Abstract
Abstract Many wild populations of animals conform to the ideal despotic distribution (IDD) in which more competitive individuals exclude less competitive individuals from high quality resources. Body size and aggressiveness are two important traits for resource defense, and they positively covary so that larger individuals are usually more aggressive. Using Bachman’s sparrows, we tested the hypothesis that larger birds are more aggressive and are thus able to compete for the best quality territories. We found that larger males were more aggressive, and more aggressive birds fledged at least one young. However, we did not find consistent relationships between aggressiveness and habitat characteristics. Our results suggest that Bachman’s sparrows meet most of the predictions of the IDD. Frequent ecological disturbances, such as fires, might disrupt the IDD or make it difficult to detect. Additional studies are needed to test for relationships between ecological disturbances and territorial behaviour.
Highlights
The ideal free distribution (IFD; Orians, 1969; Fretwell & Lucas, 1970; Fretwell, 1972) explains how animals should distribute themselves in environments with patchy distributions of resources
We found support for both predictions; both body size and aggressiveness varied among males (Tables A3 and A4 in the Appendix), and larger males were more aggressive than smaller males (Figure 1)
These data support the prediction of the ideal despotic distribution (IDD) for variation in competitiveness in male Bachman’s sparrows
Summary
The ideal free distribution (IFD; Orians, 1969; Fretwell & Lucas, 1970; Fretwell, 1972) explains how animals should distribute themselves in environments with patchy distributions of resources (food, mates, nesting habitat). Ideal despotic distribution in Bachman’s sparrow as exploiter density increases, and individuals select the most profitable patch relative to the number of existing competitors in the patch. It follows that high quality habitats contain more resources and attract a higher density of competitors. Individuals typically vary in their competitive ability, and resources are often defended to the exclusion of others
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