Habitat selection of the desert night lizard (Xantusia vigilis) on Mojave yucca (Yucca schidigera) in the Mojave Desert, California

Kirsten Boylan1, Robert Degen2, Carly Sanchez3, Krista Schmidt4, Chantal Sengsourinho5

University of California, San Diego1, University of California, Merced2, University of California, Santa Cruz3, University of California, Davis4 , University of California, San Diego5

ABSTRACT

The Mojave Desert is a massive natural ecosystem that acts as a biodiversity hotspot for hundreds of different species. However, there has been little research into many of the organisms that comprise these ecosystems, one being the desert night lizard (Xantusia vigilis). Our study examined the relationship between the common X. vigilis and the Mojave yucca (Yucca schidigera). We investigated whether X. vigilis exhibits habitat preference for fallen Y. schidigera log microhabitats and what factors make certain log microhabitats more suitable for X. vigilis inhabitation. We found that X. vigilis preferred Y. schidigera logs that were larger in circumference and showed no preference for dead or live clonal stands of Y. schidigera. When invertebrates were present, X. vigilis was approximately 50% more likely to also be present. These results suggest that X. vigilis have preferences for different types of Y. schidigera logs and logs where invertebrates are present. These findings are important as they help in understanding one of the Mojave Desert’s most abundant reptile species and the ecosystems of the Mojave Desert as a whole.

INTRODUCTION such as the Mojave Desert in California. Habitat selection is an important The Mojave Desert has extreme factor in the shaping of an ecosystem. temperature fluctuations, ranging from Where an animal chooses to live and below freezing to over 134.6 degrees forage can affect distributions of plants, Fahrenheit (Schoenherr 2017). It is also predators and prey, and can influence extremely dry, with less than 10 inches ecosystem processes. Habitat selection of rain per year on average (Schoenherr usually occurs at smaller, local scales 2017). Because of these harsh climatic (Penalver-Alcazar et. al. 2016). This is a characteristics, species that inhabit this significant concept in harsh region often have specific habitat environments with limited resources, requirements and preferences in order to survive (Schoenherr 2017).

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Our study investigated the habitat understanding of X. vigilis distribution selection and preference of the desert and ecology in the Mojave Desert. night lizard (Xantusia vigilis). As a sedentary vertebrate, the X. vigilis METHODS spends most of its life hidden beneath Study Site fallen vegetation, rocks, and debris (Marlow 2000). Its prey includes We conducted our research within the termites, beetles, spiders, ants, and Sweeney Granite Mountains Desert various other invertebrates. The X. Research Center in the Mojave Desert in vigilis is believed to have a stable California. Sites were within a two-mile population and is listed as a species of radius from the research center and least concern. This species’ life history is were chosen based on high Y. schidigera unique in that they produce two to four presence. Each macro-plot spanned 50 offspring per year with limited m by 100 m. We collected data over a dispersion as they form family groups span of four days from November 5–8, (Mattern 2016). Some studies have 2017. been conducted regarding the Data Collection relationship between X. vigilis and the Joshua tree (Yucca brevifolia) while less At each site, we sampled every is known about X. vigilis and its downed Y. schidigera log, avoiding logs interactions with the Mojave yucca (Y. with woodrat middens. Sampling schidigera). involved gently flipping and shaking logs The purpose of our study was to to look for X. vigilis and invertebrates. investigate X. vigilis’ relationship with Y. We caught all X. vigilis by hand and used schidigera and to examine patterns both forceps to capture invertebrates before in habitat preference and potential preserving them in vials containing 91% bottom-up mechanisms between these ethanol. Each log and X. vigilis was two species. We sought to determine returned to its original place once whether X. vigilis exhibited microhabitat measurements were taken. For each X. preference in different Y. schidigera vigilis, we measured mass (g) and snout- characteristics such as size and clonal to-vent (SVL) length (mm). We also status. Additionally, we examined recorded Y. schidigera circumference whether certain Y. schidigera (m) and noted whether each sampled characteristics provided more optimum stand of Y. schidigera was alive or dead. habitat for X. vigilis. Lastly, by examining We identified invertebrates by the potential bottom-up mechanisms in morphospecies and calculated their the relationship between invertebrate species richness as the number of presence (as a proxy for food resources) morpho-species found under each Y. and the presence of X. vigilis, we schidigera log. investigated why certain Y. schidigera might be preferable. Our study provides baseline data that lends to a greater

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Statistical Analyses RESULTS All statistical analyses were performed Out of 108 sampled Y. schidigera logs, using R 3.4.1. Using logistic regression, 54% had X. vigilis present. As log we examined the relationship between circumference increased, the probability Y. schidigera characteristics (clonal of encountering X. vigilis under that log diameter, log height, length, increased (n = 108, p = 0.01; Figure 1a). circumference) and presence of X. The probability of encountering vigilis. We also used logistic regression invertebrates also increased as log to examine the relationship between Y. circumference increased (n = 108, p = schidigera characteristics (clonal 0.01; Figure 1b). There was no diameter, log height, length, significant difference in X. vigilis circumference) and presence of presence between dead and live Y. invertebrates. We used t-tests to schidigera stands (n = 108, p = 0.19; investigate differences in X. vigilis Figure 2a). The presence of presence and invertebrate presence invertebrates under dead Y. schidigera between dead and live stands of Y. did not differ from under live Y. schidigera. Finally, we used a t-test to schidigera stands (n = 108, p = 0.23; analyze the correlation between Figure 2b). Lastly, the proportion of Y. invertebrate and X. vigilis presence. schidigera with X. vigilis present was

Figure 1. Probability of Xantusia presence (1a) invertebrate presence (1b) by yucca circumference. Relationship between Y. schidigera circumference and the probability of encountering X. vigilis (1a) and invertebrate presence (1b) shown by logistic regression.

