Presentations

Below you find the movie registrations or the slides of some of the presentations I have given in recent months.

DEB symposium 2015, Marseille, April 28, 2015

The following is a video registration of my keynote lecture at the 2015 DEB symposium, entitled Modeling energy budgets in ecology: DEB theory, hosted at the Centre international de rencontres mathématiques, Marseille.

Abstract

Dynamic Energy Budget (DEB) models describe how individual organisms acquire and use energy from food and have therefore been argued to consistently link different levels of biological organisation. Various types of DEB models, differing in the organisation and precedence of metabolic processes such as growth, maintenance and reproduction, have been proposed and investigated, although recently the term DEB theory has become more and more identified with the framework developed by Kooijman.
In this lecture I will address the question to what extent differences between DEB models affect the dynamics at the population and community level. I will show that maintenance costs, which are accounted for in all DEB models, have a crucial influence, but that metabolic organisation is of lesser importance. I will furthermore show that population and community dynamics are mostly determined by differences in the capacity of individuals with different body sizes or in different stages of their life history to transform food into new biomass. Such differences, which I refer to as ontogenetic asymmetry in energetics, are however influenced more by the types of food that individuals forage on in different stages of their life history than by their internal energetics. Ontogenetic shifts in resource use during life history are therefore likely to have a larger influence on population and community dynamics than the details of the individual energy budget.

Ecole Normale Supérieure, Paris, May 16, 2014

Abstract

The majority of animal species on Earth have a complex life cycle, characterised by distinct shifts in ecological niche during ontogeny. These ontogenetic niche shifts involve changes in resource use, habitat as well as susceptibility to predators. Ontogenetic niche shifts are especially common among species that grow over a substantial range of body size between birth and maturation. Recent theory has shown that an ontogenetic niche shift in consumers, which exploit different resources during their juvenile and adult stage, may lead to alternative stable equilibria in a consumer-2 resources system. The consequences of ontogenetic niche shifts for the dynamics of communities involving multiple trophic levels are, however, as of yet unknown.
I will discuss the effects of an ontogenetic shift in resource use by consumers on the possible equilibria of a community of 2 resources, one or two consumer and up to two predator species as predicted by stage-structured biomass models. Bistability between an equilibrium with and without predators may occur over a range of resource productivities for generalist predators that forages on both consumer stages to an equal extent. On the other hand, specialist predators that specialise on either juvenile or adult consumer individuals are predicted to go extinct when alone if the productivity of the resource for their main prey is increased. When together, however, persistence of the two predator species in stable equilibrium with the consumer is guaranteed over the entire range of resource productivities for which they can not survive on their own. Finally, we will show that ontogenetic niche shift may also have surprising consequences for competition between consumer species, in particular in the presence of shared predators.

BES Symposium 2015, Sheffield, March 23, 2015

Abstract

Many problems in ecology and evolution revolve around the question how individual life history influences population and community dynamics or vice versa how the population and community setting influences selection and adaptation of individual life histories. Physiologically structured population models are well suited to address such questions as this class of models represents the reproduction, development and mortality of individuals during their life history as dependent on the state of the individual itself and the environment it lives in. These structured population models hence consistently translate the individual life history to the population level and in turn account for density dependent, population feedback on life history through changes in the environment that the individual experiences. In contrast to the more familiar matrix or integral projection models, the individual life history is described in continuous time, for example, by a dynamic energy budget model for individual body size and energy reserves.
In recent years, a general methodology has been developed to carry out demographic, equilibrium (bifurcation) and evolutionary analysis of physiologically structured population models, which in its simplest form boils down to the numerical evaluation of the Lotka integral equation for computing population growth rates. The same methodology can also be used to calculate equilibrium states of non-linear, density-dependent PSPMs as a function of model parameters and to carry out evolutionary analysis on life history parameters using the Adaptive Dynamics approach. The methodology has been implemented in a software package that allows for full analysis of physiologically structured population models from the specification of the key ingredients of an individual’s life history only: its development, reproduction and mortality and its interactions, both intra- and interspecific, with its environment. The software is written in C but can be used from either Matlab or R to carry out computations.
This presentation was used in a workshop during the BES Symposium Demography Beyond the Population in 2015. A ZIP file including the material used during the workshop, such as hand-outs, is available for download here.

BES Annual Meeting 2014, Lille, December 10, 2014

Abstract

Many problems in ecology and evolution revolve around the question how individual life history influences population and community dynamics or vice versa how the population and community setting influences selection and adaptation of individual life histories. Physiologically structured population models are well suited to address such questions as this class of models represents the reproduction, development and mortality of individuals during their life history as dependent on the state of the individual itself and the environment it lives in. These structured population models hence consistently translate the individual life history to the population level and in turn account for density dependent, population feedback on life history through changes in the environment that the individual experiences. In contrast to the more familiar matrix or integral projection models, the individual life history is described in continuous time, for example, by a dynamic energy budget model for individual body size and energy reserves.
In recent years, a general methodology has been developed to carry out demographic, equilibrium (bifurcation) and evolutionary analysis of physiologically structured population models, which in its simplest form boils down to the numerical evaluation of the Lotka-Euler integral equation for computing population growth rates. Even more recently, this methodology has been implemented in a software package that allows for full analysis of physiologically structured population models from the specification of the key ingredients of an individual’s life history: its development, reproduction and mortality and its interactions, both intra- and interspecific, with its environment. In this presentation I will give a brief introduction to the general methodology and illustrate with a few examples how the software package can be used for demographic, equilibrium and evolutionary analysis of this general class of structured population models.