The spatial scaling of species interaction networks

Networks are everywhere. From computers on the Internet to nerve cells connected by axons in the brain. Ecological networks have been defined as the backbone of biodiversity, describing who interacts with whom in nature for a given location and time. However, interactions between species vary through space and time generating changes in network structure as the scale of observation changes.

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The paper in Nature Ecology & Evolution is here:

Understanding the spatial scaling of biodiversity across the globe is a major challenge for ecological research. Even more so given the current threats facing biodiversity due to different components of global change. A good understanding of how species richness (a component of biodiversity) increases with area has been so far achieved; and, to some extent, the mechanisms behind this scaling are understood. However, the same isn’t true for the number and the organisation of ecological interactions (another component of biodiversity). How does network structure change as we increase the spatial scale of observation?

Motivated by basic mechanisms influencing the Species-Area Relationships (SARs), like beta-diversity patterns across local communities, we set out to discover the fundamental processes behind the spatial scaling of interaction networks. We joined forces with a group of internationally recognised experts in the field of spatial food webs to find the potential ecological drivers of Network-Area Relationships (NARs).

We developed a theoretical and predictive framework to understand the variation of the properties of ecological networks (e.g., connectivity, trophic level composition, trophic chain length) across spatial scales; from small to large areas. With three simple theoretical models, we tested the effect of specific spatial processes (e.g., dispersal) on community assembly and structure, which allowed us to present a number of testable predictions on network-area relationships (NARs) for multi-trophic communities.

These realisations have prompted us to search for empirical evidence of the different patterns of the spatial scaling of network structure. We have now gathered biotic interactions data from ecological systems across the globe, from different regions, habitats, and interaction types across different spatial scales. The next step is thus use this data to reveal the scaling of interaction networks in space and, based on the shape of these relationships and our theoretical predictions, try to infer the possible spatial processes behind them. Our study therefore opens up new research avenues towards a better understanding of the spatial scaling of biodiversity, which is crucial to generate predictions of potential effects on ecological communities of habitat loss and fragmentation in a changing world.

Nuria Galiana

PhD Student, CNRS