The Contribution of environmental variables on small mammal species richness and relative abundance in Eastern Nevada

The purpose of this study is to determine how four environmental variables: elevation, latitude, soil type, and vegetation impact the relative abundance of Peromyscus maniculatus and the species richness of small mammal populations in Eastern Nevada. In order to complete this study, a survey of small mammals was completed in the following 8 Eastern Nevada valleys: Delamar, Dry Lake, Dry LakeMuleshoe,Cave, Lake, Snake, Spring, White River. In each valley, transects of Sherman live traps will be set up for 3 consecutive nights (O'Farrell et al 1977). Data on elevation, latitude, soil type, and vegetation were taken at each trap site. Non-parametric PLR was then used to assess which variables were significant in determining P. maniculatus relative abundance and overall species richness. Polytomous logistic regression showed that soil was the only significant variable in determining species richness and relative abundance with a P-value of<.001. Acknowledgments I would like to thank a number of people for helping me turn an idea into a thesis. First and foremost, the Southern Nevada Water Authority for help with trapping efforts, specifically Zane Marshall, SNWA Sr Biologist, Environmental Planning and Aaron Ambos, SNWA Environmental Biologist II, Environmental Planning who also served as content advisors; Dr. Timothy Farnham, Department of Environmental Studies, UNLV, thesis class advisor and mentor; Sean Harris, Senior Research Biologist, SWCA, for help with data analysis and general formatting; and lastly, the 2005-2006 thesis class for reading draft after draft on my thesis. With out all of these people this thesis would not have become what it is today. Thank you. Introduction The purpose of this study is to determine how four environmental variables: elevation, latitude, soil type, and vegetation impact the relative abundance ofPeromyscus maniculatus and the species richness of small mammal populations in Eastern Nevada. For this study a small mammal includes species within the Order Rodentia. Previous studies have determined that latitude and elevation are the two most universal ecological gradients (McCain 1994). In other words, it is likely that latitude and elevation will be driving forces for both species richness and relative abundance. On a global scale it has been shown that biodiversity decreases with increased latitude and elevation (Lomolino et al 2005). Soil and vegetation were chosen because large-scale features of habitats can affect the distribution of small mammals (Wolff et al 1997). In particular, some small mammals are favored by changes in resource availability (Tabeni and Ojeda 2005). This is reflected in the increased abundance of small mammals in areas disturbed by ranching activities (Jones and Longland 1999). Species richness of small mammals is an important conservation issue for many reasons. Biological diversity encompasses the infinite variety of life and living processes that have and will occur in the biosphere (Child 2003). In this particular study, determining what factors drive the species richness of small mammal populations in Eastern Nevada is important because it will help conservation efforts in that particular area. For instance, it may help determine appropriate land use designations. Through this study, I will be able to provide the factors determined to be significant for small mammal habitat so that land managers can make informed decisions. Small mammal relative abundance is the other critical component of this study. Relative abundance is an important concept when applied to diversity. For example, a particular area may have a low diversity or low species richness, meaning there are not very many different types of small mammals found there. However, if this same area has a high relative abundance for a particular species, perhaps that species is well suited for that habitat or the habitat itself is beneficial to the species (Anderson and Gutzwiller 1996). This concept often happens in disturbed habitats. In the Great Basin, a study determined that habitats with feral horse grazing had less community completeness and 1.1 7.4 tunes greater P. maniculatus than sites without feral horse grazing (Beever and Brussard 2004). Peromyscus maniculatus was chosen for the relative abundance study for many reasons. In most areas of Nevada P. maniculatus is the most abundant mammal (Hall 1946). Peromyscus maniculatus is also known to inhabit a tremendous number of environments, from deserts to grasslands to woodlands (Zeveloff 1988). Furthermore, they are active throughout the year (Zeveloff 1988). This particular study is only aimed at determining the driving factors for relative abundance of P. maniculatus and species richness in small mammals of Eastern Nevada. Future research can be done to compare these factors and determine how to improve the biodiversity of this particular area. This study will therefore contribute to the future research of Northeastern Nevada's ecological gradients and biodiversity. Similar studies involving environmental variables and small mammals have been completed in the past. A study done on species diversity of seed eating desert rodents in sand dune habitats concluded that the diversity of shrubs has no direct effect on the diversity of rodents (Brown 1973). However, according to Price et al, Heteromyid distributions were correlated to vegetation in earlier studies (1978). Similarly, O'Farrell and Clark (1986) found that there was a tendency for higher small mammal species diversity in more diverse habitat types. Questions/Hypothesis Two specific questions will be asked regarding the four factors. First, which factors: elevation, latitude, soil type, or vegetation, affect the relative abundance of small mammal populations in Eastern Nevada? To answer this question, P. maniculatus, a widely