Natural History of an Introduced Population of Squirrel Treefrogs (Hyla squirella) on the Delmarva Peninsula

Hyla squirella was not known to occur on Delmarva until an established population was discovered at the southernmost tip of the peninsula in the Eastern Shore of Virginia Natural Wildlife Refuge in 2005. Male vocalizations were heard periodically throughout the refuge during daytime and evening hours from 27 May to 7 September 2006. Large choruses of males were heard 27 May and 9 and 27 June 2006. A large breeding event was observed on 9 June in a temporary pond. The smallest mature male was 27 mm SVL and weighed 1.1 g and the smallest mature female was 31 mm SVL, 1.7 g, and gravid. Mean adult male SVL was significantly smaller than the mean for adult females. Metamorphs found on 19 October averaged 13.0 ± 0.21 mm SVL and weighed 0.164 ± 0.009 g. Ecological and life history parameters of the introduced population of H. squirella on Delmarva do not appear to differ from those of populations in the natural portion of its range. This established population offers opportunities to elucidate a variety of questions about northward range expansion, genetics, and tolerance limits.

Inter-signal interaction and uncertain information in anuran multimodal signals

Disentangling the influence of multiple signal components on receivers and elucidating general processes influencing complex signal evolution are difficult tasks. In this study we test mate preferences of female squirrel treefrogs Hyla squirella and female túngara frogs Physalaemus pustulosus for similar combinations of acoustic and visual components of their multimodal courtship signals. In a two-choice playback experiment with squirrel treefrogs, the visual stimulus of a male model significantly increased the attractivness of a relatively unattractive slow call rate. A previous study demonstrated that faster call rates are more attractive to female squirrel treefrogs, and all else being equal, models of male frogs with large body stripes are more attractive. In a similar experiment with female túngara frogs, the visual stimulus of a robotic frog failed to increase the attractiveness of a relatively unattractive call. Females also showed no preference for the distinct stripe on the robot that males commonly bear on their throat. Thus, features of conspicuous signal components such as body stripes are not universally important and signal function is likely to differ even among species with similar ecologies and communication systems. Finally, we discuss the putative information content of anuran signals and suggest that the categorization of redundant versus multiple messages may not be sufficient as a general explanation for the evolution of multimodal signaling. Instead of relying on untested assumptions concerning the information content of signals, we discuss the value of initially collecting comparative empirical data sets related to receiver responses.

Pond hydroperiod alters the effect of density-dependent processes on larval anurans

Many studies examine how changes (disturbances) to the abiotic environment alter the intensity of species interactions by directly changing the numbers of individuals involved in the interaction but few studies examine how the abiotic environment affects how strongly individuals interact with each other. We conducted an experiment to evaluate how pond hydroperiod affected the ability of two larval anuran species ( Hyla squirella and Bufo terrestris ) to interact with intraspecific and interspecific competitors. Pond hydroperiod altered how an increase in the abundance of intraspecific competitors affected fitness components of B. terrestris but not for H. squirella. Specifically, an increase in intraspecific abundance caused a reduction in B. terrestris survivorship in short hydroperiod ponds but had no effect on fitness components of B. terrestris in long hydroperiod ponds. Interspecific competition did not occur between these species in either short or long hydroperiod ponds. Our study highlights the point that the strength of density-dependent processes operating in the aquatic environment can depend on pond hydroperiod. Consequently, the extent to which processes operating in the aquatic environment contribute to the regulation of population and metapopulation size for amphibians will also likely depend on pond hydroperiod.