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OF ECOLOGY SMALL MAMMALS IN THE NORTHERN CHIHUAHUAN DESERT by MELINDA L. CLARY, B.S. A THESIS IN BIOLOGY Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Accepted December, 2000 ACKNOWLEDGEMENTS Funding for this project was provided by a Department of Defense grant (MIPR W52EU251606913) administered by William Whitworth at USACERL. I would like to thank Donna J. Howell and Brian Locke who were Directorates of the Environment at the Fort Bliss Military Base for their direction and assistance in this study. I would also like to thank additional personnel at Fort Bliss Military Base (Kelly Fischer, Shane Offut, Will Roach, and Keith Landreth), as well as the Davis Dome staff for assistance during this project. I would like to acknowledge the New Mexico Department of Game and Fish for issuing a scientific collecting permit (# 2865). I also thank Darin Bell, Darin Carroll, Cody Edwards, Kristina Halcomb, Ted Jolley, Oleksiy Knyazhnitskiy, Nicole LewisOritt, Stacy Mantooth, Roslyn Martinez, Cole Matson, Anton Nekrutenko, Mark O'Neill, Lottie Peppers, Dr. Calvin Porter, Heather Roberts, Brenda Rodgers, Irene Tiemann-Boege, Jeff Wickliffe, and Dr. Frank Yancey II, for assistance in collection and preparation of specimens. Jody Martin and Nick Parker of the Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, provided important administrative support during this study. I would like to acknowledge my committee members Drs. Robert D. Bradley, Robert J. Baker, and Clyde Jones for their direction and encouragement throughout my graduate career. I would especially like to thank my major advisor Dr. Robert D. Bradley 11 for his patience and guidance throughout the many stages of this project. I am grateful to Dr. Richard E. Strauss for his everlasting enthusiasm and patience while providing direction and insight on the statistical analyses generated in this study. I would also like to express sincere gratitude to President David Schmidly for his constant positive encouragement in m>' endeavors. I would like to thank my colleagues Kristina Halcomb, Amy Halter, Nicole LewisOritt, Francisca Mendez-Harclerode, and Marcia Revelez for their advice and support through not only the technical aspects of the project, but also through the difficult times of my career. I would especially like to thank Darin Carroll and Cody Edwards who have stood by me since the beginning of my degree. I am grateful to them for their professional assistance in this project, as well as for their constant encouragement always forcing me to smile. Their presence in my career has been invaluable. A special thanks to my parents Ron and Carlita Clary and sister Jeana Clary for their ever-present love and motivation which encouraged me to pursue this degree. I would never have made it this far without them. m TABLE OF CONTENTS ACKNOWLEDGEMENTS ABSTRACT LIST OF TABLES LIST OF FIGURES CHAPTER I. INTRODUCTION ii v vii viii 1 II. A CHECKLIST OF MAMMALS FROM TWELVE HABITAT TYPES AT FORT BLISS MILITARY BASE, 1997-1998 III. SMALL MAMMAL COMMUNITIES AND HABITAT ASSOCIATIONS IN THE CHIHUAHUAN DESERT IV. SUMMARY APPENDIX: MATLAB FUNCTIONS 7 40 74 78 IV ABSTRACT Fort Bliss Military Base, located in Dona Aiia and Otero counties, New Mexico and El Paso County, Texas, is within the northern limits of the Chihuahuan Desert. A small mammal survey was conducted biannually from Spring 1997 to Fall 1998 on twelve vegetatively distinct habitats. Each habitat contained two duplicate grids constructed with census and assessments lines as a modification of O'Farrell's method (1977) and sampled using Sherman live-traps. Sampling generally occurred on two periods of three consecutive nights (one for census lines and one for assessment lines) for a total of 35,136 trap nights. The data obtained from this project (number of captures, traps of capture, species, etc.) will be used to determine the status of rodent communities within the twelve habitats. Analyses utilizing the obtained data include: relative abundance of each species; species diversity per habitat and season; species composition per habitat (rodent community assemblages); rodent density per habitat (number of captured individuals/hectare); survivability of each species (proportion of individuals recaptured at a given time); and movement of each species (mean squared deviations from the centroid of activity). During the study, 2,091 individuals (19 species) were captured. Diversity was highest in the sandy arroyo scrub habitat (Simpson's = 0.8859) and lowest in the coppice dune habitat (Simpson's = 0.4120). On the basis of species composition, all grassland habitats grouped together with a bootstrap support value of 58% and the acacia hillside and sand) an'oyo scrub habitats clustered with a value of 85%. Rodent density was highest in the swale habitat (39.16 individuals/ha) and lowest in the coppice dune habitat (9.95 individuals/ha). Heterom\ ids displa\ ed the greatest longe\'it>' with six species surviving through the 18-month stud)' period. Onychomys leucogaster had the highest a\ erage movement (4.59 mean squared deviations-MSD) and Sigmodon hispidus had the lowest average movement (2.43 MSD). Results from this study provide baseline information concerning small mammals of the Chihuahuan Desert. In addition, these data provide military personnel with the necessary information to make decisions concerning the possible impact of military activity on small mammal communities. VI LIST OF TABLES 2.1 2.2 Description of the 12 habitats sampled in this study Number of males and females obtained from each census line sampled in the Spring 1997 Number of males and females obtained from each census line sampled in the Fall 1997 Number of males and females obtained from each census line sampled in the Spring 1998 Number of males and females obtained from each census line sampled in the Fall 1998 Number of males and females obtained from each census line sampled during all four trapping seasons Average rainfall (mm) per season for each of the twelve habitats on Fort Bliss Military Base The Simpson's diversity index (Simpson, 1949) was used to determine species diversity per season for each of the 12 habitats on Fort Bliss Military Base 26 29 2.3 31 2.4 33 2.5 35 2.6 37 3.1 59 3.2 61 vu LIST OF FIGURES 2.1 3.1 3.2 3.3 Map of Fort Bliss Military Base Photographs of the 12 habitats on Fort Bliss Military Base Example of the grid system utilized in this study A grid point-coordinate system was used to determine small mammal movements Rainfall patterns for each habitat on Fort Bliss Military Base Species diversity values per habitat and season compared to seasonal rainfall averages A cluster analysis depicting habitats that grouped together based on similarities of rodent species composition Rodent density, defined as the number of captures per hectare, for each of the four trapping periods at Fort Bliss Military Base Survivorship for each species based on percentages of recaptures taken from the total initial captures at 6, 12, and 18 months Survivorship rate (1 - the exponential rate of decline) of small mammal species 39 62 64 65 66 3.4 3.5 67 3.6 68 3.7 69 3.8 70 3.9 71 3.10 Average species movements depicted as the mean squared deviation from the centroid of activity for each species (p = < 0.001) 72 Average movements depicted per habitat as the mean squared deviations from the centroid of activity to each trap station of capture (p = 0.002) 3.11 73 Vlll CHAPTER 1 INTRODUCTION This thesis provides ecological information of small mammals that serves as baseline data for a large-scale study on Fort Bliss Military Base. In 1996, Dr. Donna J. Howell, Directorate of the Environment at Fort Bliss Military Base, contacted Drs. Robert J. Baker and Robert D. Bradley of the Department of Biological Sciences at Texas Tech University regarding their acceptance as Pi's on Research Work Order (RWO) #25 "Small Mammal and Reptile Abundance, Diversity, and Associations with Habitat on the McGregor Range, Fort BHss." Dr. Howell served as supervisor of this research project and the Pi's were to follow her experimental design, which was already in place prior to the PFs involvement. Eight students were identified to form the core of the research team and trained in identification of rodent species likely to occur in the Fort Bliss region. Actual collecting times were scheduled for Spring 1997, Fall 1997, Spring 1998, and Fall 1998. Dr. Brian Locke replaced Dr. Howell in the final stages of the project. Despite studies previously conducted on Fort Bliss Military Base concerning the status of small mammals (Jorgensen, 1996; Jorgensen and Demarais, 1996; Root, 1997; Weeks, 1997), few studies are available for comparing mammal species among and between different habitat types. Such a study is necessary to provide information about each habitat for Fort Bliss Military Base personnel to consider when planning military training activities. Training operations in military areas have the potential to alter floral and faunal habitats. Such activities have been shown to affect ecosystem stability (Baumgardner, 1990; Brattstrom and Bondello, 1983; Carroll et al., 1999; Edwards et al., 1998; Gese et al., 1989; Shaw and Diersing, 1990; and Stephenson et al., 1996) and therefore should be considered when planning military operations. Due to the steady increase in human populations and urbanization of surrounding public lands, it is becoming necessar) for military personnel to ecologically manage the acres of non-de\'eloped land on their properties in order to preserve areas for existing wildlife. The information for small mammals pro\ided by this project at Fort Bliss Military Base (identifying habitats of high diversity, presence of rare species, etc.) will be used to develop resource management methods (avoiding areas of high rodent diversity, density, etc.) while incorporating the need for military training activities. This project's study area was located in the northern regions of the Chihuahuan Desert within the Tularosa Basin and is typified by lowland valleys, rocky hillsides, and scattered arroyos (Jorgensen, 1996; Monasmith, 1997). The desert fauna within this region experience unpredictable fluctuations in climatic conditions and amount of precipitation. Regardless, many species manage to maintain relatively stable populations in these adverse conditions (Zeng and Brown, 1987). The Chihuahuan Desert is one of the most diverse areas for small mammals (Schmidly, 1974; Brown and Zeng, 1989; Zeng and Brown, 1987; Kotler and Brown, 1988). The region has extraordinarily diverse flora and fauna. Eight orders, 24 families, 60 genera, and approximately 119 species of mammals inhabit this desert (Schmidly, 1974). The second chapter of this thesis represents the following publication: Clary, M. L., D. M. Bell, C. W. Edwards, T. W. Jolley, O. Knyazhnitskiy, N. Lewis-Oritt, S. J. Mantooth, L. L. Peppers, I. Tiemann-Boege, F. D. Yancey, II, D. J. Howell. B. A. Locke, R. J. Baker, and R. D. Bradley. 1999. Checklist of Mammals from Twelve Habitat Types at Fort Bliss Military Base; 1997-1998. Occasional Papers Museum, Texas Tech University. 