PRESENCE OF POTENTIAL PREDATORS AND THERMAL ENVIRONMENTS OF TEXAS
HORNED LIZARDS (PHRYNOSOMA CORNUTUM)
By
Tabea Malinowski, B.S.
A
Thesis
In
ARID LAND STUDIES
Submitted to the Graduate Faculty
of Texas Tech University in
Partial Fulfillment of
the Requirements for
the Degree of
MASTER OF SCIENCES
Approved by
Robin M. Verble, Ph. D.
Chair of Committee
Gad Perry, Ph. D.
Clint W. Boal, Ph. D.
Mark A. Sheridan, Ph. D.
Dean of the Graduate School
August 2014
Copyright
© 2014
Tabea Malinowski
Texas Tech University, Tabea Malinowski, August 2014
ACKNOWLEDGEMENTS
I would like to thank my advisor Dr Robin Verble and the faculty and
students of the Natural Resources Management Department of Texas Tech
University for their support, encouragement, and assistance throughout the course
of my master’s education. Neither my research project, nor my thesis would have
been possible without their help.
I would also like to thank the Beach family, who allowed me to use their
ranch for my fieldwork and Krista Mougey, who accompanied me during my data
collection and helped with her expertise about the Texas horned lizard.
A special thanks goes to my committee members Dr Gad Perry and Dr Clint Boal for
their guidance, suggestions and expertise within the Texas horned lizard project.
This thesis is the result of their support and guidance during my year at Texas Tech
University.
Last but not least, I express my gratitude to my family, especially my parents
and siblings, Svea and Per, and to my friends, Franziska, Clara, and Dorit, who
always supported me with their advice and their emotional as well as moral support.
I dedicate this thesis to my family, friends, and committee members.
Thank you very much for letting me have this experience and supporting me during
this project and my master’s education.
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS………………………………………………………………...................................ii
ABSTRACT…………………………………………………………………………………………………...….….vi
LIST OF TABLES......................................................................................................................................viii
LIST OF FIGURES………………………………………………………………..……..….……………...…...…ix
LIST OF ABBREVIATIONS……………………………………….……..…………………..………...……....xi
I. LITERATURE REVIEW...........................................................................................................................1
Abstract…………………………………………………………………………………………………..…1
Introduction……………………………………………………………………...……….……………….…..1
THL Habitat……………………………………………………………………………….……………...…...2
Morphology……………………………………………………………………...……...………..……………4
Biology…………………………………………………………………………...….…………………...……...5
Thermal Physiology…………………………………………………………………..………...………….6
Prey and Feeding Behavior………………………...………………………...…………………………8
Predators and Predator Defense……………………………………………………...……………...9
Predator Ecology……………………………………………………………………………...……….….11
THL Decline…………………………………………………………………...…...……………...….……..14
Research Questions…………………………………………………………....…………………....……15
Literature Cited………………………………………………………...……………………..……...……16
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II. SURVEYS OF POTENTIAL PREDATORS OF TEXAS HORNED LIZARDS.......................22
Abstract………………………………………………………………………………………………………..22
Introduction……………………………………………….……………………....………………......……22
Questions…………………………………………………………………………………...…25
Hypotheses…………………………………………………………..……………………….25
Materials and Methods……………………………………………………...………….………………26
Study Area…………………………………………………………………………………….26
Field Methods and Data Collection………………..……………..…………………27
Statistical Analysis…………………………………….………………………..…………28
Results……………………………………………………...……………………….……………...………….28
Discussion…………………………………………………………………………………………...………..29
Tables…………………………………………………………………….……………………………...……..33
Figures……………………………………………………….………………………………………...………35
Literature Cited………………………………………………...………………………………….....……40
III. TEXAS HORNED LIZARDS THERMAL ENVIRONMENTS...................................................43
Abstract……………………………………………………………………………..…………………………43
Introduction……………………………………………………………………………….………...………43
Questions……………………………………………………………………….………….....46
Hypotheses………………………………………………………………………..…………46
Materials and Methods…………………………………………………………………...…….………47
Study Area………………………………………………………………………………….…47
Field Methods and Data Collection…………………..…………………..…………48
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Statistical Analysis……………………………………….…………….…………….……49
Results……………………………………………………………………………...…..……...………………49
Discussion…………………………………………………………………………………..…………...……50
Tables…………………………………………………………………………..…………………….……..…54
Figures……………………………………………………………………….………………………...………56
Literature Cited…………………………………………………...………………………………….....…72
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ABSTRACT
The Texas horned lizard (Phrynosoma cornutum) is one of thirteen species
that make up the genus Phrynosoma. Their range extends from Canada to
Guatemala, and they live in arid and semiarid desert regions. Due to their low
motility and conspicuous foraging locations, horned lizards are often susceptible to
predators. Several studies have emphasized the importance of habitat and
environmental conditions to Texas horned lizards; however, less is known about
their thermal biology and recent decline.
My thesis aims to increase our understanding of Texas horned lizard thermal
biology, predation and possible reasons of their recent decline.
These aspects are essential to future conservation measures, efforts, and
considerations.
I conducted a predator survey using camera traps and plastic lizard models
to estimate the visibly of lizards to potential hunting predators within three habitat
types. Coyotes and roadrunners represent a threat to Texas horned lizards and a
feasible occurrence of an overpopulation of these predators in a small and isolated
habitat might have an impact on the decline besides anthropogenic factors.
I also measured temperatures at ten distinct locations in which Texas horned
lizards have been observed by researchers on the study site using iButtons. The
purpose of this survey was to create a thermal profile of horned lizard habitat and
examine the thermal constraints of their environments. Within the thermal
environment of the Texas horned lizard, thermal areas (microhabitats) with diverse
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mean temperatures were observed and adaptations to their daily routine within
their habitat were made.
