species to establish and can both positively and negatively affect species diversity of an assembling community. To test these hypotheses, we used an individual-based simulation model where a foundation species of varying genotypic diversity competes with subordinate species on a spatially heterogeneous lattice.
Results/Conclusions
In support of our proposed scenarios, we found that genetic diversity of foundation species significantly affected equilibrium community diversity, measured as species richness. An increase in genetic diversity potentially gives the foundation species a wider species niche space. In most cases, simulations show the intuitive result that this wider niche allows less niche space for other species, decreasing species richness. However, in cases with a low level of environmental heterogeneity, increasing genetic diversity can cause the foundation species niche space to be over-dispersed, resulting in a weak, but significant and consistent positive relationship between genetic diversity and species richness. Regression of equilibrium diversity showed that these effects of genotypic diversity were secondary (i.e., lower r2 values) to the larger effects of overall foundation species fitness and level of habitat variability. The novel aspect of incorporating genotype diversity species in community assembly models include predictions of both positive and negative relationships between species diversity and genetic diversity, and the conditions under which these factors are potentially relevant. Mechanistically, these relationships reflect differential niche availability imposed by the foundation species.