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Figure 2. Xantusia and invertebrate presence by yucca status. Relationship between Y. schidigera mortality and the probability of encountering X. vigilis (2a) and other invertebrates (2b) shown by proportion of X. vigilis or invertebrates present with binomial error in relation to Y. schidigera status.

significantly greater when invertebrates were present (n = 108, p < 0.01; Figure 3). None of the other tests (regarding diameter, height, length) were significant.

DISCUSSION Overall, we found that X. vigilis seem to exhibit habitat preference based on quality level of Y. schidigera, and that these habitat associations may be driven by greater resource availability. The many variables of Y. schidigera show that there is heterogeneity within X. vigilis habitat structure. We found an abundance of X. vigilis in the macro-plots, but they only inhabited

Figure 3. Xantusia presence by invertebrate half of the available logs. A case in presence. Relationship between invertebrate Southern Nevada found that there was presence and X. vigilis presence is shown by preference of Y. schidigera to Y. the proportion of X. vigilis with binomial error brevifolia when found in the same area in relation to where invertebrates are present (Deacon et al. 1966). This study under logs. supports our speculations that X. vigilis

identify Y. schidigera as an optimal habitat; even in areas with other types of yucca present, X. vigilis still prefer Y.

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schidigera. After analyzing multiple Y. did not differ significantly. In contrast, schidigera variables, we determined Deacon et. al. (1966) found that the there were two main log presence of a live Y. schidigera characteristics that X. vigilis showed provided shade and assisted in preference for. moisture retainment in the understory. Our study showed that X. vigilis were Because of this study, we predicted more likely to be found under Y. this may have an influence on habitat schidigera when invertebrates were selection in X. vigilis since it will help present. Detritivorous insects, such as keep them cool in the arid desert. One termites and ants, prefer to consume reason we may not have found a the fiber of decayed plants (Morafka correlation between the presence of 1973). These detritivores are the main live Y. schidigera and the presence of food source of X. vigilis (Morafka X. vigilis is the existence of animals 1973). Favorability of logs containing such as desert woodrats (Neotoma detritivorous insects also occurred in lepida). X. vigilis have been shown to Pinnacles National Park (Morafka be absent from Y. schidigera with N. 1973). Xantusia vigilis commonly lepida middens, suggesting predation resided in digger pine that contained (Miller 1951). Even without the termites, and X. vigilis stomach presence of a midden in Y. schidigera, contents revealed they were also the N. lepida may use these plants for eating ants (Morafka 1973). Both our cover and foraging, deterring X. vigilis. study and Morafka (1973) indicate that Predator presence may counteract the food availability is the main driving potential benefits of being near a live force behind X. vigilis habitat selection. Y. schidigera stand. Our study also showed that X. vigilis Although our study measured and prefered larger fallen Y. schidigera compared multiple variables of habitat logs. Increased habitat area is a preference, the main factors that necessity as X. vigilis reside in family determine habitat preference were not groups for one to four years at a time recorded. According to Penalver- (Marlow 2000). X. vigilis are known to Alcazar et al. (2016), spatial congregate during the winter season in heterogeneity models require data on large numbers, with up to 14 different sexes and age class of a individuals under one log (Marlow selected species to truly define a 2000). Because X. vigilis are reclusive species’ ecological requirements. and socially aggregated, increased Nevertheless, we were able to define habitat area and the presence of some characteristics of X. vigilis’ invertebrates in logs is essential to preferred habitat that future studies reduce competition. could build upon. As X. vigilis is highly Finally, our study did not find a vulnerable to changes in abiotic and significant difference in X. vigilis’ biotic conditions, it is important to preference for dead or live Y. understand not only habitat schidigera stands. Insect presence in preference, but spatial heterogeneity dead or live Y. schidigera stands also to determine future population

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dynamics. Exponential urbanization of Habitat Relationships System California desert land will transform the Department of Fish and Wildlife California Interagency Wildlife Task Group. ecological landscape to the disadvantage of X. vigilis. Finally, Mattern, J. 2016. Desert night lizard (Xantusia knowledge of X. vigilis habitat vigilis). Retrieved 10 November 2017. preference and spatial heterogeneity will allow the future prediction of Miller, M. 1951. Some aspects of the life history of the yucca night lizard, Xantusia response to habitat alterations from vigilis. Copeia, 1951(2):114–120. climate change. Morafka, D. J., and B. H. Banta. 1973. The ACKNOWLEDGEMENTS distribution and microhabitat of Xantusia vigilis in the Pinnacles National This work was performed at the Monument, San Benito and Monterey University of California’s Sweeney Counties, California. Society for the Study Granite Mountains Desert Research of Amphibians and Reptiles, 7:97–108. Center, doi:10.21973/N3S942. Penalver-Alcazar, M., Aragon, P., Breedveld, M. REFERENCES C., P. S. Fitze. 2016. Microhabitat selection in the common lizard: implications of Deacon, J. E., Bradley, W. G., and K. S. Moor. biotic interactions, age, sex, local 1966. Habitat of the lizard Xantusia vigilis processes, and model transferability in Southern Nevada. The Southwestern among populations. Ecology and Evolution Naturalist 11:126–128. 6:3594–3607.

Marlow, R. 2000. Life history account for Schoenherr, A. A. 2017. A natural history of desert night lizard. California Wildlife California (Second ed.). Oakland, CA: University of California Press.

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