Edwards Plateau Of Central Texas Research Articles

Reinterpretation of the Wisconsinan Mammalian Fauna and Paleoenvironment of the Edwards Plateau, Texas

Paleoenvironmental implications of Wisconsinan mammalian faunas of the Edwards Plateau in central Texas are reevaluated following reassignment of fossil jumping mice ( Zapus ) from Schulze Cave to the eastern species, Zapus hudsonius . In contrast to previous interpretations, influences of western alpine-meadow associations are viewed as minor, represented by only one species, Sorex vagrans . Instead, the fauna was heavily influenced by eastern mesic-adapted species that retreated north and east during post-Wisconsinan desiccation of the region.

Variation and Hybridization in Elaphe bairdi (Serpentes: Colubridae)

Variation and Hybridization in Elaphe bairdi (Serpentes: Colubridae)

Response of the Pedernales River of Central Texas to Late Holocene Climatic Change

Abstract Geomorphological investigations of modern fluvial systems are based on the premise that stream channels develop an equilibrium morphology that represents an accommodation to the relationship between the independent variables of discharge and sediment supply. Long-term changes in this relationship, often due to climatic change, result in morphological and sedimentary adjustments by the fluvial system that are commonly recorded in alluvial sedimentary sequences. The Pedernales River is a bedload-dominated stream that drains the eastern margins of the Edwards Plateau in Central Texas. In the upper third of the valley, there is a complex alluvial sequence that offers considerable insight into the long-term evolution of this largely erosional landscape. This paper is concerned with the detailed and temporally well-defined late Holocene record, and provides an example of widespread morphological and sedimentary adjustments to subtle changes in climate. Through much of the late Holocene, from ca. 4500 t...

Microsite Requirements for Germination and Establishment of Three Grass Species

The safe sites, i. e., microsite requirements for germination and establishment, were partially characterized for three of the dominant grass species of the Edwards Plateau of central Texas, Aristida longiseta, Bouteloua rigidiseta and Stipa leucotricha. Seeds were germinated and grown in field-collected soil in a greenhouse under different watering regimes and in soil-filled benches with various soil surfaces and with adult plants. Both watering regime and microsite type strongly affected germination and establishment. Litter and rocks, but not the proximity of an adult plant, increased germination, survival and growth. A safe site for these species appears to be a microsite that prevents desiccation. Differences among the species in the relative favorableness of different types of microsites were slight. Species differed more in the timing of germination. Since the timing of rainfall and of temperature fluctuations varies considerably between years in central Texas, different cohorts of seedlings, and hence different species, may be successful in different years.

Secondary Contact and Hybridization in the Texas Cave Salamanders Eurycea neotenes and E. tridentifera

Unusual levels of individual and populational variation and character discordance in three samples of troglobitic Eurycea from the Edwards Plateau of central Texas indicate hybridization between Eurycea neotenes and E. tridentifera. The two species are microsympatric but exhibit habitat segregation in one case, are contiguously allopatric in the same cave system in another, and appear to interact as vagrants in the third. E. neotenes and E. tridentifera seem to be evolving reproductive isolation at Honey Creek Cave, where hybrids are uncommon. Eurycea troglodytes and E. latitans are shown to be invalid taxa, the former consisting of a hybrid swarm of temporally variable composition and the latter being a troglobitic population of E. neotenes which episodically incorporates individuals of E. tridentifera. Variation in the interactions of the parental species on contact is ascribed to differences in the opportunity for ecological segregation permitted, the relative frequencies of incursion of the parental taxa through time, and differences in the escape behavior of intermediate and advanced troglobites in cave systems which periodically receive influxes of flood-borne epigean fish.

AN ECOLOGICAL COMPARISON OF UPLAND DECIDUOUS AND EVERGREEN FORESTS OF CENTRAL TEXAS

Scrub evergreen forests cover most of the cedar breaks region of the Edwards Plateau of central Texas; however, limited strips of deciduous forests are found on north‐facing slopes just below the limestone caprock. Dominant species occurring in the deciduous forests in descending order of importance include Quercus texana, Q. glaucoides, Juniperus ashei, Diospyros texana, Prunus serotina, Aesculus pavia, Juglans nigra, and Fraxinus texensis. Nineteen woody species were found in the deciduous forests. Forty‐eight percent of the species were exclusive to the deciduous forest community. The deciduous forests had a statistically greater number of species/stand and a higher density. The deciduous species found in the strip forests had combined relative density, dominance and importance values of 59, 93 and 72%, respectively. Dominants in the evergreen forest were J. ashei and D. texana, which had relative density, dominance, and importance values totaling 90, 97 and 93%, respectively. Total dominance was the same for both communities; however, J. ashei dominance was 20 times higher in the evergreen forests. Soils of the deciduous forests were significantly deeper and rockier. Also, these soils had higher organic contents and water retention capacities. The potential field capacity (PFC) was 3.47 times higher for the deciduous forest soils resulting in a 2.36‐fold increase in the water availability index (WAI). Factors regulating distribution and composition of the deciduous forest communities appear to be insolation and PFC, resulting in part from differences in topographic position.

