| Description |
Anthropogenic disturbances to natural environments can create "natural experiments" that provide insight into ecological and evolutionary processes. Islands are particularly important laboratories for studying evolutionary ecology because they are home to unique communities that are particularly sensitive to disturbance. For instance, introductions of parasites and pathogens into island ecosystems can have devastating consequences for native hosts; however, they also provide a way to study the mechanisms of host defense against a novel threat. In this dissertation, I investigate the effects of human disturbance on the evolutionary ecology of birds in the Galápagos Islands. I focus on two notable ways humans have altered Galápagos ecosystems: the introduction of a parasitic nest fly, Philornis downsi, and urbanization of the town of Puerto Ayora. The majority of my dissertation examines interactions between P. downsi and Galápagos mockingbirds, an endemic Galápagos passerine. Although previous work suggested that mockingbirds are tolerant to P. downsi, I find that in years in which rainfall and food are limited, mockingbirds are much more vulnerable. These results demonstrate that tolerance is labile in hosts and requires adequate resources. In addition, I document carry-over effects of P. downsi on subsequent reproductive investment of mockingbirds. I show that parasitism can have indirect costs for hosts, as the introduction of a novel stressor can cause hosts to adjust resource allocation. The remainder of my dissertation explores potential evolutionary responses of Galápagos birds to environmental change. I focus on DNA methylation, an epigenetic marker on DNA molecules that can affect gene expression and phenotype without altering DNA sequence. I test for effects of P. downsi on DNA methylation of mockingbird nestlings, and effects of urbanization on DNA methylation of Darwin's finches. While I did not observe effects of P. downsi on methylation of mockingbird nestlings, urbanization does appear to affect methylation profiles of Darwin's finches. In summary, my work shows that Galápagos birds may often be able to respond to recent anthropogenic disturbance; however, these responses may be mediated by environmental conditions. These results have implications for the survival of wildlife populations in a rapidly changing world. |
