Individual covariation in life-history traits: seeing the trees despite the forest

American Naturalist
By: , and 



We investigated the influence of age on survival and breeding rates in a long-lived species Rissa tridactyla using models with individual random effects permitting variation and covariation in fitness components among individuals. Differences in survival or breeding probabilities among individuals are substantial, and there was positive covariation between survival and breeding probability; birds that were more likely to survive were also more likely to breed, given that they survived. The pattern of age-related variation in these rates detected at the individual level differed from that observed at the population level. Our results provided confirmation of what has been suggested by other investigators: within-cohort phenotypic selection can mask senescence. Although this phenomenon has been extensively studied in humans and captive animals, conclusive evidence of the discrepancy between population-level and individual-level patterns of age-related variation in life-history traits is extremely rare in wild animal populations. Evolutionary studies of the influence of age on life-history traits should use approaches differentiating population level from the genuine influence of age: only the latter is relevant to theories of life-history evolution. The development of models permitting access to individual variation in fitness is a promising advance for the study of senescence and evolutionary processes.
Publication type Article
Publication Subtype Journal Article
Title Individual covariation in life-history traits: seeing the trees despite the forest
Series title American Naturalist
Volume 159
Issue 1
Year Published 2002
Language English
Contributing office(s) Patuxent Wildlife Research Center
Description 96-105
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title American Naturalist
First page 96
Last page 105
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