The role of habitat quality in shaping evolutionary dynamics, population dynamics, and conservation planning

Abstract

Understanding ecological and evolutionary consequences of variation in habitat quality is increasingly important as biologists seek to address human-mediated environmental change. I investigated effects of natural temperature variation on individual fitness and population dynamics of Drosophila melanogaster inhabiting rotting apples in orchards. I also examined how critical habitat designations have influenced recovery plans for threatened and endangered species.I exposed D. melanogaster to field temperatures in rotting apples and measured survivorship and development time. Extreme temperatures in sun-exposed apples reduced survivorship of D. melanogaster by more than 50% relative to that in shaded apples. This difference is comparable to that caused by seasonal changes in ambient temperature, and suggested that selection will target traits conferring greater heat resistance.I next conducted a 3 x 2 factorial experiment that revealed an interaction effect of ethanol and temperature variation between shaded and sun-exposed apples on development time. Adverse effects of high ethanol concentrations and extreme temperatures in sun-exposed apples mitigated one another. Expected correlation between selection for ethanol and heat resistance depends on whether this result derived from cross-induction of physiological stress responses or abiotic interactions between temperature and ethanol.To test an hypothesis that habitat heterogeneity reduces climate-induced population variability, I established populations of D. melanogaster during summer and autumn in large field cages that enclosed "landscapes" of rotting apples. I manipulated habitat heterogeneity with shade cloth to create homogeneous landscapes of either shaded or sun-exposed apples, and heterogeneous landscapes with both. Population density and growth rate varied less between summer and autumn in heterogeneous cages than in either homogeneous treatment. These results suggested that managing for habitat heterogeneity may reduce population variability and thus mitigate risks of stochastic extinction.Lastly, I examined how critical habitat designations influenced recovery plans for threatened and endangered species. Plans for species with critical habitat were not more likely than others to prescribe habitat-based recovery actions or habitat-based recovery criteria. Findings suggested that recovery plans for endangered species have not benefited from critical habitat designations and raised questions about how policies might be amended so that future recovery plans will benefit.