Date of Award

2-2010

Degree Name

MS in Biological Sciences

Department

Biological Sciences

Advisor

Royden Nakamura

Abstract

Alien fish have been implicated in the decline of Rana draytonii (California red-legged frog) and Pseudacris regilla (Pacific treefrog) populations. Micropterus salmoides (largemouth bass) is a common sport fish that has been introduced into the sympatric range of these two anuran species; however, no studies have investigated the individual influence that this alien fish has on these two species. I conducted M. salmoides control or eradication experiments during a four year study in two ponds within the Transverse Mountain Range of Santa Barbara County, California. Changes in the densities of all life stages of R. draytonii and P. regilla were assessed through repeated visual encounter surveys. In response to the manipulations of the M. salmoides populations there was an increase in the density of both species. For R. draytonii, this salient increase in density was recorded in the larval and metamorph life stages. For P. regilla, a slight, yet steady increase in the density of adult, metamorph, and larval life stages was recorded. My results suggest that M. salmoides can be controlled or eradicated from lentic waterbodies and provides reasonable evidence that the negative effects of this species on R. draytonii and P. regilla populations can be minimized or reversed. The reversal of these effects may translate into increases in the densities and potential recruitment of these two native anurans. Therefore, my results provide tentative support that the control or eradication of M. salmoides where they cohabitate with these two species may be a viable conservation measure for R. draytonii and P. regilla populations. Since my study was performed at a very local scale and all results are strictly observational and descriptive, additional studies should be performed at a larger spatial scale and buttressed with controlled laboratory and field enclosures experiments to identify the causal factors responsible for the identified patterns.

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