The role of large-scale descriptors and morphological status in shaping ground beetle (Carabidae) assemblages of floodplains in Germany

Abstract

Floodplains are inhabited by diverse and abundant ground beetle assemblages that are adapted to the frequently changing habitat conditions. While there have been many studies on the composition of riparian ground beetle communities in individual floodplains, the general patterns responsible for their composition remained obscure. We used data on 352 ground beetle samples taken at 224 sites along rivers and their floodplains in Germany to analyse how natural large-scale descriptors and floodplain morphological status (near-natural vs. degraded vs. restored sites) determine the composition of ground beetle assemblages. For each site we compiled data on region, slope and dominant floodplain substrate, and on floodplain morphological status (near-natural, degraded or restored conditions). Hierarchical clustering revealed eight main clades and a clear hierarchy of parameters, with floodplain slope being responsible for the two main clades, followed by ‘region’ and ‘dominant floodplain substrate’ that structure the second and third orders of division. Some of the third-order clades are exclusively or predominantly composed of near-natural or restored sites, indicating that sites of high morphological status are inhabit by a distinct ground beetle community in a given region. Indicator species analysis resulted in indicators for all regions (132 indicators species) and slope (122 indicator species) categories and for almost all classes of dominant floodplain substrate (117 indicator species). Most of the indicator species with high predictive values and sensitivities belong to the genus Bembidion. For the morphological status categories, we identified 126 indicator species in total: 112 related to near-natural conditions, 13 for restored sites and only a single species for degraded conditions. Our results underline that slope, region and dominant floodplain substrate are among the main natural drivers of riparian ground beetle community composition and the suitability of ground beetles to indicate degradation and restoration processes.