A Habitat Suitability Analysis of Texas Horned Lizards in Texas and New Mexico

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Authors Piehler, Reid

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A HABITAT SUITABILITY ANALYSIS OF TEXAS HORNED LIZARDS IN TEXAS AND NEW MEXICO

By

REID WOLFGANG PIEHLER

MASTER OF SCIENCE GEOGRAPHIC INFORMATION SYSTEMS TECHNOLOGY FINAL PROJECT

THE UNIVERSITY OF ARIZONA

2021

To my Mom and Dad.

ACKNOWLEDGMENTS

I would like to thank my parents and my brother for all their love and support. I also want to thank my darling Emily for all her help, compassion, and understanding throughout this undertaking. I could not have done this without them, and I am deeply grateful for everything.

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TABLE OF CONTENTS

page

ACKNOWLEDGMENTS ...... 3

LIST OF TABLES ...... 5

LIST OF FIGURES ...... 7

LIST OF ABBREVIATIONS ...... 9

ABSTRACT ...... 10

INTRODUCTION ...... 11

Texas Horned Lizards and their habitat ...... 11

DATA AND METHODOLOGY ...... 19

Variables and Datasets ...... 19 Dataset Maps and Metadata ...... 25 Methodology ...... 40 Workflow Charts ...... 46

ASSUMPTIONS AND RESULTS ...... 48

Assumptions ...... 48 Results and Models ...... 49 Spatial and OLS Models ...... 55 Habitat Suitability Map ...... 58 Most Suitable Area Maps ...... 58 Least Suitable Area Maps ...... 61

DISCUSSION AND CONCLUSION...... 62

Discussion ...... 62 Conclusion ...... 67

LIST OF REFERENCES ...... 69

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LIST OF TABLES

Table page

Table 2-1: Texas Horned Lizard Watch 10 – Year Summary Report 1997 - 2006 ...... 25

Table 2-2: Checklist of the Amphibians and Reptiles of New Mexico, USA with Notes on Taxonomy, Status, and Distribution...... 25

Table 2-3: TIGER/Line Shapefile, Texas, Current County Subdivision State-based ..... 26

Table 2-4: TIGER/Line Shapefile, New Mexico, Current County Subdivision State- based ...... 26

Table 2-5: GABI Project Distribution of Red Harvester Ants (Pogonomyrmex barbatus) ...... 27

Table 2-6: Early Detection & Distribution Mapping System, Distribution of Red Imported Fire Ants (Solenopsis invicta) ...... 27

Table 2-7: NLCD Land Cover (CONUS) All Years ...... 30

Table 2-8: National Hydrography Dataset ...... 31

Table 2-9: Climate at a Glance Data, Temperature and Precipitation, Texas and New Mexico ...... 33

Table 2-10: North America Elevation 1-Kilometer Resolution GRID ...... 36

Table 2-11: Annual Estimates of the Resident Population, New Mexico ...... 36

Table 2-12: Texas Population Estimates Program ...... 37

Table 2-13: New Mexico Road Centerlines ...... 37

Table 2-14: TxDOT Roadway Inventory ...... 38

Table 2-15: Natural Gas Pipelines ...... 38

Table 2-16: County Estimates: Cattle – New Mexico ...... 39

Table 2-17: Texas Counties: Cattle Population in 2012 ...... 39

Table 3-1. Spatial Error Model for Texas Horned Lizard Habitat Suitability in Texas. .. 55

Table 3-2. OLS Model for Texas Horned Lizard Habitat Suitability in New Mexico...... 56

Table 3-3. Top Ten Most Suitable Counties in Texas for Texas Horned Lizards...... 56

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Table 3-4. Top Ten Most Suitable Counties in New Mexico for Texas Horned Lizards...... 56

Table 3-5. Top Ten Least Suitable Counties in Texas for Texas Horned Lizards...... 57

Table 3-6. Top Ten Least Suitable Counties in New Mexico for Texas Horned Lizards...... 57

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LIST OF FIGURES

Figure page

Figure 1-1: Texas Horned Lizard (Kansas Herpetofaunal Atlas) ...... 17

Figure 1-2: Texas Horned Lizard Eating an Ant (San Antonio Zoo) ...... 18

Figure 1-3: Texas Horned Lizard after Shooting Blood from its Eyes (David G. Koziol) ...... 18

Figure 2-1: Texas Horned Lizard Range Map ...... 25

Figure 2-2: Red Harvester Ant and Imported Fire Ant Range Map ...... 26

Figure 2-3: Majority Land Classification Map ...... 27

Figure 2-4: Percentage Developed Map ...... 28

Figure 2-5: Percentage Forest Map ...... 28

Figure 2-6: Percentage Hay, Crops, or Pastures Map...... 29

Figure 2-7: Percentage Wetlands Map ...... 29

Figure 2-8: Percentage Shrubs Map ...... 30

Figure 2-9: Percentage Herbaceous Map ...... 30

Figure 2-10: River Density by County Map ...... 31

Figure 2-11: Average Tree Canopy Value Map ...... 32

Figure 2-12: Total Water Body Area by County Map ...... 32

Figure 2-13: Average Temperature in January Map ...... 33

Figure 2-14: Average Temperature in June Map ...... 34

Figure 2-15: Average Precipitation in January Map ...... 34

Figure 2-16: Average Precipitation in June Map ...... 35

Figure 2-17: Average Elevation by County Map ...... 35

Figure 2-18: Population Density by County Map ...... 36

Figure 2-19: Road Density by County Map ...... 37

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Figure 2-20: Natural Gas Pipeline Density by County Map ...... 38

Figure 2-21: Cattle Population Density by County Map ...... 39

Figure 2-22: Study Workflow ...... 46

Figure 2-23: Spatial Regression Decision Process (Anselin, 2005) ...... 47

Figure 3-1: Habitat Suitability Map of Texas Horned Lizards in Texas and New Mexico ...... 58

Figure 3-2: Habitat Suitability Map of Texas Horned Lizards in the Edwards Plateau and Big Bend Region, Texas ...... 58

Figure 3-3: Habitat Suitability Map of Texas Horned Lizards in North East New Mexico and the Texas Panhandle ...... 59

Figure 3-4: Habitat Suitability Map of Texas Horned Lizards in South New Mexico and West Texas ...... 59

Figure 3-5: Habitat Suitability Map of Texas Horned Lizards in South Texas ...... 60

Figure 3-6: Habitat Suitability Map of Texas Horned Lizards in West Texas ...... 60

Figure 3-7: Habitat Suitability Map of Texas Horned Lizards in East Texas ...... 61

Figure 3-8: Habitat Suitability Map of Texas Horned Lizards in North West New Mexico ...... 61

Figure 4-1: 600th Successful Texas Horned Lizard Hatching at the Fort Worth Zoo ..... 68

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LIST OF ABBREVIATIONS

TPWD Texas Parks and Wildlife Department

OLS Ordinary Least Squares

FIPS Federal Information Processing System

GABI Global Ant Biodiversity Informatics

NLCD National Land Cover Database

NHD National Hydrography Dataset

USGS United States Geological Survey

EPA Environmental Protection Agency

NOAA National Oceanic and Atmospheric Administration

NCDC National Climatic Data Center

USDA United States Department of Agriculture

TxDOT Texas Department of Transportation

NGA National Geospatial-Intelligence Agency

INEGI Instituto Nacional de Estadística y Geografía

LM Lagrange Multiplier

AIC Akaike Information Criterion

VIF Variance Inflation Factor

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ABSTRACT

The Texas Horned Lizard (Phrynosoma cornutum) is a state-protected lizard native to the American Southwest. To rebuild the Texas Horned Lizard population, they are bred in captivity and released into the wild. Identifying factors that impact habitat suitability is vital to finding the proper areas for release and reintroduction.

Environmental and human factors were examined in Texas and New Mexico counties native to the Texas Horned Lizard, as well as counties without known sightings, to determine which factors most impact habitat suitability. Four statistical and geospatial software packages were used to map, analyze, and evaluate 24 potential variables and it was discovered that elevation, road density, natural gas pipeline density, seasonal rainfall, land use category, and proximity to Red Harvester Ants are all statistically significant to Texas Horned Lizard habitat suitability at a 95% confidence level. Texas

Horned Lizards are most prevalent in counties with low elevation, high percentage of open water or snow, low precipitation levels, and native habitats for Red Harvester Ants.

Horned Lizards are also less prevalent where road density or natural gas pipeline density is high. No significant difference was detected in habitat suitability relative to

Imported Fire Ants as suggested in previous studies. To protect viable environments for

Texas Horned Lizard reintroduction, pipeline and road construction should be limited in the most suitable regions: eastern and southern New Mexico, the southern Gulf Coast, the Texas Panhandle, Edwards Plateau, and along the Rio Grande.

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INTRODUCTION

Texas Horned Lizards and their habitat

Texas Horned Lizards (Phrynosoma cornutum) are small, desert lizards that have long been a beloved staple in the ecosystems of the American Southwest. They are commonly found throughout Texas and Oklahoma, as well as parts of Kansas, New

Mexico, Northern Mexico, and Arizona (Johnson Linam, 2008). Certain Native American tribes viewed Horned Lizards as a sign of good luck and groups of horned lizards were said to protect against unseen dangers (Donaldson, 1992). Horned Lizards are also a symbol of strength in the Hopi, Navajo, Papago, Pima, Tarahumara and Zuni cultures

(Hodges and Pianka, 2021). Horned Lizards were first observed by Europeans during

Francisco Hernandez’ 1570-1577 expedition in Mexico, where he witnessed Texas

Horned Lizards squirting blood from their eyes to ward off predators (Hodges, 2019).

