A paradox in individual-based models of populations.

Jaap Van Der Meer

doi:10.1093/conphys/cow023

Abstract

The standard dynamic energy budget model is widely used to describe the physiology of individual animals. It assumes that assimilation rate scales with body surface area, whereas maintenance rate scales with body volume. When the model is used as the building block of a population model, only limited dynamical behaviour, the so-called juvenile-driven cycles, emerges. The reason is that in the model juveniles are competitively superior over adults, because juveniles have a higher surface area-to-volume ratio. Maintenance requirements for adults are therefore relatively large, and a reduced assimilation rate as a result of lowered food levels will easily become insufficient. Here, an alternative dynamic energy budget model is introduced that gives rise to adult-driven cycles, which may be closer to what is often observed in reality. However, this comes at the price of a rather odd description of the individual, in that maintenance scales with body area and assimilation rate with body volume, resulting in unbounded exponential body growth. I make a plea to solve the paradox and come up with reliable descriptions at both the individual and the population level.

Highlights

The scope of conservation physiology includes the development of mechanistic relationships between population declines and physiological processes (Cooke et al, 2013) or, as Metcalfe et al (2012) stated, ‘conservation physiology is the study of physiological responses of organisms to environmental changes and human-induced impacts, and their implications for population ... dynamics’
I believe that a major gap still exists between what we observe at the level of the individual and what we know about population dynamics
For the standard dynamic energy budget (DEB) model, the relationship between critical resource density expressed in terms of the scaled functional response, and scaled body length, immediately follows from equation 16: f* = l

Summary

Introduction

The scope of conservation physiology includes the development of mechanistic relationships between population declines and physiological processes (Cooke et al, 2013) or, as Metcalfe et al (2012) stated, ‘conservation physiology is the study of physiological responses of organisms to environmental changes and human-induced impacts, and their implications for population ... dynamics’. The scope of conservation physiology includes the development of mechanistic relationships between population declines and physiological processes (Cooke et al, 2013) or, as Metcalfe et al (2012) stated, ‘conservation physiology is the study of physiological responses of organisms to environmental changes and human-induced impacts, and their implications for population ... To deduce population phenomena from physiological processes at the individual level is, a general challenge in ecology, with many hidden pitfalls that are not widely recognized. I believe that a major gap still exists between what we observe at the level of the individual and what we know about population dynamics. Almost all models of individual physiology, when used as a building block in population models, will lead to so-called juvenile-driven cycles, which is a type of population dynamics that is not very often observed in nature. The paradox is that descriptions at the individual level do not directly lead to reliable descriptions at the

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