Abstract:

The negative density-dependent hypothesis focuses mainly on conspecific interactions to explain the coexistence of diverse species in natural communities. The hypothesis describes the impairment of performance among conspecific individuals due to resource competition, predation of pests (e.g., pathogen, herbivore) and so on. Impairment of conspecific individuals decreases growth and increases mortality, thereby freeing space for other species, and thus promotes coexistence of diverse species. There are three main kinds of density dependent effects including distance-dependence of mortality and abundance of offspring near parents (Janzen-Connell hypothesis), density dependent thinning (random-mortality hypothesis), and community compensatory trends (CCT). Research has shown that density dependence among phylogenetically closely-related species results partially from competition for similar resources. This fact led to the proposal of species herd protection and phylodiversity dependence models. Density dependence has long history of study and the recent establishment of a global network of large-scale forest dynamic plots facilitates the detection of density dependence in natural communities. However, there are many challenges when testing for density dependence. For example, some previous studies can not disentangle density dependence from other confounding effects, and most studies focus exclusively on the tropical zone, seldom considering other zones. Therefore, though strong evidence to contrary does not exist, debate continues on the importance of density dependence in maintaining diverse-species coexistence.

Key words: density dependence, conspecific individuals, distance dependence, community compensatory trend (CCT), phylodiversity dependence