Network-based food availability affects the keystoneness of predators and functional diversity of the marine food web

Marine predators play an important role in food webs, and their food availability affects the structure and function of marine ecosystems. In this research, we calculated 6 network-level topological indices and the keystone index for predator nodes. We also quantified the functional homogenization degree of the food web by using a measure of functional diversity. We simulated food availability variation by adding or deleting a link to each predator node and recalculating the above indicators in turn when generating a new network. We found that increased food availability can increase the topological complexity in food webs, yet top predators show less plasticity in network structure than lower predators. The resulting variability in average path length may be related to the threshold at which omnivory affects food web stability. When food availability ranges from 0.3 to 0.6, predators at higher trophic levels may have a positive impact on the stability of the food web, as an interplay between bottom-up and top-down mechanisms. In addition, high food availability may lead to functional homogenization, particularly in predators with lower trophic levels. For top predators, reduced food availability is more conducive to the resilience of network functional diversity. Finally, increasing food availability increases the relative positional importance of predator nodes in the network. Especially for top predators, this amplifies their top-down effects on lower levels in the food web. This research reveals the mechanistic basis of the homogenization of marine food webs and contributes a theoretical basis for the effective management of marine ecosystems.