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AG Trillmich
AG Krüger
AG Bischof
AG Steinfartz
AG von Engelhardt
AG Hoffman
Als Teil der Langzeitforschungen an Mäusebussarden sind von unserer Arbeitsgruppe inzwischen über 500 Individuen mit Flügelmarken ausgestattet worden. Die Marken sind weiss und die individuelle Kennzeichnung besteht aus einer schwarzen Zahl oder einem Buchstaben und einer Zahl. Dabei gibt es sowohl z.B. die Kombination "4B" als auch "B4". Für jede Ablesung einer Flügelmarke sind wir sehr dankbar. Wichtig sind folgende Informationen: welche Flügelmarke, wann gesehen, wo gesehen. Bitte melden Sie alle Beobachtungen an:
oliver.krueger(at)uni-bielefeld.de
“Nothing makes sense in biology except in the light of evolution” and “fitness is the currency of evolution”, these are two famous statements and they describe the conceptual underpinning of my research interests in animal behaviour.
The unifying feature of my different research projects is life history strategy evolution, the way natural selection optimises the entire life of an organism. Differences between individuals and their life histories are evaluated by natural selection on the basis of fitness. Hence it is of paramount importance to measure fitness if we want to attach biological meaningfulness to animal behaviour. However, animal behaviour and life history strategies do not evolve in isolation. Individual behaviour is bound to have consequences at the population level and, conversely, populations set the stage for the evolution of life history strategies and animal behaviour. As a consequence, by studying life history strategies, my research is encompassed by a triangle of evolution, ecology and ethology. Only detailed knowledge of individual fitness allows one to decompose individual behavioural variation into components of genotypic and phenotypic quality, as well as environmental effects.
At first sight, birds of prey may seem unsuitable study species because of their long lifespans, but my common buzzard (Buteo buteo) study has been running for 22 years. This not only permits analyses which are normally applied to much shorter-lived species but also enables me to test whether paradigms set by the study of short-lived species apply to long-lived species as well or whether our understanding is biased by the few short-lived model organisms. Individual behaviour is bound to have cumulative effects at the population level and of course population density is bound to affect individual behaviour. Detailed individual-based data as well as population data are necessary to study these interactions. The study on goshawks (Accipiter gentilis) now runs for 36 years and yields fitness data as well as population fluctuations which allow me to bridge the gap between individual behaviour and population dynamics. I was able to show that a very important life history trait such as age at first breeding is crucial for the fitness of the individual and that it is strongly mediated by habitat heterogeneity. This habitat heterogeneity also regulates the population dynamics. By integrating life history strategy research into population ecology, it is possible to gain a much deeper understanding of individual fitness as well as population phenomena.
My second current research interest is avian host-parasite co-evolution. This project allows me to work experimentally which is quite difficult in birds of prey. In this context, I am involved with fieldwork in South Africa to look at the adaptations and counter-adaptations in one particular system (the jacobin cuckoo (Clamator jacobinus) and its cape bulbul (Pycnonotus capensis) host). Through a combination of experiments and modelling, I try to explain specific features of this host-parasite system and use its relative simplicity to test general hypotheses, such as the evolutionary lag and the evolutionary equilibrium hypotheses. This particular system offers absolutely unique possibilities to study experimentally adaptations and counter-adaptations. The cuckoo lays an egg that is completely different from the host egg and still no egg-rejection is detectable, meaning that the host has not had enough evolutionary time to evolve egg-rejection or that egg acceptance is an optimal strategy. Another striking feature is that host and parasite chicks do not produce loud begging calls and so one means for the parasite to induce the host to preferentially feed it is not available. The jacobin cuckoo chick also shows pre-incubation development which gives the chick a head-start, but the significance of this adaptation remains untested. I am in the process of obtaining a fitness data set of the host species population which would enable me to quantify the strength of selection pressure operating on the host to evolve defences against brood parasitism. This approach has almost never been feasible due to the difficulties obtaining fitness data for host species. Since the jacobin cuckoo does not always reduce host breeding success to zero if it parasitizes (host and cuckoo chick are sometimes raised together), this host-parasite system is at an intermediate stage of the co-evolutionary arms race and might provide important insights into avian brood parasitism and the co-evolutionary process in general. I have also started to combine experiments and modelling to test whether the lack of counter-adaptations by the host is best explained by the evolutionary lag (the host will be selected to evolve a defence) or evolutionary equilibrium (costs of evolving a defence are higher than the benefits of that defence) hypotheses. It seems not only that the evolutionary equilibrium hypothesis is more likely, but so far unreported from any co-evolution studies, increased parasitism selects for fewer defences in the host.
Quite often, very interesting questions are not amenable to experimental manipulation. The comparative approach, where different taxa are compared, has proved to be a successful alternative. Over the last 20 years, radical new methods have become available which have increased analytical power. They take a phylogeny explicitly into account and hence deal effectively with the problem of phylogenetic inertia (closely related species have similar trait values due to common descent). In addition, these new methods allow testing of the temporal ordering of evolutionary events, so evolutionary pathways can be established. This increases the explanatory power of the comparative approach immensely. I have developed a comparative approach to explain the evolution of brood parasitism in cuckoos. The results seem to indicate that the evolution of brood parasitism is a consequence of changes in ecology, rather than the cause of these changes. This comparative approach will be developed further together with N. Davies from the University of Cambridge and M. Sorenson from the University of Boston. We will look at the diversity of breeding strategies and life histories across the whole family of cuckoos and study life-history evolution and speciation. Here, first results indicate that the evolution of brood parasitism promotes speciation as a result of increasing adaptation to a particular host. In addition, I have used comparative approaches to study the evolution of life history traits in birds of prey and owls, sexual size dimorphism and speciation.
As I am in the process of building up my research group in Bielefeld, I would very much welcome applications from students and Postdocs who would like to work with me. If you are interested in any of the projects described above, please contact me.
