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Amphibians and aquatic invertebrates have complex life histories that link aquatic and terrestrial food webs. It has been suggested that amphibian reproduction is an important source of carbon to some aquatic systems. Movement of organisms across the aquatic-terrestrial habitat boundary can represent important subsidies to the receiving habitat. Subsidies are organisms, nutrients, or detritus that cross habitat boundaries and are consumed, and these allochthonous inputs can affect food web structure. Predators can alter subsidies by consuming organisms that would otherwise move across habitat boundaries. Predator induced shifts in habitat selection are a well known non-lethal effect in aquatic systems. In certain aquatic beetles, mosquitoes and frogs, the chemical cues of a predator can trigger avoidance behavior and fewer eggs are oviposited in pools. Inputs called active subsidies involve these behavioral choices of habitat selection.
We hypothesized that presence of a predator will decrease active subsidies from the terrestrial system. However, passive allochthonous inputs like leaf litter fall involuntarily and should be unaffected by predation risk. Thus predation risk should shift the relative importance of these active and passive aquatic subsidies.
Although it has been speculated that active inputs contribute a significant source of carbon and energy, our study shows that in open pool aquatic systems, passive allochthonous inputs contribute larger amounts of carbon and energy.
In this study, there is an effect of predators on habitat selection in organisms with complex life cycles, but predators are not significantly affecting overall carbon and energy inputs to mesocosms
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