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LIST OF TABLES
1. Counted potential predators by camera trapping during the 30 day
fieldwork…..………………………………………………………………………………...…………..33
2. Percentage of potential predators detected within the treatments:
dense vegetation, road, and ranchland during the 30 day field
study……...……………………………………………………………………………………………..…34
3. Means for one-way ANOVA for the distinct locations…………………………………54
4. Temperatures (°C) of the distinct locations (30 March 2014)…….………………55
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LIST OF FIGURES
1. Attached transmitter on a lizard model……………………………………….……..….…35
2. Camera trap attached to a fence and a small tree……………………...……….………36
3. Camera trap on a mesquite shrub……………………………………………………………..37
4. Species composition of detected potential predators……..………………....……….38
5. Distribution of detected potential predators in the treatments:
dense vegetation, road, and ranchland……………………………………………………...39
6. Ibutton on a mesquite trunk………………………………………………………........……….56
7. Mean temperatures of distinct locations within the THL habitat………........…..57
8. Representative daily temperature curve of the mean
temperatures of the distinct locations (30 March 2014;
mean of temperature across all microhabitats)…………………………………..…..…58
9. Representative daily temperature curve of the temperatures
of the 9 different distinct locations (30 March 2014)……………………………..…..59
10. Representative daily temperature curve of the temperatures
of the treatment: Ant mound (30 March 2014)………………………………………….60
11. Representative daily temperature curve of the temperatures
of the treatment: In the soil (30 March 2014)…………………..........................………61
12. Representative daily temperature curve of the temperatures
of the treatment: On a stone (30 March 2014)………................................……………62
13. Representative daily temperature curve of the temperatures
of the treatment: On the ground (30 March 2014)…………………………………..…63
14. Representative daily temperature curve of the temperatures
of the treatment: On the road (30 March 2014)…………………………………………64
15. Representative daily temperature curve of the temperatures
of the treatment: In the shadow (30 March 2014)………………………………..……65
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16. Representative daily temperature curve of the temperatures
of the treatment: On a trunk (30 March 2014)…………………….………………….…66
17. Representative daily temperature curve of the temperatures
of the treatment: Under a trunk (30 March 2014)…………………………………..…67
18. Representative daily temperature curve of the temperatures
of the treatment: In a yucca plant (30 March 2014)………………………………...…68
19. Representative daily temperature curve of the mean
temperatures of the distinct locations (30 March 2014;
mean of temperature across all microhabitats) combined
with the daily routine of the Texas horned lizard……………………………….....…..69
20. Representative daily temperature curve combined with
the lizards’ behavior in the night and morning…………………………………….....…70
21. Representative daily temperature curve combined with
the lizards’ behavior at noon and in the afternoon………………………………...…..71
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LIST OF ABBREVIATIONS
cm = centimeter
df =
degree of freedom
g=
gram
ha = hectare
m=
meter
mm = millimeter
μg = microgram
km = kilometer
N=
number of individuals in a population
P=
Probability
THL= Texas horned lizard
Ӽ² = chi-square
°C = degrees Celsius
%=
percent
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CHAPTER I
LITERATURE REVIEW
Abstract
Texas horned lizards (Phrynosoma cornutum) are one of thirteen species
within the genus Phrynosoma. They range from Canada to Guatemala and occur in
the states of Texas, Oklahoma, New Mexico and Kansas. They inhabit arid and
semiarid desert regions within a harsh environment. Texas horned lizards are
myrmecophagous with harvester ants representing a large portion of their diet. Due
to their low motility and conspicuous foraging locations, horned lizards are often
susceptible to predators. Several studies have emphasized the importance of habitat
and environmental conditions to Texas horned lizards; however, less is known about
their thermal biology and recent decline.
Introduction
Texas horned lizards (Phrynosoma cornutum; THL) are one of thirteen
species that comprise the genus Phrynosoma (collectively, the horned lizards;
Manaster, 1997). They are members of the Iguanidae, one of the biggest modern
lizard families (Sherbrooke, 2003). Horned lizards are commonly referred to as
horny toads, because of their similarity in appearance to toads (Henke and Fair,
1998). All Phrynosoma possess a suite of morphological characteristics including a
flat shape and cranial horns, from which they derive their name (Sherbrooke, 2003).
Their range extends from Canada to Guatemala, and they often live in arid and
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semiarid desert regions (Manaster, 1997). THL inhabit open and flat terrain within
rocky or sandy environments (Hutchinson and Larimer, 1960).
All species of the genus are myrmecophagous, but differ in the portion of ants
that comprise their diets (Meyers, 2006); Phrynosoma cornutum is a highly
myrmecophagous species (up to 90% ants in diet; Meyers, 2006). Due to their low
motility and conspicuous foraging locations, horned lizards are often susceptible to
predators, including snakes, coyotes, foxes, hawks and other raptorial birds
(Sherbrooke, 2003).
THL Habitat
Horned lizards are widespread and common in North America (Manaster,
1997). Texas horned lizards’ range lie east of other Phrynosoma species
(Sherbrooke, 2003); they are often found in the Southern Great Plains and are
spread across the states of Texas, Kansas, Oklahoma, New Mexico, Colorado, Arizona
(Manaster, 1997), and northeastern Mexico (Sherbrooke, 2003). Their natural
environment is the open country of arid and semiarid regions where grassland
species and sparse vegetation of shrubs and small trees are the dominant vegetation
(Ludeke et al., 2005; Sherbrooke, 2003; Whiting et al., 1993). Whiting et al. (1993)
found that the distribution of THL depends primarily on habitat and disturbance,
especially vegetation cover, rather than on prey availability. They also found that
THL densities in optimal habitats were around 3 lizards/ha (Whiting et al., 1993).
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Across their range, Texas horned lizards were declining considerably. Due to
this, the state of Texas designated the Texas horned lizard as threatened in 1977.
One reason for this decline was habitat fragmentation and isolation (McIntyre,
2003). To improve future conservation measurements and save THL from further
decline, more studies should emphasize habitat preferences of Texas horned lizards
(Burrow et al., 2001). Burrow et al. (2001) found that horned lizards prefer areas
with diverse microhabitats, where they can hide from predators and abiotic
influences (i.e., extreme temperatures, weather events). Burrow et al. (2001) also
observed that THL use areas of short vegetation cover as well as bare soil for
foraging and thermoregulation throughout the day, except during afternoons
because of high solar radiation. During the highest temperatures of the day, THL
hide under stones, litter, shrubs and small trees to protect themselves from heat
exposure and against predators (Burrow et al., 2001).
Further, habitat structure appears to have a strong effect on the perception
and behavioral mechanisms of predators and prey (Morice et al., 2013). Specifically,
environmental geometry can dictate the rules of pursuit and evasion within a habitat
(Morice et al., 2013). From these observations, it appears that conservation
management should focus on creating a habitat containing a mosaic of woody
vegetation, grasslands with low vegetation height and intermixed bare soil (Burrow
et al., 2001).
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Morphology
The morphology of THL is genus-typical and includes camouflaged skin
patterns, which are an adaptation to the soils of their environments (Sherbrooke,
2003). Animals’ skin patterns often resemble their habitats and often have a
protective function (Norris and Lowes, 1964). Background color-matching
organisms often live in uniform colored habitat such as desert areas (Norris and
Lowes, 1964). Generally, the color of rocks, soil, or vegetation cover is mimicked by
these species (Norris and Lowes, 1964). The camouflaged skin of THL works as
insurance against detection by predators and is enhanced in the presence of danger
by their staying immobile (Sherbrooke, 2003). THL skin color ranges from reddishbrown over grayish-brown to ocher-brown (Sherbrooke, 2003). These lizards have
a distinct white line in the middle of their back, which may mimic the shape of a
grass blade (Norris and Lowes, 1964, Sherbrooke, 2002). Parker and Kerckhoff
(1937) described color changes in Phrynosoma cornutum, regulated by activities of
their melanophore system. They are able to blanch their skin color during periods
of high temperatures and darkness or to darken it as a response to low
temperatures and strong light influences (Parker and Kerckhoff, 1937).
THL are approximately 70 mm snout to vent length (SVL; Sherbrooke, 2003).
Generally, females are larger than males (Zamudio, 1998) and reach a maximum
length of around 115 mm (Sherbrooke, 2003). Horned lizard cranial horns contain
true bone and surround their skull; they may have evolved as a defense mechanism
to prevent predators from swallowing them (Sherbrooke, 2003). Their flattened
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shape help them warm rapidly by maximizing exposure to solar radiation but also
decrease their running speed during escape from predators (Sherbrooke, 2003).
Their body shape is thought to further impair their mobility in high and dense
vegetation (Sherbrooke, 2003).
Biology
Texas horned lizards are oviparous (Cahn, 1926). Reproduction usually takes
place between April and mid-July (Ballinger, 1974). Females start mating at two
years of age and after they have reached 70 mm SVL and lay approximately 29 eggs
per year in a single clutch (Ballinger, 1974). THL females burrow in the soil, lay
their eggs, and backfill the nest to protect it from exogenous influences and
predators (Allison and Cepeda, 2009). The hatchlings burrow out of the nest upon
emergence (Allison and Cepeda, 2009). Within their first weeks of life, THL
hatchlings prey on harvester ants (e.g. Pogonomyrmex rugosus) < 4 mm in length
(Allison and Cepeda, 2009).
