Temporal variability of lotic macroinvertebrate communities.

Understanding temporal variability in ecological communities is critical to monitoring and managing biodiversity and ecosystem function. However studies of community variability over large temporal and spatial scales are scarce, partly because suitable data are rare. The principal aim of this study was to use two previously unutilized data sets to examine long-term temporal variability of flowing water macroinvertebrate communities in order to understand better the patterns in this variation and role of environmental factors and community composition in driving it. The first data source comprised invertebrate data from a national water quality monitoring programme. Four main findings arose from this analysis. Firstly, that temporal variability exhibits a complex pattern across multiple spatial scales. Secondly, that factors relating to climate, land use and local scale habitat stability are important determinants of variability. Thirdly, that these relationship are nonlinear with threshold values above which there is a sudden change in temporal variability. Fourthly, that community composition is related to temporal variability with specific taxa contributing disproportionately to community variability due to their biological and ecological traits. The second data source was a freshwater invertebrate survey carried out within a single catchment in 1979. Re-sampling of selected sites was conducted as part of this study providing a comparison of patterns within and between years. Whilst patterns of community structure were consistent between years, there was considerable variation in the identity of taxa and spatial relationships between communities over time. This seems likely to result from improvements in river quality over the last 30 years. The combination of long-term and large spatial scale community data has provided unique insight into temporal variability. In the river systems of England and Wales environmental factors exert a strong influence on communities driving variability however, their influence is mediated through the taxa present within the system.