Density dependent and density independent relationships during a twenty-seven year study of the population dynamics of the benthic macroinvertebrate community of a chemically unstable lake

Data are given on net precipitation, water chemistry, vegetation cover and the population dynamics of 20 taxa of benthic macroinvertebrates from the total of 40 recorded in the lake. The relationships between data sets were investigated by bivariate analysis. The relationships between abiotic factors are best described by linear equations as are some relationships between Sigara concinna, Sigara dorsalis, Potamopyrgus jenkinsi and environmental factors. The relationships of numbers of Gammarus tigrinus with temperature, Sigara stagnalis with conductivity, Corixidae with time and Sigara lateralis, Theromyzon tessulatum and Piscicola geometra with vegetation cover are best described by exponential equations. The relationships between the population dynamics of pairs of certain taxa viz. Gammarus tigrinus and G. duebeni, G. tigrinus and Asellus aquaticus, G. tigrinus and Corixidae, Sigara dorsalis and S. concinna, are best described by power equations. The relationship of vegetation cover with time and the population dynamics of many taxa are best described by logarithmic logistic equations. Both density dependent and density independent relationships appear to be responsible for changes in numbers and taxa within the total community. Density independent relationships are most important at times of environmental change while density dependent relationships, though operating continuously, are most important when conditions are stable.