HABITAT PARTITIONING BY TWO CONGENERS (GAMBUSIA GEISERI AND GAMBUSIA NOBILIS) AT BALMORHEA STATE PARK, TEXAS

摘要

Three species of Gambusia occupy waters in the Pecos River System. Gambusia qffinis is widely distributed in eurythermal waters, and G. geiseri and G. nobilis occupy stenothermal spring-fed waters (Hubbs, in press). No prior published report demonstrates habitat segregation between the two stenothermal fishes. Gambusia nobilis is restricted to four spring-associated habitats in Texas and New Mexico and is listed as endangered federally and by both states. Gambusia geiseri is native to the Comal and San Marcos springs and has been introduced into west Texas presumably in the 1930s (Hubbs & Springer 1957). Because the two fishes occupy stenothermal waters, it is possible that the introduced G. geiseri negatively impacts the abundance of the native G. nobilis. The 200 x 4 x 0.5m deep Balmorhea State Park refuge canal was constructed in order to enhance the abundance of G. nobilis and the endangered (U.S. and Texas) Cyprinodon elegans. Seine status surveys have shown that C. elegans abounds in the refuge canal and that G. nobilis is often less abundant than G. geiseri. This study was undertaken to examine the relative abundance of the two species of Gambusia between environments exhibiting different configurations of aquatic vegetation (primarily Chard) by use of dip net samples.