The diversity and succession of phytoplankton communities in disturbance-free environments, using the model PROTECH

A phytoplankton community model was used to examine the effect of a number of key variables on the diversity and succession of an eight-species community. Four functional groups, based upon morphology, were represented within the community and the following variables were changed: temperature, mixing depth, grazing, light, nitrogen and phosphorus levels. It was hypothesed that: 1) under certain strongly selective environmental conditions a predictable functional group would dominate; 2) under controlled conditions largely devoid of allogenic forces, the influence of autogenic processes would be considerable and lead to a decrease in diversity and; 3) stratified conditions create environmental heterogeneity and thus will give rise to a relative increase in diversity. There was support for the first two hypotheses, but the last prediction was rejected. It was instead suggested that because of the vertical, one-dimensional light environment in a water column, the environment becomes more selective with reduced mixing depth, leading to reduced diversity.