Threshold Extinction in Food Webs

TL;DR

This paper investigates how increasing the energy intake threshold for species persistence in food webs affects secondary extinction patterns, revealing that even small increases can cause disproportionate biodiversity loss.

Contribution

It introduces a quantitative approach to analyze how higher species sensitivity, modeled as energy intake thresholds, influences secondary extinctions in food webs, extending beyond binary extinction models.

Findings

Small increases in energy threshold significantly raise secondary extinctions.

Higher connectivity nodes are more vulnerable to extinction as thresholds rise.

Quantitative thresholds alter predictions of ecosystem robustness.

Abstract

Understanding how an extinction event affects ecosystem is fundamental to biodiversity conservation. For this reason, food web response to species loss has been investigated in several ways in the last years. Several studies focused on secondary extinction due to biodiversity loss in a bottom-up perspective using in-silico extinction experiments in which a single species is removed at each step and the number of secondary extinctions is recorded. In these binary simulations a species goes secondarily extinct if it loses all its resource species, that is, when the energy intake is zero. This pure topological statement represents the best case scenario. In fact a consumer species could go extinct losing a certain fraction of the energy intake and the response of quantitative food webs to node loss could be very different with respect to simple binary predictions. The goal of this paper is to analyze how patterns of secondary extinctions change when higher species sensitivity are included in the analyses. In particular, we explored how food web secondary extinction, triggered by the removal of most connected nodes, varies as a function of the energy intake threshold assumed as the minimum needed for species persistence. As we will show, a very low increase of energy intake threshold stimulates a disproportionate growth of secondary extinction.