A general parameterized mathematical food web model that predicts a stable green world in the terrestrial ecosystem

TL;DR

This paper introduces a parameterized mathematical model of terrestrial food webs that predicts herbivore and carnivore biomass densities, explaining the stability of the green world and aligning with empirical data.

Contribution

It presents a novel, parameterized model capable of predicting absolute biomass densities in terrestrial food webs, integrating ecological factors and explaining the stability of the green world.

Findings

Model predicts stable low herbivore biomass in terrestrial ecosystems.

Good agreement between model predictions and empirical biomass data.

Plant nutritive value correlates with herbivory intensity and defense mechanisms.

Abstract

Terrestrial ecosystems are generally green and only a small part (<10%) of the plant matter is consumed by herbivores annually,but the reason has been unclear due to the lack of food web models for predicting the absolute herbivore biomass in physical units. Here, I present a simple parameterized mathematical food web model that can predict the biomass density of herbivores h (kg protein/m3) and carnivores c from ecological factors such as the nutritive values of plants np (kg protein/m3), herbivores nh, and carnivores nc, searching efficiency (volume) of carnivores S (/day), eating efficiency (speed) of herbivores eh (/day) and carnivores ec, respiratory decrease in herbivore and carnivore biomasses, dh (/day) and dc, absorption efficiency of herbivores and carnivores h (ratio) and c, and probabilities of carnivores preying on herbivores or carnivores, Phc (ratio) and Pcc.The model predicts a stable equilibrium with low herbivore biomass h sufficient to keep the world green if the food web consists of the three trophic levels, plants, herbivores and carnivores; intraguild predation of carnivores exists; np<nh,nc; S>>eh, and Phc>Pcc >0,which are well-realized in above-ground terrestrial ecosystems where plant-rich "green world" is common. The h and c calculated from our model showed good agreement with those from empirical observations in forests, where both h and c are ca. 100 mg (fresh biomass/m2), and in savannahs. The model predicts that the nutritive values and digestibility of plants are positively correlated with h and the intensity of herbivory, which theoretically explains the out-door defensive effects of the anti-nutritive or quantitative defenses (e.g., tannins, protease inhibitors) of plants, and predicts that c and c/h are positively correlated with the relative growth rate of herbivores. The present model introduced parameterized realities into food web theory.