192: / + 1-16. The author line for this publication includes all field crew members who served on the project for two or more seasons, the project supervisor, and the project Pi's. Included in this chapter is a descriptive list of small mammal species accounts on Fort Bliss Military Base in addition to tables presenting the relative abundance of each species. Descriptions of the 12 distinct habitats are provided. The third chapter represents the following manuscript being prepared for publication: Clary, M. L., R. E. Strauss, R. J. Baker, and R. D. Bradley. Small Mammal Communities and Habitat Associations in the Chihuahuan Desert. In prep. This chapter includes various ecological analyses of the Fort Bliss Military Base rodent communities including community diversity, composition, density, species survivorship, and movement. Each analysis was compared among all habitats and seasons. The fourth chapter consists of recommendations for future work on Fort Bliss Military Base. These recommendations were based on the results obtained from the analyses utilized in Chapter III. The primary objective for this study was to identify the species of small mammals present on the base. Once this was achieved, the species density and diversity of each of the 12 habitats was determined. The results from these ecological parameters were compared among the habitats to decipher which habitats are the most fragile (i.e., low species diversity and density values). These fragile habitats were recognized as areas of avoidance for military activities. Through this avoidance, the biodiversity of ecosystems present at Fort Bliss Military Base may be preserved. Literature Cited Baumgardner, G. D. 1990. Mammal surveys on land condition trend plots at Fort Hood Texas. Unpublished report for U. S. Army Construction Engineering Research Lab. Department of Wildlife & Fisheries Sciences, Texas A&M University, College Station, TX, 136pp. Brattstrom, B. H. and M. C. Bondello. 1983. Effects of off-road vehicle noise on desert vertebrates. Pages 167-206 in Enviromiiental effects of off-road vehicles; impacts and management in arid areas (R. H. Webb and H. G. Wilshire, eds.). SpringerVerlag, New York, N.Y. Brown, J. H. and Z. Zeng. 1989. Comparative population ecology of eleven species of rodents in the Chihuahuan Desert. Ecology. 70:1507-1525. Carroll, D. S., R. C. Dowler, and C. W. Edwards. 1999. Estimates of relative abundance of the medium-sized mammals of Fort Hood, Texas, using scent-station visitation. Occasional Papers, Museum, Texas Tech University, 188:1-10. Edwards, C. W., R. C. Dowler, and D. S. Can-oil. 1998. Assessing medium-sized mammal abundance at Fort Hood military installation using live-trapping and spotlight counts. Occasional Papers, Museum, Texas Tech University, 185:1-23. Gese, E. M., O. J. Rongstad, and W. R. Mytton. 1989. Change in coyote movements due to mihtary activity. Journal of Wildlife Management, 53:334-339. Jorgensen, E, E. 1996. Small mammal and herpetofauna communities and habitat associations in foothills of the Chihuahuan Desert. Unpublished Ph. D. dissertation, Texas Tech University, Lubbock, TX. Jorgensen, E. E. and S. Demarais. 1996. Final Report; Small mammal and herpetofauna habitat associations and communities on the McGregor Range, Fort Bliss; Sacramento Mountain foothills. Directorate of Environment, Fort Bliss, El Paso, Texas. 197 pp. Monasmith, T. J. 1997. Fire effects on small mammals and vegetation of the northern Chihuahuan Desert. Unpublished Master's thesis, Texas Tech University, Lubbock, Texas. Root, J. J. 1997. Microsite and habitat boundary influences on small mammal capture, diversity, and movements. Master's Thesis, Texas Tech University, Lubbock, Texas. Schmidly, D. J. 1974. Factors governing the distribution of mammals in the Chihuahuan Desert region. Pp. 163-192 in Transactions of the Symposium on the Biological Resources of the Chihuahuan Desert region United States and Mexico (D. H. Riskind and R. H. Wauer, eds.). Sul Ross State University, Alpine, TX. Schmidt, R. H. 1986. Chihuahuan climate. Pp. 40-63 in Second Symposium on resources of the Chihuahuan Desert region. (J. C. Barlow, A. M. Powell, B. N. Timmermann, eds.). Chihuahuan Desert Institution, Alpine, TX. Shaw, R. B. and V. E. Diersing. 1990. Tracked vehicle impacts on vegetation at the Pinon Canyon maneuver site. Colorado. Journal of Environmental Qualit) 19:234-243. Stephenson, T. R., M. R. Vaughn, and D. E. Andersen. 1996. Mule deer movements in response to military activity in southeast Colorado. Journal of Wildlife Management, 60:777-787. Weeks, B. E. 1997. Niche partitioning mechanisms of desert heteromyid rodents. Master's Thesis, Texas Tech University, Lubbock, Texas. Zeng, Z. and J. H. Brown. 1987. Population ecology of a desert rodent: Dipodomys merriami in the Chihuahuan Desert. Ecology, 68:1238-1340. CHAPTER II A CHECKLIST OF MAMMALS FROM TWELVE HABITAT TYPES AT FORT BLISS MILITARY BASE, 1997-1998 The Fort Bliss Military Base is located in Dona Ana and Otero counties. New Mexico, and El Paso County, Texas. This army base occupies approximately 4,523 km^ (452,279 ha) and is bordered by the Sacramento Mountains to the north, the Organ Mountains to the west, and the Franklin Mountains to the southwest. Fort Bliss Military Base is bisected by U.S. Highway 54, resulting in the Dona Ana Range to the west and the McGregor Range to the east. This region, located within the northern area of the Chihuahuan Desert (Shreve, 1942), is characterized by a semiarid to arid climate and is often classified as a desert grassland (Gardner, 1951; Schmidt, 1986). Geographically, Fort Bliss is located within the Tularosa Basin and is typified by lowland valleys, rocky hillsides, and scattered arroyos (Jorgensen, 1996; Monasmith, 1997). Two unusual physiographic features found in this region include coppice sand dunes and Otero Mesa. A small mammal survey was conducted using census lines as described in O'Farrell (1977) in 12 distinct habitat types on McGregor Range in May 1997, September-October 1997, May 1998, and September-October 1998. This study was designed to collect baseline data concerning small mammal diversity and habitat preference. This paper is an 7 account of species trapped. Analyses and discussion of diversity, seasonal change, and movements will be addressed in subsequent articles. Methods and Materials The research design for this study involved sampling small mammals (rodents) in 12 distinct habitat types with two replicates (census lines) per habitat. Brief descriptions of the 12 habitat types are provided in Table 2.1. This includes the locality of each census line given in Universal Transverse Mercater (UTM) coordinates and a list of the dominant plant species associated with each census line. Habitat selection was done in conjunction with ongoing floral studies by other Fort Bliss personnel and attempts were made to utilize the same or nearby areas for both the floral and small mammal studies (Fig. 2.1). At each census line, two parallel trap lines 30 m apart (240 m in length) were established with trap stations placed at 10 m intervals along each line resulting in a total of 50 traps. Each census line was sampled using Sherman (H.B. Sherman Trap Co., Tallahassee, FL) live-traps baited with bird seed and rolled oats during two seasonal periods (Spring and Autumn) for two consecutive years (1997 and 1998). Sampling of the census lines usually occurred on three consecutive nights during each trapping period, resulting in 14,400 trap nights. Occasionally, due to full moon phases, weather, and military operations and schedules, it was not possible to sample particular census lines on the three consecutive nights. Therefore, we were forced to postpone consecutive night sampling for periods of one to four days. Individuals captured on census lines were identified, weighed, sexed, toe-clipped (Animal Care and Use Committee, 1998), assigned 8 a TK number (Texas Tech University Museum identification number), and released at the site of capture. For simplicity, references to all individuals reported herein are by season and year rather than by the actual date of capture; likewise, census lines are used for localities rather than the actual UTM coordinates. These data are pro\ided in Tables 2.2-2.6. A reference collection of voucher specimens and tissue samples for at least one adult male and one adult female, representative of each species, was prepared and deposited in the Museum, Texas Tech University. In addition, toes obtained during the toe-clipping procedures were preserved in lysis buffer (Longmire et al. 1997) and serve as voucher material for specimens obtained during this study. Nomenclature followed Jones et al. (1997) and specimens were identified using keys and characteristics from Davis and Schmidly (1994), Findley (1987), and Findley et al. (1975). Additionally, a few species were observed but not trapped on the Fort Bliss Military Base. These observations are listed in a separate section (Species Observed in the Results and Discussion). Results and Discussion A description of the 12 habitats and 24 census lines, including UTM coordinates and dominant plant species, is presented in Table 2.1. During the two years of this study (1997 and 1998), 2,091 individuals representing 19 species of small mammals were obtained from the 24 census lines (Tables 2.2-2.6). In the initial year (1997), the greatest diversity and relative abundance of the 19 species was observed. The two trapping seasons in 1997 accounted for 72.4% of the individuals (1,513) captured. Most species (17 of 19) declined in relative abundance from 1997 to 1998 with 578 (28% of the total) individuals captured in 1998. However, there were two exceptions, Neotoma albigula and Neotoma micropiis. which increased in relative abundance during 1998. Of the four trapping periods (Spring 1997, Fall 1997, Spring 1998, and Fall 1998), efforts during Spring 1997 resulted in the most diversity (19 species) and abundance (44% of the total). The Spring and Fall 1998 trapping seasons resulted in the lowest number of captures with only 288 individuals representing 18 species in the Spring and 290 individuals representing 15 species in the Fall. During the two-year study, the Chilopsis arroyo habitats (census lines 13 and 8) accounted for the greatest small mammal diversity with 14 of 19 species. Likewise, one of the swale sites (census line 10) possessed the highest number of captures (148 individuals) for any individual census line. Trapping efforts from 1997-1998 on one of the coppice dune sites (census line 21) resulted in the lowest species diversity (5 of the 19 species) and the least number of captures (16 individuals). Taxa Documented by Live-Trapping The taxa described below are arranged phylogenetically following Davis and Schmidly (1994). Actual numbers of captures per taxon, census line, and season are listed in Tables 2.2-2.6. 10 Spermophilus spilosoma marsinatus Bailev. 1902 Spotted Ground Squirrel Seven individuals (3 males and 4 females) of Spermophilus spilosoma were obtained. In all cases, individuals were obtained either in open grasslands or in open areas associated with dunes. A female was obtained in Spring 1997 in a grama grassland (census line 15), two females were obtained in Fall 1997 in a coppice dune and a mixed desert scrub habitat (census lines 21 and 22), and a female was obtained in Spring 1998 in a grama grassland (census line 11). A male was obtained in Spring 1997 in a creosote grassland (census line 12) and two males were obtained in Spring 1998, one each in a nonstabilized dune (census line 1) and grama grassland (census line 11). Individuals of iS. spilosoma were obtained during every season except Fall 1998. Although this species appears to be relatively rare, it should be noted that the paucity of individuals obtained probably was a result of sampling design (traps not open during diurnal hours) and not indicative of actual abundance. Perognathus flavescens apache Merriam. 1889 Plains Pocket Mouse Perognathus flavescens was the least abundant nocturnal species obtained with seven individuals (5 males and 2 females) captured. This species typically was obtained in habitats with relatively moderate amounts of vegetation. Two females were obtained in Fall 1997, onefi-oman acacia hillside (census line 16) and the other from a mixed desert scrub habitat (census line 22). A male was obtained in Spring 1997 in a sandy arroyo 11 scrub habitat (census line 3), two males were obtained in Fall 1997, one each in a sandy arroyo scrub habitat (census line 3) and a succulent hillside habitat (census line 7), and two males were obtained in Spring 1998 on a succulent hillside habitat (census line 7). P. flavescens was most abundant during Fall 1997 (57% of total captures of this species) and individuals were obtained every season except Fall 1998. Perognathus flavus flavus Baird. 