Colloquially, they are known by a variety of names, such as “Horned Frogs” and “Horny

Toads”. Texas Horned Lizards are covered in spiny scales, with the largest horns protruding from the crown of their skull. When fully grown, they can weigh between 25 and 90 grams, and measure between 69 and 114 millimeters for females and 94 millimeters for males (Walker, 2018).

Historically, Texas Horned Lizards were some of the most common and abundant reptiles in Texas and Oklahoma. However, their population has recently been in a steady decline, leading to their current status. The native population of Texas

Horned Lizards began declining in the early 1950’s, due in part to them being sold to tourists as souvenirs, prompting Texas to start protecting them in 1967 (Dingus, 1982).

Currently it is illegal to own a Texas Horned Lizard without government approval. They have since become the focus of breeding and reintroduction initiatives to rebuild their

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wild population. These initiatives are spear-headed by organizations such as the Fort

Worth Zoo, Dallas Zoo, San Antonio Zoo, Tinker Air Force Base, Texas Christian

University, and the Texas Parks and Wildlife Department. Finding the best sites for reintroduction is critical to ensuring the animal’s survival and the expansion of the native population. To this end, the native habitats of Texas Horned Lizards have been studied so that similar reintroduction locations can be identified. While these studies have been largely conducted at the microhabitat level by Texas agencies, there are relatively few studies that identify potential habitats at the state and interstate levels. Since Horned

Lizards have been shown in a 1999 study to move their home range throughout the seasons, the suitability of an area needs to be examined beyond just the microhabitat

scale (Fair and Henke, 1999). Additionally, while Texas Horned Lizards have been

extensively studied in Texas and Oklahoma, very little information exists regarding their

habitats and range inside the neighboring state of New Mexico.

Habitat selection for the Texas Horned Lizard is influenced by a multitude of

factors such as availability of prey, extent of livestock grazing, proximity to certain types

of ground cover, and proximity to predators and nuisance animals. The main prey of

choice for the Texas Horned Lizard is the Red Harvester Ant (Pogonomyrmex

barbatus), which comprises about 69% of their daily diet (Fair, 1995). Red Harvester

Ants are among the largest of all harvester ants and are commonly mistaken for Red

Fire Ants (Texas A&M, 2021). Red Harvester Ants can be found throughout a variety of

environments across the Southwestern United States, “ranging from the edges of the

desert and grasslands up to lower elevation pine forests (up to 1850 meters), pinyon-

juniper and oak forests, sagebrush, [and] riparian habitats” (Mackay and Mackay, 2014).

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They have been observed extensively throughout southwestern, central, and northeastern New Mexico as well as central and western Texas (Guénard et al, 2017).

The main food sources for Red Harvester Ants are seeds and dead insects which they collect in their nests to feed the queen and the rest of the colony (Drees, 2014). While building their nests, these ants clear out all vegetation within three to six feet of the subterranean nest opening. The result is a barren patch of soil that distinguishes

Harvester Ant colonies from fire ants, which are known to build small mounds without

clearing vegetation. Harvester Ants will also build foraging trails to and from the nest,

allowing them to easily bring food back to the colony. These foraging trails are incredibly

important to Red Harvester Ant colonies and workers will expend the same effort in

clearing trails as they would foraging for food. Harvester Ant foraging trails are equally

important to Texas Horned Lizards because they allow the lizards to easily identify where their favorite prey will be. These trails are quite vulnerable to changes in land

usage and such changes can impact both ant and Texas Horned Lizard behavior

(Gordon, 1986). For instance, overgrazing in native grasslands decreases the amount

of groundcover, causing Harvester Ants to disperse as soon as they leave the nest. This

in turn removes ant trails that lizards would use for foraging and forces the lizards to

hunt nearer to the ant nests (Whiting et al., 1993). When the lizards are forced to forage

near the ant colonies, it elevates the importance that Harvester Ant availability plays in

the suitability of the overall habitat.

Texas Horned Lizards are normally found in, “grasses interspersed with cacti,

yucca, mesquite, and other assorted woody shrubs and small trees (Whiting et al.,

1993). In the mornings and evenings Texas Horned Lizards prefer bare ground and

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areas of herbaceous vegetation as a means of thermal regulation (Burrow et al., 2001).

Similarly, in the afternoons they are usually found in areas with more woody vegetation to escape from the heat (Burrow et al., 2001). With these specific habitat requirements,

Texas Horned Lizards tend to thrive in areas with a “mosaic of bare ground, herbaceous

vegetation, and woody vegetation in close proximity” (Burrow et al., 2001). The

expansion of human infrastructure continues to constrict the best suited habitats for

Texas Horned Lizards. Building roads and natural gas pipelines requires stripping the ground bare of vegetation, often robbing Texas Horned Lizards of the shrubs and woodlands that they need. However, some light human development may benefit Texas

Horned Lizards, since settlement tends to ward off some of their main predators such as coyotes and snakes. Because of this, Texas Horned Lizards are often found in the post oak savannah ecoregion of Texas, which is categorized by moderate levels of development “and less intensive agriculture” (Johnson Linam, 2008).

Since Texas Horned Lizards are neither particularly fast nor intimidating, they will usually rely on surrounding camouflage to evade predators. Texas Horned Lizards will conceal themselves in short, herbaceous brush to avoid detection by larger and faster predators. For smaller predators, the Texas Horned Lizard will bury itself in sand to escape from swarm attacks (Webb and Henke, 2003). Because of this, Texas Horned

Lizards often choose habitats with an abundance of sandy soil such as deserts and grasslands. As is the case for many animals native to desert environments, Texas

Horned Lizards have evolved so they can exist far from fresh water sources. The most impressive of their evolutionary adaptations is a capillary system between the scales

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that collects water from wet sand or dew and passively moves the water to the Texas

Horned Lizard’s mouth (Comanns et al., 2015).

The main predators of the Texas Horned Lizard are coyotes, birds of prey, snakes, squirrels, cats, and dogs (Horned Lizard Conservation Society, 2021). To protect itself from coyote and dog attacks, the Texas Horned Lizard has developed the ability to squirt blood out of its eyes to irritate and deter predators. The Texas Horned

Lizard can squirt blood several times further than its body length when defending itself.

Blood squirting is more common in larger Texas Horned Lizards since they have more blood and body mass at their disposal (Middendorf and Sherbrooke, 2001). When a

Texas Horned Lizard is attacked “they close their eyes and the eyelids appear to inflate”

(Oklahoma Department of Wildlife Conservation, 2021). The lizard will then shoot a stream of foul-smelling, bitter blood toward the attacking predator. It is speculated that the “chemicals in the blood that produce the bitter taste may be derived from the ants they eat” (Oklahoma Department of Wildlife Conservation, 2021). This response appears to have evolved specifically to repel canid attacks. In a laboratory setting,

Texas Horned Lizards squirted blood 100% of the time when exposed to aggressive canids in simulated attacks (Middendorf and Sherbrooke, 1992). Conversely, Texas

Horned Lizards rarely squirt blood when attacked by other types of predators such as roadrunners and snakes (Middendorf and Sherbrooke, 1992). This form of self-defense is unique to certain species of Horned Lizards and remains one of their most defining characteristics.

Another creature that greatly impacts Texas Horned Lizard populations is the

Red Imported Fire Ant (Solenopsis invicta). Red Imported Fire Ants are native to Brazil

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and Argentina and have a large invasive presence in most of Central America (Collins and Scheffrahn, 2016). Red Imported Fire Ants invaded the southern United States through the port of Mobile, Alabama between 1933 and 1945 (Buren et al., 1974). At the

time, Mobile was one of the busiest ports in the country and was a frequent stop for

cargo shipments from South and Central America. Since cargo ships often drop ballast

to reduce their draft while in port, it is most likely that fire ants were accidentally

introduced when infested ballast soil was dumped overboard (United States Department

of Agriculture, 2021). Once they arrived in the United States, fire ants continued to

spread across the southeastern states, with a range that now spans from central Texas

to North Carolina as well as down to south Florida and up to central Tennessee. Once

Red Imported Fire Ants spread to a new environment, they quickly establish multiple

colonies, each occupying a different small dirt mound. When a fire ant colony is

disturbed, worker ants swarm out of the mound and overwhelm the potential predator.

The fire ants bite and inject their attacker with an alkaloid venom that causes acute pain

and pustules (Collins and Scheffrahn, 2016). Fire ants are rarely seen directly attacking

native ant species. However, the presence of fire ants alongside native ants may cause

predators to avoid once frequented hunting grounds to prevent painful bites and swarm

attacks (Wojcik et al., 2001). When Texas Horned Lizards are attacked by small

numbers of fire ants (< 20) they respond by consuming them just as they would native

ant species, but when the fire ants attack as a swarm in groups larger than 20, it causes

the lizards to flee and bury themselves in the sand (Webb and Henke, 2003). Most

importantly, Texas Horned Lizards are unable to “substitute fire ants for their natural

prey” and in many cases harvester ant populations are being destroyed by pesticides

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targeted at fire ants (Donaldson, 1992). So, while fire ants are not a direct physical

threat to Texas Horned Lizards, they are a substantial threat to the native ant

populations that Texas Horned Lizards rely on for sustenance. This in turn makes Red

Imported Fire Ants a potential threat to the Texas Horned Lizards’ overall habitat

suitability.