Mayhew (1965) described horned lizards as “obligatory hibernators”. They
actively accumulate fact reserves until November and then burrow underground to
overwinter (Sherbrooke, 2003). During hibernation, oxygen consumption and
associated metabolic processes drop precipitously, and the lizards survive by living
off their body fat and water reserves (Sherbrooke, 2003). Lizards resume activity
after soil temperatures warm in the spring, generally around April (Sherbrooke,
2003).
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Thermal Physiology
Thermoregulation is the process of controlling the internal body temperature
(Soule, 1963). The temperature of its body influences an organism’s physiology,
development and behavior (Stevenson, 1984). Like other reptiles, horned lizards
are poikilothermic vertebrates (Sherbrooke, 2003). Poikilotherms vary their body
temperature with the temperature of the environment (Bogert, 1949). For many
poikilothermic reptiles maintaining an isothermic body temperature relative to the
environment requires movement throughout space multiple times per day
(Wheeler, 1986).
Reptiles have developed several behavioral mechanisms to control body
temperature (Whitfield and Livezey, 1973) such as cloacal discharge, decreasing or
increasing their heart rate, panting, altering metabolic processes or by adaptations
to blood circulation patterns (Whitfield and Livezey, 1973). The mechanism and its
effectiveness depend on abiotic factors (e.g., radiation, wind, air and ground
temperature) and lizard morphology (e.g., body size, color; Stevenson, 1984). Texas
horned lizards have evolved adaptations to their dry and hot habitat, where shade
can be hard to find and water is a rare resource (Bogert, 1949). Their internal
temperature is regulated through five methods of thermoregulation: burrowing,
shade-seeking, lying in the sun, changes in body shape, and movements of
orientation (Heath, 1965). THL engage in a predictable pattern of behaviors each
day that are driven by thermoregulatory needs (Heath, 1965). They leave their
burrow early in the morning, when the ground temperature reaches 19 °C and will
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wait for the first sun rays to initiate basking (Heath, 1965). The mean body
temperature of a THL is approximately 34.9 °C; the thermal maximum is 39 °C, and
the minimum is 28 °C (Cowles and Bogert, 1944; Heath, 1965). Compared to the
temperature ranges of other day-active desert lizards, Texas horned lizards show
one of the widest thermal tolerance ranges (Kour and Hutchinson, 1970). However,
Prieto and Whitford (1971) found that the heart rate and oxygen consumption
increase with higher temperatures.
Finally, species of horned lizards which occupy a more northern or mountain habitat
warm up at a faster mass-specific rate during sun basking compared to lizards living
in southern or lower elevation regions (Diaz et al., 1996).
High temperatures or other factors in the environment may induce stress
(Ulmasov et al., 1992). A response to stress is the synthesis of heat-shock proteins
(Ulmasov et al., 1992). Heat shock proteins enable thermally stressed organisms to
buffer their bodies against the damaging effects of heat (Ulmasov et al, 1992, Carroll
and Yellon, 2000).
Lizard species of desert areas produce heat-shock proteins (specifically,
hsp70) at higher levels than non-desert lizards (Zatsepina et al., 2000). In general,
lizards living at higher latitudes have lower thermal ranges for heat shock protein
expression than lizards of southern or desert regions (Zatsepina et al., 2000).
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Prey and Feeding Behavior
Texas horned lizards are myrmecophagous, with ants comprising a large
portion (> 90%) of their diet (Sherbrooke, 2003). Especially harvester ants
(Pogonomyrmex spp.; Eifler et al., 2012), which are herbivores that feed on highenergy plant seeds, are consumed (Sherbrooke, 2003). The most important
harvester ant species for THL are P. rugosus and P. desertorum (Whitford and
Bryant, 1979). THL appear to be immune to the venomous stings of their ant prey,
and are able to detoxify a certain proportion of the ants’ venom (Sherbrooke, 2003)
via a factor in their plasma that immunizes them to a certain degree against the
venom of the harvester ants (Schmidt et al., 1989). The lethal dose of ant venom for
a THL is 162 µg venom/g body weight (Schmidt et al., 1989). Horned lizards eat
approximately 200-500 ants/day and prey upon them by waiting close to their
mound (Manaster, 1997). In addition to ants, they also opportunistically consume
caterpillars, grasshoppers, beetles, termites, and other insects (Sherbrooke, 2003).
THL feeding behavior resembles that of a toad in that they use their sticky tongue to
pick up ants (Sherbrooke, 2003). THL do not sample chemicals by using tongue
flicking to identify the source of their food, instead they forage by visually searching
for ant mounds and moving ants (Cooper and Sherbrooke, 2009). Phrynosoma
cornutum is far more active during the hottest hours of the day than other species of
the genus (Winton, 1916), and it often find its prey along the edge of vegetation or
near an ant road, where it will wait to feed on the ants (Winton, 1916).
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Predators and Predator Defense
Predation is a force controlling demographic processes and influencing the
dynamics of populations, but it is often difficult to quantify (Munger, 1986). Texas
horned lizards are prey items for many other vertebrates (Sherbrooke, 2003).
Young and small individuals are particularly vulnerable to predation, at least in part,
because they are more easily swallowed by predating organisms than are adult
lizards, which have fully developed cranial horns to defend themselves (Sherbrooke,
2003). Texas horned lizards have evolved several defensive behaviors to protect
themselves. The cranial horns of Phrynosoma are morphological weapons for
defense and evolved within the context of natural selection (Bergmann and Berk,
2012); horn length shows a positive correlation with predation pressure (Bergmann
and Berk, 2012). The Length of their horns shows a positive allometry due to
evolution and ontogeny (Bergmann and Berk, 2012). A higher pressure of
predation, leads to the evolution of longer cranial horns to protect the THL against
predation. Interestingly, Phrynosoma species that have longer horns consume a
larger portion of ants within their diet and are also slower in their movements
(Bergmann et al., 2009).
Their camouflage is a second predator defense. The main goal of camouflage
is to make prey more difficult for predators to detect (Cooper and Sherbrooke,
2012). If crypsis has no effect on a predator, THL will flee and try to hide under
stones or in dense vegetation (Sherbrooke, 2003). But because of their short limbs
and dorsally-flattened body they are often slow runners and can easily be caught
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(Sherbrooke, 2003). If they are not able to run away, they will face the predator and
are able to inflate their bodies up to twice their size (Sherbrooke, 2003), since
fleeing increases the probability of getting caught by a predator (Cooper and
Sherbrooke, 2010). Cooper and Sherbrooke (2010) found that predator shadows
would induce fleeing behavior in THL, suggesting that visual indicators were key in
detecting predators.
To protect against canid predators, THL squirt blood which contains a foultasting chemical, from their eyelids as a deterrent and to confuse the predator
(Middendorf and Sherbrooke, 1992; Sherbrooke, 2003). Generally, THL aim these
defenses at the predator’s face. The active chemical in this ejected blood is a buccal,
ocular and/or nasal irritant (Middendorf and Sherbrooke, 2001). Lambert and
Ferguson (1985) found that blood ejection is a rarely utilized defensive mechanism,
and blood squirting behaviors are not unique to horned lizards but also occur in
other Iguanidae.