1855 Silky Pocket Mouse Perognathus flavus was the most abundant species obtained during this study with 388 individuals (215 males and 173 females). This species was captured in all habitats with the exception of one of the nonstabilized dunes (census line 1) and both coppice dunes (census lines 19 and 21), and was most abundant in the grama, yucca, and creosote grasslands. Individuals of P. flavus were obtained in all four trapping seasons, but were most common in Spring 1997 when 47% of the individuals were captured. Chaetodipus hispidus paradoxus Merriam. 1889 Hispid Pocket Mouse Fifteen individuals of Chaetodipus hispidus (9 males and 6 females) were obtained from three grassland habitats. Five females were obtained in Spring 1997fi-omgrama (census line 15) and yucca grasslands (census lines 23 and 24), and a female was obtained in Autumn 1997 in a yucca grassland (census line 23). Six males were obtained in Spring 1997 in creosote (census line 12) and yucca grasslands (census lines 23 and 24), a male 12 was obtained in Fall 1997 in a yucca grassland (census line 23), and two males were obtained in Spring 1998 in a creosote grassland (census line 12). Our data indicate that this taxon is restricted to the grama, yucca, and creosote grasslands. Seventy-three percent of the C. hispidus indi\iduals were obtained in Spring 1997 and no individuals were captured in Fall 1998. This taxon was the fourth least abundant species (along with Reithrodontomys montanus) obtained. The low numbers of captures may reflect the fact that the Fort Bliss study site is located at the periphery of the distributional range of C. hispidus, where species normally are less abundant. Chaetodipus intermedius intermedius Merriam. 1889 Rock Pocket Mouse One hundred forty-eight individuals of Chaetodipus intermedius (67 males and 81 females) were obtained. This species commonly was found throughout the creosotetarbush scrub habitats as well as the acacia and succulent hillside habitats. This species was obtained during all four trapping periods and was most abundant in Spring 1997 with 44%) of the individuals being captured during this period. Chaetodipus eremicus rMearns. 1898) Chihuahuan Desert Pocket Mouse Eighty-eight individuals of Chaetodipus eremicus (59 males and 29 females) were obtained primarily within the mixed desert shrub and acacia hillside habitats. Individuals 13 of C. eremicus were obtained every season and were most abundant during Spring 1997 when 36%) of the total captures was recorded. Dipodomys merriami ambii^uus Merriam. 1890 Merriam's Kangaroo Rat Dipodomys merriami was the second most abundant species (349 individuals. 190 males and 159 females). Individuals of this taxon were obtained during all four trapping periods and from all habitat types. Spring 1997 yielded the most individuals with 38% of the total captures of this species. During Fall 1997, Spring 1998, and Fall 1998, there was a slight decrease in trap success for D. merriami. Dipodomys ordii ordii Woodhouse. 1853 Ord's Kangaroo Rat One hundred twenty-eight individuals of Dipodomys ordii (77 males and 51 females) were obtained primarily within the coppice (census lines 19 and 21) and nonstabilized (census lines 1 and 2) sand dune sites. This taxon was obtained in all four seasons and was most abundant in Spring 1997 (43% of the total captures of this species). 14 Dipodomys spectabilis baileyi Goldman. 1923 Banner-tailed Kangaroo Rat Nine individuals of Dipodomys spectabilis (5 males and 4 females) were obtained. A female was obtained in Spring 1997 on a creosote grassland (census line 12). two females were obtained in Spring 1998 on a grama grassland (census line 15), and a female was obtained in Fall 1998 on a creosote grassland (census line 18). A male was obtained in Spring 1997 on a creosote grassland (census line 18), another male was obtained in Spring 1998 on a Chilopsis arroyo habitat (census line 13), and three males were obtained in Fall 1998 on grama (census line 11) and creosote (census line 12) grasslands and a Chilopsis arroyo (census line 13). No individuals were trapped during Fall 1997. Typically, individuals of Dipodomys spectabilis were obtained in grassland habitats (creosote and grama), although two individuals were obtained in a Chilopsis arroyo habitat. This taxon was the third least abundant species obtained. Although this species appears to be uncommon throughout the study area, numerous mounds and burrow systems were observed outside of the designated census lines. The low number of individuals trapped was probably the result, in part, of the placement of census lines, as well as the trap size being too small to effectively capture this species. Reithrodontomys megalotis megalotis rSaird. 1858) Western Harvest Mouse One hundred seventeen individuals of Reithrodontomys megalotis (77 males and 40 females) were obtained. Our data indicate this species favors tall, thick grassy 15 habitats. Fifty-three percent of the total captures of this species occurred in Spring 1997. Fall 1997, Spring 1998, and Fall 1998 showed a sharp decline in the number of Reithrodontomys megalotis captures. Reithrodontomys montanus monlanus (Baird, 1855) Plains Harvest Mouse Fifteen individuals of Reithrodontomys montanus (8 male and 7 female) were obtained; primarily from the grassy areas of the dry Sacramento riverbed. Seven males were obtained in swale (census line 5) and Chilopsis arroyo (census line 8) habitats and six females were obtained in Chilopsis arroyo (census line 8) and swale (census line 10) habitats in Spring 1997. Two individuals (1 male and 1 female) were obtained in a yucca grassland (census line 24) in Fall 1997. No individuals of R. montanus were captured in 1998. Reithrodontomys montanus was the fourth least abundant species (along with Chaetodipus hispidus) obtained. Peromyscus eremicus eremicus fBaird. 1858) Cactus Mouse One hundred six individuals of Peromyscus eremicus (63 males and 43 females) were obtained throughout most of the brushy hillside areas including the acacia (census lines 9 and 16) and succulent (census lines 7 and 20) hillside habitats. Fifty-six percent of the individuals were captured in Spring 1997. 16 Peromyscus maniculatus blandus Osgood.1904 Deer Mouse This was the most commonly captured species of Peromyscus with 144 individuals (83 males and 61 females) obtained from a wide variety of habitats. These habitats ranged from dune sites to grasslands and rocky hillsides. This taxon was obtained in all four seasons with 59% of the captures for this species occurring in Spring 1997. Peromyscus leucopus tornillo Mearns. 1896 White-footed Mouse One hundred forty-nine individuals of Peromyscus leucopus (91 males and 58 females) were obtained in multiple habitats. These ranged from grama grasslands to succulent hillsides with brush and yucca species generally associated with all habitats. This species was obtained during all four trapping periods and was most abundant during the two trapping seasons in 1997, which accounted for 74% of the captures for this species. Onychomys arenicola arenicola Mearns. 1896 Mearn's Grasshopper Mouse Sixty-one individuals of Onychomys arenicola (29 males and 32 females) were obtained from census lines associated with grama and creosote grasslands as well as 17 swales and creosote-tarbush scrub habitats. This species was obtained during all four seasons and, unlike most other species, was most abundant in the Fall 1997 trapping period, which accounted for 66% of the individuals captured. Onychomys leucogaster ruidosae Stone and Rehn, 1903 Northern Grasshopper Mouse Eighty individuals of Onychomys leucogaster (46 males and 34 females) were captured in census lines associated with dune, grassland, and succulent hillside habitats. This taxon was obtained during all four trapping periods and, like its congener, was most abundant in Fall 1997 when 51% of the captures of this species occurred. Sigmodon hispidus berlandieri Baird. 1855 Hispid Cotton Rat One hundred and thirty-four individuals of Sigmodon hispidus (63 males and 71 females) were obtained primarily in the swale habitats, although a few were captured in the creosote-tarbush scrub habitats. This species was present during all four trapping seasons, but was captured predominantly during Spring 1997 when 55% of the total individuals were obtained. 18 Neotoma albigula albigula Hartlev. 1894 White-throated Woodrat One hundred sixteen indi\'iduals of Neotoma albigula (52 males and 64 females) were obtained. This species was common in the nonstabilized dune (census line 1) and acacia hillside (census lines 9 and 16) habitats, and was captured in all four trapping periods. In contrast to all other species of rodents, this species, along with Neotoma micropus, increased in abundance during the final trapping season (Fall 1998) with 32% of the total captures of this species being recorded. Neotoma micropus cane seen s J.A.Allen. 1891 Southern Plains Woodrat Thirty individuals of Neotoma micropus (18 males and 12 females) were obtained primarily from the sandy arroyo and creosote-tarbush scrub habitats. In Spring 1997, five males were obtained in sandy arroyo scrub (census line 6), Chilopsis arroyo (census line 8), creosote-tarbush scrub (census line 14), and creosote grassland (census line 18) habitats, and six females were obtained in mixed desert scrub (census line 4), sandy arroyo scrub (census line 6), creosote grassland (census line 12), creosote-tarbush scrub (census line 14), and acacia hillside (census line 16) habitats. In Fall 1997, two males were obtained in creosote grassland (census line 12) and creosote-tarbush scrub (census line 14) habitats . In Spring 1998, four males were obtained in a creosote grassland habitat (census line 12), and six females were obtained in nonstabilized dune (census line 2), mixed desert scrub (census line 4), creosote grassland (census line 12), and creosote-tarbush scrub 19 (census line 14) habitats. In Fall 1998, seven males were obtained in nonstabilized dune (census line 2), mixed desert scrub (census line 4), Chilopsis arroyo (census line 13), creosote-tarbush scrub (census line 14), succulent hillside (census line 20), and mixed desert scrub (census line 22) habitats. This species, along with N. albigula, increased in abundance in Fall 1998. Species Observed Many mammal species occurring on the Fort Bliss Military Base were not trappable with our experimental design and trapping methods. These species were recorded as observations and are presented below. These observations are not included with the data presented in Tables 2.2-2.6. Sylvilagus audubonii goldmani rNelson. 1904) Desert Cottontail Individuals of Sylvilagus auduboni were observed from succulent hillside and mixed desert scrub habitats. This species was observed throughout the Fort Bliss Military Base on each census line and habitat type. Lepus californicus texianus Waterhouse. 1848 Black-tailed Jack Rabbit Several individuals of this species were observed during each of the four collecting periods. This taxon typically occupied the more open grassland areas and roadsides. 20 Cynomys ludovicianus arizonensis Mearns. 1890 Black-tailed Prairie Dog Several individuals were observed in prairie dog towns located in the open grassland habitats on Otero Mesa. Canis latrans texensis Bailev. 1905 Coyote Evidence of this species (tracks, scat, and dens) was noted throughout all habitats. Additionally, several individuals were observed along roadsides throughout the Fort Bliss Military Base. Urocyon cinereoargenteus scottii Mearns. 1891 Gray fox Two individuals were observed near census lines 6 and 7 (sandy arroyo scrub and succulent hillside). The secretive nature of this species created difficulty in estimating the abundance of this taxon. 21 Taxidea taxus berlanderi Baird. 1858 American Badger A single specimen was observed in Spring 1997 near census line 8 {Chilopsis arroyo). In addition, many excavations of rodent burrows were noted and may indicate that badgers are common. Lynx rufus bailevi Merriam. 