Testing the Enemy Release Hypothesis in Ungulates (Artiodactyl and Perissodactyl) and Carnivores

Lauren Kleine, a student from Colorado State University, examined the enemy release hypothesis in a project directed by Dr. Patrick Stephens and Dr. J.P. Schmidt.

Abstract:  The Enemy Release Hypothesis (ERH) predicts that invasive species will achieve greater success in non-native ranges due in part to escape from parasites found in their native ranges. The purpose of our study was to determine whether members of mammal populations occurring outside their native ranges are generally infected by fewer parasites than those from populations of the same species within their native ranges. We used the Global Mammal Parasite Database version 2.0 to investigate 39 species with entries from both inside and outside of their native ranges. For each species, Parasite Species Richness (PSR) was calculated for each species in native and non-native ranges, as well as measures of sampling effort. We used a Generalized Additive Model (GAM) of PSR as a function of sampling effort to generate residual values of PSR. Residual values were then used to test for differences in PSR in native vs. invasive ranges. In final analyses restricted to well-studied hosts, we found a significant reduction in PSR in invasive ranges. This study highlights the importance of considering sampling effort measures when comparing species richness values, and lends support to the enemy release hypothesis.

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