From individuals to communities: Habitat complexity affects all levels of organization in aquatic environments

Habitat complexity describes a wide array of spatial distribution patterns of physical structures in habitats. It affects aquatic ecosystems on multiple levels from individuals (e.g., foraging behavior) to species interactions (e.g., predation, prey selection) and entire communities (e.g., biodiversity, food web structure). We present a conceptual framework to classify these effects and use it to summarize recent advances in the field. We identify three main research gaps and limitations preventing a full synthesis of the effects of habitat complexity on aquatic communities and ecosystems. Habitat complexity is often characterized using ad hoc measures, which limits cross-experimental comparison and meta-analytical and modeling approaches. The effects of habitat complexity on communities and ecosystems can also involve feedback loops on lower levels of organization including the habitat complexity itself. Such ecological feedbacks can influence habitat formation and amplify or mitigate the direct effects of habitat loss and simplification or habitat restoration on populations and communities, yet are surprisingly little understood. Finally, most studies examine habitat complexity on the presence-absence scale. This limits our ability to recognize nonlinear responses across habitat complexity gradients, which occur in many contexts in aquatic habitats. Since nonlinear responses can stabilize or destabilize population and community dynamics, we call for the use of a higher resolution of habitat complexity in future studies. We conclude that currently degraded habitats offer exciting opportunities for combining restorative efforts with research that could combine multi-level experiments and monitoring to improve our understanding of the role of habitat complexity across aquatic ecosystems. This article is categorized under: Water and Life > Nature of Freshwater Ecosystems Water and Life > Conservation, Management, and Awareness

Automated summary

Habitat complexity influences aquatic ecosystems at multiple levels but there are research gaps and limitations hindering a full synthesis of its effects. High-resolution studies and consideration of ecological feedback are needed to better understand the role of habitat complexity in aquatic communities and ecosystems. Future research should focus on non-linear responses and incorporate multi-level experiments and monitoring to improve our knowledge in this area.