A Study on Plant Diversity In Tropical Forests of Kolli Hills |

ABSTRACT:

Evidence concerningmechanisms hypothesized to explain species coexistence in hyper-diversecommunities is reviewed for tropical forest plants. Three hypotheses receivestrong support. Niche differences are evident from non-random spatialdistributions along micro-topographic gradients and from a survivorship growthtradeoff during regeneration. Host-specific pests reduce recruitment nearreproductive adults (the Janzen Connell effect), and, negative densitydependence occurs over larger spatial scales among the more abundant speciesand may regulate their populations. A fourth hypothesis, that suppressedunderstory plants rarely come into competition with one another, has not beenconsidered before and has profound implications for species coexistence. Thesehypotheses are mutually compatible. Infrequent competition among suppressedunderstory plants, niche differences, and Janzen-Connell effects may facilitatethe coexistence of the many rare plant species found in tropical forests whilenegative density dependence regulates the few most successful and abundantspecies.