an analysis of reciprocal exchange of helping behavior in the red-cockaded woodpecker (Picoides borealis)

摘要

We examine the frequency of reciprocal exchanges of helping behavior in three red-cockaded woodpecker populations to determine if such exchanges might constitute a significant fitness benefit of helping.Specifically, we determine how often helpers,once they become breeders, are assisted by young they previously helped raise. The estimated frequencies of reciprocal exchange of helping based on survival and status transition porbabilities are low (2%). Observed frequencies of reciprocity are significantly higher than estimated frequencies in two of the three populations studied, suggesting that male fledglings more often remain on their natal territory as helpers if another helper is already present. High rates of retention of young males as helpers on high-quality territories or preferential helping of kin, as well as preferectial helping of former care-givers, might explain this result. When the analysis is restricted to helpers unrelated to the young they help raise, which controls for preferential helping of kin and largely eliminates effects of territory quality, empirical estimates of the frequency of reciprocity do not differ from estimates calculated from population demography. We conclude that young males do not preferentially help former caregivers and that reciprocal exchange of help is not an important factor in the evolution of helping behavior in the red-cockaded woodpecker. In this species, all known benefits of helping behavior are indirect (i.e., derived through kin selection) rather than direct. We discuss the occurrence of unrelated helpers in this context.