Direct and indirect interactions between two ranid frogs, pickerel frogs (Rana palustris) and leopard frogs (Rana pipiens)
I examined the possible role of direct and indirect interactions on the diet and habitat use of sympatric populations of Leopard frogs ('Rana pipiens') and Pickerel frogs ('Rana palustris'). To determine if 'R. palustris' and 'R. pipiens' are interacting indirectly, through the consumption of common prey, I compared the diet of 'R. pipiens' between sites where they are syntopic with 'R. palustris' and sites where they are allotopic. No evidence was found that 'R. palustris' and 'R. pipiens ' were interacting indirectly through food resources. Although the diets of 'R. pipiens' and 'R. palustris' had a high degree of overlap, there were no consistent shifts in diet when the two species were syntopic. I compared microhabitat selection by calling males of 'R. palustris ' and 'R. pipiens' between syntopic and allotopic populations to test the hypothesis of interspecific territoriality between these ecologically similar species. Calling male 'R. pipiens' and 'R. palustris ' partitioned microhabitat when syntopic. In the syntopic population, calling male 'R. palustris' shifted their micro-habitat use in a direction which reduced overlap with 'R. pipiens', whereas calling 'R. pipiens' used the same microhabitat in both allotopic and syntopic populations. Heterospecific and conspecific calls were broadcast to male 'R. palustris' and 'R. pipiens'. ' Rana palustris' responded to calls of 'R. pipiens' in the same manner as they did to conspecific calls, but 'R. pipiens ' did not respond to calls of 'R. palustris'. These differences between the two species are consistent with the hypothesis that territorial behaviour by 'R. pipiens' has a direct effect on the reproductive behaviour and habitat selection of 'R. palustris'.