Project Under Construction

• Research Problem

• Biogeography

  • Some Themes in Biogeography

• Habitat Fragmentation

  • Human Causes of Habitat Fragmentation

  • The Role of Natural Disturbance Regimes

  • Effects of Habitat Fragmentation on Species Diversity

• Endangered Species

  • Endangered Species in Texas

• Biogeography and GIS

• Balcones Cayonlands National Wildlife Refuge

  • Description

  • Flora

  • Fauna
    • Golden-cheeked warbler

    • Black-capped vireo

What is habitat fragmentation and how does it affect endangered species? It is a broad question; there are untold numbers of causes and effects of habitat modification. In order to answer, we need to consider our role as geographers within the ultimate goal of species conservation. A subset of the discipline, biogeography, approaches such questions with an emphasis on the distribution of diversity on a variety of scales. We will assume the role of biogeographers for this exercise; as such, we will answer this question by identifying suitable habitat for endangered species within a study area in Central Texas, the Balcones Canyonlands National Wildlife Refuge.

More specifically, we will be identifying sites that fit habitat criteria for Golden-cheeked warblers and Black-capped vireos. It should be noted that while we cannot address all of the biological considerations for habitat preference with the given data set, we can identify to some extent those patches of vegetation that are large enough and have suitable canopy cover for either species. Color aerial photography and a digital base map showing hydrography will be provided for this analysis. In addition, students will compare their habitat assessments with sightings recorded by field biologists with differential GPS.

Biogeography is a subset of geography that deals with the distribution of plants and animals over the earth's surface and the processes which affect this distribution. A biogeographer approaches these processes on a variety of scales, from global to local. For instance, we can consider the effects of global climatic regimes (such as temperature, light, moisture and wind) on the worldwide distribution of vegetation or, alternately, we can examine these same factors found within a micro-environment, such as a desert spring. However, biogeographers examine more than just climate regimes; they also consider the influence of geomorphic factors, soil sciences, and ecosystem processes. Admittedly, each of these sub-fields is a discipline within itself. Biogeographers tend to specialize in one or more of these subjects, for each is rich in uncertainty and complexity. For our exercise, we will be "specialists" in the realm of ecological processes.

---

Ecological processes are amazingly complex. These concepts involve interactions between species, like the familiar "food-chain" theories, but also incorporate communal, symbiotic, competitive and predator/prey relationships. These relationships can occur amongst members of the same species or between groups of different species that interact within biotic communities. In addition, we can examine the interactions between organisms and several inorganic factors: water, temperature, altitude, and so on. While these are all important ecological considerations, they do not even approach the complications that arise when we think about the influence of humans on the natural world. We modify habitat. To some extent, this alteration may not be harmful to other species. However, if carried out at an unsustainable rate, habitat modification can jeopardize the well-being of untold numbers of species and communities. Because human-caused habitat alteration is rooted in our resource use, biogeographers are often called in to the politcal and economic realm. The role of a biogeographer in this case is in environmental management: how best to retain sufficient habitat for species while allowing adequate use of resources to sustain our own species? This is the question that faces anyone or any group that attempts to establish reserves or refuges for various organisms. Indeed, this is the consideration facing the Refuge in this exercise. We will examine the results of fragmentation on the habitat for endangered species.

The term "habitat fragmentation" indicates an overall decrease of some habitat type or the partitioning of habitat into smaller, more isolated parcels. Fragmentation is a complex process that we most often associate with human settlement patterns: road-building, clearing of land for agriculture and grazing, and urban encroachment. The following diagram is a typical illustration of the destruction of forest as a consequence encroaching human settlement. Notice that, rather than a landscape of total ecological destruction, the forested habitat is instead reduced to a small patchwork of remaining forest.

The most prevalent cause of habitat fragmentation has more to do with human consumption of resources than natural disturbance regimes. Our consumption of resources has risen as human populations have grown. Inversely, our efficiency of resource use has decreased. The result has been increasing exploitation of our natural resources. Through our manipulation of ecosystems, we have fragmented or completely lost vital habitat for untold numbers of species.

It should be noted that habitat fragmentation is not purely anthropomorphic in origin. Most ecosystems are periodically subject to alteration by fire, flood, wind and landslides. The effects of these disturbances may seem disastrous ecologically, but it is important to remember that these ecosystems evolved in the presence of these disturbances. Thus, they are adapted to disturbance and, in fact, may even rely on these processes for rejuvenation. Frequent disturbance is a stabilizing element in many ecosystems.

The effects of anthropogenic habitat loss or degradation on the numbers and types of species in an ecosystem are still unfolding. Some species are able to survive in a mosaic of human land uses. Others may colonise nearby suitable habitat. Certain species may persist in the leftover fragments, provided that these patches are large enough or that there are "corridors" of habitat between patches through which species can travel. If the habitat continues to be degraded or destroyed, the end result could be the extinction of species.