Generally, this study aims to examine which environmental, human, and

ecological factors most influence the habitat suitability for the Texas Horned Lizard.

Once identified, local and state agencies can then use these factors to determine which

areas are best suited for Horned Lizard reintroduction, so they have the highest chance

of survival. As reintroduction efforts begin to take effect, the population levels of Texas

Horned Lizards can stabilize and grow so they can continue to be a central fixture in

southwestern ecology for years to come.

Figure 1-1: Texas Horned Lizard (Kansas Herpetofaunal Atlas)

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Figure 1-2: Texas Horned Lizard Eating an Ant (San Antonio Zoo)

Figure 1-3: Texas Horned Lizard after Shooting Blood from its Eyes (David G. Koziol)

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DATA AND METHODOLOGY

Variables and Datasets

In this habitat suitability analysis, the main response variable is the prevalence of

Texas Horned Lizards across Texas and New Mexico. For the state of Texas, this information comes from the Texas Horned Lizard Watch 10-Year Summary Report, which was conducted by the Texas Parks and Wildlife Department (TPWD) from 1997 to 2006 and was prepared by Lee Ann Johnson Linam (Table 2-1). This watch was conducted by volunteers and TPWD biologists, with volunteers, “conducting transects that collect quantitative data on horned lizard and ant density” as well as reporting

“incidental sighting of horned lizards wherever they occur,” and the biologists confirming, “if they had seen a horned lizard in their counties of responsibility in the past three years” (Johnson Linam, 2008). The volunteer sighting response is represented in four categories based on the percentage of volunteers who saw the Texas Horned

Lizard over the course of the study. These categories are: 0%, 0.01-25%, 25.01-75%, and >75%. For the biologist sightings, the map is divided into three categories: counties where all biologists saw Texas Horned Lizards, counties where only some of the biologists saw the Texas Horned Lizard, and counties where none of the biologists saw the Texas Horned Lizard. Both maps were presented by TPWD in a presentation format and were converted to shapefiles in 2021 (Figure 2-1). For the state of New Mexico, data on Texas Horned Lizard sightings comes from the Checklist of the Amphibians and

Reptiles of New Mexico, USA, with Notes on Taxonomy, Status, and Distribution by

Charles Painter, James Stuart, Tomasz Giermakowski, and Leland Pierce (Table 2-2).

This report lists, “the native and non-native amphibians and reptiles that have been verified as established in the state of New Mexico” and thus lists the counties where

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Texas Horned Lizards have been sighted, both natively and due to introduction (Painter et al., 2017). This list of counties was converted into a shapefile so it could be included as part of the response variable.

Since little data exists at the subcounty level for Texas Horned Lizard sightings, this analysis is conducted at the county level. County shapefiles for the study area are from the United States Census Bureau TIGER/Line database. The shapefile for New

Mexico is current as of 2007 and the shapefile for Texas was last updated in 2016

(Table 2-3 and Table 2-4). The United States Census Bureau distributes demographic data at the subcounty level. Since most of the Texas Horned Lizard data was at the

county level, these subcounty areas were merged using their county FIPS codes. This

was done to ensure all data in this study was at the county level.

The TPWD study noted “an apparent positive relationship between the presence

of Texas Horned Lizards and the presence of harvester ants (Pogonomyrmex sp.), their

preferred food source” (Johnson Linam, 2008). Because of this, harvester ant

prevalence is included as a variable in this analysis. The data on Red Harvester Ant

(Pogonomyrmex barbatus) range comes from the Global Ant Biodiversity Informatics

(GABI) Project, which compiles data on over 340,000 different ant species, to include

their native and invasive ranges (Guénard et al., 2017). The data obtained from GABI

lists all areas where Red Harvester Ants have been observed by researchers or where

they have been documented in literature (Table 2-5). These areas were combined to

create a list of all counties in the Red Harvester Ant’s native range, and this list was

then converted into a shapefile for analysis. The TPWD study also notes that the

“distributions of Texas Horned Lizards and Red Imported Fire Ants may not be

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independent” and that a high density of fire ants had a negative effect on the Texas

Horned Lizard prevalence in an area (Johnson Linam, 2008). This is most likely due to the Red Imported Fire Ants disrupting the Red Harvester Ant ecosystem, and the Texas

Horned Lizard’s inability to properly digest Red Imported Fire Ants. Because of this implied negative correlation, Red Imported Fire Ant prevalence was also included as a potential analysis variable. To incorporate this factor, Red Imported Fire Ant range data was retrieved from the University of Georgia, Center for Invasive Species and

Ecosystem Health, last updated January 2021 (Table 2-6). This data is comprised of all counties in the US where imported fire ants have been observed. This list was then converted to a shapefile for analysis (Figure 2-2).

To model the Texas Horned Lizard’s preferred habitat, which is noted to be “arid and semiarid areas, characterized by open country of scant vegetation”, land cover, river density, water body density, and tree canopy data were included as potential variables (Whiting et al., 1993). The land cover classification data comes from the

United States Geological Survey (USGS) National Land Cover Database (NLCD) which provides data on 16 different land cover classifications “at a 30m resolution” (Multi-

Resolution Land Characteristics Consortium) (Table 2-7 and Figures 2-3, 2-4, 2-5, 2-6,

2-7, 2-8, and 2-9). Both the river data and the water body data come from the

Environmental Protection Agency (EPA) National Hydrography Dataset (NHD) and were clipped to the extent of the study area (Table 2-8). To isolate only naturally occurring streams and rivers, all other categories in the dataset such as ditches, water pipelines, and underground conduits were excluded. For the rivers and streams, the line features were aggregated to find the average length of all rivers per square kilometer in each

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county (Figure 2-10). A similar process was used to find the average area occupied by bodies of water per square kilometer (Figure 2-12). These measures are to find the water feature density of each county so that it may be included as a variable in the analysis. The tree canopy data comes from the USGS NLCD and provides the average tree canopy color at a 30m resolution. This data has been aggregated at the county level and provides an approximate measure of tree health and density (Figure 2-11).

To establish the average climate for each county in Texas and New Mexico,

average precipitation, average temperature, and elevation data were added as variables

for analysis. This data is courtesy of the National Oceanic and Atmospheric

Administration (NOAA) National Climatic Data Center (NCDC) and includes the 100-

year average temperature and precipitation by month, for every county in Texas and

New Mexico (Table 2-9). The NCDC data also includes precipitation and temperature

for any month, its rank among other counties in that state, and the variation from the

historical average. To account for seasonal changes in precipitation and temperature,

measurements from January and June were included in this study (Figures 2-13, 2-14,

2-15, and 2-16). This data is updated annually so all climate datasets are current as of

December 2020. The elevation data comes from the USGS North America Elevation 1-

Kilometer Resolution Grid (Table 2-10). This dataset provides elevation data for all

North America and was built by the USGS, the US National Geospatial-Intelligence

Agency (NGA), the Centre for Topographic Information of Natural Resources Canada,

and the Instituto Nacional de Estadística y Geografía (INEGI). This dataset provides the

average elevation for each square kilometer in North America. The data is current as of

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2007 and was clipped to the study area extent. It was then aggregated to get the average elevation, in meters, for each county (Figure 2-17).

To account for human factors that may influence the Texas Horned Lizard’s habitat suitability, population density, road network, and natural gas pipeline data were all added as possible factors. The population data for New Mexico comes from the US

Census Bureau Population Division’s Annual Estimates of the Resident Population covering April 1, 2010 to July 1, 2019 (Table 2-11). Population data for Texas comes from the Texas Population Estimates Program, published by the Texas Demographic

Center, and it is current as of 2019 (Table 2-12). All population estimates were normalized by the county area in square kilometers to get the population density for

each county (Figure 2-18). New Mexico road network data is courtesy of the New

Mexico Resource Geographic Information System, where each road is represented by

its centerline and the network is current as of January 2021 (Table 2-13). Texas road

network data comes from the Texas Department of Transportation (TxDOT) and

includes all types of roads in the state, from residential streets to interstates (Table 2-

14). Like the New Mexico road network, each road is represented by its centerline and

was last updated November 2020. Both networks were merged to create one

comprehensive road network representative of the complete study area. Road density

per square kilometer was calculated for each county using this joined network (Figure 2-

19). This was done to aggregate all roads at the county level and represent how densely developed each county’s road network is. Natural gas pipeline data for both

Texas and New Mexico comes from the US Department of Homeland Security’s

Homeland Infrastructure Foundation (Table 2-15). This dataset covers all pipelines used

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to move natural gas throughout the continental United States and was last updated

June 2019. This polyline network was clipped to the extent of the study area and, like the road network, was aggregated to determine the pipeline density for each county

(Figure 2-20).

Since 27% of Texas Horned Lizard sightings were reported in ranching areas, cattle population density by county was included as a potential explanatory variable

(Johnson Linam, 2008). Texas cattle numbers come from the United States Department of Agriculture’s (USDA) 2012 cattle population estimates (Table 2-17). The cattle population data for New Mexico comes from a joint 2015 bulletin published by the

USDA and the New Mexico Department of Agriculture (Table 2-16). Both datasets include all beef and dairy cattle registered in each county. The total cattle population numbers were normalized by the county area to find each county’s cattle population density (Figure 2-21). This cattle population density was then included as a possible factor.

