Species effects on ecosystem processes are modified by faunal responses to habitat composition

Abstract Heterogeneity is a well-recognized feature of natural environments, and the spatial distribution and movement of individual species is primarily driven by resource requirements. In laboratory experiments designed to explore how different species drive ecosystem processes, such as nutrient release, habitat heterogeneity is often seen as something which must be rigorously controlled for. Most small experimental systems are therefore spatially homogeneous, and the link between environmental heterogeneity and its eVects on the redistribution of individuals and species, and on ecosystem processes, has not been fully explored. In this paper, we used a mesocosm system to investigate the relationship between habitat composition, species movement and sediment nutrient release for each of four functionally contrasting species of marine benthic invertebrate macrofauna. For each species, various habitat conWgurations were generated by selectively enriching patches of sediment with macroalgae, a natural source of spatial variability in intertidal mudXats. We found that the direction and extent of faunal movement between patches diVers with species identity, density and habitat composition. Combinations of these factors lead to concomitant changes in nutrient release, such that habitat composition eVects are modiWed by species identity (in the case of NH 4 –N) and by species density (in the case of PO 4 –P). It is clear that failure to accommodate natural patterns of spatial heterogeneity in such studies may result in an incomplete understanding of system behaviour.