Raptorial birds pose a significant risk for Texas horned lizards. Hawks and
falcons are two common visual predators of THL; they can recognize lizards from a
height of around 915 m (Sherbrooke, 2003). Additionally, other aerial predators
such as American Kestrel (Falco sparverius), Prairie Falcon (Falco mexicanus),
Swainson’s Hawk (Buteo swainsoni), and Loggerhead Shrike (Lanuis ludovicianus) at
least opportunistically consume THL (Sherbrooke, 2003). On the ground, the
Greater Roadrunner (Geococcyx californianus), Western Diamond-Backed
Rattlesnake (Crotalus atrox), Sidewinder (C. cerastes), whip snakes (Masticophis spp.;
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Sherbrooke, 2008), such as the Western Coachwhip (Masticophis flagellum), LongNosed Leopard Lizard (Gambelia wislizenii), kit foxes (Vulpes macrotis; Middendorf
and Sherbrooke, 2004), coyotes (Canis latrans) and domestic dogs (Canis lupus
familiaris) also consume THL (Sherbrooke, 2003; Sherbrooke and Mason, 2005).
Finally, Southern Grasshopper Mice (Onychomys torridus) occasionally catch and
consume small juvenile THL (Sherbrooke, 1991; Sherbrooke, 2003).
Predator Ecology
Predator-prey relationships can have major impacts in ecological systems
(Lima, 1998). Predation leads to elimination of prey individuals from certain
habitats or ecological systems and can have impacts on the dynamics of populations
of prey as well as on the entire ecosystem (Lima, 1998).
Predators can be found in all ecosystems around the world and initiate trophic
cascades and top-down effects (Estes et al., 2001).
Texas horned lizards are a prey organism of many other vertebrates,
including common predators like coyotes, roadrunners, raptorial birds and mice.
Coyotes (Canis latrans) belong to the family Canidae (Short, 1979). These
predators range from the colder to the warmer ecosystems of North America and
consume a variety of food, including Texas horned lizards (Phrynosoma cornutum),
black-tailed jack rabbits (Lepus californicus), roadrunners (Geococcyx californianus),
and many other organisms (Short, 1979).
Roadrunners (Geococcyx californianus) are ground-active birds of the cuckoo
family occurring in the United States and Mexico (Bryant, 1916). Their diet consists
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mostly of insects, especially grasshoppers, crickets and beetles (Bryant, 1916).
However 3.4 % of their diet is represented by mammals (e.g. mice, newly-born
rabbits), 1.7 % by other birds and 3.7 % by reptiles (e.g. snakes, horned lizards;
Bryant, 1916).
Raptorial birds pose a high predation risk to horned lizards. Swainson’s
Hawk (Buteo swainsoni) is a visual predator, who inhabits grassland steppes and
desert ecosystems (Giovanni et al., 2007). Rodents (28.7 %) and reptiles as well as
amphibians (35.6 %) compromise the largest portion of their diet (Giovanni et al.,
2007). Within the group of reptiles, THL represent 12.4 % of the Swainson’s Hawks’
diet (Giovanni et al., 2007) and therefore exert a high predation risk to horned
lizards.
Sherbrooke (1991) found that predation rates between grasshopper
mice and horned lizards in captivity are 55% mortality within juvenile lizards and
0% mortality within adult lizards, due to the presence of occipital horns in adult
individuals.
Predation on the Beach Ranch was observed in several studies (e. g. Henry,
2009; Mougey, 2009). Henry (2009) assumed, that a habitat, which supports a high
number of Texas horned lizards might also support a high population size of
potential predators.
On the Beach Ranch 388 horned lizards were encountered and 117 of them
were tagged with a radio-transmitter in the field season 2005-2008 (Henry, 2009).
Survival rates within the active season (2005-2008) were 14.4% for females and
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33.7% for males (Henry, 2009). In the study of Henry (2009) a lower survival rate
in females compared to males on the Beach Ranch was observed.
In the field season 2008-2009, 74 horned lizards were tagged (Mougey,
2009). However, only 29 individuals of these 74 lizards were mature adults
(Mougey, 2009). Apparently only a small number of Texas horned lizards reach the
state of adulthood, which indicates a high predation risk on hatchlings and juvenile
lizards.
Within all years of studies, conducted on the Beach Ranch, 46 Texas horned
lizards were found dead by using telemetry (Henry, 2009). 37 of these dead
individuals (80%) seemed to have died due to predation (Henry, 2009).
Identification of predators was often difficult to ascertain, but one carcass showed
teeth marks belonging to a small rodent or cotton rat (Sigmodon spp.); three radio
transmitters were found far from the home ranges of the lizards, carried off by
predators and dropped somewhere arbitrarily; and nine of the transmitters were
excreted by snakes or the transmitter could be localized in a snake burrow (Henry,
2009). In two cases, Henry (2009) followed a radio transmitter signal and
discovered that it was coming from the inside of a snake. The detected snakes were a
coachwhip (Masticophis spp.) and a rattlesnake (Crotelus spp.) (Henry, 2009). In the
study of Henry (2009) a juvenile Texas horned lizard in the beak of a Greater
Roadrunner (Geococcyx californianus) was observed. Henry (2009) found out, that
many Texas horned lizards were predated particularly by snakes in the Rolling
Plains Ecoregion of Texas. Snakes are gape-limited predators and could therefore a
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Texas Tech University, Tabea Malinowski, August 2014
higher number of snakes could consume hatchlings and juvenile lizards more easily
(Anderson, 2012).
THL Decline
Texas horned lizards were amidst a noticeable range-wide decline. Eastern
and central Texas THL populations were the most impacted by the decline
(Sherbrooke, 2003). In recent years, THL have been extirpated from parts of
Oklahoma and regions in central and eastern Texas (Sherbrooke, 2003). To this end,
the State of Texas designated the Texas horned lizard as threatened in 1977
(Manaster, 1997).
A commonly cited reason for THL decline is that their habitats became
smaller and more isolated due to human settlement and fragmentation by roads
(Sherbrooke, 2003). The Great Plains, a typical habitat for THL, have been
transformed due to anthropogenic disturbances on a large scale (McIntyre, 2003).
Habitat fragmentation decreases dispersal and reproduction effort (Suarez and Case,
2002); roads exacerbate declines by increasing car-associated mortality
(Sherbrooke, 2003). Further, the cessation of natural processes (e.g., fire) has
allowed many habitats to be encroached by invasive vegetation, thus altering
structure and composition (Hobbs and Huenneke, 1992).
Biological invasions often have large impacts on native fauna and lead to
biodiversity loss within communities (Suarez et al., 2000). A second reason for
decline may be non-native red imported fire ants (Solenopsis invicta), which are very
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Texas Tech University, Tabea Malinowski, August 2014
aggressive and territorial. Fire ants have displaced native ants, including harvester
ants, which are the main prey for THL (Sherbrooke, 2003). Finally, increased use of
insecticides has led to a decline in the population size of harvester ants (Sherbrooke,
2003), which may be impacting THL food availability.
Research Questions
Several studies have emphasized the importance of habitat and
environmental conditions to Texas horned lizards (Burrow et al. 2001; Eifler et al.
2012; Fair and Henke, 1997; McIntyre et al. 2003; Morice et al. 2013; Whiting et al.
1993); however, less is known about their thermal biology and recent decline.
Understanding these aspects is essential to conservation measures and may reflect
an important gap in our current efforts. I pose the following questions: What are the
thermal profiles of Texas horned lizards and could knowledge about them help to
create habitats, which are convenient for THL? Second, what are potential predators
of THL in northern and central Texas? Outcomes of this research will provide
information about Texas horned lizard ecology and biology and provide a useful
background regarding their conservation.