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Dataset Maps and Metadata

Figure 2-1: Texas Horned Lizard Range Map

Table 2-1: Texas Horned Lizard Watch 10 – Year Summary Report 1997 - 2006 Year Published Owner URL Data Type

2008 Texas Parks and https://tpwd.texas.gov/ Vector Wildlife Department publications/pwdpubs/ media/pwd_rp_w 7000_1442.pdf

Table 2-2: Checklist of the Amphibians and Reptiles of New Mexico, USA with Notes on Taxonomy, Status, and Distribution Year Published Owner URL Data Type

2017 The Journal of the http://www.tws- List of counties Western Section of west.org/westernwildlife/ converted to The Wildlife Society vol4/Painter_etal Vector Data _WW_2017.pdf

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Table 2-3: TIGER/Line Shapefile, Texas, Current County Subdivision State-based Year Published Owner URL Data Type

2016 United States https://catalog.data.gov/ Vector Census Bureau dataset/tiger-line- shapefile-2016-state- texas-current-county- subdivision-state-based

Table 2-4: TIGER/Line Shapefile, New Mexico, Current County Subdivision State-based Year Published Owner URL Data Type

2007 United States http://rgis.unm.edu/rgis6/ Vector Census Bureau, distributed by the University of New Mexico

Figure 2-2: Red Harvester Ant and Imported Fire Ant Range Map

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Table 2-5: GABI Project Distribution of Red Harvester Ants (Pogonomyrmex barbatus) Year Published Owner URL Data Type

2019 The Global Ant https://antmaps.org/ Table Biodiversity index.html? converted to Informatics (GABI) mode=species&species= Vector Data Project Pogonomyrmex.barbatus

Table 2-6: Early Detection & Distribution Mapping System, Distribution of Red Imported Fire Ants (Solenopsis invicta) Year Published Owner URL Data Type

2021 The University of https://www.eddmaps.org/ Vector Georgia - Center for distribution/uscounty.cfm? Invasive Species sub=79789 and Ecosystem Health

Figure 2-3: Majority Land Classification Map

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Figure 2-4: Percentage Developed Map

Figure 2-5: Percentage Forest Map

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Figure 2-6: Percentage Hay, Crops, or Pastures Map

Figure 2-7: Percentage Wetlands Map

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Figure 2-8: Percentage Shrubs Map

Figure 2-9: Percentage Herbaceous Map

Table 2-7: NLCD Land Cover (CONUS) All Years Year Published Owner URL Data Type

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2016 US Geological https://www.mrlc.gov/ Raster Survey data/nlcd-land-cover- conus-all-years

Figure 2-10: River Density by County Map

Table 2-8: National Hydrography Dataset Year Published Owner URL Data Type

2019 US Environmental https://www.epa.gov/ Vector Protection Agency waterdata/get- nhdplus-national- hydrography- dataset-plus-data

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Figure 2-11: Average Tree Canopy Value Map

Figure 2-12: Total Water Body Area by County Map

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Figure 2-13: Average Temperature in January Map

Table 2-9: Climate at a Glance Data, Temperature and Precipitation, Texas and New Mexico Year Published Owner URL Data Type

2021 NOAA National https://www.ncdc.noaa.gov/ Table Centers for cag/statewide/rankings converted to Environmental Vector Data Information

33

Figure 2-14: Average Temperature in June Map

Figure 2-15: Average Precipitation in January Map

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Figure 2-16: Average Precipitation in June Map

Figure 2-17: Average Elevation by County Map

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Table 2-10: North America Elevation 1-Kilometer Resolution GRID Year Published Owner URL Data Type

2007 US Geological https://www.sciencebase.gov/ Raster Survey catalog/item/ 4fb5495ee4b04cb937751d6d

Figure 2-18: Population Density by County Map

Table 2-11: Annual Estimates of the Resident Population, New Mexico Year Published Owner URL Data Type

2016 United States https://gonm.biz/site- Table converted to Census Bureau selection/census- Vector Data data

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Table 2-12: Texas Population Estimates Program Year Published Owner Data URL Type

2019 Texas https://demographics.texas.gov/ Table Demographic data/tpepp/estimates/ converted Center to Vector Data

Figure 2-19: Road Density by County Map

Table 2-13: New Mexico Road Centerlines Year Published Owner URL Data Type

2021 New Mexico http://rgis.unm.edu/ Vector Department of rgis6/ Finance and Administration

37

Table 2-14: TxDOT Roadway Inventory Year Published Owner URL Data Type

2020 Texas Department https://gis- Vector of Transportation txdot.opendata.arcgis.com/ datasets/txdot-roadway- inventory

Figure 2-20: Natural Gas Pipeline Density by County Map

Table 2-15: Natural Gas Pipelines Year Published Owner URL Data Type

2019 Department of https://hifld- Vector Homeland Security geoplatform. Homeland opendata.arcgis.com/ Infrastructure datasets/natural-gas- Foundation-Level pipelines Data

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Figure 2-21: Cattle Population Density by County Map

Table 2-16: County Estimates: Cattle – New Mexico Year Published Owner Data URL Type

2015 New Mexico https://www.nass.usda.gov/ Table Department of Statistics_by_State/New_Mexico/ converted Agriculture Publications/ to Vector Annual_Statistical_Bulletin/ Data 2015/2015_NM_Ag_Statistics.pdf

Table 2-17: Texas Counties: Cattle Population in 2012 Year Published Owner URL Data Type

2012 US Department of http://www.texascounties.net/ Table Agriculture statistics/cattle2012.htm converted to Vector Data

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Methodology

The known native range of the Texas Horned Lizard is from Northern Mexico to

Kansas, and from New Mexico to Eastern Texas (TPWD, 2005). Texas Horned Lizards have been extensively studied inside of Texas and to a smaller extent within Oklahoma,

but there is relatively little research about their habitats in New Mexico, Kansas, or the

rest of the Central Southern US. In this analysis New Mexico and Texas were selected

as the primary study area. Both states were analyzed individually to see if the factors

impacting habitat suitability varied in each state. Including Texas allows for the

verification of previous findings and including New Mexico offers an opportunity to

examine Texas Horned Lizards in an understudied environment. Kansas and Oklahoma

were excluded from the study area due to time constraints. Northern Mexico was

excluded due to a lack of English language data available from the Mexican

government. Given more time, a follow-on study should be conducted including

Oklahoma, Kansas, and Mexico to establish a more complete picture of the habitat

suitability factors across the entire Texas Horned Lizard range. This study was

conducted from January to April 2021 and includes data from 1997 to present, with

some literature references dating back to 1974.

In this study the workflow can be divided into three sections: data acquisition and

preparation, modeling and factor identification, and area suitability assessment. The first

step of the data acquisition and preparation phase was to synthesize existing literature

and use it to identify potential factors for investigation. Once all potential factors were

compiled, preliminary models were constructed and analyzed for their model quality. If

the preliminary models were deemed acceptable, they were used in the suitability

assessment stage. If they were not, further modelling was done using a variety of

40

spatial models, such as spatial lag and spatial error models. The spatial model that best

fit the sample data was then used for suitability calculation. These calculations yielded

an overall suitability level for each county, which were then compiled in the results. This

workflow is depicted in the flowchart in figure 2-22.

Most of the potential factor data was obtained from a variety of government

sources, to include federal, state, and county level organizations. Since many of these

government reports are in a table format, rather than a GIS ready file, it was necessary

to merge these tables to county level shapefiles for spatial analysis. These tables were

joined to the county shapefiles using each county’s FIPS (Federal Information

Processing System) code, which is used to identify unique geographical areas. At the

county level this code is five digits long with the first two digits identifying the state and

the last three digits identifying the county (US Census Bureau, 2010). Other data

sources were available in GIS ready formats such as polyline, polygon, and raster files.

These sources were then aggregated to the county level and subsequently joined to the

county shapefiles. Polyline features were aggregated using the sum length of all line

features in a county, normalized by the county area, resulting in average length of

features per square kilometer. This method was used to establish a line feature density

for each county. Large polyline datasets, such as watersheds, were only available in

sections, so QGIS 3.14.16 was used to fuse all these sections together. Polygon

features were aggregated in a similar fashion, normalizing the sum polygon area in a

county by the county area, resulting in average area of features per square kilometer.

The process resulted in a polygon feature density for each county. The raster files were

handled in a variety of ways due to their large file size and differing resolutions. For the

41

elevation raster file, the average value was calculated for each county and that value was joined to the county shapefiles. For the land use classification data, the percentage of each classification type within each county was calculated. The majority classification type was also determined for each county. The majority classification type allows for a visual representation of where each type is dominant, and the percentages were used as potential factors in the suitability analysis. At this point in the study, all possible factors were added as fields within the county level shapefiles. After this, maps were

built to depict each possible factor across the study area. For most maps, five

categorical levels were constructed using Jenks natural data breaks. Certain maps were

not included since they depicted extraordinarily rare or undetectable factors such as:

percentage of open water, percentage of barren land, percentage of unclassified land,

or percentage of snow.

