Analysis of Succession in a Tropical Phytoplankton Community and a New Measure of Succession Rate

Abstract

Succession entails changes in the relative abundance of species in a community. The Jassby-Goldman (JG) index of succession rate is affected by any change in the relative abundance of species but weight contributions from different species unequally. There is no apparent ecological foundation for this unequal weighting. A more defensible measure of succession rate can be derived from the summed change in abundances of all species, independent of sign, expressed as a proportion of the whole community. A new index of succession rate obtained in this way is named the summed difference (SD) succession rate index. Analysis of succession in the algal and protozoal plankton community of Lake Lanao, Philippines, shows that the JG and SD succession rate indexes are positively correlated with 3 community variables: absolute rate of change in autotroph abundance (numbers or biomass), absolute rate of change in net primary production and grazing rate. The first 2 variables are measures of the overall rate of change in resource supply to the phytoplankton, and grazing intensity is a measure of selective attrition. Positive relationships between these variables and succession rate are generally stronger if succession rate is measured by the SD index rather than by the JG index. A multivariate approach shows that the variance in succession rate attributable to change in resource supply is largely distinct from that attributable to selective attrition by grazing. According to a linear model, change in resource supply accounts for about 44% of variance in succession rate, and grazing accounts for an additional 8%.