Lizard communities differ in structure, dominance, and niche partitioning in arid Southwestern U.S.

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Denise Ortega, Middle Tennessee State University, TN, Alesia J. Hallmark, Department of Biology, University of New Mexico, Albuquerque, NM, Alesia J. Hallmark, Battelle, National Ecological Observatory Network, Boulder, CO, Gregor L. Hamilton and Juan Camacho, Biology, University of New Mexico, Albuquerque, NM

Background/Question/Methods
Lizards are an abundant and diverse group of consumers in arid landscapes. Sevilleta National Wildlife Refuge (NWR) in central New Mexico is a major ecotone for reptiles, containing range boundaries for 80% of the reptile species found therein. The Sevilleta Long-Term Ecological Research program at this site has monitored many taxa, including plants, small mammals, bees, and grasshoppers, here for the past decades. Yet, little is known about the structure of lizard communities here, their effects on trophic dynamics, or how those communities are responding to climate change. Here, we ask (1) Are there differences in lizard community structure among the major biomes of Sevilleta NWR? (2) Do particular species dominate or strongly differ in abundance among habitats? and (3) Do species differ in their spatial or temporal usage of available niche space?
To answer these questions, we conducted repeated visual encounter surveys (VES) from June-August in 2019-2021. This simple method was cheap, minimally stressed the lizards, required minimal personnel, and was time-efficient. It yielded similar or better results than other trapping methods.
Results/Conclusions
In the summers of 2019-2021, we conducted visual encounter surveys of lizards within three biomes of the Sevilleta National Wildlife Refuge: Chihuahuan Desert Grassland, Chihuahuan Desert Creosote Shrubland, and Great Plains Grassland. Surveys captured similar species richness and diversity, but differing species abundance within each biomes. Multivariate ordination revealed that the biomes housed characteristic communities, even across multiple survey years. Each biome was strongly dominated by a different lizard species, but each of these were whiptails (genus Aspidoscelis). Using an indicator species analysis, we found that the abundance of the dominant whiptail species was the most distinctive trait of each community. Next, we compared the diurnal and seasonal timing of activity of each species, as well as the substrates they utilized in each biome. From this, we determined whether habitat affinity or interspecific competition was the most likely driver of each species abundance.
Our study is one of the first to quantify the abundance and community structure of lizards in this region. This is a crucial first step in understanding the vital trophic connections between lizards and other community members and establishes a baseline from which to monitor changes.