Benthic macroinvertebrates in biological surveillance: Monte carlo significance tests on functional groups' responses to environmental gradients

Functional feeding groups are evaluated as summaries of benthic macroinvertebrate communities for the Upper La Trobe river system of Victoria, Australia. Two related questions are addressed. First, ‘what is the form of response of functional groups to environmental gradients?’ Second, ‘are observed group patterns significant insofar as they are unlikely to arise in randomly defined groups of taxa?’ Five functional feeding groups are evaluated relative to an environmental space defined at the structural, taxonomic level. A three-dimensional multidimensional scaling ordination of the sample sites, based upon this structural data, reveals a strong correlation with stream order in one direction in the space, and with particle size and benthic organic matter in another orthogonal direction. With the exception of filterers, the observed high correlations of functional group abundance with this space also would have occurred in randomly-defined groups. Scrapers, while not significant as a group in terms of linear response, are significant in terms of unimodal or clumped response to this environmental space. The utilization of such clumped responses in ordination space for biological surveillance programs is discussed.