Lennart Persson

Population dynamic theory of size-dependent cannibalism

Cannibalism is characterized by four aspects: killing victims, gaining energy from victims, size–dependent interactions and intraspecific competition. In this review of mathematical models of cannibalistic populations, we relate the predicted population dynamic consequences of cannibalism to its four defining aspects. We distinguish five classes of effects of cannibalism: (i) regulation of population size; (ii) destabilization resulting in population cycles or chaos; (iii) stabilization by damping population cycles caused by other interactions; (iv) bistability such that, depending on the initial conditions, the population converges to one of two possible stable states; and (v) modification of the population size structure. The same effects of cannibalism may be caused by different combinations of aspects of cannibalism. By contrast, the same combination of aspects may lead to different effects. For particular cannibalistic species, the consequences of cannibalism will depend on the presence and details of the four defining aspects. Empirical evidence for the emerged theory of cannibalism is discussed briefly. The implications of the described dynamic effects of cannibalism are discussed in the context of community structure, making a comparison with the community effects of intraguild predation.

Predicting shifts in dynamics of cannibalistic field populations using individual-based models

The occurrence of qualitative shifts in population dynamical regimes has long been the focus of population biologists. Nonlinear ecological models predict that these shifts in dynamical regimes may occur as a result of parameter shifts, but unambiguous empirical evidence is largely restricted to laboratory populations. We used an individual–based modelling approach to predict dynamical shifts in field fish populations where the capacity to cannibalize differed between species. Model–generated individual growth trajectories that reflect different population dynamics were confronted with empirically observed growth trajectories, showing that our ordering and quantitative estimates of the different cannibalistic species in terms of life–history characteristics led to correct qualitative predictions of their dynamics.

Chapter One: Summary A Bird’s-Eye View of Community and Population Effects of Ontogenetic Development

Why start with summarizing the contents of a book? in the present case we see at least two good reasons. First, the amount of information provided in our book is without doubt quite massive. a summary provides an overview of the many topics that we cover and, we hope, reduces the risk that the reader will get lost in details and can no longer see the forest through the trees. second, and partly related to the first reason, a number of, in our mind, novel and fundamental insights (some of them were not even known to us when we started to write the book!) are advanced. here a summary serves the purpose of clearly showing how different chapters fit together in a general framework with respect to model approaches as well as results obtained. reading this summary chapter will show you the different types of community modules that we analyze (summarized in figure 1.3) and give you a clear impression of the results and insights that we present in this book. Most of all, we hope it will serve as an encouragement to delve in more detail into the chapters that follow.