Abstracts:  NVTB  PhD-day  2001

We consider population dynamics of semelparous species, i.e. such species which reproduce once in their life and then die. A population consists of several year classes. Due to competition between age classes we can observe the situation of so-called competitive exclusion. It means that only few from all year classes are present. We model the system with the aid of k-dimensional map, where k is the number of age classes. The interactions between and within age class is a feedback via environment, which is described by a scalar quantity I. Each age class is characterised by its impact on and sensitivity to environment. The questions we try to answer are: do we get coexistence or competitive exclusion? how many year classes can coexist when the other are missing? In this work we will present general formulation of this model and try to answer the questions in some simple cases, in particular if k=2,3.

Models of sympatric speciation have either considered ecological processes or sexual selection as the driving force behind the evolution of new species in sympatry. Sexual selection models specifically addressed the mechanisms underlying the evolution of reproductive isolation, and have been used to explain the sympatric origin of sibling species with very little observable ecological differentiation. I will first argue that, contrary to the claims made in the literature, the current sexual selection models cannot explain sympatric speciation, and I will pinpoint the missing ingredient of these models. Then I will present and analyse a model of sympatric speciation in which this missing ingredient is added. The model considers the interplay between sexual selection and ecological differentiation, resulting in sympatric speciation under a broad range of parameter conditions.

There exist lakes in which one can find a predatory but no prey fish (pike or perch). Here the young feed on zooplankton and the old on the young.We use cannibalism as an example of a nonlinear size structured population model which is relatively easy in the way that there is only one population. We will look especially for steady state conditions.

Host bird species of the Cuckoo, Cuculus canorus often display egg discrimination behaviour but chick-rejection behaviour has never been reported. In this talk, a model will be introduced to study a host-cuckoo association in which both population dynamics and evolutionary dynamics are incorporated in a discrete-time model. We introduce four host types, each with their own defence behaviour, displaying either egg or chick rejection, neither or both. We also introduce fitness functions for each of these host types. Although we can characterise the long term behaviour in many cases by a simple heuristic argument which is in accordance with common views in ecology, there are a number of other phenomena that are not explained within this framework: we describe stable oscillatory behaviour and coexistence of multiple host types. We analyse the scenarios in which chick rejection may establish itself and give a first explanation as to why this defence trait has never been recorded in nature.