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|Title:||Theory and Pattern of Life-History Evolution in Passerine Birds|
|Author(s):||Kulesza, George Charles|
|Department / Program:||Zoology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||A model of life-history evolution in passerine birds was developed to relate predicted traits to the maximum long-term rate of population increase. Differences in life-history traits among species were hypothesized to result from the interacting effects of mortality expressed as within-brood survivorship of offspring (resource effects), total breeding failure (nest predator effects), adult non-reproductive mortality, and adult reproductive risk. Variation in annual adult survivorship, clutch size, mating systems, and nest structure were predicted from the combined effects of various mortality factors.
Correlation analysis of life-history traits among passerine species supported parts of this general theory. Annual adult mortality was correlated with the intensity of breeding failure and independently with latitude. Breeding failure and latitudinal effects were thought to produce mortality patterns that influence the evolution of passerine life spans. Lack's hypothesis that adult mortality is directly related to the reproductive rate through density-dependent effects was not supported by this analysis. Instead, the relationship between increased reproductive rate and higher adult mortality was shown to be due to the common correlation of each of these variables with breeding failure. Breeding failure directly limits the reproductive rate, and also selects for reduced adult mortality.
Passerine clutch size has generally been shown to be greater among species occupying grassland habitats than in forest habitats. Life-history theory suggested that mortality caused by either resource limitations or nest predators may account for habitat patterns in clutch size. Experiments using artificial nests baited with quail eggs revealed significantly greater nest predation rates in forests than in grassland habitats in Illinois. This pattern supports the view that nest predation may be an important contributing factor to the evolution of passerine clutch sizes and other life-history traits.
Breeding time and energy budgets were determined for males of nine species of passerines in Illinois. It was hypothesized that species that devote a relatively large proportion of time and energy to reproductive activities will have larger clutch size and reduced breeding failure. The proportion of time spent on reproduction was significantly correlated with mean clutch size, but not with estimates for the intensity of breeding failure.
Reproductive strategies among passerine species were viewed here as being influenced by selective pressures caused by environmental mortality factors, and also by the relationship of life-history traits to each other through reproductive effort. The integration of the theoretical model, correlation patterns among traits, and field experiments and observations, generally supported this view, and suggested cause-and-effect mechanisms for the evolution of passerine life-history traits.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
|Date Available in IDEALS:||2014-12-14|