Density compensation effect in arboreal communities of the West Caucasus

Abstract

Density compensation effect (DCE) is qualified as increase of some species abundance after dropping of other species out of a community, as a consequence of unutilized resources appearance and interspecies competition abatement. DCE was first noticed about 50 years ago but till now the questions on causes of its origin, its scale and intensity remain open due to the lack of field data as well as methodological problems. In the article, these questions have been tested using arboreous tier of the West Caucasus forest phytocenoses as a case study. An analysis of actual data is conducted by means of numerical experiments. Three scenarios have been modeled: in the first one there has been assumed no manifestations of compensatory processes; in the second, after dropping some species out of community, all the other species rose in abundance; in the third, DCE was manifested through abundance increase of dominant species only. Model predictions on the analyzed parameters relationships have been checked against actual measurements. The results obtained suggest that for the DCE to occur, the absolute number of species in a community is not so much important as the ratio between their specific capacities, which is determined by environmental conditions, and the actual number of species, which may not match the capacity due to interference of regional processes (e.g., the history of cenoses formation, isolation, etc.). Thus, DCE does not appear to be an invariable consequence of environmental extremity and may occur in cenoses consisted of both many and few species.