Extinction risk and structure of a food web model

TL;DR

This study analyzes a trophic web model, revealing how small, weakly connected systems risk extinction, and identifying structural features like pyramidal organization and food chain length distributions, with implications for real biological webs.

Contribution

It provides detailed Monte Carlo simulation results on extinction risks, web structure, and food chain distributions in small, realistic food web models, extending prior theoretical work.

Findings

Small, weakly connected webs can become non-viable and extinct.

Viable webs show pyramidal structure with higher lower-level occupancy.

Food chain length distribution is exponential and weakly parameter-dependent.

Abstract

We investigate in detail the model of a trophic web proposed by Amaral and Meyer [Phys. Rev. Lett. 82, 652 (1999)]. We focused on small-size systems that are relevant for real biological food webs and for which the fluctuations are playing an important role. We show, using Monte Carlo simulations, that such webs can be non-viable, leading to extinction of all species in small and/or weakly coupled systems. Estimations of the extinction times and survival chances are also given. We show that before the extinction the fraction of highly-connected species ("omnivores") is increasing. Viable food webs exhibit a pyramidal structure, where the density of occupied niches is higher at lower trophic levels, and moreover the occupations of adjacent levels are closely correlated. We also demonstrate that the distribution of the lengths of food chains has an exponential character and changes weakly with the parameters of the model. On the contrary, the distribution of avalanche sizes of the extinct species depends strongly on the connectedness of the web. For rather loosely connected systems we recover the power-law type of behavior with the same exponent as found in earlier studies, while for densely-connected webs the distribution is not of a power-law type.