Functional role of an epifaunal grazer (Ampithoe valida) in eelgrass communities: A comparative study between native and invasive ranges
Date Thesis Awarded
Honors Thesis -- Access Restricted On-Campus Only
Bachelors of Science (BS)
Matthias Leu, Harmony Dalgleish
Invasive species often impact community structure and function differently in their introduced range than their native range. Understanding the mechanisms that drive the differences in ecological function of native and invasive species can provide valuable insight into the nature of trophic interactions, as well as the organization of natural communities. For example, Ampithoe valida, an epifaunal amphipod, is invasive to San Francisco Bay, California where it thrives at high densities and directly consumes eelgrass. However, in its native range of Chesapeake Bay, A. valida is found at low densities and preferentially consumes algae. This study manipulated amphipod density and source (e.g. native and introduced range), food type, and plant tissue origin in a series of experiments to determine if plant traits or animal traits are responsible for the differences in feeding patterns of A. valida across its native and invaded range. A linear mixed effects model was used to analyze the multiple-choice feeding preference experiments. This model framework is a novel and more powerful approach to analyzing food preferences as it provides a more flexible analysis than traditional methods, and accounts more rigorously for known sources of variation that traditional methods may incorrectly analyze. Contrary to expectations from field data, native A. valida consumed significantly more eelgrass than invasive A. valida under high mesograzer densities. Both native and invasive amphipods preferentially consumed eelgrass over Gracilaria spp. in the presence of conspecifics, while amphipods placed at low densities exhibited no preference for eelgrass. There was no evidence of increased palatability of Chesapeake Bay eelgrass to account for the increased consumption of eelgrass by native amphipods. However, native amphipods were significantly larger than invasive amphipods, and thus, consumption of eelgrass by native amphipods in these feeding experiments may be driven, in part, by their larger size.
Jenkins, Kathrynlynn W., "Functional role of an epifaunal grazer (Ampithoe valida) in eelgrass communities: A comparative study between native and invasive ranges" (2014). Undergraduate Honors Theses. William & Mary. Paper 38.
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