A Mechanism of Food-Web Complexity Emergence Under Multiple Environmental Drivers.

Understanding the mechanisms that drive the emergence and maintenance of food-web complexity under multiple environmental drivers is a central challenge in metacommunity ecology. The environmental variables (ecosystem size, resource productivity, and disturbance) are often considered as potential drivers of complex ecosystems. However, how these factors shape food-web complexity remains unclear. Here, we develop a colonization-competition tradeoff framework for complex ecological network metacommunities including multiple environmental drivers. We found that the topological complexity of ecological networks, measured by species richness, connectance, omnivory, and mean food chain length, exhibits robust, non-linear idiosyncratic responses to gradients in ecosystem size, resource productivity, or disturbance. The non-monotonicity arises from shifts in the dominance hierarchy of basal species driven by colonization-competition tradeoffs, which in turn cascade upwards to alter consumer community composition and network structure. Moreover, this result stays valid even when parameters are altered or the assumption of a strict competitive hierarchy is relaxed. It reveals that a minor change in these environmental determinants can result in significant implications for the complexity of trophic networks. Thus, this study offers a mechanistic explanation for the emergence of food-web complexity driven by multiple environmental drivers.