A spatially restricted investigation of habitat patch dynamics and Coleoptera community composition on exposed riverine sediments (ERS)

Exposed riverine sediments (ERS) are associated with heterogeneous habitat patches located within the land-river ecotone. Distinctly different micro-habitats on ERS have been identified as significant for providing important refuge for a large number of invertebrate fauna, with a particularly high abundance of Coleoptera. The River Teign has been identified as hosting high quality ERS for its presence of numerous invertebrate species of conservation concern (Sadler and Bell, 2004). Two side bars were selected for investigation due to their diverse range of habitat patches. Initial characterisation of the environmental variables for 5 visually different habitat patches on each bar was conducted for examination of habitat selection preferences exhibited by Coleoptera communities. Previous studies highlighted the significance of grain size distribution, moisture content, shade, vegetation cover, distance from water, and ground temperature for variation in Coleoptera community composition on ERS. Pitfall trapping was used over a 6 week sampling period for examination of species abundance at each habitat patch across three sampling rounds. Univariate and multivariate statistical analysis were used to identify relationships between environmental variables and for investigation of relationships between biotic and abiotic factors. Environmental variables were recognised as strongly interrelated. Temperature and shade represented the most significant factors driving difference in habitat patches. The larger study bar had significantly higher species richness, a result of greater lateral variation. Bembidion Tetracolum and Agonum albipes were the most abundant species sampled. Both species showed high fidelity for patches with bare and exposed sediments near water. The most abundant ERS specialist species was Clivina collaris, displaying associations with areas of fine sediments with shade. Supporting the work of Fowles (2004), all ERS specialist species were found in greatest abundance on areas of more dynamic ERS near water. These findings highlight the importance of maintaining dynamic river regimes which allow frequent flood inundation for rejuvenation of ERS