Generic Boundaries in Texas Cave Salamanders, and a Redescription of Typhlomolge robusta (Amphibia: Plethodontidae)

Confusion presently surrounds the systematics of the salamanders of the genera Eurycea and Typhlomolge of the Edwards Plateau of central Texas. Existing morphological evidence is reviewed and found to be inadequate to resolve the status of the genus Typhlomolge. New data on skull morphology supports the continued recognition of this genus. The advanced troglobite Typhlomolge robusta Longley, 1978, is redescribed and shown to share the features which distinguish T. rathbuni from the Texas Eurycea. Typhlomolge rathbuni and T. robusta may be parapatric in the San Marcos Pool of the Balcones Aquifer.

Variation and Taxonomy of Aesculus pavia L. (Hippocastanaceae) in Texas

The status of Aesculus pavia var. flavescens, a set of yellow-flowered populations endemic to the Edwards Plateau of central Texas, was evaluated on the basis of comparative morphology, geography, flowering phenology, and pollination ecology. Plants of typical A. pavia have red, tubular flowers with exserted stamens and are effectively pollinated by ruby-throated hummingbirds. Plants of var. flavescens have yellow, campanulate flowers with included stamens that can be pollinated effectively by large bees. These ethological reproductive isolating mechanisms are further augmented by a difference in flowering time between the two sets of populations and by geographical restriction of the yellow-flowered plants to localities on the Edwards Plateau. The yellow and red-flowered plants constitute two morphologically distinct groups, despite evidence of limited introgression in counties along the Balcones Escarpment. A yellow-flowered plant discovered in coastal east Texas may indicate the mechanism by which var. flavescens originated, but this plant is much more closely comparable to typical red-flowered var. pavia than to the yellow-flowered plants on the Edwards Plateau. An evolutionary history of section Pavia of Aesculus is presented, and it is concluded that the yellow-flowered plants of central Texas are best regarded as a taxonomic variety.

Dynamics of Pocket Gopher Distribution on the Edwards Plateau of Texas

Two species of pocket gophers are allopatric on the Edwards Plateau of central Texas but remains of both species have been found together in late Pleisto- cene and early Recent cave faunas. Geomys bursarius texensis occupies a small range in Mason and McCulloch, and perhaps Gillespie, Counties. Thomomys bottae confinalis is found in a small area in Kimble County and a broader, separated area in Edwards and Sutton counties. Thomomys b. confinalis no longer occurs at the type locality in Kerr County. No geographic variation was found in Thomomys popula- tions from the eastern Edwards Plateau, and isolation of the populations may have been relatively recent. Populations of Thomomys seem to be expanding at this time. The present small range of Geomys b. texensis may be only a remnant of its late Pleistocene range. Study of late Pleistocene small mammal assemblages from the southern Great Plains has disclosed many instances of species that lived sympatrically then but today are allopatric (Hibbard, 1970). Over most of North America, the present geographic ranges of the smooth-toothed pocket gophers (Thomomys) and the plains pocket gopher (Geomys bursarius) are separated (Hall and Kelson, 1959). The two species have been found together in late Pleistocene fossil deposits in Kansas (Schultz, 1969), Oklahoma (Stephens, 1960) and northern Texas (Dalquest, 1965). In Texas the present geographic ranges of Thomomys bottae and Geomys bursarius are separate but approach each other closely (Fig. 1) in the central part of the state. Remains from cave deposits in this same region show that the two species were sympatric from over 10,000 years ago to some 4,000 years ago, and probably later. The present allopatry is apparently a rela- tively recent development. We have attempted to cast light on the changes in distribution of these two species by mapping the distri- bution of pocket gophers of the eastern part of the Edwards Plateau, studying geographic variation in the populations involved, and attempting to find evidence of their past distribution. PRESENT DISTRIBUTION. Vernon Bailey collected a single speci- men of smooth-toothed pocket gopher 35 mi. E of Rock Springs,

