Robert C. Dowler

Denning ecology in sympatric populations of skunks (Spilogale gracilis and Mephitis mephitis) in west-central Texas

Abstract We examined den-site selection patterns for western spotted skunks (Spilogale gracilis) and striped skunks (Mephitis mephitis) co-occurring in mesquite brushland of Tom Green County, Texas. Sixteen S. gracilis and 14 M. mephitis were radiocollared to locate den sites from October 2001 through June 2003. Characteristics of dens were assessed using 23 habitat variables. S. gracilis favored den sites with dense mesquite (Prosopis glandulosa), shrubs, and cacti (Opuntia), whereas M. mephitis used these areas but also more open habitats. Den habitats of S. gracilis were more uniform than were those of M. mephitis, implying that S. gracilis is more specialized in den-site selection. Both species used multiple den sites, both above and below ground, rather than a primary den. Aboveground denning occurred year-round for both species. For S. gracilis, 56% (n = 60) of dens were above ground, but denning was more common above ground in the spring and summer. Aboveground denning was more common than belowground denning for M. mephitis in all seasons, representing 64% (n = 50) of all dens. Den habitat analysis suggests that S. gracilis, unlike M. mephitis, may be limited to areas with sufficient cover, including prickly pear cactus, for denning.

Habitat use of western spotted skunks and striped skunks in Texas

Abstract Little information on foraging habitats of sympatric species of skunks in Texas, USA, is available. We compared 11 western spotted skunks (Spilogale gracilis) and 10 striped skunks (Mephitis mephitis) using radiotelemetry data to assess habitat use during foraging at broad levels of selection in a fragmented habitat. Western spotted skunks used areas with more large mesquite (Prosopis glandulosa) trees than did striped skunks and randomly selected points. Striped skunk habitat use was not different from randomly chosen locations. Contrary to previous research, both species appear to avoid agricultural habitat. A habitat management plan may be difficult to implement for striped skunks in Texas because they did not favor any available habitat. Conservation of western spotted skunks in west-central Texas should focus on areas with older mesquite trees, areas that are now often brush controlled for management of livestock.

Tapirus pinchaque (Perissodactyla: Tapiridae)

Abstract Tapirus pinchaque (Roulin, 1829), the mountain tapir, is considered the smallest and least specialized of the 4 species of Tapirus. It is restricted to parts of temperate areas from Colombia and Ecuador to extreme northwestern Peru. It is a foliage browser that generally inhabits moist habitats that facilitate bathing; however, they are frequently found in thick bush in the cold and humid zones of the Andes between 1,400 and 4,400 m. T. pinchaque, one of the rarest mammals in the world, is listed under Appendix I of the Convention on International Trade in Endangered Species of Fauna and Flora and is considered “Endangered” by the International Union for Conservation of Nature and Natural Resources.

HELMINTHS OF SYMPATRIC STRIPED, HOG-NOSED, AND SPOTTED SKUNKS IN WEST-CENTRAL TEXAS

Twenty-eight hog-nosed skunks (Conepatus leuconotus), 23 striped skunks (Mephitis mephitis), and nine spotted skunks (Spilogale gracilis) from an area of sympatry in west-central Texas were examined for helminth parasites. Shared helminth species among all three host species were one nematode (Physaloptera maxillaris), two acanthocephalans (Pachysentis canicola, Macracanthorhynchus ingens), and one cestode (Mathevotaenia mephitis). Two nematodes (Gongylonema sp. and Filaria taxidaea) occurred in both the striped and hog-nosed skunks. One nematode (Filaroides milksi) and one acanthocephalan (Oncicola canis) were collected only from C. leuconotus. The most common helminth infections for striped and hog-nosed skunks were P. maxillaris and P. canicola. Helminth species richness was highest in hog-nosed skunks, but striped skunks had the highest prevalences and intensities of all the common helminth species. The helminth fauna of spotted skunks was markedly depauperate in terms of species richness and helminth abundance compared to the other two host species. Differences in helminth communities across these three sympatric skunks may be related to differences in their relative abundance, behavior, food habits, and geographic range.

Short-distance dispersal and lack of genetic structure in an urban striped skunk population

Striped skunks (Mephitis mephitis) act as reservoirs of many zoonotic diseases and are highly adept at persisting in urbanized landscapes in high densities. A better understanding of the interaction between skunks and the urban environment can aid in the development of management approaches to disease outbreaks, as well as provide information on wildlife responses to urbanization-induced habitat fragmentation. We studied the genetic structure of a population of striped skunks in an urban environment, assessing the presence of subpopulation structuring, sex-biased philopatry, and natal habitat—biased dispersal. Analysis of microsatellite data failed to detect any significant population clustering or evidence of natal habitat—biased dispersal, but spatial autocorrelation analyses did reveal patterns of limited dispersal (< 2 km) and suggest female-biased philopatry. Our results suggest that urban habitats provide few barriers to gene flow in striped skunks.

Activity Patterns of Two Sympatric Species of Skunks (Mephitis mephitis and Spilogale gracilis) in Texas

Abstract We used radiotelemetry to document and compare activity and movement between the western spotted skunk Spilogale gracilis, and the striped skunk Mephitis mephitis in Texas. Mephitis mephitis had a higher rate of movement than S. gracilis. Both species had highest rates of movement during autumn, coinciding with dispersal of young. With the exception of summer, M. mephitis was significantly more active than S. gracilis and generally took shorter breaks during nightly activity. We documented statistical differences in activity between species for all seasons. Highest activity of one species occurred during lowest activity of the other species, which may indicate avoidance of the larger more-dominant species, M. mephitis, by S. gracilis.

