Amphibian Declines: The Conservation Status of United States Species

Introduction

351 regional analyses (many works), taxonomically specialized (e.g., Bishop, 1943; Wright and Wright, 1949; Petranka, 1998), or incomplete (Catalogue of American Amphibians and Reptiles, Society for the Study of Amphibians and Reptiles, St. Louis, Missouri). Stebbins and Cohen (1995) do a masterful job of summarizing the highlights of amphibian life history and natural history features, but they illustrate their points using examples (rather than lists) of species that exhibit particular traits (as they must in this successful effort to provide a popular account). 2. The detailed species accounts that do exist tend to be written as narratives. Our goal was to make this information easily accessible; therefore, we organized life history, natural history, and status data into a standardized outline format. 3. Our species accounts were written or reviewed by experts on the species. 4. Species account entries are backed by references to the scientific literature, references to unpublished data, or personal communications. 5. Species accounts document not only what is known, but also indicate what we do not know about a species. By noting these information gaps, we hope to encourage future research in these areas. Collectively, our goal from using this approach coupled with our maps is to establish a foundation of facts. In the tradition of the classic North American amphibian species accounts (Bishop, 1943, for salamanders; Wright and Wright, 1949, for frogs and toads), we tie these accounts together with a considered introduction. In particular, we present here a preliminary comparison of amphibian distributions with distributions of pertinent environmental features. We also consider the distribution patterns of a number of important life history and natural history features, such as terrestrial versus aquatic development and types of aquatic development, and then supplement this analysis with data presented in tabular form. We employ an ecoregion framework to help us interpret these distribution patterns, relying not only on the mapped regional boundaries but also on an understanding of Worldwide reports of amphibian population declines and malformations prompt concern about species protection. At this point in time in the United States, we recognize 289 extant amphibian species: 103 species of frogs and 186 species of salamanders (Appendix IN-A), although the identity and relationships of species in several genera remain unresolved. Amphibians occur in nearly all habitats, and they exhibit variations in life history and natural history features that enable them to accommodate a wide range of environmental conditions (Duellman, 1999; Zug et al., 2001; Pough et al., 2004). Some species are entirely aquatic, while others spend their complete life cycles in trees or in caves. For most species, however , very little is known, and much of what we do know comes from breeding season observations. Even so, there are still species for which eggs have never been seen, so we have no idea of typical clutch size or location, and for species observed only during the breeding season, their habitat requirements at other times of the year remain unknown. With so little information available about basic species life history and natural history traits, and with some species being inaccessible for monitoring, how do we begin to manage for amphibians? And, if we cannot address important management issues, how can we hope to address conservation issues? Our objective was to develop a toolbox for managers. This toolbox consists of species accounts (the work that follows and forms the bulk of this volume) and a new digital database that links each species with geospatially referenced units. With these tools, it is possible to map distribution patterns for individual species as well as for groups of species sharing common phylogenetic , life history, ecological, or behavioral traits as revealed in the following species accounts. This digital database can be easily imported into a geographic information system (GIS) to generate such maps, as we have done here. This technology provides the means for readily viewing patterns that once were prohibitively labor intensive. The species accounts were assembled by experts and compiled in a standardized, outline format. Our rationale for compiling accounts in this manner is as follows. 1. No detailed accounts for all U.S. species currently exist. Current accounts are either unreferenced or lightly referenced summaries (e.g., Stebbins, 1985; Behler and King, 1998; Conant and Collins, 1998), based on state or Introduction MICHAEL LANNOO, ALISA L. GALLANT, PRIYA NANJAPPA, LAURA BLACKBURN, AND RUSSELL HENDRICKS 352 PART TWO, INTRODUCTION the environmental characteristics that define each ecoregion. We conclude by demonstrating how to use the toolbox with an example of an application focused...