Current Distribution of the Introduced Largespring Gambusia,Gambusia geiseri, In Texas

Abstract

The largespring gambusia (Gambusia geiseri) is a livebearing fish likely endemic to the headwaters of the San Marcos River. This species thrives in cool headwater springs and, as a result of introductions for mosquito control, may now be invasive in many springs throughout Texas. Gambusia geiseri is believed to be outcompeting its endangered congener, G. nobilis, in the San Solomon Spring in western Texas and may be a threat to other endemic, spring-dwelling Gambusia. Thus, it is important to understand its current distribution. Approximately 15 years ago, the distribution of G. geiseri was documented through much of its range; however, many sites where G. geiseri occurs presently were not explored or were previously unknown. Therefore, to update the current distribution of this species in Texas, all sites previously documented, in addition to several other sites where G. geiseri now persists, were revisited. We present updated results for the distribution of G. geiseri in Texas and also provide estimates of the size of the population at each locale.