1890 Bobcat Three individuals were observed during the first two seasons (Spring and Fall 1997) within the riparian habitats below Otero Mesa. Odocoileus hemionus crooki (Mearns. 1897) Mule Deer This species was observed throughout most areas of Fort Bliss with the exception of open grasslands. Most were noted in the early morning near brushy foothills of Otero Mesa. Antilocapra americana americana rOrd. 1815) Pronghorn This species was quite common in the grama and yucca grasslands located on Otero Mesa. Although little is known about the relative abundance of this species, on one occasion, at least 70 individuals were observed at a single site. 22 Oryx gazella (Linneaus. 1758) Gemsbok This introduced species was observed in small groups (2-5 individuals) on numerous occasions in the swale and nonstabilized dune habitats near the Sacramento Mountains. Ammotragus lervia (Pallas, 1977) Barbary Sheep or Aoudad A single individual of this introduced species was observed on the rocky slopes just below Otero Mesa. 23 Literature Cited Animal Care and Use Committee. 1998. Guidelines for the capture, handling, and care of mammals as approved by the American Society of Mammalogists. Journal of Mammalogy, 79: 1416-1431. Davis, W.B., and D.J. Schmidly. 1994. The Mammals of Texas. Texas Parks and Wildlife Department. Austin, .v + 388 pp. Findley, J.S., A.H. Harris, D.E. Wilson, and C. Jones. 1975. Mammals of New Mexico. University of New Mexico Press, Albuquerque, x + 360 pp. Findley, J.S. 1987. The Natural History of New Mexican Mammals. University of New Mexico Press, Albuquerque, x + 150 pp. Gardner, J. L. 1951. Vegetation of the Creosotebush area of the Rio Grande valley in New Mexico. Ecological Monographs, 21:379-403. Jones, C , R.S. Hoffman, D.W. Rice, M.D. Engstrom, R.D. Bradley, D.J. Schmidly, C.A. Jones, and R.J. Baker. 1997. Revised Checklist of North American Mammals North of Mexico. Occasional Papers Museum, Texas Tech University, 173:1-18. Jorgensen, E.E. 1996. Small mammal and herpetofauna communities and habitat associations in foothills of the Chihuahuan Desert. Unpublished Ph.D. dissertation, Texas Tech University, Lubbock, TX. Longmire, J. L., M. Maltbie, and R. J. Baker. 1997. Use of "lysis buffer" in DNA isolation and its implication for museum collections. Occasional Papers, Museum, Texas Tech University, 163:1-3. Monasmith, T.J. 1997. Fire effects on small mammals and vegetation of the northern Chihuahuan Desert. Unpublished Master's thesis, Texas Tech University, Lubbock, TX. 24 O'Farrell, M.J., D.W. Kaufman, D.W. Lundahl. 1977. Use of Live-trapping with the Assessment Line Method for Density Estimation. Journal of Mammalogy, 58:575-582. Schmidt, R.H. 1986. Chihuahuan climate. Pp. 40-63, in Second symposium on resources of the Chihuahuan Desert region. (.l.C. Barlow, A.M. Powell, B.N. Timmermann. eds.). Chihuahuan Desert Institution. Alpine. TX. Shreve, F. 1942. The desert vegetation of North America. The Botanical Review, 8:195246. 25 C/5 (U C3 G o o o 00 t-i x: 3 X) 00 W I I E :5 < U c/3 o x; ^ C c o u w 00 G c/) 3 X) O u C3 C H < o > C/5 (U C3 c^ -f u. X ) Z3 .. XJ ' - " C O ' rt <4Z ^3 on ., ^ ~ o o !^ E:^ 00 75 O o 4 i cu H < .5 2 2 D; ^ 3 <D O S o CI. 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O O O O en OO O '-I ^ uS en UH -H _H O O (N 00 o o o en o en O '^ 13 CN UH o ON en (N . vo VO 00 fN U S fN 00 13 On ^-i On ' 3 en n On I :z; en (U I H t/3 On on on > a r^ S a 00 it ^ t 3 On on o? 3 s o a a C5 > 2 c c o "5 o O o O o ^ ^% ^ o o is -is X3 ^ :^ i^ ^ ^ -s: -a o o tS < c c 2 u Ci ^ ^ r^ -C -C -3" -ir S" ^ <^ ;u ^ ^ K s; C O " Q H OH O O U C i Q C i f t : ; a ; ; C i , Q . , a , 0 0 pus hispidus pus intermedius lys merriami lys ordii lys spectabilis ontomys megalo ontomys montan cus eremicus CUS leucopus CUS maniculatus mys arenicola mys leucogaster Sigm n hispidus Neotom albigula micropus o s s H O H 31 -J o UH (NtN-^r-- r-en O fN t^ rt oo oo en ON r ^ fN vo O CN en in VO in (N (N cNr--o o o i n e n o N T t (Ni CN fN ( N <N CN en in en CM oo (N Tt u 2 ci ^ (N O O rn rn r j U 2 U S CN "^ '^ Cxi ^ (N in O in CJ O O NO CN e^i (N u 2 (N (N o o ^ vc r^ vf O C) N o en oo VO (N oo o tu VO (N en <N vo o en en [;: UH CN vo v o UH O <N (N en en r-en en (N (N (N (N (N CN Tj- o > vo O uS in VO CM ON CN CNI CN in ON 00 CN fN !2 u. ~^ ' fN i n I ~ O ' ^ O I -^ I en fN o ^nenen I ~~~ cN O I ' 1 in vo (i> On 3 fc fc On 05 ^ on 3 on 3 c G O '^ ? <^ hi VJ On 3 3 00 ^ a On 3 on ^J fc 3 a 3 .^ CL .03 Ia fc .^ On U en 00 Si <;> on 3 On -tS -S-S On On On On 3 3 "^ -S 2 c CO'QH 'o 00 "3 fc fc 00 00 t S-.SS 2. ^a O ^ fc 2= ^ 3 J On -2i S, On o 3 3 00 C n 3 O , -fc o o O O 5?" 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O CO g 33 H O H O _ OO o c ^ r n o fN (-sjr-fNfN"^0(NooO-^__cN -^ ^Tt fN en in vo T t en CN \ o o en in 'mr--c3N N O c^i LI, r-i C^l O u S rn r-1 o m en vc in (^1 o O (N U S u 2 U S fN UH en O u 2 ON tl^ m en vo O m o vo 22 u. r-i o (N u S 1^ t^ (N CN en en CN fN CM i n en (N O fN 12 UH vo fN (N 00 en en u S 2 tin -I ^ fN fN O en en en O ^ fN ON in fN fN ON uS T3 <U on on e On P O fc On a 4 ' o U '^" <N 'o oo C 1" ^ 03 -ii ^ 13 s Si :2 ^ ^ fi A on ^ Si 3 a .2- .^.2- g 0 Oei -^ !2 05 On 3 S 3 C -fc 03 3 ^ 2 Co ft. ft, U a a ^ QQQo^c^Q;Q:a;oo 34 S- lys merriami lys ordii lys spectabilis ontomys megal ontomys monta CUS eremicus cus leucopus cus maniculatu. lys arenicola lys leucogaster n hispidus albigula micropus ^-Q on 3 O fc 3 5 0 0 ** ^ ^ ~a 0 0 Cl 1.. ^ 0 ^ 4 03 On On ?^ ^ ?^ 0 Cu fc ^ S S -c a ^5 8 8 u u fc ^ fc 511 Zi 0 ^ - 0 0 00 00 *fc a S 0 0 ^ Q s 0 0 ^ :^:^ fN UH m U S OO ON ON o r^i in C M u S 2UH O (N o fN r<~, O ON vD Cst (U "DH ON o (N O en UH B oo O en en O en en O O O .^^ 1 U <u c P oo C (O oo UH in e<-, 0 ' DO VO (N (N ...^ O 1 en v o PU fN -^ 00 m ' o o o M-H r^ Tf (N o O (N 00 m UH O O vo c 4 ' o o (N en UH o o CM oo -^ CN CN . 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CN <N OO ' CM ^ en i n vo ^ ^ I I t I vo ^ ^^ I I vo en ON ' ' vo ' uu O CN O en ' ON CN VO (N (N O CN ON G CN fN O fN ON en 00 13 dS 03 * A en CN O -" en CN 03 On o en c: O CM ON in a o CD On 3 On .2 S ^ ^ f c 03 On 3 03 I H ^ oi 03 3 2:x3 3 '^ P 03 3 o, 2 On -fc) 3 su on a j 3 1 ? 3 3 Vj u Si ^ < C on 03 3 3 .Ci. : a <^ Ci, 03 a 'fc On on 3 K On z vd <N (U (/3 3 "^ -fc -h ^ ~2 8 :^ 3 3 ^ 03 - c - * fc^ -fc 3 3 on 03 ' ^ -^ ::^ o c fc Oo Oo I"! a a a s s o 2 -fc o o U 2 ^ -fc -fc ^ ^ J : Ci. Ci. C i , - ~ 3 3 3 <J VJ On On on >% ? ^ 03 00 c: = -Ci -Cj a fc o a fc aa "^ 2 = 00 c ^ ft. OH Q Q Q ft; ft; ft. 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Approximate locations for the 24 grids sampled in this study. 39 CHAPTER III SMALL MAMMAL COMMUNITIES AND HABITAT ASSOCIATIONS IN THE CHIHUAHUAN DESERT Abstract From May 1997 to October 1998, a small mammal study was conducted at the Fort Bliss Military Base to compare the ecology of small mammals among 12 distinct habitat types. Each habitat type contained two replicate grids for analysis, examined each for six nights (three for census lines and three for assessment lines) per trapping period during Spring 1997, Fall 1997, Spring 1998, and Fall 1998. Data recorded from each capture on the grids included TK number (Texas Tech Museum identification number), species identification, sex, weight, date of capture, toe-clip number (cross-referenced with the TK number), and trap station of capture. The capture data were used in the following analyses: species diversity, density, and composition per habitat, survivability of species, and movement of each small mammal species. Species diversity was highest in the sandy arroyo scrub habitat (Simpson's index value = 0.8859) and lowest in the coppice dune habitat (Simpson's index value = 0.4120). The swale habitat possessed the highest rodent density value with 39.16 individuals per hectare. Results from a species composition cluster analysis revealed that habitats with comparable vegetative composition (such as the three grasslands: yucca, grama, and creosote) formed clusters 50% or more of the time. Species within the family Heteromyidae were most successful in terms of survivability with six species surviving 40 for at least 18 months. The insectivore Onychomys leucogaster displayed the greatest average movement of 3.94 MSD among the species and the highest average movement across all species was found in the moderately vegetated acacia hillside habitat (3.96 MSD). Introduction Desert ecosystems are characterized as one of the most unique and diverse areas in the United States and embody an abundance and diversity of flora and fauna unique to most habitats. This diversity is in itself phenomenal due to many species maintaining exceptionally stable populations despite the unpredictable fluctuations in the environment (Zeng and Brown, 1987). Free-standing water is rarely available in these dry, arid ecosystems. This lack of available water can be detrimental for species living in most other environments. Animals residing in deserts have adapted certain morphological and physiological characteristics which enable them to live and thrive in an environment that is unsuitable for other species (Ghobrial and Nour, 1975). These characteristics have resulted in an abundance and diversity of rodent species in desert ecosystems. Despite this abundance, there appears to be partitioning of resources or some level of coexistence among desert rodent communities of southwestern North America, resulting in desert rodents being ideal subjects for studies of coexistence, competition, and community structure (Heske et al, 1994). The Chihuahuan Desert is located in the southernmost portion of the Great American Desert with its region lying in the area bounded by the 90^^ and 108^^ 41 meridians and the 2ist and 33^^ parallels (Milstead, 1960). It includes parts of southern New Mexico, all of Texas west of the Pecos River (except for the Guadalupe Mountains), the eastern half of Chihuahua, the western portion of Coahuila, and parts of Durango, Zacatecas, Nuevo Leon, San Luis Potosi, Aguascalietes, and Tamaulipas (Schmidly, 1974). The region has a diverse flora and fauna including eight orders, 24 families, 60 genera, and roughly 119 species of mammals (Sclimidly, 1974). The Fort Bliss Military Base includes a relatively small portion of the northern region of the Chihuahuan Desert. It occupies approximately 4, 523 km2 (452,279 ha), ranging from El Paso County, Texas to Otero County, New Mexico, and is divided by U.S. Highway 54, with the Dona Aiia Range to the west and the McGregor Range to the east. It is characterized as a desert grassland with a semiarid to arid climate located within the Tularosa Basin which is typified by lowland valleys, rocky hillsides, and scattered arroyos (Gardner, 1951; Schmidt, 1986; Jorgensen, 1996; Monasmith, 1997). The objectives are: (1) compare small mammal (rodent) composition among the 12 unique habitats in the Chihuahuan Desert to determine which contain relatively high species diversity values of small mammals and which are "fragile" (those containing relatively low diversity values), (2) compare small mammal densities per habitat and determine any influence of vegetative cover, (3) determine if the amount of rainfall influences density or diversity, (4) determine the survivability of each small mammal species, and (5) compare the average movement among species and habitats to determine the influence of vegetative density on rodent activities. 