Network theory predicts ecosystem robustness across environmental conditions

Network theory quantifies how changes in species richness, S , lead to changes in the number of interactions (or links) between species, L . Networks with a steep relationship between L and S have a high number of links per species, making the network resistant to collapse and therefore more robust. However, changes in S often coincide with environmental shifts, which can lead to impacts on L that are not expected from network theory. In this article, we constructed relationships between L and S for 18 ecosystems using 1081 observations collected across 420 environmental conditions. We found that environmental noise (unspecified spatio-temporal variation) and environmental gradients (directional environmental change) commonly affected ecological network size ( S and L ), community composition, and also induced network rewiring, which means that species changed interaction partners as the environment changed. Yet, we found the log( L ) ~ log( S ) relationship to be remarkably constant across environmental conditions. Specifically, the slope of this relationship remained constant across conditions, implying consistency in how species loss proportionally affects L . Our results therefore show that network theory predicts ecosystem robustness across environmental conditions. These results suggest generality to how environmental drivers operate at the level of ecological networks, which is encouraging for conservation.