Landscapes of facilitation: The effects of positive interactions on community structure

Our world’s biodiversity has long been under pressure, in most cases due to human activities. The conservation of biodiversity requires more than the protection of a nature reserve. It calls for knowledge of and insights in the many interactions that occur between the different species that are present. For a long time ecological research focused on negative interactions such as competition and predator-prey relations. However, in recent decades focus shifted towards the role of positive interactions on community structure. When different species facilitate one-another, for example by providing shade, shelter or structure, a domino-effect can occur. In so-called facilitation cascades a primary habitat-forming species facilitates a secondary habitat-former, which on its turn promotes biodiversity and species abundance. These positive interactions are sensitive to variation in traits and function of habitat-forming species. It turns out that oysters and mussels – seemingly similar species – facilitate the development of different macroalgae and associated species due to their different ecological function, and the morphology of macroalgae affects the species that are being facilitated. Furthermore, a single primary habitat-former can generate multiple facilitation cascades that positively effect biodiversity on both long and short spatial scales. This strongly connects different habitats via a network of positive interactions. These complex networks highlight the importance of cross-habitat management initiatives that aim to promote biodiversity by conserving habitat-forming species and their positive interactions.