42 Methods The research design for this study involved sampling small mammals (rodents) in 12 distinct habitat types with each containing two replicate grids. The 12 habitats analyzed in this study were characterized by range botanists, based on vegetative composition and density, and labeled as: sandy arroyo scrub, nonstabilized dune, coppice dune, creosote-tarbush scrub, mixed desert scrub, grama grassland, creosote grassland, yucca grassland, swale, acacia hillside, Chilopsis arroyo, and succulent hillside habitats (Figure 3.1). Brief descriptions of the habitats are provided in Table 2.1 including a list of the dominant plant species associated with each habitat. Each of the habitat types was ranked on the basis of percent vegetative cover from 1 (0.0-20.0%) to 5 (80.0-100.0%). Two grids, each with census and assessment lines, were constructed for each habitat type. The experimental design for this project was described in Clary et al. (1999). Census lines, including two parallel trap lines 30 m apart (240 m in length) established with trap stations placed at 10 m intervals along each line resulting in a total of 50 traps were used for initial captures. The assessment lines, containing 72 traps, formed a diamond-like configuration about the census lines and were utilized for estimating recaptures on each grid (Figure 3.2). Each of these lines (census and assessment) was sampled using Sherman live-traps (H.B. Sherman Trap Co., Tallahassee, FL) baited with birdseed and rolled oats during two seasonal periods (Spring and Fall) for two consecutive years (1997 and 1998). Generally, sampling of the grids typically occurred on three consecutive nights on the census lines followed by sampling for an additional three consecutive nights on the assessment lines. Total trapping efforts 43 produced 35,136 trap nights. Informative data were recorded for each individual captured on census lines (TK number -Texas Tech Museum identification number, identification to species level, weight, sex, toe-clip number -to be cross-referenced with the TK number, and trap station and date of capture) followed by the individual being released at the site of capture. Captures on assessment lines were identified from toe-clip patterns and the date and trap station of capture were recorded. For this study, it was assumed that animals encountered traps randomly in a particular habitat and neither the sex, age, or dominance of an animal influenced capture probabilities. A reference collection of voucher specimens and tissue samples for at least one adult male and one adult female, representative of each species, was prepared and deposited in the Museum, Texas Tech University to provide historical and physical documentation. In addition, toes obtained during the toe-clipping procedures were preserved in lysis buffer (Longmire et al, 1997) and serve as voucher material for specimens obtained during this study. Nomenclature followed Jones et al. (1997) and specimens were identified using keys and characteristics from Davis and Schmidly (1994), Findley (1987), and Findley and Caire (1974). To determine monthly precipitation, a rain gauge was attached to a T-post and placed at the first trap station of each grid. Rainfall was recorded (in millimeters) at the first of each month from April 1997 to October 1998. In some cases, minor disturbances on the grids (i.e., cattle) affected the reliability of some of the gauges and monthly accumulation could not be recorded. These incidences were not included in the 44 accumulation averages of the affected grid. The recorded rainfall for each month was averaged for each habitat and season (Table 3.1). All statistical analyses used in this study were generated in the software program Matlab (Matlab 5.2, 1998). Species diversity was calculated for each rodent species using the Simpson's diversity index (Simpson, 1949). This index utilizes the number of species present in a habitat (species ricliness) and the number of individuals within each species (evenness) to estimate species diversity. Species diversity values were compared between and among habitats to determine which habitats possessed the highest diversity. In addition, diversity values were compared to the vegetative density (percent cover) of each habitat using correlation analyses. Clustering methods similar to those used by Brown and Heske (1990) were used to determine species composition similarities among the habitats. Species composition was compared among the habitats by a UPGMA cluster analysis of species count correlations among habitats. The cluster analysis was bootstrapped for 1000 iterations and those habitats grouping together at least 50%) of the time (bootstrap support value = 0.05) were recognized. The average rainfall from each trapping period was tabulated and compared with each habitat's diversity value through correlation analyses to determine the influence of rainfall on rodent community diversity. Rodent density per habitat was defined as the number of individuals captured per hectare. The results from this analysis were compared among habitats and seasons. Percent cover (vegetation) per habitat was compared to the results from the rodent density analysis through correlation analyses to determine if concentrations of vegetation 45 had an effect on small mammal density. In addition, regression analyses were utilized to determine any influences of rainfall. Survivability, defined as the proportion of individuals from a given cohort surviving at a given time (Lincoln et al., 1982), was calculated for each species. Comparisons were made among species using the proportion of individuals (per species) recaptured from the total initial captures at six-month intervals (6. 12, and 18 months). In addition, regression analyses were generated using the number of captures and trapping period (time) and applied per species to determine the exponential survivorship rate of decline (r). The average movement for each species was determined by converting the trap stations and traps of capture per grid to points on an x,y point-coordinate system. The centroid (median) of activity for each recaptured individual was generated based on the assemblage of captures and squared deviations from the centroid to each trap of capture were averaged (Figure 3.3). The deviations were then averaged per species (mean squared deviations, MSD) and compared among the species. In addition, the deviations were averaged per habitat to determine if the differences in vegetative density (percent cover) among the habitats affected the amount of movement among the residing species. An analysis of variance (ANOVA) was generated to determine significant differences among the species and habitat movement averages. Pairwise comparisons were utilized to determine significant differences within the species and habitat groups. 46 Resuks Diversity Nineteen species were obtained from the 12 habitats. Habitat and seasonal species diversity values are shown in Table 3.2. Estimates of species diversity, for the four trapping periods, indicated that the sandy arroyo scrub habitat possessed the highest rodent diversity (Simpson's index = 0.872). Several other habitats possessed similar diversity values including Chilopsis arroyo (0.828), acacia hillside (0.816), creosotetarbush scrub (0.816), succulent hillside (0.803), swale (0.802), yucca grassland (0.796), creosote grassland (0.742), and mixed desert scrub (0.707) habitats. Species diversity was lowest in the coppice dune habitat (0.384); whereas nonstabilized dunes (0.645) and grama grassland (0.472) had low to medium diversity values. Results from correlation analyses showed a positive correlation (0.56) of habitat species diversity and vegetative percent cover. However, despite this trend of correlation between the two parameters, it was not significant (p < 0.05). Species diversity for most grids remained relatively unchanged between trapping periods (Spring 1997, Fall 1997, Spring 1998, and Fall 1998) and between years (1997, 1998). However, small mammal diversity increased in the nonstabilized dune habitat during 1998 (Spring and Fall), decreased in the coppice dune habitat during 1998 (Spring and Fall), decreased in the mixed desert scrub habitat during Spring 1998, and was lowest in the yucca grassland habitat during Spring 1997. All interpretations on community diversity as a function of rainfall were based on direct observation and correlation analyses. The rainfall in Spring 1998 had the lowest 47 average (5 mm) recorded during the study (Figure 3.4). The recorded seasonal rainfall was positively correlated with the seasonal diversity values of the mixed desert scrub, succulent hillside, acacia hillside, creosote-tarbush scrub, and coppice dune habitats with correlation coefficients of 0.61, 0.72, 0.63, 0.11, 0.36, respectively (Figure 3.5). However, these positive correlations were not significant (p < 0.05) based on a Student's /-test. Results from the UPGMA cluster analysis revealed certain habitats grouping together by species composition similarities with a bootstrap support value of at least 0.50 at 1000 iterations (Figure 3.6). The coppice dune and mixed desert scrub habitats clustered with a bootstrap support value of 0.55 and the three grasslands (creosote grassland, grama grassland, and yucca grassland) clustered with a bootstrap value of 0.58. In addition, the acacia hillside, sandy arroyo scrub, and succulent hillside habitats clustered with a bootstrap support value of 0.71 with two of the habitats, acacia hillside and sandy arroyo scrub, clustering with a bootstrap support value of 0.85. Density Rodent densities were determined per habitat by calculating the number of captured individuals per hectare (Figure 3.7). Results from the swale habitat exhibited the highest rodent density value of 39.16 individuals/lia. Other habitats having relatively high values of rodent density were the acacia hillside (38.82 individuals/ha), Chilopsis arroyo (33.40 individuals/ha), and creosote grassland (30.04 individuals/ha) habitats. The lowest rodent density (9.95 individuals/ha) was found in the coppice dune habitat. The grama 48 and yucca grassland habitats also contained relati\ely low rodent densities (17.90 and 21.30 individuals/ha, respectively). Relationships between vegetation and rodent densities for each habitat were examined by correlation analyses. Percent cover of vegetation and rodent densit> were positiveh' correlated (0.67) across all habitats and significant at p < 0.05. In addition, regression analyses were generated to determine the influence of rainfall on rodent densities per season. Although there appeared to be a decrease in density for some of the habitats during low accumulation periods, no significant values (p < 0.05) were found in the analyses. Survivability The proportion of individuals recaptured from the total number of initial captures was calculated at six-month intervals for each species (Figure 3.8). At six months, 16 of the total 19 captured species were recaptured. Due to deficient sample sizes, the following species were excluded from the regression analysis: Spermophilus spilosoma, Perognathus flavescens, Chaetodipus hispidus. and Reithrodontomys montanus. The percentage of recaptures per species ranged from 3.3% for Neotoma micropus to 26.1% for Dipodomys merriami. Thirteen species were recaptured at 12 months with the percentage of recaptures per species ranging from 0.7% for Sigmodon hispidus to 11.1%) for Dipodomys spectabilis. Six of the thirteen species were from the family Heteromyidae and possessed the highest recapture percentages (3.4-11.1 %o). Ten species were recaptured after 18 months with six of the species from the family Heteromyidae. The 49 species percentages ranged from 0.7% for Peromyscus leucopus and P. maniculatus to 11.1%) for Dipodomys spectabilis. The results from the regression analysis (Figure 3.9) indicated Neotoma micropus had the highest exponential rate of decline (r = -0.56) from the beginning to the completion of the study. Other species with high exponential rates of decline were Onychomys arenicola (r = -0.39), Sigmodon hispidus (r = -0.37), and Reithrodontomys megalotis (r = -0.35). Dipodomys merriami had the lowest exponential rate of decline (r = -0.18) followed by Chaetodipus intermedius (r = -0.185), Dipodomys ordii (r = -0.19), Perognathus flavus (r = -0.21), and Chaetodipus eremicus (r = -0.21). Movement When calculating the average movement traveled by each species, six species were eliminated on the basis of inadequate sample size: P. flavescens, C hispidus, D. spectabilis, R. montanus, N micropus, and Spermophilus spilosoma. The mean squared deviations were calculated from the centroid (median) of activity to each trap station of capture and averaged for each species (Figure 3.10). The averages among the remaining 13 species differed significantly (p = < 0.001). Onychomys leucogaster had the highest movement average (3.94 MSD) followed by P. maniculatus (3.87 MSD), D. merriami (3.81 MSD), O. arenicola (3.72 MSD), and D. ordii (3.71 MSD). The lowest average movement of 2.50 MSD was exhibited by S. hispidus. Other low average values were found for R. megalotis and P. flavus with averages of 2.65 and 2.74 MSD, respectively. 