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TR-214

Rare, Threatened and Endangered Species of the Rio Grande/Rio Bravo Basin: A Bibliography

Karine Gil, Neal Wilkins

The Rio Grande/Rio Bravo Basin drains some of the harshest terrain in North America. The river and its tributaries are major drainages for the plateau shrub lands of central New Mexico, the Chihuahuan Desert and the Tamaulipan Mezquital. The Chihuahuan Desert of New Mexico, Texas and Mexico ranks as the world’s most biologically diverse desert ecoregion, supporting a species richness of more than 100 mammals, 250 birds, 100 reptiles and 20 amphibians (Ricketts et al. 1999). Likewise, the Tamaulipan Mezquital of South Texas and adjacent Mexico is considered one of the "last great habitats" in North America due its unique biological resources (Fulbright and Bryant 2002).

Over time, native plants and animals in the regions surrounding the Rio Grande have adapted to extreme cycles of prolonged drought, flood, repeated fires and the recurrent pressures of large grazing animals. As a consequence, many species have developed specialized strategies for enduring these environmental pressures. Often, it is the most specialized of these species that becomes endangered with extinction when the historical cycles of drought, flood, fire and grazing are abruptly altered. Likewise, many of these species are not able to readily adapt to habitat changes or the highly modified environments that can develop with the introduction of non-native species.

Although it maintains a significant biological value, much of the Rio Grande/Rio Bravo Basin is highly degraded when compared to its condition of 50 to 100 years ago (Ricketts et al 1999). Human impacts from water diversion, changing land use, urbanization and the introduction of non-native species inevitably impacts some native plants and animals, and the ecosystems upon which they depend. As a result, some species are in danger of extinction and become the subject of conservation concern. Technically, under the US Federal Endangered Species Act (ESA), those species listed as "endangered" are considered to be in danger of extinction throughout all, or a major portion, of their range. A "threatened" species is considered likely to become endangered in the foreseeable future. Under state endangered species acts, the designations are similar, except that the focus tends to be on the species’ status within the boundaries of the state.

Because of the complicated administrative process often involved in listing endangered and threatened species under the ESA (and sometimes under the corresponding state acts), the numbers of threatened or endangered species do not always reflect the overall condition of a region’s biological resources. However, those trends that consistently lead to “endangered” or “threatened” designations may highlight ecosystems at risk of loosing substantial biological diversity. We offer the following work partly for the purpose of exploring and discovering those trends.

The purpose of this publication is to provide an easily-accessible reference to the scientific information on those species listed as endangered or threatened under the federal ESA or a similar state process. This bibliography includes references, annotations, and Internet citations for more than 400 sources of scientific information for 181 species of threatened or endangered concern in the Rio Grande/Rio Bravo Basin. This publication and its searchable database are a significant starting point for planners and those conducting environmental assessments, as well as students and researchers interested in rapidly accessing and reviewing scientific literature.

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