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Effects of introduced trout on ecosytem subsidy and amphibian decline.

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Adjacent communities can be linked by fluxes of nutrients and prey across habitat boundaries. A predator introduced into one community could affect the ecosystem subsidy entering another community if the predator has large impacts on its community structure. Sport fish have been introduced to thousands of formerly fishless lakes worldwide and these introductions have been Adjacent communities can be linked by fluxes of nutrients and prey across habitat boundaries. A predator introduced into one community could affect the ecosystem subsidy entering another community if the predator has large impacts on its community structure. Sport fish have been introduced to thousands of formerly fishless lakes worldwide and these introductions have been implicated in altering native aquatic biota. Changes in the aquatic community structure could indirectly affect terrestrial predators that feed on aquatic prey. My goals were to (1) understand the consequences of trout introductions on native aquatic fauna, (2) quantify the effects of fish on aquatic insect subsidy from lakes to the terrestrial landscape, and (3) explore the indirect consequences of fish stocking on vertebrate predators inhabiting terrestrial habitats. I conducted a 4-year whole-lake replicated experiment to test the effects of introduced trout at scales relevant to the ecosystem subsidy of lake basins. Twelve lakes subject to three different fish treatments (continued fish stocking, cessation of stocking, and fish removal) were compared to four fishless reference lakes. Pre-treatment data were collected in 2003 and post-treatment surveys were conducted in 2004-2006. From June-September, crews sampled the 16 study lakes every two weeks. Amphibians and snakes were monitored via visual surveys and mark-recapture and aquatic insects were sampled using benthic sweeps and emergence traps. Densities of Cascades frogs (Rana cascadae) increased dramatically in the fish removal lakes and were comparable to reference lakes by 2006. Survival and recruitment of adult frogs increased significantly following fish removals, but remained low at the fish-containing lakes. Large-bodied emerging insect biomass and abundance increased in the fish removal lakes following fish removals. Fish density was a more important predictor of emerging aquatic insect abundance than habitat variables. Trout also affected amphibians indirectly through snake predation. Analyses of the diet, distribution and density of two sympatric garter snake species revealed that trout introductions likely facilitated the geographic expansion of Thamnophis atratus , an opportunistic fish and amphibian predator, by providing consistent alternative prey. In conclusion, fish introductions modify the structure of adjacent aquatic and terrestrial communities by affecting both aquatic prey and terrestrial predators.


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Adjacent communities can be linked by fluxes of nutrients and prey across habitat boundaries. A predator introduced into one community could affect the ecosystem subsidy entering another community if the predator has large impacts on its community structure. Sport fish have been introduced to thousands of formerly fishless lakes worldwide and these introductions have been Adjacent communities can be linked by fluxes of nutrients and prey across habitat boundaries. A predator introduced into one community could affect the ecosystem subsidy entering another community if the predator has large impacts on its community structure. Sport fish have been introduced to thousands of formerly fishless lakes worldwide and these introductions have been implicated in altering native aquatic biota. Changes in the aquatic community structure could indirectly affect terrestrial predators that feed on aquatic prey. My goals were to (1) understand the consequences of trout introductions on native aquatic fauna, (2) quantify the effects of fish on aquatic insect subsidy from lakes to the terrestrial landscape, and (3) explore the indirect consequences of fish stocking on vertebrate predators inhabiting terrestrial habitats. I conducted a 4-year whole-lake replicated experiment to test the effects of introduced trout at scales relevant to the ecosystem subsidy of lake basins. Twelve lakes subject to three different fish treatments (continued fish stocking, cessation of stocking, and fish removal) were compared to four fishless reference lakes. Pre-treatment data were collected in 2003 and post-treatment surveys were conducted in 2004-2006. From June-September, crews sampled the 16 study lakes every two weeks. Amphibians and snakes were monitored via visual surveys and mark-recapture and aquatic insects were sampled using benthic sweeps and emergence traps. Densities of Cascades frogs (Rana cascadae) increased dramatically in the fish removal lakes and were comparable to reference lakes by 2006. Survival and recruitment of adult frogs increased significantly following fish removals, but remained low at the fish-containing lakes. Large-bodied emerging insect biomass and abundance increased in the fish removal lakes following fish removals. Fish density was a more important predictor of emerging aquatic insect abundance than habitat variables. Trout also affected amphibians indirectly through snake predation. Analyses of the diet, distribution and density of two sympatric garter snake species revealed that trout introductions likely facilitated the geographic expansion of Thamnophis atratus , an opportunistic fish and amphibian predator, by providing consistent alternative prey. In conclusion, fish introductions modify the structure of adjacent aquatic and terrestrial communities by affecting both aquatic prey and terrestrial predators.

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