Predation risk influences food-web structure by constraining species diet choice

The foraging behaviour of species determines their diet and, therefore, also emergent food-web structure. Optimal foraging theory (OFT) has previously been applied to understand the emergence of food-web structure through a consumer-centric consideration of diet choice. However, the resource-centric viewpoint, where species adjust their behaviour to reduce the risk of predation, has not been considered. We develop a mechanistic model that merges metabolic theory with OFT to incorporate the effect of predation risk on diet choice to assemble food webs. This ‘predation-risk-compromise’ (PR) model better captures the nestedness and modularity of empirical food webs relative to the classical optimal foraging model. Specifically, compared with optimal foraging alone, risk-mitigated foraging leads to more-nested but less-modular webs by broadening the diet of consumers at intermediate trophic levels. Thus, predation risk significantly affects food-web structure by constraining species’ ability to forage optimally, and needs to be considered in future work.

---

Fig 1. Illustration of the Optimal Foraging (OF) and Predation Risk-Compromise (PR) models for predicting the diet breadth of a focal consumer. Under the OF model (a and b), the predicted diet for a consumer is the one that yields maximum net consumption. Under the PR model (a, c–e) predation risk, Prisk, is incorporated as a constraint on optimal foraging, resulting in a diet with a risk-compromise consumption rate (Crisk, the point closest to, while still being above, the horizontal dashed line in d) lying somewhere between the OF maximum, Copt, and a minimum metabolically-feasible consumption rate threshold, Cmin. Both models are applied to all consumer species in a community to assemble model food webs. Note that we focus on the diet-broadening strategy in the PR model, which ‘propagates’ iteratively during food-web assembly, as described in the main text.

---

Published in Ecology Letters, 2019

Authors: Hsi-Cheng Ho, Jason M. Tylianakis, Jonathan X. Zheng, Samraat Pawar

Full text