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Texas Tech University, Tabea Malinowski, August 2014
Literature Cited
ALLISON, P. S., AND J. C. CEPEDA. 2009. Nesting and hatchling behavior of the
Texas horned lizard (Phrynosoma cornutum). The Southwestern Naturalist
54:211-213.
ANDERSON, W. M. 2012. Home range, habitat use, and conservation of the Texas
horned lizard (Phrynosoma cornutum) in central Texas. Master’s thesis,
Texas Tech University, Lubbock, TX.
BALLINGER, R. E. 1974. Reproduction of the Texas horned lizard, Phrynosoma
cornutum. Herpetologica 30:321-327.
BERGMANN, P. J., AND C. P. BERK. 2012. The evolution of positive allometry of
weaponry in horned lizards (Phrynosoma). Journal of Evolutionary Biology
39:311–323
BERGMANN, P. J., J. J. MEYERS, AND D. J. IRSCHICK. 2009. Directional
evolution of the stockiness coevolves with ecology and locomotion in
lizards. Evolution 63:215–227.
BOGERT, R. B. 1949. Thermoregulation in reptiles, a factor in evolution.
Evolution 3:195-211.
BRYANT, H. C. 1916. Habits and food of the roadrunner in California. University
of California Publications in Zoology 17:21-58.
BURROW, A. L., R. T. KATZMEIER, E. C. HELLGREN, AND D. C. RUTHVEN.
2001. Microhabitat selection by Texas horned lizards in southern Texas. The
Journal of Wildlife Management 65:645-652.
CAHN, A. R. 1926. The breeding habits of the Texas horned toad, Phrynosoma
cornutum. The American Naturalist 60:546-551
CARROLL, R., AND D. M. YELLON. 2000. Heat shock proteins in myocardial
protection. Eurekah.com 1-14.
COOPER, W. E., JR., AND W. C. SHERBROOKE. 2012. Choosing between a rock
and a hard place: camouflage in the round-tailed horned lizard Phrynosoma
modestum. Current Zoology 58:541–548.
16
Texas Tech University, Tabea Malinowski, August 2014
COOPER, W. E. JR., AND W. C. SHERBROOKE. 2010. Crypsis influences escape
decisions in the round-tailed horned lizard (Phrynosoma modestum).
Canadian Journal of Zoology 88:1003–1010.
COOPER, W. E. JR., AND W. C. SHERBROOKE. 2010. Initiation of escape
behavior by the Texas horned lizard (Phrynosoma cornutum). Herpetologica
66:23–30.
COOPER, W. E. JR., AND W. C. SHERBROOKE. 2009. Prey chemical
discrimination by tongue flicking is absent in the Texas horned lizard,
Phrynosoma cornutum. Journal of Herpetology 43:688-692.
COWLES, R. B., AND C. M. BOGERT. 1944. Thermal Tolerance. Bulletin of the
American Museum of Natural History 83:261–296.
DIAZ, J. A., D. BAUWENS, AND B. ASENSIO. 1996. A comparative study of the
relation between heating rates and ambient temperatures in lacertid lizards.
Physiological Zoology 69:1359-1383.
EIFLER, D. A., M. A. EIFLER, AND T. K. BROWN. 2012. Habitat selection by
foraging Texas horned lizard, Phrynosoma cornutum. The Southwestern
Naturalist 57:39–43.
ESTES, J., K. CROOKS, AND R. HOLT. 2001. Predators, ecological role of.
Encyclopedia of Biodiversity 4:857-878.
FAIR, W. S., AND S. E. HENKE. 1997. Effects of habitat manipulations on Texas
horned lizards and their prey. The Journal of Wildlife Management 61:13661370.
GIOVANNI, M. D., C. W. BOAL, AND H. A. WHITLAW. 2007. Prey use and
provisioning rates of breeding Ferruginous and Swainson’ hawk on the
southern great plains, USA. The Wilson Journal of Ornithology 4:558-569.
HEATH, J. E. 1965. Temperature regulation and diurnal activity in horned
lizards. University of California Press, California.
HENKE, S. E., AND W. S. FAIR. 1998. Management of the Texas horned lizards.
Wildlife Management Bulletin of the Caesar Kleberg Wildlife Research
Institute, Texas, A&M University-Kingsville, Management Bulletin No. 2.
17
Texas Tech University, Tabea Malinowski, August 2014
HENRY, E. 2009. Ecology, home range, and habitat selection of the Texas horned
lizard (Phrynosoma cornutum) in the southern high plains of Texas. Master’s
thesis, Texas Tech University, Lubbock, TX.
HOBBS, R. J., AND L. F. HUENNEKE. 1992. Disturbance, diversity, and invasion:
implications for conservation. Conservation Biology 6:324-337.
HUTCHINSON, V. H., AND J. L. LARIMER. 1960. Reflectivity of the integuments
of some lizards from different habitats. Ecology 41:199-209.
KOUR, E. L., AND V. H. HUTCHINSON. 1970. Critical thermal tolerances and
heating and cooling rates of lizards from diverse habitats. Copeia 2:219229.
LAMBERT, S., AND G. M. FERGUSON. 1985. Blood ejection frequency by
Phrynosoma cornutum (Iguanidae). The Southwestern Naturalist 30:616-617.
LIMA, S. L. 1998. Nonlethal effects in the ecology of predator-prey interactions.
Bioscience 48:25-34.
LUDEKE, K., D. GERMAN, AND J. SCOTT. 2005. Texas vegetation classification
project: interpretive booklet for phase I, Texas Parks and Wildlife Department
and Texas Natural Resources Information System.
MANASTER, J. 1997. Horned lizards. Texas Tech University Press, Texas.
MAYHEW, W. W. 1965. Hibernation in the horned lizard, Phrynosoma m’calli.
Comparative Biochemistry and Physiology 16:103-119.
MCINTYRE, N. E. 2003. Effects of the conservation reserve program seeding
regime on harvester ants (Pogonomyrmex), within implications for the
threatened Texas horned lizard (Phrynosoma cornutum). The Southwestern
Naturalist 48:274-277.
MEYERS, J. J., A. HERREL, AND K. C. NISHIKAWA. 2006. Morphological
correlates of ant eating in horned lizards (Phrynosoma). Biological Journal of
the Linnean Society 89:13–24.
MIDDENDORF, G. A., AND W. C. SHERBROOKE. 2001. Blood-squirting
variability in horned lizards (Phrynosoma). Copeia 4:1114-1122.
18
Texas Tech University, Tabea Malinowski, August 2014
MIDDENDORF, G. A., AND W. C. SHERBROOKE. 1992. Canid elicitation of
blood-squirting in a horned lizard (Phrynosoma cornutum). Copeia 2:519-527.
MIDDENDORF, G. A., AND W. C. SHERBROOKE. 2004. Responses of Kit foxes
(Vulpes macrotis) to antipredator blood-squirting and blood of Texas horned
lizards (Phrynosoma cornutum). Copeia 3:652-658.
MORICE, S., S. PINCEBOURDE, F. DARBOUX, W. KAISER, AND J. CASAS. 2013.
Predator-prey-evasion games in structurally complex environments.
Integrative and Comparative Biology 53:767-780.
MOUGEY, K. 2009. Radio transmitter mass: Impacts on home range, daily
displacement, and endurance in Texas horned lizards and bearded dragons.
Master’s thesis. Texas Tech University, Lubbock, Texas.
