Long-term change in river invertebrate communities

Abstract

Finding rules that govern species distribution and coexistence is a fundamental aim of ecological research. The rapidly expanding and increasingly mobile human race is challenging our understanding of some these rules. Using long-term macroinvertebrate data collected from two river systems with contrasting legacies from human activity, this thesis investigates drivers of change in community structure and function, mechanisms underpinning these changes and how these changes affect the accurate assessment of the ecological condition of river systems. The reformation of the river invertebrate communities within the River Clyde system was not predicted by the simple improving measures of water physico-chemistry or life history characteristics of the re-colonising community. This has serious implications for the accurate assessment of river health which is at present largely reliant on the physio-chemical tolerance of macroinvertebrates to indicate prevailing environmental conditions. It is argued that reference condition predictions, like those obtained from the RIVPACS programme, may not be suitable when assessing the ecological health of a river subjected to long-term modification from human activity, like the River Clyde. Significant differences in the stable isotope signatures of resident and colonising populations of Rhyacophila dorsalis (a predatory Trichopteran) provided insight into some mechanisms underlying differences between reforming communities. Trophic position estimates for some colonising populations of R. dorsalis were shown to be lower than expected considering their predatory status and, colonisation patterns were significant in predicting changes in occupied trophic position. The River Endrick is recognised internationally in terms of biodiversity. Over the last 50 years, the diversity of macroinvertebrate fauna of the river has significantly reduced, five species have become locally extinct and there has been a significant change in the distribution of 29 other species. The macroinvertebrate community in the headwater of the river has undergone a dramatic change in structure and function. The contrasting changes to the headwater community and changes in the structure and function of the macroinvertebrate community in the river system require further investigation. This thesis demonstrates the importance of investigating long-term change