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UBC Theses and Dissertations

The effects of habitat preference, environmental heterogeneity, and inter-individual variation on fitness Germain, Ryan Ross


Theory predicts that animals breeding in heterogeneous landscapes should select habitat likely to maximize individual fitness, but identifying the fine-scale environmental characteristics which influence habitat preference and affect fitness is often problematic. While many studies quantify relationships between habitat preference and the reproductive success of their occupants, few are able to separate the independent effects of inter-individual variation among animals in a population from the effects of habitat on indices of fitness. In this thesis, I used up to 39 years of nesting, survival, and pedigree data from a resident, island population of song sparrows (Melospiza melodia) to identify fine-scale environmental characteristics which influenced habitat preference, determine whether preferred habitats positively affected fitness, and distinguish the relative effects of preferred habitats on indices of fitness from those due to inter-individual variation among song sparrows within the population. Song sparrows in this population exhibited marked preference for habitats that conferred positive effects on individual fitness via annual reproductive success and survival. Females nesting in preferred habitats also began breeding earlier, exhibited more energetically efficient incubation behaviour, and produced more offspring that recruited the population than those nesting in less-preferred sites. Preferred habitats in this system had more shrub cover, more edge, and deeper soil. The potential benefits of occupying preferred habitats included greater early season food availability and shelter from predators and inclement weather during both the breeding and non-breeding seasons. Despite the positive effects of preferred habitats on fitness, the relative contributions of habitat to indices of fitness were substantially less than those related to inter-individual variation in phenotype, genotype and developmental stage (measured as relative lifetime reproductive success, additive genetic and permanent individual variance, and age). Together, results from this thesis suggest that inter-individual variation in ‘quality’ can be more influential of fitness than habitat quality in free-living populations, and highlight the importance of estimating the relative contributions of inter-individual variation when attempting to identify the environmental correlates of fitness in natural systems.

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