The importance of determining species sensitivity to environmental change: a tree frog example

Conservation schemes typically place species into categories, ranging roughly from rare to common or from vulnerable to least concern. Although a species may not be categorized as rare or vulnerable, it still may be sensitive to environmental change and, therefore, at risk of decline. To illustrate the importance of determining species sensitivity, we documented the relative sensitivities of four species of tree frogs, none of which have been designated particularly rare or vulnerable, to environmental change. Our research was conducted in central Florida, where prior research had suggested that Dryophytes femoralis and Dryophytes gratiosus were more sensitive to environmental change than Dryophytes cinereus and Dryophytes squirellus . A comparison of species characteristics and a field study of local abundances supported the dichotomy. Particularly, important environmental factors affecting the two more‐sensitive species adversely appear to be habitat selectivity, at a smaller scale, and nearness to the species’ southern range limits, at a larger scale. We suspected that one of the more‐sensitive species, D. gratiosus , is particularly sensitive to environmental change and that the cause is related to reproduction and/or growth. A series of laboratory analyses suggested strongly that the realized production of adults was less for D. gratiosus than for D .  femoralis . Despite their identical placement in categorization schemes, the four species exhibited substantial differences in sensitivity to environmental change. A strong case can be made that the degree of sensitivity of D. gratiosus warrants increased conservation attention for the species. Our results indicate the potential value of field work and the generation of species‐specific information in improving categorization schemes, of broadening the categorization criteria typically employed, to accommodate sensitivity to environmental change, and of considering geographical scale in categorization schemes more than is done at present.