Controls on the distribution of specialist invertebrates inhabiting exposed riverine sediments in England and Wales

Occupying a disjointed and vulnerable habitat, specialist Coleoptera associated with Exposed Riverine Sediments (ERS) are shown to exhibit high levels of adaptation. An assessment of the English and Welsh habitat resource confirms the presence of strong geographical and physical restraints on its distribution which partially explain the rarity of some of the associated Coleoptera. Assemblage studies reveal the presence of multiple adaptive strategies that enable specialists to utilise the resource in spite of perceived environmental pressures, and the strength of these morphological and behavioural adaptations can be used to predict abundance and distribution at alpha, beta and gamma levels. Furthermore, adaptations enforce varying nutrient acquisition strategies which spatially define communities. This study demonstrates the need specialist invertebrates have for a complex and highly connected ERS habitat with English and Welsh rivers, that exhibits structural variation along a longitudinal gradient. Reliant on riverine processes and subsidies the habitat and its associated invertebrates are symptomatic of a healthy and naturally structured lotic system operating laterally and across reach scales