|
The Mammals
of Texas - Online Edition DIVERSITY OF LAND MAMMALS There is considerable change in the diversity of Texas mammals with geography. To illustrate this, species diversity has been depicted along a series of quadrats positioned along two transects that traverse the state (one stretching in a west to east direction from El Paso to Beaumont and another beginning at Dalhart in the northern part of the state and continuing southeastward to Brownsville) (Figure 1). Species diversity exhibits a general decrease along the transect from El Paso to Beaumont (Figure 2, transect A). The lowest diversity is in the Blackland Prairies region (quadrats 12 and 13) and the highest is in the Guadalupe Mountains of the Trans-Pecos (quadrat 3). Major shifts in the diversity pattern are evident on either side of the Balcones Escarpment (between quadrats 10 and 12), and between the western portion of the Edwards Plateau (quadrat 4) and the Guadalupe Mountains in the Trans-Pecos (quadrat 3). The pattern is much more irregular, without any general trend, along the north to south transect (Figure 2, transect B). Diversity is highest in the Escarpment Breaks of the High Plains (quadrat 5), the Balcones Canyonlands of the Edwards Plateau (quadrats 10 and 11), and the subtropical brushlands of the South Texas Plains (quadrat 17). Diversity along this transect is lowest in the Rolling Plains region (quadrat 7) and the coastal sands of the South Texas Plains (quadrat 15). Species diversity can also be viewed in terms of habitat diversity and land area. To evaluate this, the diversity of Texas mammals was examined with respect to the 10 major vegetation regions in the state. Figure 3 shows the plot of the number of species in each vegetative region versus the log of the land area for that vegetative type. The regions of lowest mammalian diversity in Texas are in the eastern half of the state (Pineywoods, Gulf Prairies and Marshes, Post Oak Savannah, Blackland Prairies, and Cross Timbers region) and on the High Plains. Areas of highest mammalian diversity are in the Trans-Pecos, Edwards Plateau, South Texas Plains, and Rolling Plains. Two important generalizations are evident about the diversity of Texas mammals. First, there is no strong correlation between land area of the vegetation regions and species diversity. For example, the High Plains region is slightly larger in area than the Trans-Pecos region yet it supports only about half as many species of mammals. Second, those natural regions of Texas where vegetative and topographic heterogeneity are the greatest provide a broader spectrum of potential mammalian habitats and thus support a greater number of mammalian species. Other topics under Texas Mammals:
|