In the modeling and factor identification portion of this study, the first step was to

conduct ordinary least squares (OLS) regression to identify the factors that are

statistically significant in predicting Texas Horned Lizard habitat suitability. Potential

variables were deemed statistically significant if they were shown to have a p-value less

than 0.05, this indicating that with 95% confidence they significantly explain data

variation. Beyond this criteria, certain variables of interest were added for examination because they were identified in prior studies as significant, such as prevalence of

Imported Fire Ants and Red Harvester Ants. This regression was conducted using forwards and backwards selection to identify the factors of influence. The criterion of

this selection process was to minimize Akaike Information Criterion (AIC) while also

keeping Variance Inflation Factor (VIF) for each potential variable below 7.5. This

42

forward and backwards factor selection was conducted using the statistical software

package JMP since it could rapidly handle this computationally heavy task. Minimizing

AIC helps reduce the risk of overfitting or underfitting the model, and thus preserves

model quality. Keeping the VIF below 7.5 keeps autocorrelation to an acceptable

amount, therefore ensuring that multiple variables are not explaining the same response

in Texas Horned Lizard habitat suitability. If multiple variables are explaining the same

response, an unimportant variable might mistakenly represent the variation caused by

another valuable variable and thus cloud the model results. The main measures used to

assess the overall model quality were the Coefficient of Determination (R2) and

Adjusted Coefficient of Determination (Adjusted R2). R2 is a value that represents the

percentage of data variation that is explained by the regression model. Adjusted R2 also shows how much variation is explained by the model but it is affected by the number of model terms, thus lowering the overall score if extraneous variables are included. This serves to prevent overfitting the model. Some additional tests were used in assessing model quality such as the Jarque-Bera test and the Breusch-Pagan test. The Jarque-

Bera test looks for model bias and the resulting probability should not be significant, and the Breusch-Pagan test examines if there is “non-constant variance in the errors” and should also not be significant (Anselin, 2005). All these criteria were taken together to determine which OLS model best fit the study data and selected response variable.

One of the assumptions about OLS is that the data points are spatially independent of each other, and since this is rarely the case in the natural world, further steps were required to investigate the spatial relationships between factors of interest.

To examine the extent of these spatial relationships, Lagrange multiplier (LM) error, LM

43

lag, Robust LM error, Robust LM lag, and Moran’s I error were calculated and examined for both models. Moran’s I examines the overall spatial autocorrelation in the study area, and the LM and Robust LM statistics are used to examine if OLS is a suitable model or if a different, spatial regression model is appropriate. See figure 2-23 for an

explanation of how these statistics are used in the spatial regression decision process.

If the LM or Robust LM statistics are significant, it indicates that the response error is

not constant across the study area. This implies that a model factor may be significant in one area, but not meaningful in another, and thus violates the assumptions of OLS regression. In this analysis, the spatial error model was used to estimate habitat suitability in Texas. The spatial error model uses an additional term, which is the sum of

“the deviations from regression predictions that are observed in the neighborhood of the target location,” to account for the spatial aspect of the response errors (University of

Arizona, 2021). By isolating this error, the spatial error model provides a better estimate

of the model term effects, since this spatial error is now no longer hidden within the

model terms.

The calculation of these statistics required the creation of a spatial weights

matrix. To create a spatial weights matrix, the “queen” topological scheme was used.

This scheme considers all the polygons that border the target when creating a

neighborhood. This topological scheme can be impacted heavily by border effects at the

edge of the study area, however these effects were not deemed significant since many

of the study area borders, such as Arizona, Colorado, and Louisiana are not native

habitats of the Texas Horned Lizard and thus should not be used to influence its habitat

suitability.

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After finding viable models, the study moved into the area suitability assessment stage. To accomplish this, suitability values were calculated using the regression equations for each model. In the New Mexico OLS model these values were calculated

using ArcGIS Pro. The suitability values for the Texas spatial error model were

calculated using GeoDa. These suitability values were calculated individually for each

state since they use two different model equations. They were then divided into five

levels per state (Very Poor, Poor, Average, Good, and Excellent) using Jenks natural

data breaks. This allows us to roughly compare the levels of one state to the levels of

another since the values themselves cannot be directly compared. These area

suitability results were then compared to the data maps of significant factors to confirm

that their regression coefficients were consistent with the results of previous studies.

Once these results were confirmed, the suitability values were compiled into an overall

habitat suitability map of the study area, which can be seen in figure 3-1.

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Workflow Charts

Figure 2-22: Study Workflow

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Figure 2-223: Spatial Regression Decision Process (Anselin, 2005)

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ASSUMPTIONS AND RESULTS

Assumptions

To address time and data availability constraints in this analysis, some assumptions had to be made about the datasets and subsequent results. The main assumption is that habitat suitability is constant across each county. While this excludes

the changes in micro terrain, development, and biodiversity at the subcounty level, it is

necessary since most habitat data is only available at that resolution. Given the number

of counties included in the study area (254 in Texas and 33 in New Mexico) the sample

size is sufficient to determine which counties are most suitable for the Texas Horned

Lizard. Once these counties are identified, they can be used to guide future analysis at

the subcounty level to determine the ideal micro and macro habitats for Texas Horned

Lizards. Another assumption is that river and lake density combined with precipitation

data is sufficiently indicative how much surface water and moisture is available for the

county’s ecosystem. This assumption was made because suitable data on soil drainage

and groundwater tables were not available. Should these data sources become

available, they should be incorporated into future analysis to provide a more complete

picture of water availability. Additionally, this study assumes that road density, land use

category, and population density are sufficient to determine the extent of human

development for each county. This assumption was necessary due to time constraints

since there are near endless amounts of human factor datasets available. While there

are certainly other factors that indicate human development, these three factors address

the construction extent and the population footprint of an area. Further studies should

consider other human factors such as light and noise pollution for a full spectrum view

of human impact on Texas Horned Lizards. The final assumption necessary for this

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study is that cattle population density is representative of the ranching extent in each county. While this data does not give the precise value as to how many kilometers are allocated for cattle grazing, it does present a ratio of cattle to land mass. When this ratio

is examined across a multi-county area it will be insightful enough to determine if

ranching activity impacts Texas Horned Lizard habitat suitability.

Results and Models

After conducting OLS regression on the study area, models for Texas Horned

Lizard habitat suitability were constructed for New Mexico and Texas. The New Mexico

model was found to be the better of the two. Since it had an adjusted R2 of 0.805, it was

able to explain most of the response variation (Table 3-2). Furthermore, the New

Mexico model was found to not have significant skew with a Jarque-Bera value of 0.814

(p = 0.666) and had a constant variation of errors with a Breusch-Pagan value of 3.409

(p = 0.637). This indicates that the errors within the data are normally distributed,

satisfying one of the major assumptions of OLS regression. Since this assumption is

met, the model terms and coefficients accurately represent the data. Thus, the habitat

suitability values derived from this model correctly reflect reality. This model showed

that the significant factors in Texas Horned Lizard habitat suitability in New Mexico

were: average county elevation (p = 0.000), road density (p = 0.001), natural gas

pipeline density (p = 0.011), the presence of Harvester Ants (p = 0.005), and the

percentage of land classified as snow (p = 0.033). This model also did not have a

significant Moran’s I value (p = 0.751), LM lag value (p = 0.489), or LM error value (p =

0.312) indicating that there was no notable spatial autocorrelation, and thus analysis

could proceed.

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Upon examining the model performance and spatial autocorrelation statistics,

OLS was determined to be an acceptable model for New Mexico, but not for Texas. The

Texas OLS model’s overall predictive quality was mediocre, with an adjusted R2 of

0.4166 and an Akaike information criterion value of 221.955. This OLS model also failed

further tests for model quality, with a Breusch-Pagan value of 17.143 (p = 0.009) and a

Jarque-Bera value of 24.788 (p = 0.000). These failures indicate that the OLS model’s

errors are not only skewed, but also are not normally distributed. The model’s

diagnostics for spatial dependence found that Moran’s I (p = 0.003), Lagrange Multiplier lag (p = 0.034), and Lagrange Multiplier error (p = 0.017) were all statistically significant.

With Moran’s I value indicating significant spatial autocorrelation, the adjusted and standard R2 values for this model were no longer valid, because autocorrelation

prevents accurate assessment of the model term effects. Since spatial autocorrelation

allows model effects change across the study area, it is impossible to properly estimate

what effect a model term has on the overall output. Since both the LM lag and LM error

values were significant, the Robust LM error and Robust LM lag values were used to

identify which spatial model would best fit the data. For the Texas model, since the

Robust LM error value (p = 0.149) was closer to being statistically significant than the

Robust LM lag value (p = 0.332), a spatial error model was constructed to correct for

spatial variation. This spatial error model delineated more of the data variation and

yielded a higher Adjusted R2 value (0.4476) than its OLS counterpart (Table 3-1). This

indicates that the spatial error model explains more of the data variation than the OLS

model. This model also resulted in a lower Akaike Information Criterion (216.64) than

before (221.955), indicating that the spatial error model is better than the standard

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regression model. It should be noted however, that the spatial error model still failed the

Breusch-Pagan test, indicating that error variance is still non-constant even with the added spatial term. This spatial error model showed that in Texas the significant factors

for Texas Horned Lizard habitat suitability were: natural gas pipeline density (p = 0.017), average precipitation in January (p = 0.000), the presence of Harvester Ants (p =

0.015), and the percentage of open water (p = 0.002). Two other factors, average county elevation (p = 0.100) and cattle population density (p = 0.194) were not significant but were kept in the model to correct some of the data skew.

