Empirical Evidence of the role of Heterogeneity in Ratio‐dependent Consumption

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Abstract
An increased probability of death is thought to be an inherent risk of dispersal. To examine this hypothesis, were monitored 381 radiomarked Ruffed Grouse (Bonasa umbellus) over 6 yr to determine if their vulnerability to mortality increased during dispersal. Estimates of mortality were calculated for the two distinct phases of dispersal: transience, a period of extensive movement from one area to another, and colonization, the period when an animal attempts to become established in a new area. Among juveniles (nonresidents), approximately equal proportions of both sexes exhibited transience, and for similar lengths of time. The difference between juvenile male and female mortality estimates was not significant during either transience or colonization. From autumn to spring (natal dispersal), juvenile transient dispersers did not experience greater mortality than colonization dispersers. Among adults, transience was more common among females than males, yet no mortality was recorded among either sex of adult transient dispersers. Residents (adults) survived at a higher rate than juveniles in either transient or colonization dispersal. However, the cost (i.e., increased mortality) of transience was greater for juveniles than adults, suggesting comparisons between different phases of dispersal be made within similar age classes. It was concluded that Ruffed Grouse, both adults and juveniles, were not more vulnerable to mortality during transient dispersal than during colonization dispersal.

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