Environ centrality reveals the tendency of indirect effects to homogenize the functional importance of species in ecosystems

TL;DR

This paper introduces environ centrality, a new method to quantify species importance in ecosystems, revealing that indirect effects tend to homogenize species' functional roles and emphasizing the significance of detritus and nutrient recyclers.

Contribution

The paper presents a novel mathematical approach, environ centrality, to measure species importance considering direct and indirect effects in ecosystem networks.

Findings

Indirect effects homogenize species importance in ecosystems.

Detritus and nutrient recyclers are key in energy-matter flow.

Species importance distribution is concentrated among few dominant species.

Abstract

Ecologists and conservation biologists need to identify the relative importance of species to make sound management decisions and effectively allocate scarce resources. We introduce a new method, termed environ centrality, to determine the relative importance of a species in an ecosystem network with respect to ecosystem energy--matter exchange. We demonstrate the uniqueness of environ centrality by comparing it to other common centrality metrics and then show its ecological significance. Specifically, we tested two hypotheses on a set of 50 empirically-based ecosystem network models. The first concerned the distribution of centrality in the community. We hypothesized that the functional importance of species would tend to be concentrated into a few dominant species followed by a group of species with lower, more even importance as is often seen in dominance--diversity curves. Second, we tested the systems ecology hypothesis that indirect relationships homogenize the functional importance of species in ecosystems. Our results support both hypotheses and highlight the importance of detritus and nutrient recyclers such as fungi and bacteria in generating the energy--matter flow in ecosystems. Our homogenization results suggest that indirect effects are important in part because they tend to even the importance of species in ecosystems. A core contribution of this work is that it creates a formal, mathematical method to quantify the importance species play in generating ecosystem activity by integrating direct, indirect, and boundary effects in ecological systems.