American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Density-dependent adaptive topography in a small passerine bird, the collared flycatcher”

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Bernt-Erik Sæther, Steinar Engen, Lars Gustafsson, Vidar Grøtan, and Stefan J. G. Vriend (Jan 2021)

This study shows that density-dependent selection affects evolution of reproductive strategies in collared flycatchers

Read the Article (Just Accepted)


The adaptive topography is a central concept in evolutionary biology, describing how the mean fitness of the population changes with gene frequencies or mean phenotypes. We use expected population size as quantity to be maximized by natural selection to show that selection on pairwise combinations of reproductive traits of collared flycatchers caused by fluctuations in population size generated an adaptive topography with distinct peaks often located at intermediate phenotypes. This occurred because r- and K-selection made phenotypes favored at small densities different from those with higher fitness at population sizes close to the carrying capacity K. The fitness decreased rapidly with a delay in the timing of egg-laying with a density-dependent effect especially occurring among early-laying females. The number of fledglings maximizing fitness was larger at small population sizes than close to K. Finally, there was directional selection for large fledglings independent of population size. We suggest that these patterns can be explained by increased competition for some limiting resources or access to favorable nest sites at high population densities. Thus, r- and K-selection based on expected population size as evolutionary maximization criterion may influence life history evolution and constrain the selective responses to changes in the environment.