occurring deer mouse in Nevada, will be used to estimate relative abundance (Hall 1946). The factors will then be analyzed using a principle component analysis. This analysis will determine which factors are most important for the relative abundance of P. maniculatus in Eastern Nevada. The second question will ask which of these factors; elevation, latitude, temperature, or habitat, affect the species richness of small mammal populations in Eastern Nevada. During trapping, 15 different species of small mammals were caught in a number of different Eastern Nevada valleys. These species along with the driving factors will be analyzed with the principle component analysis, thus determining which factors are the most important for the relative abundance and species richness of these particular communities. hi this study, I hypothesize that the relative abundance of P. maniculatus and species richness of small mammals in Eastern Nevada will be affected by change in elevation, latitude, soil type, and vegetation. Due to the relatively narrow geographic area encompassed by this study it is possible that latitude will have little to no affect on species richness and relative abundance. Furthermore, past research indicates that soil type and vegetation will be the determining factors for relative abundance and species richness of small mammals in Eastern Nevada. In order to complete this study, a survey of small mammals will be completed in the following 8 Eastern Nevada valleys: Delamar, Dry Lake, Dry LakeMuleshoe,Cave, Lake, Snake, Spring, White River, hi each valley, transects of Sherman live traps will be set up for 3 consecutive nights (O'Farrell et al 1977). The transects will be located in primary vegetation types determined by a REGAP data set. The traps will be baited in the evening and checked in the morning. The animals found will be identified by experts from the Southern Nevada Water Authority. Animals will be marked to keep track of recaptures. Once an exhaustive small mammal survey of each of the valleys mentioned is complete, the data collected will be compiled into a database. During the surveys, the elevation and latitude data will be taken by a Global Positioning System (GPS), the soil data will come from onsite observations, and the vegetation types will be identified using the Region-Wide Gap Analysis Program (REGAP). The data specifically associated with the four variables (elevation, latitude, soil type, and vegetation) along with mammals collected, will then be analyzed using a multiple variable analysis technique. For this particular study, polytomous logistic regression (PLR), a type of multiple variable analyses will be used. The results will show which variable, vegetation, latitude, elevation, or soil is most important when determining relative abundance and species richness for Eastern Nevada. Study Area The study area encompasses 9600 square miles of Eastern Nevada and falls roughly between the towns of Alamo, Nevada to the South and Ely, Nevada to the North. The area is bordered to the East by the State of Utah and to the West by Highway 318. In the Southern portion of the study area, in Delamar and Dry Lake Valleys, the floristic community transitions from the Sonoran Province (Mojavean Subprovince) to the Great Basin Province (Flora of North America, V. 1, Chpt. 6). The remainder of the study area falls strictly within the Great Basin floristic province. The area also encompasses both Lower and Upper Sonoran life zones. Methods Data Collection The small mammal surveys were conducted between 17 May and 14 October 2005 in the following Eastern Nevada basins: Cave, Delamar, Dry Lake, Lake, Spring, Snake, and White River Vallies (Map: Appendix A). The specific survey site locations were chosen based on the Region-Wide Gap Analysis Program (REGAP) vegetation data and field observations of specific vegetation communities (Ramsey 2000). Within each valley several unique vegetative communities were sampled. Using the REGAP's Intersecting Vegetation Coverage Description, each community was classified as one of the following: • Great Basin Pinyon-Juniper Woodland • Great Basin Xeric Mixed Sagebrush Shrubland • Inter-Mountain Basins Big Sagebrush Shrubland • Inter-Mountain Basins Big Sagebrush Steppe • Inter-Mountain Basins Greasewood Flat • Inter-Mountain Basins Mixed Salt Desert Scrub • Inter-Mountain Basin Semi-Desert Shrub Steppe Soil types at the survey sites were determined by onsite observations. Each soil type was classified as one of the following: • Loam • Sand with gravel • Loam with sand • Sand dunes • Loam with sand and gravel • Sand dunes with gravel • Loam with silt • Silt • Loam with silt and gravel • Silt with sand • Sand At each survey site, small mammal species richness and relative abundance was determined using mark and recapture (Nietfield 1996). Small mammals were captured using 12 inch Sherman folding live traps (Maly and Crawford 1985). The traps were laid out in two parallel transects, A and B lines, 53 meters apart (O'Farrell and Clark 1986). At the beginning of the A line, UTM coordinates were recorded. This served as a reference point and as the latitude variable of the study. Elevation was recorded at this same location. Each transect consisted of 20 single trap stations spaced 15 meters apart (Transect Layout and Trap: Appendix B). Traps were baited with a seed, oat, and peanut butter mixture (Schemnitz 1996) and set in the late afternoon. Traps were checked after sunrise the following morning. At both set and check time; temperature, cloud cover, and wind speed were recorded since weather can affect the capture of small mammals (Gentry et all966). Moon phase was also noted (Data Sheet: Appendix D). All captured animals were weighed and identified to species, sex, sexual condition, and age. Occasionally, foot and tail measurements were taken to identify between similar species. New captures were marked by clipping a small patch of hair on