There are two definitions of endangered species: one biological and one legal. Biologically, an endangered species is one that, under current conditions, cannot maintain a viable population and will therefore go extinct. Extinction can occur locally, with other populations of the species existing elsewhere, or globally as the last surviving members of a species. Legally, an endangered species is one which is listed under the Endangered Species Act (1973) (ESA) as in danger of extinction "as a consequence of economic growth and development" despite "adequate concern and conservation." The difference between the two definitions is slight, but significant. Legal attention has the advantage of legal protection of the species from further modification of the environment. For more information on the Endangered Species Act itself or the applications of the ESA, please consult the on-line texts listed below:

• The full on-line text of theEndangered Species Act (1973)
• The US Fish and Wildlife Endangered Species Program provides links to further information on the Endangered Species Act, Listed and Candidate Species (including recovery plans and a review of Category 1 and Category 2 species as of August 31, 1995) and a copy of the May/June 1995 Endangered Species Bulletin. This page also has a very useful link to the University of Michigan's Endangered Species Update.

• TheEnvironmental Protection Agency Federal Register of Endangered Species access Notices (provided by the US Fish and Wildlife Service) of Receipt of Applications for permits to "conduct certain activities" with endangered species.

• Other Sites for Natural Resource and Environmental Information is a list of links is provided by Dr. Alan Fisher, the National Data Administrator for the US Fish and Wildlife Service.

---

There are 78 state and federally listed endangered species in Texas. Two of these, the Golden-cheeked warbler and the Current endangered species listings in Texas provided by the Texas Parks and Wildlife Department.
• New Releases issued by Region 2 (Southwest region) of the US Fish and Wildlife Service. This includes the text for a recent Plan Permitting Develpment in Black-Capped Vireo and Golden-Cheeked Warbler Habitat

With the introduction of GIS to the field of biogeography, we have commandeered a powerful key to understanding the natural world. Given the pertinent field data, we can display the distribution of biological elements over any given area. By applying the distribution of species and their habitats to a graphic format, we can easily and quickly define those areas which can be targeted for preservation, restoration, limited uses or further study. This technique now is being used nationwide in the Gap Analysis Project and by various environmental managers who are attempting to secure the future of endangered species. Used alone or in conjuction with other quantitative techniques, such as modeling, GIS is steadily increasing our capacity for ecological understanding. We will be using GIS in this exercise to determine areas of suitable habitat for endangered species within the Balcones Canyonlands National Wildlife Refuge, here in Central Texas.

In Central Texas, we are fortunate to have a wide variety species in a unique set of communities. However, these areas have been altered in historic time to the extent that species are disappearing. The following discussion outlines briefly one such area, the Balcones Canyonlands, and the use of digital technology in determining suitable habitat for two endangered species found within the Balcones Canyonland National Wildlife Refuge.

The Balcones Canyonlands is an ecologically diverse belt through Central Texas distinguished by steep, wooded canyons and streams along the eastern and southern regions of the Edwards Plateau. The Canyonlands support a great number and variety of species, many of which are integral members of unique biological communities. Small, localized habitats play a major role in this region's diversity; for example, there are 64 species of cave fauna within a single cave in western Travis County--this is the highest diversity of cave fauna found within the southwestern United States.

The Balcones Canyonlands National Wildlife Refuge is located in the Post Oak Ridge section of the Edwards Plateau. The Refuge was established in 1991 under the authority of the Endangered Species Act (1973), the Fish and Wildlife Act (1956, as amended) and the Land and Water Conservation Fund Act (1965, as amended). The proposed boundaries of the Refuge encompass 40,000 acres in Travis, Williamson and Burnet Counties. At present, the US Fish and Wildlife Service has acquired approximately 14,000 acres in western Travis County.

The Post Oak Ridge segment of the Edwards Plateau includes at least 1,500 plant species and over 120 native tree species. This number includes several species of endemic plants, 22 endangered plant species and several unique vegetation communities. Because this region is at the junction of the Edwards Plateau and the Lampasas Cut Plain physiographic sections, there is a diverse arrangement of hydrologic, geologic and climatic features that "blend", resulting in an unusual mosaic of species. The vegetation types can range from eastern deciduous trees to both Rocky Mountain species and Mexican neotropical species. More commonly, the vegetation communities found here include oak-juniper woodlands, post-oak-grassland savannas, mesic deciduous forests, stream bottom riparian forests, low shrub communities and communities of smallish plants (such as mosses) found in and around springs and seeps.

The Balcones Canyonlands support at least 375 species of birds, one-third of which nest in this region. 110 of these species are neotropical migrants (birds that migrate between northern breeding grounds and wintering grounds in Central and South America). Within this region, there is habitat for 55 species of mammals (including 9 neotropical migratory bat species), 70 species of reptiles and 80 species of fish. At least two of the above mentioned species are listed with the US Fish and Wildlife Service as "endangered" species under the Endangered Species Act.

---

The nesting habitat of the Golden-cheeked warbler (Dendroica chrysoparia) occurs only in Central Texas. The proposed refuge contains 9,000 acres of actual or potential warbler habitat. We will be using information on preferred vegetation types and canopy cover to determine the extent of warbler habitat within a section of the Refuge. More information is on the way soon!

---

Central Texas contains a good amount of actual or potential nesting for the black-capped vireo (Vireo atricapillus). The proposed Refuge contains at least 14,000 acres of actual or potential vireo habitat. We will be using information on preferred vegetation types and canopy cover to determine the extent of vireo habitat within a section of the Refuge. More information is on the way soon!