Once these significant factors were determined, a suitability value was calculated for each county using the two model equations. This statistic ranged from -0.287 to

1.312, where values near or below zero indicate that county is poorly suited, and values

near or above one indicates that county is well suited for Texas Horned Lizard

reintroduction and habitation. Using this statistic, a list was also made of the ten most

suitable counties in Texas and the ten most suitable counties in New Mexico. These

lists can be seen in tables 3-3 and 3-4, respectively. Additionally, lists of the ten least

suitable counties in each state were also constructed and can be seen in tables 3-5 and

3-6. It is worth noting that since the suitability statistics for Texas and New Mexico were

derived from two different equations, this statistic should not be used to compare

counties between states. It should be used only to compare counties within their

respective state. The intent is that these top counties would now become targets of the

reintroduction and population restoration efforts.

In Texas, out of the top ten most suitable counties, six are on the southern Gulf

Coast from Corpus Christi to Brownsville, with Cameron County being the most suitable

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(Figure 3-5). The two most likely reasons for this are that these counties are the only counties along the Texas Gulf Coast home to Harvester Ants, and they have relatively little pipeline density. While the Gulf Coast is a major natural gas hub, most of natural

gas processing happens further to the north between Corpus Christi and Houston. In

addition to these factors, south Texas and the Rio Grande Valley are made up of a mix

of sandy soil and shrubs, which is the Texas Horned Lizard’s favorite soil type and

ground (Carr, 2021). Furthermore, much of south Texas is owned by large ranching

families, such as King Ranch, which has limited how much development can take place.

As a result, Kleberg, Kenedy and Willacy counties remain sparsely populated with much

of the native fauna and flora undisturbed. Of the other four most suitable counties, two

are located on Edwards Plateau around Del Rio, and the other two are in the Texas

Panhandle east of Lubbock (Figures 3-2 and 3-6). The Edwards Plateau is mainly

comprised of shrubs and grasslands and is ranked as one of the top ten ecoregions for

reptiles, making it a perfect site for Texas Horned Lizard reintroduction (Cook and

Olson, 2021). The Texas Panhandle is also largely sparsely populated and is mainly

comprised of sandy soil and moderate agriculture. Road and natural gas pipeline

densities are also remarkably low in much of the Texas Panhandle, so the human

impact on a population of Texas Horned Lizards would be minimal. Furthermore, these

counties are all traditional homes of the Texas Horned Lizard which have arid climates

and dense Harvester Ant populations. All these factors combined indicates that the best

areas to reintroduce Texas Horned Lizards are: south Texas, the Texas Panhandle, the

Edwards Plateau, and the Rio Grande Valley.

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This analysis also revealed that the least suitable region within Texas is east

Texas, particularly between the Sabine and Neches rivers, with the least suitable county being Panola County (Figure 3-7). This area of east Texas has a similar climate to

Louisiana and thus receives a heavy amount of precipitation. Excessive rainfall is

detrimental to Texas Horned Lizard habitat suitability, making it difficult for east Texas to

support a healthy population. The flora of east Texas is also not appropriate for Texas

Horned Lizards. East Texas is covered in dense pine forests that do not provide the

necessary camouflage for Texas Horned Lizards. These shady pine forests also do not

allow Texas Horned Lizards to properly thermoregulate themselves, since they cannot

easily access sunny areas. The area between the Sabine and Neches rivers also has

an above average density of natural gas pipelines. Natural gas pipeline density has

been shown to negatively impact Texas Horned Lizard habitat suitability, so this higher

density makes the area even more unsuitable. Additionally, most of the soil in east

Texas is full of red clay. This high clay concentration makes it difficult for Texas Horned

Lizards to burrow when they are attacked by predators. Furthermore, Red Harvester

Ants are not found in east Texas. This implies that if Texas Horned Lizards were

reintroduced into east Texas, they would be deprived of their main food source. While

they may be able to sustain themselves on other ant species, it is unlikely that they

would be as healthy as Texas Horned Lizards elsewhere.

In New Mexico, six of the ten most suitable counties are in the eastern part of the

state, between the Sangre de Christo and Sacramento Mountains and the Texas border

(Figure 3-3). The remaining four counties are all located along the southern border of

New Mexico, from Alamogordo to the Mexico/Arizona borders (Figure 3-4). This is

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because these counties are all at lower elevations compared to the rest of New Mexico, many of which are also sparsely populated and have little pipeline activity. Because of the lower elevation, the temperature will stay within a range that can support a population of Texas Horned Lizards. Given the sparse population and minimal natural gas pipeline activity, reintroduced Texas Horned Lizards would likely be free from human interference. This would allow an introduced population to mix with the native

Texas Horned Lizard population and grow without external disturbances. Additionally, most of these counties are home to Red Harvester Ants. Therefore, reintroduced Texas

Horned Lizards would have an abundant available food source. All these factors

combined indicate that the best areas in New Mexico to reintroduce Texas Horned

Lizards are Guadalupe County, southeastern, and southwestern New Mexico.

This analysis found that the least suitable regions in New Mexico are the

mountainous regions from Gallup to Albuquerque, and northeast of Santa Fe through

the Sangre de Christo Mountains, with the least suitable county being Los Alamos

County (Figure 3-8). The average elevation in this area of New Mexico is well over 5000

feet above sea level. At such a high elevation, the temperature can vary wildly

throughout the day, which makes it difficult for reptiles to properly maintain their internal

body temperature. In addition to this, northern New Mexico is one of the more densely

developed areas of the state. With Los Alamos, Santa Fe, and Albuquerque this region

boasts a considerable amount of dense road development. Additionally, these urban

centers in northwestern New Mexico are one of the only regions in the state that

process and store significant amounts of natural gas. As a result, this area is above

average in terms of natural gas pipeline density. All these factors combined, imply that

54

northern and northwestern New Mexico are currently unable to support a healthy Texas

Horned Lizard population and reintroduction efforts should focus elsewhere.

Spatial and OLS Models

Table 3-1. Spatial Error Model for Texas Horned Lizard Habitat Suitability in Texas. R2 value: 0.4476, Akaike Info criterion: 216.64, Breusch-Pagan value: 17.476 (p = 0.007)

Variable Coefficient Standard Error Z-value Probability Constant 1.1248 0.1305 8.6182 0.0000 Elevation -0.0002 0.0001 -1.6417 0.1007 Pipeline Density -0.5136 0.2160 -2.3778 0.0174 Precipitation (Jan) -0.2587 0.0396 -6.5419 0.0000 Cattle Pop Density -0.0015 0.0019 -1.2982 0.1942 Harvester Ants 0.1454 0.0598 2.4302 0.0151 % Open Water 0.0113 0.0038 3.0107 0.0026 Lambda 0.2255 0.0934 2.4146 0.0158

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Table 3-2. OLS Model for Texas Horned Lizard Habitat Suitability in New Mexico. Adjusted R2 value: 0.8054, Akaike Info criterion: -1.2435, Breusch- Pagan value: 3.4091 (p = 0.6372), Jarque-Bera value: 0.8140 (p = 0.6656)

Variable Coefficient Standard Error T-value Probability Constant 2.8005 0.2117 13.2257 0.0000 Elevation -0.0012 0.0001 -10.4300 0.0000 Pipeline Density -3.0979 1.1348 -2.7300 0.0110 Road Density -0.3383 0.0944 -3.5856 0.0013 Harvester Ants 0.2704 0.0884 3.0604 0.0049 % Snow 3662.32 1634.19 2.2411 0.0334

Table 3-3. Top Ten Most Suitable Counties in Texas for Texas Horned Lizards.

County FIPS Code Suitability Score State Region Cameron 48061 1.163 Gulf Coast Willacy 48489 1.093 Gulf Coast Kenedy 48261 1.062 Gulf Coast Aransas 48007 1.046 Gulf Coast Calhoun 48057 1.003 Gulf Coast Val Verde 48465 0.995 Edwards Plateau Hall 48191 0.984 Texas Panhandle Terrell 48443 0.970 Edwards Plateau Kent 48263 0.968 Texas Panhandle Kleberg 48273 0.967 Gulf Coast

Table 3-4. Top Ten Most Suitable Counties in New Mexico for Texas Horned Lizards.

County FIPS Code Suitability Score State Region Quay 35037 1.311 Southeast Doña Ana 35013 1.194 Southwest Hidalgo 35023 1.160 Southwest Eddy 35015 1.085 Southeast Luna 35029 1.073 Southwest De Baca 35011 1.039 Southeast Guadalupe 35019 1.029 Northeast Chaves 35005 1.005 Southeast Roosevelt 35041 0.988 Southeast Otero 35035 0.966 Southwest

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Table 3-5. Top Ten Least Suitable Counties in Texas for Texas Horned Lizards.

County FIPS Code Suitability Score State Region Panola 48365 -0.197 East Texas Orange 48361 -0.180 East Texas Newton 48351 -0.162 East Texas Hardin 48199 -0.144 East Texas Gregg 48183 -0.141 East Texas Jasper 48241 -0.134 East Texas Tyler 48457 -0.124 East Texas Harrison 48203 -0.093 East Texas Shelby 48419 -0.075 East Texas Rusk 48401 -0.069 East Texas

Table 3-6. Top Ten Least Suitable Counties in New Mexico for Texas Horned Lizards.