MUNGER, J. C. 1986. Rate of death due to predation for two species of horned
lizard, Phrynosoma cornutum and P. modestum. Copeia 3:820-824.
NORRIS, K. S., AND C. H. LOWE. 1964. An analysis of background colormatching in amphibians and reptiles. Ecology 45:565–580.
PARKER, G. H., AND W. G. KERCKHOFF. 1937. The color changes in lizards,
particularly in Phrynosoma. Laboratories of the Biological Sciences
California Institute of Technology.
PRIETO, A. A., AND W. G. WHITFORD. 1971. Physiological responses to
temperature in the horned lizards, Phrynosoma cornutum and Phrynosoma
douglassii. Copeia 3:498-504.
SCHMIDT, P. J., W. C. SHERBROOKE, AND J. O. SCHMIDT. 1989. The
detoxification of ant (Pogonomyrmex) venom by a blood factor in horned
lizards (Phrynosoma). Copeia 3:603-607.
SHERBROOKE, W. C., AND J. R. MASON. 2005. Sensory modality used by
coyotes in responding to antipredator compounds in the blood of Texas
horned lizards. The Southwestern Naturalist 50:216-222.
SHERBROOKE, W. C. 2008. Antipredator responses by Texas horned lizards to
two snake taxa with different foraging and subjugation strategies. Journal of
Herpetology 42:145-152.
19
Texas Tech University, Tabea Malinowski, August 2014
SHERBROOKE, W. C. 1991. Behavioral (predator-prey) interactions of captive
Grasshopper mice (Onychomys torridus) and horned lizards (Phrynosoma
cornutum and P. modestum). American Midland Naturalist 126:187-195.
SHERBROOKE, W. C. 2003. Introduction to horned Lizards of North America.
University of California Press, California.
SHERBROOKE, W. C. 2002. Do vertebral-line patterns in two horned lizards
(Phrynosoma spp.) mimic plant-stem shadows and stem litter? Journal of Arid
Environments 50:109–120.
SHORT, H. L. 1979. Food habits of coyotes in a semidesert grass-shrub habitat.
Forest Service U.S. Department of Agriculture, Research Note 364 pp. 1-4.
SOULE, M. 1963. Aspects of thermoregulation in nine species of lizards from
Baja California. Copeia 1:107-115.
STEVENSON, R. D. 1984. The relative importance of behavioral and
physiological adjustments controlling body temperature in terrestrial
ectotherms. The American Naturalist 126:362-386.
SUAREZ, A. V., AND T. J. CASE. 2002. .Bottom-up effects on persistence of a
specialist predator: ant invasions and horned lizards. Ecological Applications
12:291–298.
SUAREZ, A. V., J. Q. RICHMOND, AND T. J. CASE. 2000. Prey selection in horned
lizards following the invasion of Argentine ants in southern California.
Ecological Applications 10:711–725.
ULMASOV, K. A., S. SHAMMAKOV, K. KARAEV, AND M. B. EVGENEV. 1992.
Heat shock proteins and thermoresistance in lizards. Proceedings of the
National Academy of Sciences of the United States of America 89:1666-1670.
WHEELER, P. E. 1986. Thermal acclimation of metabolism and preferred body
temperature in lizards. Journal of Thermal Biology 11:161-166.
WHITFIELD, C. L., AND R. L. LIVEZEY. 1973. Thermoregulatory patterns in
lizards. Physiological Zoology 46:285-296.
WHITFORD, W. G., AND M. BRYANT. 1979. Behavior of a predator and its
prey: the horned lizard (Phrynosoma cornutum) and harvester ants
(Pogonomyrmex spp.). Ecology 60:686-694.
20
Texas Tech University, Tabea Malinowski, August 2014
WHITNING, M. J., J. R. DIXON, AND R. C. MURRAY. 1993. Spatial distribution of
a population of Texas horned lizards (Phrynosoma cornutum:
Phrynosomatidae) relative to habitat and prey. The Southwestern Naturalist
38:150-154.
WINTON, W. M. 1916/17. Habits and behavior of the Texas horned lizard,
Phrynosoma cornutum, Harlan. I+II. Copeia 36/39:81-84/7-8.
ZAMUDIO, K. R. 1998. The evolution of female-biased sexual size dimorphism: a
population-level comparative study in horned lizards (Phrynosoma).
Evolution 52:1821-1833.
ZATSEPINA, O. G., K. H. A. ULMASOV, S. F. BERESTEN, V. B. MOLODTSOV, S. A.
RYBTSOV, AND M. B. EVGENEV. 2000. Thermotolerant desert lizards
characteristically differ in terms of heat-shock system regulation. The
Journal of Experimental Biology 203:1017–1025.
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CHAPTER II
SURVEYS OF POTENTIAL PREDATORS OF TEXAS HORNED LIZARDS
Abstract
I conducted a predator survey using camera traps and plastic lizard models
to estimate the visibly of lizards to potential predators within three habitat types.
Coyotes and roadrunners represent a significant threat to Texas horned lizards
besides anthropogenic factors.
Introduction
The Texas horned lizard is prey for many other vertebrates (Sherbrooke,
2003). In particular, juvenile lizards and hatchlings are most often predated
(Manaster, 1997). Due to their small body size, they are more easily swallowed than
adult lizards. Also, their cranial horns are not yet completely developed so they
cannot defend themselves against predators (Sherbrooke, 2003).
Predators can be found among various animal taxa, including mammals, birds
and other reptiles. Snakes, such as the Western Diamond-backed Rattlesnake
(Crotalus atrox), Sidewinder (C. cerastes), and Whip Snakes (Masticophis spp.;
Sherbrooke, 2003; Sherbrooke, 2008), and lizards, such as the Long-nosed Leopard
Lizard (Gambelia wislizenii) are the most common reptilian predators (Sherbrooke,
2003). Additionally, many raptorial birds pose a risk for Texas horned lizards
(Sherbrooke, 2003). For example, hawks and falcons are visual predators that can
recognize lizards from a height of around 915 meters (Sherbrooke, 2003). Also
diurnal ground-nesting birds, such as Roadrunners (Geococcyx californianus), easily
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catch THL (Sherbrooke, 2003) and therefore pose a significant threat to them.
Finally, THL also are prey for mammals, especially canids like Kit Foxes (Vulpes
macrotis), Coyotes (Canis latrans), and domestic dogs (Canis lupus familiaris)
(Middendorf and Sherbrooke, 2004; Sherbrooke, 2003; Sherbrooke and Mason,
2005), which are visual hunting predators and common throughout the state of
Texas.
Texas horned lizards are a prey organism of many other vertebrates,
including common predators such as coyotes, roadrunners, raptorial birds, and
mice.
Coyotes (Canis latrans) belong to the family Canidae (Short, 1979). These
predators range from the colder to the warmer ecosystems of North America and
consume a variety of food, including Texas horned lizards (Phrynosoma cornutum),
black-tailed jack rabbits (Lepus californicus), roadrunners (Geococcyx californianus),
and many other organisms (Short, 1979).
Roadrunners (Geococcyx californianus) are ground-active birds of the cuckoo
family occurring in the United States and Mexico (Bryant, 1916). Their diet consists
mostly of insects, especially grasshoppers, crickets and beetles (Bryant, 1916).
However 3.4 % of their diet is represented by mammals (e.g. mice, newly-born
rabbits), 1.7 % by other birds and 3.7 % by reptiles (e.g. snakes, horned lizards;
Bryant, 1916).
