Predicting the sign of trophic effects: individual-based simulation versus loop analysis

Virág Fábián

doi:10.1007/s42974-021-00068-1

Abstract

Food web research needs to be predictive in order to support decisions system-based conservation. In order to increase predictability and applicability, complexity needs to be managed in such a way that we are able to provide simple and clear results. One question emerging frequently is whether certain perturbations (environmental effects or human impact) have positive or negative effects on natural ecosystems or their particular components. Yet, most of food web studies do not consider the sign of effects. Here, we study 6 versions of the Kelian River (Borneo) food web, representing six study sites along the river. For each network, we study the signs of the effects of a perturbed trophic group i on each other j groups. We compare the outcome of the relatively complicated dynamical simulation model and the relatively simple loop analysis model. We compare these results for the 6 sites and also the 14 trophic groups. Finally, we see if sign-agreement and sign-determinacy depend on certain structural features (node centrality, interaction strength). We found major differences between different modelling scenarios, with herbivore-detritivore fish behaving in the most consistent, while algae and particulate organic matter behaving in the least consistent way. We also found higher agreement between the signs of predictions for trophic groups at higher trophic levels in sites 1–3 and at lower trophic levels in site 4–6. This means that the behaviour of predators in the more natural sections of the river and that of producers at the more human-impacted sections are more consistently predicted. This suggests to be more careful with the less consistently predictable trophic groups in conservation management.

Highlights

In complex ecological systems, the multiplicity of direct and indirect interactions makes it difficult to provide simple and clear predictions on the effect of single-node perturbations
(4) we investigate if there is a correlation between the network centrality of a trophic group and the sign-agreement between the two models predicting its effects on other groups
The predicted signs of effects for each trophic group are shown in Fig. 3, for each of the 6 sites (Fig. 3a–f)

Summary

Introduction

The multiplicity of direct and indirect interactions makes it difficult to provide simple and clear predictions on the effect of single-node perturbations. Considering effect sign is critically important if food web models are to be extended to ecological interaction networks: this is the way how to complete antagonistic. Community Ecology (2021) 22:441–451 predator–prey interactions with positive feedback loops (Dong et al, 2020; Ulanowicz, 1995) and mutualisms (Leemans et al, 2020). Loop analysis (Levins, 1974; Puccia & Levins, 1985a), mixed trophic impact (Bondavalli & Ulanowicz, 1999; Ulanowicz & Puccia, 1990), signed topological importance (Liu et al, 2010, 2020) and dynamical simulations (Jordán et al, 2012) can be used but their relationship is not straightforward (i.e. whether they provide similar or complementary information). Loop analysis has been used extensively together with topological network analysis (e.g. Ortiz et al, 2013, 2015, 2017)

Methods

Results

Conclusion