Evaluating the Relationship Between Free-Living Biodiversity and Disease Risk Using Experimental Manipulations:  An example from freshwater ponds of California

Summerside, Margaret R.

Undergraduate Honors Thesis

Evaluating the Relationship Between Free-Living Biodiversity and Disease Risk Using Experimental Manipulations: An example from freshwater ponds of California Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/m613mz08n

Abstract

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.

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