PARENT SESSION
Oral Session #70: Invasive Species: Aquatic.
Presiding: S. Juliano
Wednesday, August 7. 1:00 PM to 4:45 PM. Grand Ballroom East, Radisson.
An emergent multiple predator effect may cause biotic resistance to invasion of a stream fish assemblage.
Harvey, Bret*,1, White, Jason1, Nakamoto, Rodney1, 1 USDA Forest Service, Arcata, CA 95521
ABSTRACT- The Eel River in northwestern California contains about 30 fish species, half of them introduced. Among the introduced species are three cyprinids native to other parts of California. While the correspondence between habitat requirements and habitat availability in the Eel Drainage appears equally strong for all three species, their invasions of the drainage vary dramatically in spatial extent. This study tested the hypothesis that the introduced cyprinid with the most restricted range in the drainage, speckled dace (Rhinichthys ocsulus), is limited by biotic interactions mediated by the availability of benthic cover. An artificial stream experiment revealed an emergent multiple predator effect on the survival of speckled dace when faced with both native (sculpin, Cottus spp.) and non-native (Sacramento pikeminnow, Ptychocheilus grandis) predators, but also suggested that the amount of benthic cover did not strongly influence this outcome. In 1-d trials, mortality of speckled dace in the presence of both predators averaged 82%, while the two predators separately caused 25 and 31% mortality. One likely explanation for this result is a lack of predator-free space for speckled dace in the presence of both sculpins and Sacramento pikeminnow. This apparent example of biotic resistance to invasion occurs in a lotic fish assemblage with few resident species, and suggests that the order of arrival of introduced fishes has influenced the composition of invaded assemblages at the drainage scale.
KEY WORDS: stream fishes, multiple predator effects, invasion resistance, cyprinidae