Food web size and shape differ in their environmental control

Food-web structure governs community stability and ecosystem functioning, yet its environmental controls remain poorly understood. We analyzed 1,046 food webs from 26 Neotropical sites spanning broad environmental gradients in energy, temperature, hydrologic disturbance and ecosystem size to understand how these factors contribute to determining food web structure. All food webs were from the same widespread system and sampled using standardized methods. We found that food-web size increased with locally available energy and ecosystem size, but decreased with regional aridity and precipitation variability. In terms of shape, food webs became shorter and wider in regions with low primary productivity, high temperatures and drought-prone climates. Thus, food web size and shape were controlled by different environmental drivers acting at different spatial scales, likely reflecting divergence in the underlying mechanisms. Environmental effects on food web size were mediated by the abundance and traits of species, but food web shape was not. These findings reveal how local environmental conditions and regional climate structure ecological networks, providing a basis for forecasting food-web restructuring under environmental change.