50 The averaged mean squared deviations across species also were compared among the twelve habitats (Figure 3.11). These average movements differed significantiy (p = 0.002). Average movements were highest for small mammals from the acacia hillside habitat (3.96 MSD). Similar results were found for rodents from the grama grassland and mixed desert scrub habitats with 3.80 and 3.79 MSD, respectively. Results indicated that the lowest average movement value was for small mammals from the succulent hillside habitat with 2.66 MSD. Resuhs were similar with the swale and creosote grassland habitats (3.06 and 3.26 MSD, respectively). Despite the significant differences found from the ANOVA generated across species and habitat groups, no significant differences resulted in the pairwise comparisons within each group. Discussion With few exceptions, there appeared to be little difference among diversity values in reference to trapping period or year within the same habitat type. This may be expected due to the short duration of the study. The low diversity seen in coppice dune habitats (mainly D. merriami and D. ordii) was possibly a result of kangaroo rats being more efficient foragers in open habitats when compared to other species. These findings are similar to those found by Harris (1984), Kotier (1984), and Kotler and Brown (1988). In terms of overall species diversity, habitats characterized by high percent vegetative cover (> 60%)) including the swale, Chilopsis arroyo, sandy arroyo scrub, and acacia hillside habitats were most significant. The more productive a habitat is, the less frequently competition occurs among species (Brown, 1975). Conversely, the coppice 51 dune habitat (< 20% vegetative cover) consistently demonstrated a paucity of small mammals. This is probably a result of coppice dunes being inferior habitat for certain species. There is little cover and seed-producing plants associated with this habitat and seed production is the key determinant of rodent species diversity in desert ecosystems Brown (1975). Diverse communities of small mammals have been found to exist more frequently in densely vegetated habitats than in sparsely vegetated habitats (Jorgensen, 1996; Brown and Zeng, 1989). In a study of desert rodent communities in the Mojave Desert, species diversity increased with increasing vegetative cover (Hafner, 1977). Although the results in the correlation analyses were not significant, the decrease in rodent diversity observed in some of the habitats during Spring 1998 may be due to the low average precipitation recorded that season. The fiuctuations of rainfall directly affect water and forage availability. Water accessibility may play a significant role in coexistence of desert rodents. The effects of available moisture, vegetative density, and habitat complexity are intricately involved in determining the diversity of rodent communities (Christian, 1980; Hafner, 1977). Rodent density results were similar to those found in the species diversity analysis. Habitats characterized by dense vegetation (> 60% vegetative cover) contained higher densities of rodents. The swale habitat was characterized as having the highest percent vegetative cover (80-100%)) and therefore, exhibited the highest rodent density. Results from the correlation analyses revealed a significantly positive correlation between rodent density and percent cover of vegetation. These results of high densities of rodents in densely vegetated habitats may be due to the rodents' preference to a sufficient 52 availability of seed-producing plams. As noted by Thompson (1982), the mean densities of seeds and the variation in those densities are greater beneath vegetation. In addition, the ample amount of vegetation may be beneficial as adequate cover to serve as protection from predators (Kotler and Brown, 1988). Results from the correlation analysis revealed a significantly positive correlation between seasonal rodent density and rainfall. The drought period in Spring 1998 seemed to have an adverse effect on rodent density in most of the habitats. As stated above, water availability is crucial to most rodent species. Some species of heteromyids are known to even slow the processes of reproduction during times of low resource availability. As shown by the survivorship analyses, only 2.0 % of the total number of initial captures across species were recaptured after 18 months. The probability of survival may vary with individual characteristics and also as a function of various environmental variables (Lebreton et al., 1992). For example, the family Heteromyidae had 6 out of the 10 species recaptured after 18 months (ranging from 1.6% to 11.1 % of initial captures). o Their success may be due to certain morphological and metabolic adaptations characteristic of this family. For example, the genus Dipodomys has many attributes, such as inflated auditory bullae and bipedal ity, which enhance senses and speed for avoidance of predators in addition to foraging efficiency. Other members of the family Heteromyidae, including Chaetodipus sp. and Perognathus sp., are known to aestivate during times of low seed availability. 53 Higher movement averages were present in the habitats characterized by relativel> sparse vegetative cover (< 40% cover). These sites were primarily dominated by bipedal species {Dipodomys sp.) while more densely vegetated sites (> 40.0% cover) contained primarily quadrepedal species. Some microhabitat theories suggest that morphological adaptations such as locomotion allow species to utilize specific microhabitats (Price, 1978; Price and Brown, 1983; Kotler, 1984). Large, bipedal kangaroo rats {Dipodomys sp.) are associated with open microhabitats while small, quadrupedal pocket mice {Perognathus sp.) are associated with shrubby microhabitat (Harris, 1984). For Dipodomys merriami the presence of open areas is the most important factor affecting its distribution (Congdon, 1974). The high average movements found in Onychomys sp. may be the result of their characteristic guild. Having a diet consisting of primarily insects requires members of this genus to travel greater lengths in pursuit of food in comparison to coexisting herbivores. The low average movement found in S. hispidus may be a result of its herbivore feeding guild as well. This herbivorous species was predominately found within the swale habitat which contained the lowest average movement across species and is characterized by abundant, dense vegetation (> 80% vegetative cover). As shown by the results from the above parameters, stable population dynamics cannot be attributed to any single combination of traits (Brown and Zeng, 1989). Species diversity, rodent density, and survivability cannot be defined based on the occurrence of a single environmental factor. All ecological components of the desert ecosystem are intricately intertwined. Vegetative composition, density, and rainfall have all proven to 54 be factors affecting rodent community ecology. The organization of a community and its patterns of temporal change reflect thefluctuationsof species populations that comprise the community (Brown and Heske, 1990). 55 Literature Cited Brown, J.H. 1975. Geographical ecology of desert rodents. Pp. 315-341, in Ecology And Evolution of Communities (M. L. Cody & J. M Diamond, eds.). The Belknap Press of Harvard University Press, Cambridge, Massachusetts. Congdon, J. 1974. Effects of habitat quality on distributions of three sympatric species of desert rodents. Journal of Mammalogy, 55:659-662. Davis, W.B., and D.J.Schmidly. 1994. The Mammals of Texas. Texas Parks and Wildlife Department, Austin, x + 388 pp. Findley, J.S. 1987. The Natural History of New Mexican Mammals. University of New Mexico Press, Albuquerque, x + 150 pp. Findley, J.S. and W. Caire. 1974. The status of mammals in the northern region of the Chihuahuan Desert. Pp. 127-140, in Transactions of the Symposium on the Biological Resources of the Chihuahuan Desert region United States and Mexico (D.H. Riskind and R.H.Wauer, eds.). Sul Ross State University. Gardner, J.L. 1951. Vegetation of the Creosotebush area of the Rio Grande valley in New Mexico. Ecological Monographs, 21:379-403. Ghobrial, L.I. and T.A. Nour. 1975. The physiological adaptations of desert rodents. Pp. 413-444., in Rodents in Desert Environments (I.Prakash and P.K. Ghosh, eds.). W. Junk, Publishers. The Hague. Hafner, M.S. 1977. Density and diversity in Mojave Desert rodent and shrub communities. Joumal of Animal Ecology, 46: 925-938. Harris, J.H. 1984. An experimental analysis of desert foraging ecology. Ecology, 65: 1579-1584. Heske, E.J., J.H. Brown, and S. Mistry. 1994. Longterm experimental study of a Chihuahuan Desert rodent community: 13 years of competition. Ecology, 75(2): 438-445. Jones, C , R. S. 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Lincoln, R.J., G.A. Boxshall, and P.F. Clark. 1982. A Dictionary of Ecology, Evolution, and Systematics. Cambridge University Press, New York, NY, x + 298 pp. Longmire, J.L., M. Maltbie, and R.J. Baker. 1997. Use of "lysis buffer" in DNA isolation and its implication for museum collections. Occasional Papers, Museum, Texas Tech University. 163:13. Matlab V. 5.2. 1998. The Math Works, Inc., Upper Saddle River, NJ. Milstead, W.W. 1960. Rehct species of the Chihuahuan Desert. Southwestern NaturaHst, 5(2):75-88. Monasmith, T.J. 1997. Fire effects on small mammals and vegetation of the northern Chihuahuan Desert. Unpublished Master's thesis, Texas Tech University, Lubbock. Price, M. V. 1978. The role of microhabitat in structuring desert rodent communities. Ecology, 60(2): 4-49. Price, M.V. and J.H. Brown. 1983. Patterns of morphology and resource use in North American desert rodent communities. Great Basin Naturalist Memoirs, 7: 117134. 57 Schmidly, D.J. 1974. Factors governing the distribution of mammals in the Chihuahuan Desert region Pp. 163-192, in Transactions of the Symposium on the Biological Resources of the Chihuahuan Desert region United States and Mexico (D.H. Riskind and R.H. Wauer, eds.). Sul Ross State University, Alpine, TX. Schmidt, R.H. 1986. Chihuahuan climate. Pp. 40-63, in Second symposium on Resources of the Chihuahuan Desert region. (.l.C. Barlow, A.M. Powell. B.N. Timmermann, eds.). Chihuahuan Desert Institution. Alpine, Texas. Simpson, E.H. 1949. Measurement of diversity. Nature, 163 (4148): 688. Thompson, S.D. 1982. Microhabitat utilization and foraging behavior of bipedal and quadrupedal heteromyid rodents. Ecology, 63(5): 1303-1312. Zeng, Z. and J.H. Brown. 1987. Population ecology of a desert rodent: Dipodomys merriami in the Chihuahuan Desert. Ecology, 68: 1238-1340. 58 CD > 0 u^ I^ 0 0 0 0 o en ^ ^ m^ r-^ en 0 0 ly^ 0 ir^ m^ (N mi ^ mi en oi ^ d ^ r~^ en en OO ON a\ ' ' 7 1 CO <q ir^ 0 0 0 0 10 10 CN VO 0 mi 0 03 tin 10 vo 0 vo in (N 0 10 mi m^ c/3 (U CD r-H Ui 00 ON ON OJ B m) 0 0 10 0 n5 ^ _( ,cti <+H ^H _c 00 'C 0 r-^ mi mi OJ mi m ^ t^ m ^ <N 0 0 10 0 mi mi CN mi G cd &< ;-( <U > < (U Ofi 03 t^ ON ON . H 0 j ti. m^ ir^ m ^ cd m ^ vo m ^ en mi (N CD mi m ^ i/n m ^ m ^ cr> mi mi ON ON C . 