Undergraduate Honors Theses

Thesis Defended

Spring 2016

Document Type


Type of Thesis

Departmental Honors


Ecology and Evolutionary Biology

First Advisor

Dr. Pieter Johnson

Second Advisor

Dr. Chelsea Wood

Third Advisor

Dr. Abby Hickcox

Fourth Advisor

Dr. Rebecca Safran


How changes in biodiversity affect infectious diseases remains largely unknown. As biodiversity on Earth continues to change, due both to invasive species introductions and native species losses, understanding this relationship will become increasingly important in the study of disease outbreak. Trematodes, which are parasitic flatworms with complex life cycles, offer a useful system in which to study the effects of change in biodiversity on rates of disease prevalence. Here, we used a field experiment to evaluate the effects of change in bird diversity and abundance on patterns of infections by trematode in California freshwater ecosystems. We deployed large-scale environmental manipulations designed to alter visitation rates by definitive avian hosts, either by attracting birds, deterring birds, or leaving bird behavior unchanged. We then measured the resulting bird visitation patterns through time-lapse photography. At each site, we also estimated the diversity and prevalence of trematode infections within freshwater snails, which function as the first intermediate hosts for trematodes. Our manipulations were highly effective at attracting birds, and “attractant” sites exhibited significantly higher bird abundance and richness relative to other treatments. Deterrent manipulations did not significantly reduce bird abundance and richness. Across all sites, bird richness correlated strongly with bird abundance, suggesting low levels of competition among host species, with implications for the potential of dilution in this ecosystem. Host abundance/richness were unrelated to infection prevalence, possibly owing to drought conditions at many study sites. These results suggest that large-scale manipulations can effectively alter patterns of host abundance and diversity with potential relevance for management.