Larval distributions of spring peepers and chorus frogs: Regulating factors and the role of larval behavior.

Abstract

Larval chorus frogs (Pseudacris triseriata) and spring peepers (P. crucifer) are distributed within ponds that range from ephemeral (dry each summer) to permanent. Across this gradient larval chorus frogs have their highest relative abundance in ephemeral ponds, while spring peepers are found alone in permanent ponds. Predators tend to be more numerous, and include larger taxa in more permanent ponds. However, there can be a large degree of variation in both time of drying and predator density between years. Within natural ponds spring peeper larvae grow and develop slower, but survive better than chorus frogs during the period between hatching and prior to metamorphosis or pond drying. Following two consecutive wet years (when few ponds dried) the relative abundance of spring peeper larvae increased. A field experiment conducted in six natural ponds demonstrated that the relative performance (e.g. survivorship, metamorphic size) of chorus frogs was highest within a temporary pond and lowest within a permanent pond. Competition among Pseudacris larvae was generally unimportant and performance was mainly influenced by pond drying and the intensity of predation, both of which varied substantially among ponds (even comparing ponds with similar drying histories). Laboratory experiments manipulating the nonlethal presence of tadpole predators and food density revealed that a behavior trait, the proportion of time spent active (activity), was associated with growth rate, while evidence from other studies suggests that activity was also associated with risk of predation (via higher rates of encounter and detection by predators). Facultative reductions in activity occurred in both species in response to predator presence and were coupled with lower growth rates. Chorus frog larvae also tended to be faster growing than spring peepers. These results suggest that interspecific differences in activity may contribute to differences in larval performance and larval distributions. The general nature of this tradeoff suggests that it may also be important in other systems.