1-H vo 'St mi (N mi m^ m^ D, 00 t-H ^ ^ J^ 2 Xi C hilopsis Arrc ser 00 0 B 0 0 X 2 0 o <D TD 0 ;^ c 00 4:: 00 C/5 *-> Q . -H > s c uccul wale -S "oo c/3 ^ S2 E o cd o < 0 cd ;-! <U D X) VH 03 H *-> Mixed andy -* > c3 < a on C O 00 00 00 u t-i U U i-( U Z 59 ppi u eos eos 0 <u 0 27. <u c 3 (U 0 m^ <o cri vo m^ C5 m^ 0 0 m^ m^ 0 CD m) mi cd m3 > o '^ o oo ON ON ' 1 o CD m3 m^ m^ _, cd PH ^ CO VH (D +-> F-K i-H OO ON ON bi CD C mi o m^ ^ _ 4 3 c I ( P 00 C^ c <D GO r-o ON ,-^ *-"! a m3 CN VH <u > < m ^ cd ti. ON ON 0/ m^ CN G 1 ( o o m^ }-< D CO G l-H G O CO CO Cd CO 4 o o 3 >^ ed VH > < G O CO 1-H Xi cd o ffi cd Cd (/) 60 .707 .802 .803 .828 816 742 816 384 o '^ '^ Cxi CD cd (U VH CO C O CO o vo OO ^o r^ o o o o o o CD CD CD cd CO i-^ O sea C/3 e \ \ Cd i^ d) .696 o. -t > *.,, oo ON ON cd tin cB -t ' -t > 'co cd (U i > -a CO 1-H X cd J=l o r-o oo o r^ oo v CD O ON CD ^ MD CD ON , , CN OO CD r- r- -^ r--CD O Tt mi CD mi ' N ^ r-; o --f m) t^ CD OO o r^ CD ..G o cd (U O (U U( a o CO < 4=! u OO 0\ C CO ON 's I-H -1 > (U =i cd m^ 00 CO m3 vo OO o (U T3 > c . 1H - oo "t ^ CD ON oo CD -^ O ^ vo rr- o oo CM ,H CM m3 ro -^ oo m3 lO oo <N (N CD oo oo CD K. -4 > . 1 H VH O CO T3 CO =3 TD on Cd ive * > VH 00 a, ^ ^ rt o H . (U CO (Tt * > cd ON ON m3 Cd ti. OO 0\ oc ^ oo rr-; O vo r^ CD o oo O ro (N O oo oo oo m3 CD m3 o ro vo vo ro ON ro mi O oo c^ C3N ON t H <N m3 m3 CD vo r^ 0<5 CD 00 oo ro (N r^ oo oo mi OO vo I ro oo ro ON ro G 1-H r^ ^ rCD m^ ro oo CD ro (N ^ O^. ON I/O ^^ VH 00 ex o n 20S0te-Tarb ush Sc Arroyo Scrub xed Desert Scrub bilized Dune cculent Hill side Grassland Gras;sland oyo ppic e Dune 0 < 03 C<5 ro cd * > 1H - X CO wale cd cd >-> O Cd G 00 "^^ -rS: *f^ cd B cd i-H H Z c 3 00 p 00 0 20S0te }-i VH 0 < 0 u u u 61 cca Grassla p acia Hillsid < u T3 G >- 796 cd 472 X o (U J3 m3 Nonstabilized Dune (1) Coppice Dune (1) Grama Grassland (1) Yucca Grassland (2) Mixed Desert Scrub (2) Creosote Grassland (3) Figure 3.1 Photographs of the 12 habitats on Fort Bliss Military Base. The numbers in parentheses signify each habitat's percent vegetative cover. (1) 0-20%; (2) 20-40%; (3) 40-60%; (4) 60-80%; (5) 80-100% 62 Succulent Hillside (3) Acacia Hillside (3) Sandy Arroyo Scrub (4) Chilopsis Arroyo (4) Creosote - Tarbush Scrub (4) Figure 3.1 Continued. Swale (5) 63 CJ Cj -v; ' ed CO ^ ro (D l-i G 00 64 /K cd c/3 4 ' ^ ' ^ > < < ^ CO CO CO ed <4-< O bO 65 O o lA) ^ O . s P 00 (JO in ^-^ iri ^--' rT:r 00 ON ~~- ON ON t ^ ON r-i mi N ' o (U ^ O cd ~c >Q. 00 o\ :i: ca U_ C 1Q. GO oo S . ON > (U ^ IHH t^ o rj c zl) c; G > C3 I * ^H -o o < u O H CO G DH CX Cd H d ^ioso, ./ ^ c/3 Cd O C Q ^ T-H TB^H - Cd D ^'-.. 1-H S CO -H 1 I oo C Q -d o tin C O * > CO CO . <U <) L X> ^ cd ^ G - G VH o cd cd D H (U G ^ Cd 1 t * ' -> c2 G C ^ O O X X3 (/3 CO VH (tuui) llBjum-a 66 Rai for rt ro <u i-H ttem abi tats cd 1 1 CO a > Cd X ;^ ^ 'S G 00 tin Species Diversity per Habitat and Season f 1 000 g 0.800 Q g 0.600 t/5 T 3 Nonstabilized Dune Sandy Arroyo Scrub Mixed Desert Scrub (0.61) Swale Spring 1997 Fall 1997 Spring 1998 Fall 1998 -5i^-Succulent Hillside (0.72) - Chilopsis Arroyo . 'c a 0.400 . 0.200 J 0.000 Season g 1.000 - Acacia Hillside (0.63) I I --m. Grama Grassland -T4 Creosote Grassland -^< Creosote-Tarbush Scrub (0.11) - * Coppice Dune (0.36) 7 0.000 c5 e 60.0 -^50.0 ^40.0 = 30.0 S 20.0 ^ 10.0 0.0 Spring 1997 Fall 1997 Spring 1998 Fall 1998 Season Yucca Grassland Average Seasonal Rainfall Average rainfall (mm) Spring 1997 Fall 1997 Spring 1998 Fall 1998 Season tFigure 3.5. Species diversity values per habitat and season were compared with ^ seasonal rainfall averages. Positive correlation coefficients are shown in parentheses. 67 liside CO CO -a s rt cru TS o cru Ian TJ d c C! 00 -C oo G o ^ ,o ras Creosc>te-t arb ass Ilsi Sandy Arroy o 4> ffi -^ sis Arr rt CO o C/) o o c G Q (U N X cd -t ' CO a > CO c o (U DH O Acacia Yucca Creos Gram a c (J (J Q CL. 3 CO Q 73 X O O C TD O (U Swale 3 3 U a o S s C O ? ^ cd C 1 6 .X, *co X CO C <U ^ o 00 VH A! <4-H ^ ^ <U <U (U cd oc *-' DH O DH C> r^ CO Cd X X X ^ 00-5 o o .S 'I F? >-' m CO ^ ed O o <L) CO P DH vq fO <L> 00 68 ON ON r- OO ON * ' ON * ^H r^ ON ^ oo ON 00 ON 00 ^ all G '-"' tin c DH ^ cd UH 00 C/Q f i t ! sojrudBOO-^ JO O/Q 70 megalo manich _5 ^ 5U fc: -Ci <i3 Ci Ci D D D <K O hispidu Q.,' Oi CO D D O ^ microp Co arenici leiicog * S o * a flavesc ens I * C3 * -5 S t^ a cu s u ^ S: i^ =o s > ^ o Swa] M.D S.A. G G X G i-. CJ G (U OO 00 o t-H -a < u CHAPTER IV SUMMARY Fort Bliss Military Base is a multi-use, highly active military operation in terms of training activities, which include the use of tank, missile, and terrestrial combat procedures. Previous studies have demonstrated how these activities can have adverse effects on the wildlife populations existing on these military areas (Baumgardner, 1990; Brattstrom and Bondello, 1983; Carroll et al., 1999; Edwards et al, 1998; Gese et al., 1989; Shaw and Diersing, 1990; Stephenson et al., 1996). The main objective of this study was to provide baseline information, which is to be used in the development of a management plan that will allow training operations to be conducted on the base while avoiding negative impacts on its ecosystems. Many of the variables examined in this study were constant between trapping period and year and no distinct patterns in species diversity or rodent density were detected among or between habitats. In addition, no habitat was found to possess a unique fauna. Despite the lack of significant findings, there are suggested recommendations for managing the military landscape in order to prevent future conditions that may be of threat to Fort Bliss Military Base's faunal communities. Some of the habitats analyzed in this study should be used cautiously for military activities due to their high species diversity and rodent density values. The swale, Chilopsis arroyo, sandy arroyo scrub, and acacia hillside habitats may be important for maintaining overall diversity of the rodent community based on results of high species 74 diversity and rodent density. Likewise, as some of these habitats are relatively rare on the Fort Bliss Military Base, special attention should be given in terms of limiting training and other military activities that may have an adverse effect on these habitats. In particular, the swale habitat is one of the rarest habitats on the base and therefore should be given priority. Alternatively, one could argue that those habitats possessing low species diversity or rodent density values could be exploited for military activities because little is risked in terms of biodiversity. However, some of these habitats are rare, such as the coppice dune habitat. This habitat represents a fragile community and any disturbance may have a serious impact. Based on this observation, it is advised that military activities in these particular habitats be minimal. Water is a vital resource for rodent populations and this was demonstrated by the notable decline of species diversity and rodent density in most of the habitats during extensively dry periods (Spring 1998). Although the correlation analysis results were not significant, it may be necessary to restrict certain activities following prolonged dry periods, especially in those habitats given priority due to their rich biodiversity or rarity. Insights into the dynamics of community composition and species populations must come from long-term studies (Brown and Heske, 1990). The findings reported by Heske et al. (1994) in their 13-year desert rodent study presented results that were more representative of possible fluctuations in present populations. An 18-month study such as this one cannot provide such justifiable interpretations. For instance, both years of the study received a higher than normal amount of precipitation and consequently, data could 75 not be obtained for drought years akhough Spring 1998 was an exceptionally dry season. Fluctuations in precipitation may have an impact on vegetation and therefore alter plant composition within habitat types over the long term. It is difficult to ascertain if the results presented in this study are refiective of stable Chihuahuan Desert communities or if they are isolated occurrences. Therefore, to obtain more accurate data concerning the interaction between rodent communities and habitat preferences, a long-term project is suggested. The seasonal temporal fluctuations also are difficult to elucidate without additional comparative years. Although the results found in this study are informative, a more long-term project is advised to depict the true characteristics and interactions of rodent communities and their habitats. 76 Literature Cited Baumgardner, G. D. 1990. Mammal surveys on land condition trend plots at Fort Hood Texas. Unpublished report for U. S. Army Construction Engineering Research Lab. Department of Wildlife & Fisheries Sciences, Texas A&M University, College Station, TX, 136pp. Brattstrom, B. H. and M. C. Bondello. 1983. Effects of off-road vehicle noise on desert vertebrates. Pages 167-206 in Environmental effects of off-road vehicles; impacts and management in arid areas (R. H. Webb and H. G. Wilshire, eds.). Springer-Verlag, New York, N.Y. Brown, J.H. and E. J. Heske. 1990. Temporal changes in a Chihuahuan Desert rodent community. Oikos, 59:290-302. Carroll, D. S., R. C. Dowler, and C. W. Edwards. 1999. Estimates of relative abundance of the medium-sized mammals of Fort Hood, Texas, using scent-station visitation. Occasional Papers, Museum, Texas Tech University, 188:1-10. Edwards, C. W., R. C. Dowler, and D. S. Carroll. 1998. Assessing medium-sized mammal abundance at Fort Hood military installation using live-trapping and spotUght counts. Occasional Papers, Museum, Texas Tech University, 185:1-23. Gese, E. M., O. J. Rongstad, and W. R. Mytton. 1989. Change in coyote movements due to military activity. Journal of Wildlife Management, 53:334-339. Heske, E.J., J.H. Brown, and S. Mistry. 1994. Long-term experimental study of a Chihuahuan Desert rodent community: 13 years of competition. Ecology, 75: 438-445. Shaw, R. B. and V. E. Diersing. 1990. Tracked vehicle impacts on vegetation at the Pinon Canyon maneuver site, Colorado. Journal of Environmental Quality 19:234-243. Stephenson, T. R., M. R. Vaughn, and D. E. Andersen. 1996. Mule deer movements in response to military activity in southeast Colorado. Joumal of Wildlife Management, 60:777-787. 