County FIPS Code Suitability Score State Region Los Alamos 35028 -0.287 Northwest Cibola 35006 -0.057 West Bernalillo 35001 -0.043 West McKinley 35031 -0.041 Northwest Taos 35055 0.000 North Rio Arriba 35039 0.086 North Santa Fe 35049 0.099 North Sandoval 35043 0.200 Northwest Catron 35003 0.216 West Colfax 35007 0.256 Northeast

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Habitat Suitability Map

Figure 3-1: Habitat Suitability Map of Texas Horned Lizards in Texas and New Mexico

Most Suitable Area Maps

Figure 3-2: Habitat Suitability Map of Texas Horned Lizards in the Edwards Plateau and Big Bend Region, Texas

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Figure 3-3: Habitat Suitability Map of Texas Horned Lizards in North East New Mexico and the Texas Panhandle

Figure 3-4: Habitat Suitability Map of Texas Horned Lizards in South New Mexico and West Texas

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Figure 3-5: Habitat Suitability Map of Texas Horned Lizards in South Texas

Figure 3-6: Habitat Suitability Map of Texas Horned Lizards in West Texas

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Least Suitable Area Maps

Figure 3-7: Habitat Suitability Map of Texas Horned Lizards in East Texas

Figure 3-8: Habitat Suitability Map of Texas Horned Lizards in North West New Mexico

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DISCUSSION AND CONCLUSION

Discussion

Of the significant variables identified, many were expected and validate the findings of previous studies. The benefit of re-identifying these factors is that they confirm the site selection accuracy of current breeding and reintroduction programs.

Such factors are precipitation levels, elevation, proximity to Harvester Ants, and road density. Other identified factors were unexpected and may present new information with

opportunities for further research. These factors are percentage of snow, percentage of

open water, and natural gas pipeline density. Currently reintroduction efforts release

Texas Horned Lizards in central Oklahoma, South Texas, the Texas Panhandle, and

the Texas Hill Country. Of these sites, two were confirmed to be excellent areas for

Texas Horned Lizard reintroduction. This result is promising because it corroborates

that most the current efforts are reintroducing Texas Horned Lizards where the chance

of survival is highest. Conversely, the Texas Hill Country was found to be a poor or

average area to reintroduce Texas Horned Lizards. While the Hill Country is not ideal

for Texas Horned Lizard reintroduction, it is close to the Edwards Plateau which is

perfect for sustaining a habitat of Texas Horned Lizards. Unfortunately, none of the

current breeding and reintroduction efforts release Texas Horned Lizards in New

Mexico. Ideally, the results of this study can be used to expand current efforts into New

Mexico to help rebuild Texas Horned Lizard populations throughout their former natural

habitats.

As hypothesized, precipitation levels and elevation were found to be significant

model factors. Since the Texas Horned Lizard is a desert reptile, it is predictable that

precipitation levels are significant to overall suitability. Unexpectedly, precipitation levels

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were only a significant factor in the Texas model, not in the New Mexico model. This is likely a result of a comparative lack of variation in rainfall levels across New Mexico.

While average January rainfall in Texas varies from less than one inch to well over four and a half inches, the average January rainfall in New Mexico is never over an inch and a half. With such little variation in the generally arid New Mexican climate, it follows that rainfall would likely not be significant to any animal native to New Mexico, including the

Texas Horned Lizard. Similarly, elevation was found to only be a significant factor in the

New Mexico model. This is likely due to other factors being more important to Texas

Horned Lizard habitats in Texas. Horned Lizards are abundant in both the Rio Grande

Valley and the high desert around Big Bend National Park. These areas have vastly different elevations and yet they still successfully support large numbers of Texas

Horned Lizards. However, the topography of New Mexico is much more mountainous than that of Texas, with New Mexico’s highest point being nearly 5,000 feet taller than the highest point in Texas. While Horned Lizards have been known to thrive in the lower elevation areas of New Mexico, the alpine climate of northern and northwestern New

Mexico tends to be too cold and rugged for large populations of reptiles to survive. With such large variance in elevation and climate, it follows that elevation is a more important

factor to the herpetofauna of New Mexico.

Also as expected, road density and Red Harvester Ant proximity were also

confirmed significant factors in Texas Horned Lizard habitat suitability. This analysis

found that road density was only a significant factor in the New Mexico model, and not

in the Texas model. The reasons for these phenomena are not presently clear and this

should be a subject of future investigation. It may be a result of differences in overall

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road density between the two states, or possibly, differences in unpopulated land usage. Further research may also be able to determine if this result is influenced by other factors such as road type or highway and city planning. Additionally, the presence of Red Harvester Ants was found to be significant in both models. In each case Red

Harvester Ant presence was positively correlated to Texas Horned Lizard habitat suitability. Current conservation projects highly consider Red Harvester Ant density when selecting sites to reintroduce Texas Horned Lizards. For example, the San

Antonio Zoo reintroduction project will not consider a location for potential use if it does not at least have a sizable population of harvester ants, and usually they will only select sites where the harvester ant population outnumbers the Imported Red Fire Ant population (Gluesenkamp, 2020). Corroborating the previous study findings indicates that proximity to Red Harvester Ants should continue to be of the highest concern to current and future Texas Horned Lizard conservation projects.

While these previous factors are consistent with the expected outcome, the other three significant factors were not initially hypothesized to be of interest. These factors being: percentage of open water, percentage of snow, and natural gas pipeline density.

These factors suggest that there is a benefit to the Texas Horned Lizard to be around snowy areas or areas with an abundance of open water. Since the Texas Horned Lizard is native to arid environments, and it cannot survive on the snowy mountain peaks of

New Mexico, the significance of these factors demands further investigation. This result

may be significant due to some unseen ecological benefit, such as lack of a particular

predator. Alternatively, it may be due to a common error in land use determination, such

as classifying bright white sand as snow. Another potential explanation is that since

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sand is plentiful near water sources, Texas Horned Lizards may be able to burrow away more easily from predators. In this case, this factor’s significance may reflect the soil composition rather than land use itself. Since both factors were found to be highly

significant, but the background reason cannot be ascertained, it is recommended that

future studies investigate the link between Texas Horned Lizard habitats and the

availability of open water and snow.

The other unexpected factor, natural gas pipeline density, is perhaps the most

interesting component of this study. Natural gas pipeline density was found to be highly

significant across the study area. Furthermore, in both states a high density of pipelines

was detrimental to the overall habitat suitability. Initially, it could be assumed that

natural gas pipelines would be as damaging to the environment as any other type of

urban development, such as road or building construction. However, this study found

that while road density did not have a significant impact in Texas, natural gas pipeline

density was the largest negative factor on overall habitat suitability. Initially it was

suspected that natural gas producing counties in Texas were already poorly suited for

Texas Horned Lizards because the sheer number of pipelines made these areas

unequipped to handle most wildlife. However, this theory is dispelled because natural

gas pipeline density was also found to be significant to habitat suitability in New Mexico,

where the overall natural gas infrastructure is much smaller. Since natural gas pipeline

density was found to be highly significant in two states with vastly different infrastructure

sizes, this result cannot be attributed to coincidence. In New Mexico it was found that

natural gas pipeline density was 9.16 times more harmful to overall habitat suitability

than road density, when both were increased by one kilometer per square kilometer.

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The increased danger that natural gas pipelines pose to native ecosystems is likely because of how pipeline routes are chosen and constructed. While road networks tend

to grow predictably with an expanding human footprint, natural gas pipelines are

frequently constructed across large swaths of sparsely developed land. This is typically

done to keep pipeline construction costs and community disruption to a minimum.

Ecologically, this means that ecosystems impacted by natural gas pipelines are often

immediately shocked with its construction, rather than subjected to gradual

encroachment. This impact speed may make it more difficult for ecosystems to adapt and recover. Furthermore, building natural gas pipelines involves clearing all groundcover along the length of the pipeline. This robs many organisms of necessary food supplies and ground cover. If the pipeline is above ground, this area is usually kept barren by the energy company to allow for easy inspection and maintenance. If the pipeline in underground, all roots must be ripped up to place pipe sections, which greatly slows vegetation recovery. In either scenario, the ecological impact is severe and will take years to recover, if it ever does so. Given the potential danger natural gas pipelines may pose to Texas Horned Lizards and other native species, it is recommended that further research investigate pipeline impacts on Horned Lizards, particularly at the microhabitat level. In the meantime, further construction of natural gas pipelines should be suspended in vulnerable ecosystems to prevent additional damage to at risk flora and fauna.

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Conclusion

This study determined that the ideal habitats for Texas Horned Lizards in Texas and New Mexico are: eastern and southern New Mexico, south Texas, the southern

Gulf Coast, the Texas Panhandle, the Edwards Plateau, and along the Rio Grande.

