Nonadditive effects of consumption in an intertidal macroinvertebrate community are independent of food availability but driven by complementarity effects

Suboptimal environmental conditions are ubiquitous in nature and commonly drive the outcome of biological interactions in community processes. Despite the importance of biological interactions for community processes, knowledge on how species interactions are affected by a limiting resource, e.g. low food availability, remains limited. Here, we tested whether variation in food supply causes non-additive consumption patterns, using the macroinvertebrate community of intertidal sandy beaches as a model system. We quantified isotopically labelled diatom consumption by three macroinvertebrate species (Bathyporeia pilosa, Haustorius arenarius and Scolelepis squamata) kept in mesocosms in either monoculture or a 3-species community at a range of diatom densities. Our results show that B. pilosa was the most successful competitor in terms of consumption at both high and low diatom density, while H. arenarius and especially S. squamata consumed less in a community than in their respective monoc...