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Life history and environmental correlates of survival rates in tropical birds Scholer, Micah Noel

Abstract

Current thinking suggests that survival, and consequently lifespan of organisms, can be understood in terms of trade-offs between self-maintenance and reproduction, and constraints imposed by physiological mechanisms, such as metabolic intensity. While comparative studies show that many life history traits covary predictably with climate, few studies have examined variation in survival across latitudinal or elevational gradients. I paired survival rates with reproductive, morphological, behavioral, and physiological traits, as well as environmental variables to quantify the intrinsic and extrinsic drivers shaping avian life histories. In Chapter 2 I ask whether tropical birds around the world are longer lived than their temperate counterparts. My results suggested an inverse relationship between latitude and survival in the northern hemisphere, but this pattern is dampened or absent for the majority of southern hemisphere species. I also showed that extrinsic factors related to climate were poor predictors of survival compared to latitude alone, and that the relationship between survival and latitude is strongly mediated by intrinsic traits ― larger, non-migratory species with smaller clutch size had the highest survival. In Chapter 3 I focus within the Neotropics to examine how a basic physiological trait (basal metabolic rate; BMR) is linked to survival of montane and lowland birds. I found that lower BMR predicted higher survival, regardless of the elevation at which species occurred. In addition, elevation had a direct negative effect on survival, perhaps due to harsher abiotic conditions, low site fidelity, or both at higher elevations. To help facilitate estimates of age-specific survival in future studies, I determined the molt ageing criteria for South American manakin species in Chapter 4, which can be used to distinguish juveniles from adults. Like many temperate species, the occurrence of a partial preformative molt allowed separation of age classes based on the presence of molt limits. By drawing on both variation within the tropics and across birds globally, this dissertation provides new evidence of the connections between the high survival rate of tropical birds, their life history traits, and the environment.

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