Influence of Forest Canopy Cover on the Breeding Pond Distributions of Several Amphibian Species

Abstract

This study examines the influence of forest canopy cover on the breeding pond distributions of wood frogs (Rana sylvatica), leopard frogs (R pipiens), and American toads (Bufo americanus). Survey results indicated that wood frogs bred in both openand closed-canopy ponds, whereas leopard frogs and toads did not. We conducted two experiments in 1.5-m2 cages set in natural ponds to evaluate species' performance in open- and closed-canopy ponds. The first experiment was conducted in two open-canopy and two closed-canopy ponds and demonstrated that tadpole growth and survivorship for all three species were higher in open-canopy ponds. Wood frogs, however, also grew and survived well in closed-canopy ponds, whereas performance of leopard frogs and toads was very poor in closed-canopy ponds. Competition between species was asymmetrical; wood frogs affected leopard frogs, but the reverse effect was negligible. The second experiment was conducted in the two closed-canopy ponds with wood frogs and leopard frogs and indicated that food supplementation dramatically increased both survivorship and growth rate of leopard frogs. There was no effect of food addition on wood frog survivorship and a minimal effect on growth rate. Resource differences between open- and closedcanopy ponds therefore appear to have a strong influence on distributions of these species. Dissolved oxygen concentrations also were lower in closed- than in open