The effect of density compensation in species-poor plant communities of mainland areas (on the example of the Western Caucasus)

There is much evidence of the effect of density compensation in the island biota, while the data on its distribution pattern and reasons of appearance in the inland communities are still insufficient and contradictory. We have evaluated the intensity of the effect of density compensation in species-poor plant communities of the natural (seminatural), anthropogenic, and fragmented habitats of the Western Caucasus as one of the inland regions. For this purpose, we have compared the species diversity, relative density (biomass) of predominating species, and mean occurrence of accompanying species in closed communities, as well as the species diversity and mean occurrence of species for open communities. The data show that the domination level and mean occurrence of species in the species-poor phytocenoses may differ and may be related to species organization and the regime of local disturbances. Among the studied communities, the rise in the mean species occurrence, contrary to the species diversity, was only revealed for segetal cenoses and plant groups of meander bars, which are mainly formed by species with R-strategy. We suppose that the effect of density compensation in closed communities mainly results from a drop in the density of predominating species as a result of local disturbances or other reasons, in combination with the limited size of their species pool.