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Reproductive rates under competition

30 October 2009

Promotie: mw. M. Nicolaus, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen
Proefschrift: Reproductive rates under competition
Promotor(s): prof.dr. J.M. Tinbergen, J. Komdeur
Faculteit: Wiskunde en Natuurwetenschappen
Contact: tel. 050-363 2206, e-mail:

Reproductive rates under competition

Marion Nicolaus has shown that animals do not only base their reproductive decisions on environmental parameters like food or shelters but also on their social environment, i.e. on the number and types of competitors present in the habitat. Only a restricted number of studies has tested this idea experimentally and that is why her results are so important.

Understanding how reproductive rates evolve implies that the action of natural selection on individual behavioural and reproductive decisions should be studied. Natural selection is expected to lead individuals to behave in a way that maximizes their genetic contribution to future generations (i.e. their fitness). Identifying which selective forces play a role in decision making and at which scale these forces influence individual choices is crucial to understanding the adaptive significance of individual variation in behaviour. Nicolaus investigated how the social composition of local environment affects the fitness consequences of variation in behavioural and reproductive decisions in a wild great tit (Parus major) meta-population. She also examined the spatial scale at which selection on individuals mediated by social factors takes place. For that, she manipulated the local breeding densities (time period 1) and the local juvenile density and sex ratio (time period 2) of different “plots”. The latter manipulation was achieved by swapping young of known sex among nests in different plots. Nicolaus’ results showed, apart from interesting effects of social environment on juvenile dispersal and settlement, that the fitness consequences of variation in brood sizes were indeed affected by the social environment. Therefore her thesis confirms that social environment (density and sex ratio) is an important selective pressure acting on reproductive rates and helps to understand micro-evolutionary processes acting on fitness related traits.

Last modified:15 September 2017 3.38 p.m.

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