Spatial Guilds in the Serengeti Food Web Revealed by a Bayesian Group Model

TL;DR

This paper introduces a Bayesian method to identify functional and spatial groupings in food webs, revealing that the Serengeti ecosystem's structure combines spatial and trophic organization, which supports theories on ecosystem persistence.

Contribution

A novel Bayesian computational approach that flexibly identifies both functional and spatial groups in food webs, applied to the Serengeti ecosystem.

Findings

Network structure reflects spatially distinct plant groups and trophic interactions.

Food web groups combine spatial patterns with trophic guilds.

Results support theories on spatial coupling and energy channels for ecosystem persistence.

Abstract

Food webs, networks of feeding relationships among organisms, provide fundamental insights into mechanisms that determine ecosystem stability and persistence. Despite long-standing interest in the compartmental structure of food webs, past network analyses of food webs have been constrained by a standard definition of compartments, or modules, that requires many links within compartments and few links between them. Empirical analyses have been further limited by low-resolution data for primary producers. In this paper, we present a Bayesian computational method for identifying group structure in food webs using a flexible definition of a group that can describe both functional roles and standard compartments. The Serengeti ecosystem provides an opportunity to examine structure in a newly compiled food web that includes species-level resolution among plants, allowing us to address whether groups in the food web correspond to tightly-connected compartments or functional groups, and whether network structure reflects spatial or trophic organization, or a combination of the two. We have compiled the major mammalian and plant components of the Serengeti food web from published literature, and we infer its group structure using our method. We find that network structure corresponds to spatially distinct plant groups coupled at higher trophic levels by groups of herbivores, which are in turn coupled by carnivore groups. Thus the group structure of the Serengeti web represents a mixture of trophic guild structure and spatial patterns, in contrast to the standard compartments typically identified in ecological networks. From data consisting only of nodes and links, the group structure that emerges supports recent ideas on spatial coupling and energy channels in ecosystems that have been proposed as important for persistence.