Introduction of relative abundance distribution (RAD) indices, estimated from the rank-frequency diagrams (RFD), to assess changes in community diversity

Quantifying a relative abundance distribution based on the sampling of a se t of species is a widespread problem in ecology. A number of diversity indi ces have been proposed and used in numerous works in spite of a lack of sta tistical characteristics and tests of comparison. The relative abundance di stribution can also be described using rank-frequency diagrams but fitting these diagrams to mathematical models such as the Zipf-Mandelbrot model rem ains problematic. Strong correlation between the Zipf-Mandelbrot model para meters prevent their estimation by optimization algorithm. In light of this , new indices of sampled communities are introduced here. These indices are two linear regression slopes estimated from rank-frequency diagrams. The n umerous statistical studies that have been carried out on linear regression models are used to compare sampled communities. These new indices possess characteristic properties with an ecological meaning. Correlations between these indices, the Zipf-Mandelbrot model parameters and an evenness diversi ty index are examined. An ecological application is made using entomologica l data as an example. This example consists of a transect from the edge of a pond to a dry forest along which 60,000 insects were sampled from six dif ferent sampling stations. Using the new indices described here, station C, located at the edge of that area subject to influence from the pond, is dif ferentiated from the other stations. This station would seem to present the lowest degree of niche diversity and the lowest evenness, and recent obser vations confirm the deterioration of this station.