Utilization of Southwestern Bat Caves by Terrestrial Carnivores

Utilization of bat caves in the southwestern United States by terrestrial mammals was investigated. Raccoons (Procy-on lotor) and striped skunks (Me phitis mephitis) made considerable use of the caves, feeding on fallen bats at the entrances and within the caves. Ringtail cats (Bassariscus astutus), opossums (Didelphis virginianus) and other terrestrial mammals appeared to use the caves less extensively. There was evidence of raccoon denning in at least one cave. No evidence of any canids using the caves was found. INTRODUCTION Numerous reports in the literature cite incidental observations of associations between bats and other native fauna; frequently these are reports of predation on bats. Many such reports refer to reptiles (Stager, 1942; Barr and Norton, 1965; Mankins and Meyer, 1965), raptorial birds (Stager, 1941; Downing, 1961; Perry and Rogers, 1964), or other species (Martin, 1961; Elwell, 1962) feeding on bats or living in bat caves; but only a few reports refer to terrestrial carnivores' feeding on bats (Sperry, 1933; Constantine, 1967) and occasionally being seen in bat caves. This study was undertaken to learn more about the association that exists between large bat caves and native terrestrial carnivores of the southwestern United States. It seemed probable that predators seeking food might be attracted to caves, particularly during the warmer months when these caves are inhabited by large numbers of bats. In addition to providing food for the predators, the caves might also be used for shelter. MATERIALS AND METHODS The four caves studied-Bracken, James River, Ney and Davis Blowout-are multichambered caverns in limestone formations on the Edwards Plateau in central Texas. They were selected because they are known to harbor large bat populations in summer months (Davis et at., 1962). Mexican free-tailed bats (Tadarida brasiliensis mexicana) use these as nursery caves, and, between May and August, large numbers of lactating females and flightless suckling young are found in the caves. Lesser numbers of other free-tailed bats and bats of other species are frequently found in these caves during the warm months. Each cave has at least one entrance readily accessible to any terrestrial mammal. Bracken is approximately 12 miles W of New Braunfels, Comal Co., Texas. The summer bat population has 1 Rabies Control Unit, Viral Zoonoses Section, Viral Diseases Branch, Epidemiology Program, Center for Disease Control, U. S. Public Health Service, P. 0. Box 363, Lawrenceville, Georgia 30245. 2Las Cruces, New Mexico.

The Reproductive Cycle of Male White-Tailed Deer in Central Texas

A study of 50 male Texas white-tailed deer (Odocoileus virginianus) showed the reproductive cycle occurred in three phases: primary development, full production, and rest. This three-phase cycle had not been described previously. Initiation of antler growth was accompanied by partial stimulation of testicular development during the primary development phase. In the full production phase, the seminiferous tubules were stimulated further by some factor, presumably testosterone, which enabled spermatogenesis to proceed to maturity. These changes coincided with the shedding of the velvet from the antlers. Involution of the seminiferous tubules and abscision of the antlers were followed by a short period of testicular rest and were characteristic of the rest, the third phase. Peak spermatic production occurred in the latter half of November and early December. Fifty male specimens of Texas whitetailed deer from the Edwards Plateau of Texas in Mason, McCulloch, and Sutton counties, were collected to determine the normal reproductive cycle. A description of the reproductive behavior in white-tailed deer of the nearby Llano Basin has been published, but was primarily concerned with herd reproduction as determined by examination of female reproductive tracts and census data (Teer 1964). This study was designed to extend separate observations of the reproductive cycle of male deer in New York (Cheatum and Morton 1946), Massachusetts (Wislocki 1943), and southern Texas (Illige 1951). Our gratitude is expressed for the help and encouragement of Dr. C. H. Bridges, Mrs. Lucille Schultz, and R. Gardner. Additional thanks are expressed to Mrs. Dorthea Robinson for her typing skill and editorial efforts. METHODS Two male deer were collected at biweekly intervals throughout the year from September 1, 1962, to August 31, 1963, in Mason, McCulloch, and Sutton counties in the Edwards Plateau of central Texas. Immediately after collection, the deer were weighed and their ages estimated using the technique described by Severinghaus (1949). A necropsy was performed to observe the gross appearance of all organs and antler development of the deer. The testes were incised and preserved in 10 percent buffered formalin along with representative tissues of other organs. After fixation, the testes and accessory sex glands were dissected free from extraneous material and weighed. Tissue sections were cut from the testes approximately 4 mm from the incised surface, imbedded in paraffin, and sectioned at 6 microns. In the preparation of the sections for microscopic study, hematoxylin and eosin stains were routinely employed. Detailed observations of the sections were recorded and correlated with the gross appearance, testicular weights, and antler development. 1 This is a contribution of a cooperative project between the Texas Parks and Wildlife Department and the Department of Veterinary Pathology, College of Veterinary Medicine, through the Agricultural Experiment Station, Texas A & M University, supported by Pittman-Robertson Project W-90-R.