Raptorial birds pose a high predation risk to horned lizards. The Swainson’s
Hawk (Buteo swainsoni) is a visual predator, who inhabits grassland steppes and
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desert ecosystems (Giovanni et al., 2007). Rodents (28.7 %) and reptiles as well as
amphibians (35.6 %) compromise the largest portion of their diet (Giovanni et al.,
2007). Within the group of reptiles, THL represent 12.4 % of the Swainson’s Hawks’
diet (Giovanni et al., 2007) and therefore exert a high predation risk to horned
lizards.
Sherbrooke (1991) found that predation rates between grasshopper mice
and horned lizards in captivity are 55% mortality within juvenile lizards and 0%
mortality within adult lizards, due to the presence of occipital horns in adult
individuals.
Due to predation pressures, the Texas horned lizards have evolved defensive
behaviors to protect themselves. Their camouflage is one of the most useful
strategies; THL skin color matches the soils and vegetation types of their habitats
(Manaster, 1997). If their crypsis does not deter a predator, they will flee and hide
under stones or in higher vegetation (Sherbrooke, 2003). Their short limbs and
dorsally-flattened body impede their ability to run quickly (Sherbrooke, 2003).
When horned lizards must face a predator, they inflate their bodies up to twice their
normal size (Sherbrooke, 2003). When engaged, they may also bite (Sherbrooke,
2003) and/or squirt foul-tasting blood from their eyelids to confuse predators
(Middendorf and Sherbrooke, 1992; Sherbrooke, 2003).
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Questions
To identify potential predators of THL, a survey via camera traps was
conducted to document potential predators on the study site, with the following
questions emerging: What species are potentially predating THL on the ranchland?
Do potential predators react to the plastic models of THL? And if the models attract
potential predators, would there be a difference in recognition of models with radiotransmitter collars attached to their back or without?
Hypotheses
I expect more potential avian predators to be recorded on the camera traps
than potential terrestrial predators. Most visually hunting birds are diurnal
(Muhkin et al., 2009), as well as the Texas horned lizard (Sherbrooke, 2003) and
therefore might be a higher predation risk to THL than terrestrial mammals, like
coyotes, which are nocturnal (White et al., 1994). I also hypothesize that potential
predators documented by the camera traps will not attack the THL models due to
lack of motion and the artificial smell. Most predators cue in on motion during
hunting (Buss, 2005) or hunt after the specific smell of their prey organism
(Conover, 2007). In this case the plastic models of THL would not attract the
attention of potential predators.
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Materials and Methods
Study Area
This work was conducted on the Beach Ranch, a privately owned ranch;
approximately 26 kilometers east of Post, in Garza County, Texas. The ranch is
situated in the foothills of the Caprock escarpment of the Llano Estacado, which is
located in the Southern Great Plains (Smith, 2003). The elevation of the area is
approximately 794 m above sea level (Richardson et al., 1975). On average,
approximately 48 cm of rain falls per year, mostly in late spring and early summer
(May and June; Richardson et al., 1975). Garza County has minimum average
temperatures of -2 C° in the month of January and maximum average temperatures
of 35 C° in July (Richardson et al., 1975). The soils are mostly fine sandy loams or
clay soils (Richardson et al., 1975).
The land is used primarily for livestock (cattle) grazing. In recent years no
prescribed fires have taken place, so the grassland is succeeding into shrubland. The
most common vegetation types are grassland prairie and desert shrubland
(Richardson et al., 1975). Mesquite (Prosopsis spp.) is the dominant woody species
in the area. Other common species in the area include blue grama (Bouteloua
gracilis), buffalograss (Buchloe dactyloides), broomweed (Amphiachyris
dracunculoides), western ragweed (Ambrosia psilostachya) and sideoats grama
(Bouteloua curtipendula; Fowler, 2005). Some typical desert plants such as the
cholla (Opuntia imbricata) and the prickly pear cactus (Opuntia spp.) also occur on
the study site (Richardson et al., 1975).
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Field Methods and Data Collection
I conducted a predator survey to estimate the populations of common and
potential THL predators. I used camera traps (MOULTRIE D-444 and A-5/A-8
Digital Game Camera; Moultrie, Alabaster, Alabama) to document potential
predators (Safari Limited®, Miami Gardens, Florida). Game cameras were powered
by 4-6 C-cell batteries and used a 16 GB SD-card as storage. Cameras were capable
of night photography via an LED flash. The approximate detection range was 14 +/1.5 m and the optical field view was 55 degrees.
Camera trapping is a good method to monitor animals, especially carnivores
without direct captures (Kelly and Holub, 2008). I placed camera traps in three
distinct locations—around harvester ant mounds (N = 3), along roadsides (N = 3),
and in dense vegetation (N = 4). At the survey temporal midpoint, a fake radiotransmitter collar was attached to the model. The fake transmitters were made from
clay and cable binders (Fig. 1). Small stones and dirt were used to camouflage the
transmitters, per protocols that are in use for real transmitters (R. Granberg, pers.
comm.).
Each model was placed in the center of the view for the camera (Soisalo and
Cavalcanti, 2006). The camera traps were placed at a height of approximately 50 cm
above the ground and strapped on mesquite shrubs or cattle gates (Fig. 2; Fig. 3).
Traps were in place from 15 March – 15 April 2014 and programmed to be triggered
by motion with a 60 second delay, which was the shortest possible time interval for
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these camera traps and to get as many photos taken as possible. Photos were
downloaded weekly.
Statistical Analysis
I evaluated the photographs taken by the camera traps of all observed
animals using a Chi-square test (Ӽ²) to compare the number of potential predators
taken by the camera traps between different species and between different
treatments (ant mounds, dense cover, roads). Chi-square is a statistical test, which
analyzes data of counted frequencies within different treatments (Franke et al.,
2012). Additionally, I used contingency analysis to examine the percent of potential
predators that occurred in each treatment.
Statistical analyses were run in JMP® Software (Statistical Discovery™ from
SAS, Cary, New York). Graphs were created using Sigmaplot (Systat Software, San
Jose, California).
Results
In total, cameras recorded 85 photographs of potential predators (Table 1).
Potential predators included Brown Thrashers (Toxostoma rufum) (N = 2; 2.35%),
coyotes (Canis latrans) (N = 14; 16.47%), American Crow (Corvus brachyrhynchos ) (N
= 1; 1.18%), mice (Family Muridae) (N = 37; 43.53%), raccoon (Procyon lotor) (N =
1; 1.18%), Greater Roadrunners (Geococcyx californianus) (N = 9; 10.59%) and feral
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pigs (Sus scrofa) (N = 21; 24.71%; Fig. 4). There were significant differences in
potential predator occurrence between treatments (Chi Square = 117.331; df = 12; p
< 0.0001). Birds were mainly observed in dense vegetation; Brown Thrashers and
Greater Roadrunners were observed exclusively in dense vegetation (100%). The
majority of feral pigs (57.14%) were observed on roads, and the remaining portion
was found in the ranchland (42.86%). Coyotes were found primarily on roads
(78.57%). Mice were found exclusively in the ranchland (Table 2; Fig. 5). There was
no effect of attached transmitters on detection of potential predators (Chi Square =
10.491, p = 0.1055). During the course of this study, no photos were taken of
potential predators attacking the model. Most of the potential predators, especially
mice and roadrunners, in the photos appeared curious and examined the models.
