Structure of insect-plant networks across broad environmental gradients

Understanding changes in community dynamics along ecological gradients are a major goal of community ecology. Recent studies utilizing an ecological network approach have found insect-plant communities to have inherent structural properties. Nestedness, or the tendency for specialist species to interact primarily with generalist species, has been shown in theoretical works to increase the stability of plant-pollinator interactions. Modularity, or the tendency of species to interact primarily in clusters, may increase stability of plant-herbivore interactions. In a meta-analysis, we examined the relationships between structure of 23 plant-herbivore and 25 plant-pollinator networks across gradients of temperature, precipitation, net primary productivity, and elevation on a global scale. 12-year datasets describing temperature, precipitation, and net primarily productivity were used to determine averages and variability of these environmental conditions for each network site. We examined residuals of network structure and species richness to remove the bias of species richness from the relationship between environmental variables and network structure. Plant-herbivore networks significantly increased in modularity and decreased in nestedness with increases in average temperature and precipitation. Modularity increased and nestedness decreased in trophic networks with increases in variability of temperature and precipitation. Plant-pollinator networks significantly increased in nestedness and decreased in modularity with increases in average temperature.  Nestedness decreased and modularity increased with variability in temperature. Understanding these relationships is beneficial when predicting responses of biodiversity to climate change at a community-level. By linking ecosystem-level dynamics to the structure of ecological networks, this study identifies potential environmental mediators of community stability. Understanding the influence of environmental properties is important for testing the robustness of ecological networks to environmental change.