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PeerJ. 2019 Aug 15;7:e7444. doi: 10.7717/peerj.7444. eCollection 2019.

Experimental removal of introduced slider turtles offers new insight into competition with a native, threatened turtle.

Author information

1
Department of Environmental Science, Policy, and Management, UC Berkeley, Berkeley, CA, United States of America.
2
Department of Forestry and Natural Resources, University of Kentucky, Lexington, KY, United States of America.
3
Department of Biology, University of Hawaii at Manoa, Honolulu, HI, United States of America.
4
Urban Nature Research Center & Section of Herpetology, Natural History Musem of Los Angeles County, Los Angeles, CA, United States of America.
5
Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, United States of America.
6
Biology Department, Louisiana State University, Baton Rouge, LA, United State of America.
7
Department of Ecology and Evolutionary Biology & La Kretz Center for California Conservation Science, University of California, Los Angeles, Los Angeles, CA, United States of America.

Abstract

The red-eared slider turtle (Trachemys scripta elegans; RES) is often considered one of the world's most invasive species. Results from laboratory and mesocosm experiments suggest that introduced RES outcompete native turtles for key ecological resources, but such experiments can overestimate the strength of competition. We report on the first field experiment with a wild turtle community, involving introduced RES and a declining native species of conservation concern, the western pond turtle (Emys marmorata; WPT). Using a before/after experimental design, we show that after removing most of an introduced RES population, the remaining RES dramatically shifted their spatial basking distribution in a manner consistent with strong intraspecific competition. WPT also altered their spatial basking distribution after the RES removal, but in ways inconsistent with strong interspecific competition. However, we documented reduced levels of WPT basking post-removal, which may reflect a behavioral shift attributable to the lower density of the turtle community. WPT body condition also increased after we removed RES, consistent with either indirect or direct competition between WPT and RES and providing the first evidence that RES can compete with a native turtle in the wild. We conclude that the negative impacts on WPT basking by RES in natural contexts are more limited than suggested by experiments with captive turtles, although wild WPT do appear to compete for food with introduced RES. Our results highlight the importance of manipulative field experiments when studying biological invasions, and the potential value of RES removal as a management strategy for WPT.

KEYWORDS:

Actinemys; Biological invasions; Emys marmorata; Experimental venue; Invasive species; Trachemys scripta elegans; UC Davis Arboretum; Western pond turtle

Conflict of interest statement

The authors declare there are no competing interests.

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