Biochemical Systematics of Geomys breviceps and Two Chromosomal Races of Geomys attwateri in Eastern Texas

Ranges of Geomys attwateri and G. breviceps meet at a contact zone in eastern Texas. G. attwateri has two chromosomal races, F and G, with a diploid number of 70 but FN = 74 and 72; G. breviceps has a diploid number of 74 and FN = 72. Previous work on these species used morphological and chromosomal data to assess relationships between the species. However, questions concerning evolutionary relationships among the three forms remain unanswered. We examined allozymic data from 20 presumptive enzymatic loci for 178 individuals, including 34 chromosomal hybrids. Results indicate that there is an effective barrier to gene flow between G. attwateri and G. breviceps as indicated by presence of three fixed allelic differences. There is no apparent barrier to gene flow between the two chromosomal races of G. attwateri . Genetic exchange between the species is limited to hybrids in a narrow zone of contact. However, two pocket gophers with parental genotypes were initially identified as hybrids (based on karyotypes). Therefore, backcrossed individuals are present, but gene flow is severely restricted.

FOOD HABITS OF LONG-EARED OWLS (ASIO OTUS) AT A WINTER COMMUNAL ROOST IN TEXAS

Abstract We analyzed mammalian prey from owl pellets recovered at a winter roost of long-eared owls (Asio otus) in northwestern Irion County, Texas. Of 1,232 prey identified, the most common species were cotton rats (Sigmodon hispidus, 36%), plains harvest mice (Reithrodontomys montanus, 23%), deer mice (unidentified Peromyscus, 14%), and pygmy mice (Baiomys taylori, 10%). Approximately 80% of the biomass of the diet was the cotton rat. Other important prey were Crawfords gray shrews (Notiosorex crawfordi, 7%), hispid pocket mice (Chaetodipus hispidus, 6%), and Merriams pocket mice (Perognathus merriami, 2%). These species are rare in the reported diet of long-eared owls and represent the first information on winter food habits in Texas in the southern portion of the range of this owl. Resumen Analizamos los restos de mamíferos en egagrópilas recuperadas en un refugio invernal de búhos orejudos (Asio otus) en el noroeste del condado de Irion, Texas. De las 1,232 presas identificadas, las especies más comunes fueron las ratas de algodón (Sigmodon hispidus, 36%), ratones de llanos (Reithrodontomys montanus, 23%), ratones ciervo (Peromyscus no identificada, 14%) y ratones pigmeos norteños (Baiomys taylori, 10%). Aproximadamente el 80% de la biomasa de la dieta fue de la rata de algodón. Otras especies de presas importantes fueron la musaraña gris (Notiosorex crawfordi, 7%), el ratón de abazones crespo (Chaetodipus hispidus, 6%) y el ratón de Merriam (Perognathus merriami, 2%). Estas especies son raras en la dieta registrada de búhos orejudos y representan la primera cita de hábitos de invierno en Texas al sur de la distribución de este búho.

Genetic and Morphologic Variation in the Davis Mountains Cottontail (Sylvilagus robustus)

Abstract The Davis Mountains cottontail, Sylvilagus robustus, is an endemic species of the Trans-Pecos area of Texas. Although S. robustus previously was believed to be extirpated from the Chisos Mountains, we confirmed existence of a population. We examined intrapopulation and interpopulation variation in S. robustus, as well as the genetic relationship to the eastern cottontail (S. floridanus) using partial sequences of the mitochondrial cytochrome b and control region genes. Six morphometric traits relating to overall size and six cranial characters considered diagnostic for the two subspecies were used to confirm identification of specimens. Our morphological analysis suggested that specimens from the Chisos and Davis Mountains were S. robustus; however, low levels of genetic divergence between S. robustus and S. floridanus appeared inconsistent with species-level recognition for S. robustus.

Phylogeography of a widespread small carnivore, the western spotted skunk (Spilogale gracilis) reveals temporally variable signatures of isolation across western North America

Abstract We analyzed phylogeographic patterns in the western spotted skunk, Spilogale gracilis Merriam, 1890 (Carnivora: Mephitidae) in relation to historical events associated with Pre‐Pleistocene Divergence (PPD) and Quaternary climate change (QCC) using mitochondrial DNA from 97 individuals distributed across Western North America. Divergence times were generated using BEAST to estimate when isolation in putative refugia occurred. Patterns and timing of demographic expansion was performed using Bayesian skyline plot. Putative climatic refugia resulting from Quaternary climate change were identified using paleoecological niche modeling and divergence dates compared to major vicariant events associated with Pre‐Pleistocene conditions. We recovered three major mitochondrial clades corresponding to western North America (California, Baja, and across the Great Basin), east‐central North America (Texas, central Mexico, New Mexico), and southwestern Arizona/northwestern Mexico. Time to most recent common ancestor for S. gracilis occurred ~1.36 Ma. Divergence times for each major clade occurred between 0.25 and 0.12 Ma, with signature of population expansion occurring 0.15 and 0.10 Ma. Ecological niche models identified three potential climatic refugia during the Last Interglacial, (1) west coast of California and Oregon, (2) northwestern Mexico, and (3) southern Texas/northeastern Mexico as well as two refugia during the Last Glacial Maximum, (1) western USA and (2) southern Texas/northeastern Mexico. This study supports PPD in shaping species‐level diversity compared to QCC‐driven changes at the intraspecific level for Spilogale, similar to the patterns reported for other small mammals (e.g., rodents and bats). Phylogeographic patterns also appear to have been shaped by both habitat and river vicariance, especially across the desert southwest. Further, continuing climate change during the Holocene coupled with anthropogenic modifications during the Anthropocene appears to be removing both of these barriers to current dispersal of western spotted skunks.