Saturday, January 8, 2011

Diversity of the plant species and its density

Prologue
Monsoon forest, also called dry forest or tropical deciduous forest, open woodland in tropical areas that have a long dry season followed by a season of heavy rainfall. The trees in a monsoon forest usually shed their leaves during the dry season and come into leaf at the start of the rainy season. Many lianas (woody vines) and herbaceous epiphytes (air plants, such as orchids are present. Monsoon forests are especially well developed in Southeast Asia and are typified by tall teak trees and thickets of bamboo.
Plants of the Tropical Rainforest
Trees tower over a tropical rainforest, forming a canopy that shades the forest floor. Numerous epiphytes, plants that live on trees, live in this canopy, including orchids and mosses. Shade-loving plants, including ferns, shrubs and vines dot the forest floor among the fallen leaf litter of the canopy trees. Modern medicine owes much to the plants of the rainforest, since many pharmaceutical drugs originated there, such as curare and quinine.
Density
The factors determining species commonness and rarity are poorly understood, particularly in highly diverse communities. Theory predicts that interactions with neighbors of the same (conspecific) and other (heterospecific) species can influence a species’ relative abundance, but empirical tests are lacking. By using a hierarchical model of survival for more than 30,000 seedlings of 180 tropical tree species on Barro Colorado Island, Panama, we tested whether species’ sensitivity to neighboring individuals relates to their relative abundance in the community. We found wide variation among species in the effect of conspecific, but not heterospecific, neighbors on survival, and we found a significant relationship between the strength of conspecific neighbor effects and species abundance. Specifically, rare species suffered more from the presence of conspecific neighbors than common species did, suggesting that conspecific density dependence shapes species abundances in diverse communities. “

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