Density-Dependent Adaptive Topography in a Small Passerine Bird, the Collared Flycatcher

Area of Science:

• Evolutionary Biology
• Population Genetics
• Behavioral Ecology

Background:

• Adaptive topography describes how population fitness changes with gene frequencies or phenotypes.
• Natural selection acts to maximize expected population size.

Purpose of the Study:

• To investigate how fluctuating population sizes create adaptive topography in collared flycatchers.
• To understand the influence of r- and K-selection on reproductive traits.

Main Methods:

• Analysis of selection on pairwise reproductive traits in collared flycatchers.
• Utilizing expected population size as the criterion for natural selection.
• Examining density-dependent effects on fitness and reproductive timing.

Main Results:

• Fluctuating population sizes generated adaptive topography with peaks at intermediate phenotypes.
• r- and K-selection favored different phenotypes at small versus large population sizes.
• Fitness decreased with delayed egg-laying, showing density-dependent effects.
• Optimal number of fledglings varied with population size; directional selection for larger fledglings occurred.

Conclusions:

• r- and K-selection, driven by expected population size, influence life-history evolution.
• Competition for resources and nest sites at high densities shapes selection.
• Adaptive topography can constrain evolutionary responses to environmental changes.