Species richness

About: Species richness is a research topic. Over the lifetime, 61672 publications have been published within this topic receiving 2183796 citations.

Asymmetric density dependence shapes species abundances in a tropical tree community.

Abstract: 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.

Status of the Microbial Census

Abstract: Over the past 20 years, more than 78,000 16S rRNA gene sequences have been deposited in GenBank and the Ribosomal Database Project, making the 16S rRNA gene the most widely studied gene for reconstructing bacterial phylogeny. While there is a general appreciation that these sequences are largely unique and derived from diverse species of bacteria, there has not been a quantitative attempt to describe the extent of sequencing efforts to date. We constructed rarefaction curves for each bacterial phylum and for the entire bacterial domain to assess the current state of sampling and the relative taxonomic richness of each phylum. This analysis quantifies the general sense among microbiologists that we are a long way from a complete census of the bacteria on Earth. Moreover, the analysis indicates that current sampling strategies might not be the most effective ones to describe novel diversity because there remain numerous phyla that are globally distributed yet poorly sampled. Based on the current level of sampling, it is not possible to estimate the total number of bacterial species on Earth, but the minimum species richness is 35,498. Considering previous global species richness estimates of 10 7 to 10 9 , we are certain that this estimate will increase with additional sequencing efforts. The data support previous calls for extensive surveys of multiple chemically disparate environments and of specific phylogenetic groups to advance the census most rapidly.

Plant Species Diversity in Old-Field Successional Ecosystems in Southern Illinois

Abstract: In old—field ecosystems in the deciduous forest, plant species diversity generally increases with succession and reaches a maximum during the forest stage when structural diversity is highest and at the time when both shade—tolerant and shade—intolerant species are present together. Species diversity may be exceptionally high in succesional communities when there is a high degree of vertical and horizontal heterogeneity. Diversity may be exceptionally low in old—field ecosystems when there is strong dominance by species with alleolopathic chemicals or other effective interference methods. Species distribution curves are geometric during the first few years of succession and gradually change to lognormal as more species are added to the community, the process resulting in a high degree of evenness.

The relationship among area, elevation, and regional species richness in neotropical birds.

Abstract: The elevational gradient of species richness is often claimed to mirror the latitudinal gradient and has traditionally been explained by assuming a decrease in productivity with eleva- tion and more recently by Rapoport's rule. The influence of area on the pattern has rarely been considered. Analyses of all South American tropical land birds (more than one-fourth of the ex- tant bird species on Earth) are used to examine four species richness/elevation models: null model, Rapoport's rule, and monotonic or hump-shaped productivity/species richness relation- ships. To quantify the area effect, species-area curves were created for seven elevational zones. Not accounting for area, species richness declined monotonically with elevation, but area ac- counted for 67%-91% of the variation in species richness per zone. When area was factored out, a hump-shaped pattern emerged, with more species in the 500-1,000-m (P , .005) and 1,000- 1,500-m zones (P , .10) than in the 0-500-m zone. Rapoport's rule and the monotonic productivity/species richness relationship were thus not supported. Instead, elevational turnover rates and numbers of shared species between zones suggested that the hump-shaped pattern re- flects geometric constraints (as predicted by the null model) imposed by the narrow span of the gradient, and it is suggested that midelevational zones may represent sink habitats.