A landmark four-year study of the Big Bend black bear population is in the final phase of data analysis and reporting during 2002. The study is sponsored by the National Park Service, and implemented by the U.S. Geological Survey-Biological Resources Division and Oklahoma State University.
Among aspects of bear ecology being studied is genetic characteristics of the population, with comparison to populations in northern Mexico, west Texas, and New Mexico. Analysis of mitochondrial DNA characteristics is complete. Mitochondrial DNA is maternally inherited and indicates characteristics passed from females to their male and female offspring.
The study determined the number of haplotypes (DNA indicators of substantial relatedness) in regional bear populations, and how these types are represented in the Big Bend population. The number of types represented in a given population is an indicator of genetic diversity.
The study analyzed tissue samples of 144 bears from seven different populations. Source locations were 1) Big Bend National Park, 2) Black Gap Wildlife Management Area, 3) other Trans-Pecos sites, 4) Mogollon Mountains, New Mexico, 5) Serranias del Burro, Coahuila, 6) Maderas del Carmen Mountains, Coahuila, and 7) Sierra Madre Oriental, Tamaulipas.
Of all bears studied, five haplotypes were identified. Big Bend bears included representatives of two types. Interestingly, all Big Bend females and their documented male and female offspring were of one type. Given the rarity of migration by females, this indicates the Big Bend population could be descendents from as few as one or two founder females. The same type was found only in a minority of bears from the Serranias del Burro Mountains, Coahuila. The type was not found in Maderas del Carmen, but the Maderas sample size was small, and a minority of bears from that mountain range likely share the type. Regardless, this study confirms scientifically that the female founder(s) came from Northern Coahuila, and were representatives of a minority type in those mountains. The second lineage identified in Big Bend was found only in adult males that were not offspring of resident females and were probably migrants born elsewhere.
Big Bend bears in the study were highly related. In fact, the northern Tex/Mex population includes fewer haplotypes than reported in any other regional black bear population similarly analyzed. However, this low number of types and high relatedness does not necessarily indicate poor genetic variability. The regularity of male migration between local mountain ranges, if uninterrupted in the future, should ensure good diversity in the Big Bend population. Presence in the study of adult males representing a different type from the primary Big Bend population is an indicator of such influence.Finally, the study confirms the importance of each isolated “island” population to the future of the Tex/Mex bear population as a whole. To maintain the smaller populations in Big Bend and west Texas, strong protection is required and dispersal must not be impeded by incompatible human activity. Results from this study will long into the future help the National Park Service and its partners in conservation determine whether we are successfully providing a home for bears.