We examined the effects of the physical environment on the outcome of predatory encounters between tadpoles of the frog Rana clamitans and the fishing spider,Dolomedes triton. These species co-occur in pond habitats that vary widely in dissolved oxygen and temperature. Water temperature and oxygen levels have complex effects on the behavior of anuran larvae. Behavioral responses induced by shifting physiological requirements can increase the risk of predation on tadpoles. We experimentally manipulated treatment levels of both dissolved oxygen and temperature in trials conducted between individual predators (Dolomedes) and single prey(Rana). Environmental conditions had significant effects on the behavior of tadpoles that increased the risk of attack by Dolomedes. Under the low oxygen condition, more tadpoles were eaten, and the total amount of time spent at the surface and the number of times surfaced per minute were significantly greater. ForDolomedes, increased tadpole activity resulted in the increased expression of several predatory behaviors. We found significant treatment and interaction effects on the expression of both resting and ambush postures. In addition, survival analyses showed a significantly earlier expression of predatory behaviors in decreased oxygen level treatments.