77 APPENDIX MATLAB FUNCTIONS % Data preparation for Ft Bliss data load 'rtbliss.txt'; % Load matrix from text file [genus,species,id,grid,habitat,trap,sex, weight,season,y ear,distance,datej = ... extrcols(ftbliss); % Separate columns clear ftbliss; save ftbliss; % ANOVA of abundances among habitats, separately for each species nspecies = max(species); for current_species = 1; %:nspecies i = find(species==current_species); habitat = habitat(i); trap = trap(i); grid = grid(i); season = season(i); odd_trap = mod(trap,2); % Delete original matrix % Separate anova for each species uh = unique(habitat); for currenthabitat = 1; %:length(uh) J =find(habitat== uh(current_habitat)); htrap = odd_trap(j); hseason = season(j); hgrid = grid(j); [hseason hgrid htrap] aseason = zeros(4*24*2,l); acount = zeros(4* 24*2,1); h = 0; for hs = 1:4 % Season 78 for grid = 1:24 for trappos = 0:1 h = h+l; aseason(h) = hs; acount(h) = sum(htrap==trappos & hgrid==grid & hseason==hs); end; end; end; [acount aseasonj [F,pr,df,ss,ms,varcomp,varprop] = anova(acount,aseason) end: end; % Comparisons of density among habitats and seasons cover_by_habitat = [ 1 4 2 5 3 4 3 1 2 4 1 2 ] ; [species,specid,habitat,trap,date 1 ,date2,date3,month,year] = extrcols(surv2); [uspecid,freqcapture] = uniquef(specid); nspec = length(uspecid); hab=[]; spec = [ ]; ici=[J; cover = [ ] ; season = [ ]; for is = 1 :nspec i = find(specid=uspecid(is)); leni = length(i); m = month(i); y = year(i); s = zeros(leni,l); forj = Irleni if(isin(ma),[4:6])&yG)=97) sG) = i; elseif (isin(ma),[8:10]) & ya)=97) 79 s(j) = 2; elseif (isin(mG),[4:6]) & yG)==98) sG) = 3; else (isin(mG),[8:10]) & yG)==98) sG) = 4; end; end; s = uniquef(s,l); lens = length(s); o = ones(lens,l); hab = [hab; habitat(i(l))*o]; spec = [spec; speciesG(l))*oJ; id = [id;specid(i(l))*o]; cover = [cover; cover_by_habitat(hab(is))*o]; season = [season; s]; end; save density; else load density; end; hectares_per_habitat = 8.32; % Mean density (inds/hectare) per habitat, across seasons if(i) disp(' > Mean density per habitat'); uhab = uniquef(hab); density = zeros(length(uhab),l); for is = 1 :length(uhab) i = find(hab=uhab(is)); 80 uid = uniquef(id(i)); n = length(uid); density(is) = n / hectares_per_habitat; end; density end; % Mean density (inds/hectare) per season per habitat if(l) disp(' > Mean density per season per habitat'); uhab = uniquef(hab); nhab = length(uhab); useas = uniquef(season); nseas = length(useas); density = zeros(nhab,nseas); for ih = 1 :nhab i = find(hab=uhab(ih)); idh = id(i); seasonh = season(i); for is = 1 inseas j = find(seasonh = useas(is)); n = length(idhG)); density(ih,is) = n / hectares_per_habitat; end; end; density end; 81 % Comparisons of diversity among habitats iter= 1000; uspec = uniquef(species, 1); nspec = length(uspec); uhab = uniquef(habitat,l); nhab = length(uhab) nseas = 4; % Number and identities of species % Correlations among habitats, sum across seasons if(l) counts = zeros(nspec,nhab); % Allocate species x habitat matrix for curhab = 1 :nhab % Fill in matrix for curspec = 1:nspec i = find(species=curspec & habitat==curhab); counts(curspec,curhab) = length(i); end; end; counts kind = 4; % Diversity measure = 1-D (Simpson) [D,Ddiff,Dpr,E,Ediff,Epr] = diverdiff(counts,kind,iter) end; % Comparisons of diversity among habitats clear; close all; load ftbliss; iter= 1000; iter = 50 uspec = uniquef(species, 1); nspec = length(uspec); uhab = uniquef(habitat,l); % Number and identities of species 82 nliab = length(uhab) nseas = 4; % Correlations among habitats, sum across seasons if(0) counts = zeros(nspec,nhab); % Allocate species x habitat matrix for curhab = 1 :nhab % Fill in matrix for curspec = 1:nspec i = find(species==curspec & habitat==curhab): counts(curspec,curhab) = length(i); end; end; counts kind = 4; % Diversity measure = 1-D (Simpson) [D,Ddiff,Dpr,E,Ediff,Epr] = diverdiff(counts,kind,iter) end; % Rarefaction among habitats if(0) freq = zeros(nspec,l); % Allocate species frequencies maxind = 0; for curhab = 1 :nhab % For each habitat, habind = 0; for curspec = 1 :nspec % Get species counts i = find(species=curspec & habitat==curhab); habind = habind + length(i); end; if (habind > maxind) maxind = habind; end; end; ES = zeros(maxind,nhab); for curhab = 1 :nhab % For each habitat, 83 for curspec = 1 :nspec % Get species counts i =find(species==curspec& habitat==curhab); freq(curspec) = length(i); end; figure; cs = rarefact(freq,[ J,[ ], 1); % Rarefaction putxlab('Number of individuals in habitat'); puttitle(sprintf('Habitat %d',curhab)); ES(1 :length(es),curhab) = es: end; tofile([[l:maxind]' ES],'Rarefact.txf); ncum= [ ]; ccum = [ ]; figure; hold on; for curhab = 1 :nhab c = ES(:,curhab); i = find(c==0); if (~isempty(i)) c(i) = [ J; end; lenc = length(c); plot(l:lenc,c,'k'); text(lenc+1 ,c(lenc),tostr(curhab)); ncum = [ncum; [l:lenc]']; ccum= [ccum; c]; end; putbnd(ncum,ccum); putxlab('Number of individuals in habitat*); putylab('Expected number of species'); puttifle('All Habitats'); hold off; end; 84 % Seasonal differences of diversity within habitats if(0) counts = zeros(nspec,nseas); for curhab = 1 :nhab % Cycle thru habitats curhab for curseas = 1 :nseas for curspec = 1 :nspec i = find(species==curspec & habitat==curhab & season==curseas); counts(curspec,curseas) = length(i); end; end; rowsum = sum(counts')'; i = find(rowsum==0); counts(i,:) = [ ]; nrows = size(counts,l); counts kind = 4; % Diversity measure = 1-D (Simpson) [D,Ddiff,Dpr,E,Ediff,Epr] = diverdiff(counts,kind,iter) end; end; % Correlations of diversity with rainfall across seasons, per habitat if(l) load rainfall.txt; season_per_rainfall=[l;l;NaN;2;2;2;NaN;NaN;NaN;NaN;NaN;NaN;3;3;NaN;4;4;4]; nrainfall = size(rainfall,2); counts = zeros(nspec,nseas); for curhab = 1 :nhab curhab for curseas = 1: nseas for curspec = I: nspec % Cycle thru habitats 85 i = find(species==curspec & habitat==curhab & season==curseas); counts(curspec,curseas) = length(i); end; end; rowsum = sum(counts')'; i = find(rowsum==0); counts(i,:) = [ ]; nrows = size(counts,l): counts divers = zeros(nseas,l); evenness = zeros(nseas,l); S = zeros(nseas,l); for curseas = 1: nseas kind = 4; % Diversity measure = 1-D (Simpson) [divers(curseas),evenness(curseas),S(curseas)] = ... diversity(counts(:,curseas),kind); end; figure; X = 1 inrainfall; r = rainfall(curhab,:); subplot(2,l,l); plot(x,r,'k'); putbnd(x,r); putylab('Rainfall'); puttitle(sprintf('Habitat%d',curhab)); d = NaN*ones( I,nrainfall); for curseas = I :nseas i =find(season_per_rainfall== curseas); d(i) = divers(curseas)*ones(l,length(i)); end; i = find(~isfinite(d)); x(i) = [ ] ; dG) = [ ]; r(i) = [ ]; 86 subplot(2,l,2); plot(x,d,'k'); putbnd(x,d); putxlab('Month'); putylab('Diversity'); [rankcorr_rainfall_diversity,prob] = rankcoiT(d.r) end; end; % Correlations amonjj habitat-composition vectors load ftbliss; iter= 1000; uspec = uniquef(species, 1); nspec = length(uspec); uhab = uniquef(habitat,l); nhab = length(uhab) nseas = 4; % Number and identities of species % Correlations among habitats, sum across seasons if(0) counts = zeros(nspec,nhab); % Allocate species x habitat matrix for curhab = 1 :nhab % Fill in matrix for curspec = 1 :nspec i = find(species=curspec & habitat==curhab); counts(curspec,curhab) = length(i); end; end; counts dist = complcor(counts); upgma(dist); putxlabC I -correlation'); puttitle('UPGMA of habitats by species composition'); 87 %[dist,topo,support] = cluster(counts,'complcor',iter,l) end; % Seasonal differences within habitats if(l) counts = zeros(nspec,nseas); for curhab = 1 :nhab % Cycle thru habitats curhab for curseas = 1:nseas for curspec = 1: nspec i = find(species==curspec & habitat==curhab & season==curseas): counts(curspec,curseas) = length(i); end; end; rowsum = sum(counts')'; i = find(rowsum==0); counts(i,:) = [ J; nrows = size(counts,l); counts corrseas = corr(counts) % dist = complcor(counts) dist = eucl(counts') pr = zeros(size(dist)); incr = 1/iter; % Observed % Observed for it = 1 liter for is = 1 :nseas counts(:,is) = counts(randperm(nrows),is); end; % permdist = complcor(counts); permdist = eucl(counts'); [ij] = fmd(permdist>=dist); if(~isempty(i)) fork= l:length(i) pr(i(k)o(k)) = pr(i(k)j(k)) + incr; 88 end; end; end; pr end; end; % Comparisons of home range among habitats clear; close all; if (0) load surv.txt; load trapcrds.txt; % Optionally construct database cover_by_habitat = [ 1 4 2 5 3 4 3 1 2 4 1 2 ] ; [species,specid,habitat,trap] = extrcols(surv); [uspecid,freqcapture] = uniquef(specid); nspec = length(uspecid); hab = zeros(nspec,l); spec = zeros(nspec,l); hr = zeros(nspec,l); id = zeros(nspec,l); cover = zeros(nspec,l); for is = 1 inspec i = find(specid=uspecid(is)); hab(is) = habitat(i(l)); spec(is) = speciesG(l)); idGs) = specid(i(l)); cover(is) = cover_by_habitat(hab(is)); trapid = trap(i); u = uniquef(trapid); if(length(u)>l) 89 crds = trapcrds(trapid,:); hr(is) = homerange(crds,2); end; end; save homerange; else load homerange; end; hr = sqrt(hr); % Sqrt of mean squared deviation from centroid % Mean homerange across species if(0) disp(' > Mean homerange across species'); mean_by_species = means(hr,spec) [F,pr,df,ss,ms,varcomp,varprop] = anova(hr,spec) %[pr,H,grp_medians,pr_pairs] = kruskwal(hr,spec,1000) figure; boxplot(spec,hr, 1); putxlab('Species'); putylab('Grid distribution'); uspec = uniquef(spec); for is = 1 :length(uspec) i = find(spec==uspec(is)); ifGength(i)>l) figure; histgram(hr(i)); putxlab('Grid distribution'); puttitle(sprintf('Species%d',is)); end; end; end; 90 /o Mean cover across habitats if(0) disp(' > Mean cover across habitats'); mean_by_habitat = means(hr,hab) ^ [F,pr,dfss,ms,varcomp,varprop] = anova(hr.hab) %[pr,H,grp_medians.pr_pairs] = kruskwal(hr,hab, 1000) figure; boxplot(hab,hr,l); putxlab('Habitat'); putylab('Grid distribution'); uhab = uniquef(hab); for is = l:length(uhab) i = find(hab==uhab(is)); if(lengthG)>l) figure; histgram(hr(i)); putxlab('Grid distribution'); puttifle(sprintf('Habitat%d',is)); end; end; end; % Mean homerange across cover levels if(0) disp(' > Mean homerange across cover levels'); mean_by_cover = means(hr,cover) [F,pr,df,ss,ms,varcomp,varprop] = anova(hr,cover) %[pr,H,grp_medians,pr_pairs] = kruskwal(hr,cover,1000) figure; boxplot(cover,hr, I); putxlab('Cover level'); putylab('Grid distribution'); 91 ucover = uniquef(cover); for is = 1 :length(ucover) i = find(cover==ucover(is)); if(lengthG)>l) figure; histgram(hr(i)); put.\lab('Grid distribution'): puttitle(sprintf('Cover level %d'.is)): end; end; end; % Mean homerange across cover levels, bv species if(l) disp('> Mean homerange across cover levels, by species'); uspec = uniquef(spec); for is = l:length(uspec) disp(sprintf(' Species %d',is)); i = find(spec==uspec(is)); sample_size = length(i) [ucover,ncover] = uniquef(cover(i)); [m,s] = means(hr(i),cover(i)); cover_sampsize_mean_stderr = [ucover ncover m s] if (length(ucover)> 1) [F,pr,df,ss,ms] = anova(hr(i),cover(i)) end; end; end; % Read matrices containing info about recaptures and trap coords, and % % estimate %home-range sizes [species,specid,habitat,trap] = extrcols(surv); clear surv; trapcrds = survtraps(:,2:3); 92 [month,year] = extrcols(dates); season = zeros(size(month)); i = find(year==97 & (month>=5 season(i) = ones(length(i),l); i = find(year==97 & (month>=8 season(i) = 2*ones(length(i),l); i = find(year==98 & (month>=5 season(i) = 3*ones(length(i),l); i = find(year==97 & (month>=8 season(i) = 4*ones(length(i),l); & month<=7)); & month<=l 1)); & month<=7)); & month<=l 1)); [uspecid,freqspecid] = uniquef(specid); nspec = length(uspecid); uhrsize = zeros(nspec, 1); uhab = zeros(nspec,l); uspecies = zeros(nspec,l); useason = zeros(nspec,l); % Home-range sizes for ispec = 1 :nspec i = find(specid==uspecid(ispec)); t = trap(i); uhab(ispec) = habitat(i(l)); uspecies(ispec) = species(i(l)); useason(ispec) = season(i(l)); uhrsize(ispec) = homerange(trapcrds(t,:)); end; tofile([uspecies uspecid uhab useason uhrsize],'hrsize.txt',4); % Read matrices containing info about recaptures and trap coords, and % estimate home-range sizes load 'hrsize.txt'; [species,specid,habitat,season,hrs] = extrcols(hrsize); clear hrsize; 93 uspecies = uniquef(species,l); uhabitat = uniquef(habitat,l); useason = uniquef(season,l); nspecies = length(uspecies); nhabitats = length(uhabitat); nseasons = length(useason); % Homerange size per species per habitat if(0) results = []; for is = 1 :nspecies for ih = 1:nhabitats i = find(species==uspecies(is) & habitat==uhabitat(ih)); n = length(i); if (~isempty(i)) results = [results; uspecies(is) uhabitat(ih) n mean(hrs(i)) std(hrs(i))]; end; end; end; tofile(results,'hrspechab.txt',4); end; % Homerange size per species per season if(l) results = []; for is = 1 :nspecies for it = 1 :nseasons i = find(species==uspecies(is) & season==useason(it)); n = length(i); if (~isempty(i)) results = [results; uspecies(is) useason(it) n mean(hrs(i)) std(hrs(i))]; end; end; end; tofile(results,'hrspecseas.txt',4); end; 94 PERMISSION TO COPY In presenting this thesis in partial ftilfillment of the requirements for a master's degree at Texas Tech University or Texas Tech University Health Sciences Center, I agree that the Library and my major department shall make it freely available for research purposes. Permission to copy this thesis for scholarly purposes may be granted by the Director of the Library or my major professor. It is understood that any copying or publication of this thesis for financial gain shall not be allowed without my ftirther written permission and that any user may be liable for copyright infringement. Agree (Permission is granted.) - I ' - Student Signature Date Disagree (Permission is not granted.) Student Signature Date

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