How is the natural world structured? What effect does this structure have? Jordi Bascompte is a leading scientist seeking to answer these questions by applying network science at the interface between theoretical and empirical ecology. In his seminar he showed how mutualistic interactions, those that benefit both parties, structure ecosystems across the planet.
Mutualistic processes are common in natural communities, including well known processes such as seed dispersal and plant pollination by insects. A key finding has been the identification of a distinct pattern of ‘nestedness’ across ecosystems. He showed how this can be linked to the stability of the whole system through a simple model of the competitive and mutualistic interactions. Nested structures maximise the number of shared positive interactions between species, bringing the overall level of competition between species down and creating the potential for high biodiversity. This is empirically visible in the global positive relationship between nestedness and biodiversity.
More recent work has expanded the notion of stability to structural stability, widely used in other fields, but not yet common in ecology. This is the concept that stable structures are those that can exist in a wide range of conditions, a concept of particular pertinence in a globally changing environment. Here too there is evidence that the nestedness leads to higher structural stability.
The talk concluded with a perspective on closing the loop between ecology and evolution. Understanding network responses in a changing world can make use of phylogenetic information. Because related species tend to fulfil similar roles in a network, the loss of particular groups of species could have significant impacts on the stability of ecosystems. Furthermore, previous coevolution studies have focussed on specific pairwise relationships, but a relatively simple model of a network of coevolving species shows that there can be considerable indirect effects as evolutionary pressures have knock-on effects throughout the community.
Jordi’s talk made clear that biodiversity is more than a list of species and that considering the interactions between species is critical to fully understand ecological communities.
Chris Terry is a NERC-funded DPhil student in the Community Ecology and Mathematical Ecology research groups. His current research seeks to understand how interaction modifications impact ecological networks.