Many current reintroduction projects use areas in south Texas, the Hill Country, and the

Texas Panhandle, to place captively bred Texas Horned Lizards into the wild. The results of this study confirm the accuracy of their location selection, since both south

Texas and the Texas Panhandle were found to have good to excellent Horned Lizard habitat suitability, and these projects have had great success in those areas. However, this study also found that many counties in the Hill Country are poorly suited for Texas

Horned Lizards. Therefore, reintroduction efforts may be more effective if they are shifted to a different area. The Edwards Plateau is due west of the Hill Country and is one of the three most suitable areas in the entire state. Despite this, the Texas Horned

Lizard population on the Edwards Plateau is struggling, with only 47% of volunteers seeing the lizard over ten years, compared to 97% of volunteers in south Texas

(Johnson Linam, 2008). Based on these results, it is recommended that reintroduction efforts be expanded from the Hill Country to include the Edwards Plateau. This would place captively bred Texas Horned Lizards in an environment with better groundcover, plentiful food, and fewer outside disturbances. Furthermore, reintroduction projects should continue their operations in the Texas Panhandle and south Texas. These operations in south Texas should also be focused particularly along the southern Gulf

Coast and the Rio Grande Valley. This would protect existing populations and build the overall number of Texas Horned Lizards while achieving a maximum survival rate for both introduced and native lizards. These repopulation efforts cannot be isolated to

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Texas, and they must include the entirety of the Texas Horned Lizard’s range. Given the limited reintroduction effort in New Mexico, it is also recommended that Texan projects near the border expand their reintroduction range to include suitable areas in eastern and southern New Mexico. Furthermore, future research should continue to investigate the habitats and extent of Texas Horned Lizards in New Mexico, to potentially grow and advise New Mexican Horned Lizard reintroduction initiatives. These expansions in both states should be augmented by a concerted effort to limit road and natural gas pipeline construction in the areas found to be most suitable for Texas Horned Lizards. With these measures, reintroduction efforts will be able to build upon their current success and grow the native Texas Horned Lizard population across its traditional range so that it may be appreciated by future generations of Texans and New Mexicans.

Figure 4-1: 600th Successful Texas Horned Lizard Hatching at the Fort Worth Zoo

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LIST OF REFERENCES

Anselin, L., (2005). Exploring Spatial Data with GeoDa: A Workbook. Spatial Analysis Laboratory, Department of Geography, University of Illinois, Urbana-Champaign.

Buren, W. F., Allen, G. E., Whitcomb, W. H., Lennartz, F. E., & Williams, R. N. (1974, June). Zoogeography of the Imported Fire Ants. Journal of the New York Entomological Society, 82(2), 113-124.

Burrow, A. L., Kazmaier, R., Hellgren, E. C., & Ruthven III, D. (2001). Microhabitat Selection by Texas Horned Lizards in Southern Texas. Journal of Wildlife Management, 65(4), 645-652.

Carr, W. (2021) Some Plants of the South Texas Sand Sheet. Retrieved March 29, 2021 from http://w3.biosci.utexas.edu/prc/DigFlora/WRC/Carr-SandSheet.html

Claver, S., Silnik, S. L., & Campón, F. F. (2014). Response of ants to grazing disturbance at the central Monte Desert of Argentina: community descriptors and functional group scheme. Journal of Arid Land, 6(1), 117-127.

Collins, L., & Scheffrahn, R., (2016). Red Imported Fire Ant – Solenopsis invicta. FDACS Division of Plant Industry: University of Florida.

Comanns, P., Buchberger, G., Buchsbaum, A., Baumgartner, R., Kogler, A., Bauer, S., & Baumgartner, W. (2015). Directional, passive liquid transport: the Texas horned lizard as a model for a biomimetic ‘liquid diode’. J. R. Soc. Interface, 12:20150412.

Cook, T., & Olson, D. (2021) Edwards Plateau savanna. Retrieved March 29, 2021 from https://www.worldwildlife.org/ecoregions/na0806

Dingus, A. (1982, June). Texas Primer: The Horny Toad. Texas Monthly.

Donaldson, W. (1992). Heavy trade, red ant decline threaten rare Texas ‘horny toad’ Series: PROJECT EARTH. Austin American Statesman, 1992, C1.

Drees, B. M. (2014). Red Harvester Ants. Texas A&M AgriLife Extension, E-402, 4-06.

Fair, W. S. (1995, December). Habitat Requirements and Capture Techniques of Texas Horned Lizards in South Texas. College of Graduate Studies Texas A&M University-Kingsville

69

Fair, W. S., & Henke, S. E. (1999, December). Movements, Home Ranges, and Survival of Texas Horned Lizards (Phrynosoma cornutum). Journal of Herpetology, 33(4), 517-525.

Gluesenkamp, A. (2020). The Texas Horned Lizard Reintroduction Project: Preserving A Texas Icon. Retrieved March 29, 2021 from https://www.wildlife2020.com/the-texas-horned-lizard-reintroduction-project- preserving-a-texas-icon/

Gordon, D. M. (1986). The dynamics of the daily round of the harvester ant colony (Pogonomyrmex barbatus). Anim. Behav., 1986, 34, 1402-1419.

Guénard, B., Weiser, M., Gomez, K., Narula, N., Economo, E.P. (2017) The Global Ant Biodiversity Informatics (GABI) database: a synthesis of ant species geographic distributions. Myrmecological News 24: 83-89.

Hodges, W. (2019). About Horned Lizards. Retrieved March 12, 2021 from http://digimorph.org/resources/horned.phtml

Hodges, W. & Pianka E. (2021) Horned Lizards. Retrieved April 21, 2021 from http://www.zo.utexas.edu/faculty/pianka/phryno.html

Horned Lizard Conservation Society. (2021). What is a Horned Lizard? Retrieved March 12, 2021 from http://www.hornedlizards.org/horned-lizards.html

Janicki, J., Narula, N., Ziegler, M., Guénard, B., & Economo, E.P. (2016) Visualizing and interacting with large-volume biodiversity data using client-server web- mapping applications: The design and implementation of antmaps.org. Ecological Informatics 32: 185-193.

Johnson Linam, L. A. (2008). Texas Horned Lizard Watch: 10-Year Summary Report 1997~2006. Texas Parks and Wildlife Department, 1-12.

Mackay, W., & Mackay, E. (2014). The Ants of New Mexico (Hymenoptera: Formicidae). Laboratory for Environmental Biology, The University of Texas, El Paso.

Middendorf III, G. A., & Sherbrooke, W. C. (2001). Blood-squirting variability in horned lizards (Phrynosoma). Copeia, 2001, 1114-1122.

Middendorf III, G. A., & Sherbrooke, W. C. (1992). Canid Elicitation of Blood-Squirting in a Horned Lizard (Phrynosoma cornutum). Copeia, 1992(2), 519-527.

NLCD Land Cover (CONUS) All Years. (n.d.d) Multi-Resolution Land Characteristics Consortium. Retrieved February 5, 2021 from https://www.mrlc.gov/data?f%5B0%5D=category%3ALand%20Cover&f%5B1%5 D=category%3Aland%20cover

70

Oklahoma Department of Wildlife Conservation. (2021). Field Guide: Texas Horned Lizard. Retrieved April 21, 2021 from https://www.wildlifedepartment.com/wildlife/nongamespecies/reptiles/texas- horned-lizard

Painter, C. W., Stuart, J. N., Giermakowski, J. T., & Pierce, L. J. S. (2017). Checklist of the Amphibians and Reptiles of New Mexico, USA, with Notes on Taxonomy, Status, and Distribution. Western Wildlife, 4(29-60), 39.

Texas A&M University. (2021). Red Harvester Ants. Texas Agricultural Extension Service: The Texas A&M University System. Retrieved February 22, 2021 from http://anderson.agrilife.org/files/2011/06/red_harvester_ants.pdf

Texas Parks and Wildlife Department. (2005). Texas Horned Lizard (Phrynosoma cornutum). Retrieved March 12, 2021 from https://tpwd.texas.gov/huntwild/wild/species/thlizard/

“Texas Population Estimates Program.” TDC - Texas Population Estimates Program, Texas Demographic Center, demographics.texas.gov/data/tpepp/estimates/

United States Census Bureau. Annual Estimates of the Resident Population: April 1, 2010 to July 1, 2019. U.S. Census Bureau, Population Division. Web. May 2020. http://www.census.gov/.

United States Census Bureau. B01001 SEX BY AGE, 2019 American Community Survey 5-Year Estimates. U.S. Census Bureau, American Community Survey Office. Web. 10 December 2020. http://www.census.gov/

United States Census Bureau. (2010). Federal Information Processing System (FIPS) codes for States and Counties. Retrieved March 5, 2021 from https://transition.fcc.gov/oet/info/maps/census/fips/fips.txt

United States Department of Agriculture. (2021). “Not All Alien Invaders Are From Outer Space, Red Imported Fire Ant”. Retrieved April 19, 2021 from https://www.webcitation.org/5uNhOujmD?url=http://www.aphis.usda.gov/lpa/pubs /invasive/4fireant.html

University of Arizona. (2021). Spatial Regression: Instructor’s Supplement. GIST 602A, Module 6, 3-7.

Walker, A. 2018. "Phrynosoma cornutum" (On-line), Animal Diversity Web. Accessed March 12, 2021 at https://animaldiversity.org/accounts/Phrynosoma_cornutum/

Webb, S. L., & Henke, S. E. (2003). Defensive Strategies of Texas Horned Lizards (Phrynosoma cornutum) Against Red Imported Fire Ants. Herpetological Review, 2003, 34(4), 327-328.

71

Whiting, M. J., Dixon, J. R., & Murray, R. C. (1993). Spatial Distribution of a Population of Texas Horned Lizards (Phrynosoma cornutum: Phrynosomatidae) Relative to Habitat and Prey. The Southwestern Naturalist, 38(2), 150-154.

Wojcik, D. P., Allen, C. R., Brenner, R. J., Forys, E. A., Jouvenaz, D. P. & Lutz, R. S. (2001). Red Imported Fire Ants: Impact on Biodiversity. Nebraska Cooperative Fish & Wildlife Research Unit, Staff Publications, 47.

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