Macroinvertebrate Communities and Environment in a Southern African Mountain Stream
In a study of a second-order southern African stream, complementary classification and multidimensional scaling (MDS) techniques revealed longitudinal changes in macroinvertebrate community structure, but no temporal changes. Stepwise discriminant analysis and multiple linear regression were used to identify environmental variables correlated with the community changes but produced conflicting results depending on the information used, possibly because of strong correlations between some of the variables. The MDS plot of biotic samples illustrated that potassium levels correlated most strongly with community distribution. Because of the large number of variables now shown worldwide to correlate with faunal distributions, we suggest ways to choose the variables to suit the kind of study to be undertaken. Attempts to assign the invertebrates to functional feeding groups (FFGs) were unsatisfactory as the relevant categories are poorly defined and often inadequate for classifying the fauna. We suggest that until these categories are more clearly defined, and more uniformly applied, concepts relating to FFGs cannot be tested satisfactorily. The stream community in Langrivier is more similar to communities found in two other mediterranean ecosystems than to those in other southern African rivers, probably because of the greater predictability of flow in the former.