Physiological tolerances of high temperatures in Fynbos birds: implications for climate change

Master Thesis


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University of Cape Town

Climate change is a reality. Numerous biological systems have already responded to changes in climate, with range shifts towards higher latitudes and altitudes being one of the most common responses to climate warming. Bioclimatic envelope modelling provides a useful method for predicting a species, future distribution under a given climate change scenario. However, these models require verification with empirical evidence, including physiological information. Endotherm species (such as birds) have a thermal neutral zone (TNZ) which reflects the range of environmental temperatures over which minimal energy is required for thermoregulation. At temperatures above the TNZ, birds expend extra energy to facilitate evaporative water loss in order to maintain a stable body temperature, while some species increase their body temperature to conserve water. The increased costs of thermoregulation at temperatures above the TNZ can impair fitness, which could have implications for population persistence under climate change. The Fynbos biome of South Africa is a biodiversity hotspot and is home to a rich birdlife, including six endemic bird species. Climate change models predict an increase in temperature for this biome, which may alter the ranges of many of these species, resulting in a loss of species richness and diversity. Recent MaxEnt bioclimatic envelope modelling suggests that some Fynbos bird species may be range-restricted by temperature, while others are more likely limited by other bioclimatic variables (e.g. rainfall). These data require physiological verification.

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