Discussion
The observed potential predators can be divided coarsely into two groups-carnivores and omnivores. Carnivores included roadrunners, coyotes and brown
thrashers. This group likely exerts the most threat and predation pressure on the
lizards. Omnivores represent a lesser threat and may only take Texas horned lizards
opportunistically.
Roads provide ample opportunities for visual predators to locate prey
(Fahrig and Rytwinski, 2009). They also warm rapidly, which may attract basking
animals. Additionally, many night-active potential predators such as coyotes and
wild pigs may use the system of dirt roads across the ranch property to orientate
and easily move through the area of the ranch. I predicted more photos taken by
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potential predators close to ant mounds, the open ranchland or roads due to higher
visibility than in dense vegetation, which was supported. Exceptions are diurnal
ground active birds, which were found mostly in dense vegetation that likely
camouflages them against predators. These birds have excellent vision which
enables them to location prey in dense vegetation (Cook, 1997).
My hypothesis that there are more potential avian predators recorded by
camera traps than potential terrestrial predators was not supported; more photos
were taken of terrestrial animals. However, it may be the case that avian predators
still exert the most threat to THL, because they are hunting during the active day
period of the lizard and also possess excellent vision. Possible reasons for less
photos of avian predators are that they are flying above the range of the camera
traps and therefore did not trigger the sensor of the cameras or that they are
attracted primarily to motion, which the models do not exhibit.. Due to this reason,
there are less photos of avian potential predators.
During the course of this study, no photos were taken of predators attacking
the model. Therefore my hypothesis, that potential predators documented by the
camera traps will not attack the THL models, is supported. No attacks were
occurring for several potential reasons. First, the smell of the models may have been
off-putting or inaccurate for olfactory hunters (e.g., snakes). A second reason would
be the lack of motion that the models displayed. Most predators cue in on motion
during hunting (Buss, 2005). In addition, the models may not match the coloration
of THL perfectly. Finally, the study was conducted from mid of March to mid of
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April, and Texas horned lizards are not active very often during this season of the
year (Sherbrooke, 2003).
Attachment of the artificial radio-transmitter did not appear to impact
potential predator interest or detection. These are small devices with antennae,
which help to relocate the Texas horned lizards during studies of survival and home
range size (Burrow et al., 2002). They are also covered with soil materials, which
have a camouflage effect and could possibly reduce the attacks on THL. To
determine if the artificial transmitters have an effect on predation, a larger longterm project focusing on this research deficit should be conducted.
Additional future avenues of study should include longer term projects that
utilize more camera traps during Texas horned lizards’ active season. Additionally,
repainting the models to see if the coloration or washing the models may reduce
olfactory and visual interference. Another interesting study approach would be to
move the models via fishing lines to test the importance of movement during
hunting.
Predation on the Beach Ranch was observed in several studies (e. g. Henry,
2009; Mougey, 2009).
On the Beach Ranch 388 horned lizards were encountered and 117 of them
were tagged with a radio-transmitter in the field season 2005-2008 (Henry, 2009).
Survival rates within the active season (2005-2008) were 14.4% for females and
33.7% for males (Henry, 2009). In the study of Henry (2009) a lower survival rate
in females compared to males on the Beach Ranch was observed. In the field season
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Texas Tech University, Tabea Malinowski, August 2014
2008-2009, 74 horned lizards were tagged (Mougey, 2009). However, only 29
individuals of these 74 lizards were mature adults (Mougey, 2009). Apparently only
a small number of Texas horned lizards reach the state of adulthood, which indicates
a high predation risk on hatchlings and juvenile lizards.
Within all years of studies, conducted on the Beach Ranch, 46 Texas horned
lizards were found dead by using telemetry (Henry, 2009). 37 of these dead
individuals (80%) seemed to have died due to predation (Henry, 2009).
Identification of predators was often difficult to ascertain, but one carcass showed
teeth marks belonging to a small rodent or cotton rat (Sigmodon spp.); three radio
transmitters were found far from the home ranges of the lizards, carried off by
predators and dropped somewhere arbitrarily; and nine of the transmitters were
excreted by snakes or the transmitter could be localized in a snake burrow (Henry,
2009). In two cases, Henry (2009) followed a radio transmitter signal and
discovered that it was coming from the inside of a snake. The detected snakes were a
coachwhip (Masticophis spp.) and a rattlesnake (Crotelus spp.) (Henry, 2009). In the
study of Henry (2009) a juvenile Texas horned lizard in the beak of a Greater
Roadrunner (Geococcyx californianus) was observed. Henry (2009) found out, that
many Texas horned lizards were predated particularly by snakes in Texas.
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Texas Tech University, Tabea Malinowski, August 2014
TABLE 1--Counted potential predators by camera trapping during the 30 day
fieldwork
Potential predator: detected:
with transmitter:
without transmitter:
Coyote
Raccoon
Feral Pig
Mouse
Brown Trasher
American Crow
Roadrunner
14
1
21
37
2
1
9
6
1
9
19
0
1
1
8
0
12
18
2
0
8
Total
85
37
48
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Texas Tech University, Tabea Malinowski, August 2014
TABLE 2--Percentage of potential predators detected within the treatments: dense
vegetation, road, and ranchland during the 30 day field study
Counted
Total %
Brown
Coyote Crow
Thrasher
Mouse Raccoon Road- Feral pig Total
runner
dense
2
2.35
1
1.18
0
0.00
0
0.00
1
1.18
9
10.59
0
13
0.00 15.29
ranchland
0
0.00
2
2.35
0
0.00
37
43.53
0
0.00
0
0.00
9
48
10.59 56.47
road
0
0.00
11
12.94
1
1.18
0
0.00
0
0.00
0
0.00
12
24
14.12 28.24
Total
2
2.35
14
16.47
1
1.18
37
43.53
1
1.18
9
10.59
34
21
24.71
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Texas Tech University, Tabea Malinowski, August 2014
FIG. 1--Attached transmitter on a lizard model
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Texas Tech University, Tabea Malinowski, August 2014
FIG. 2—Camera trap attached to a fence and a small tree
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Texas Tech University, Tabea Malinowski, August 2014
FIG. 3—Camera trap on a mesquite shrub
37
Texas Tech University, Tabea Malinowski, August 2014
FIG. 4--Species composition of detected potential predators
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Texas Tech University, Tabea Malinowski, August 2014
FIG. 5--Distribution of detected potential predators in the treatments: dense
vegetation, road, and ranchland
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Texas Tech University, Tabea Malinowski, August 2014
Literature Cited
BRYANT, H. C. 1916. Habits and food of the roadrunner in California. University
of California Publications in Zoology 17:21-58.
BURROW, A. L., R. T. KAZMAIER, E. C. HELLGREN, AND D. C. RUTHVEN.
2002. The effects of burning and grazing on survival, home range, and prey
dynamics of the Texas horned lizard in a thornscrub ecosystem. The role of fire for
nongame wildlife management and community restoration: traditional uses and new
directions. General Technical Report GTR-NE-288. Newtown Square, PA: USDA
Forest Service, Northeastern Research Station. p. 43-51.
BUSS, D. M. 2005. The handbook of evolutionary psychology. John Wiley and
Sons, Hoboken, New Jersey.
CONOVER, M. R. 2007. Predator-prey dynamics: The role of olfaction. CRC Press,
Boca Raton, Florida.
COOK, W. E. 1997. Avian desert predators. Springer, Berlin, Germany. 53-70.
FAHRIG, L., AND T. RYTWINSKI. 2009. Effects of roads on animal abundance:
An empirical review and synthesis. Ecology and Society 14:21.
FRANKE, T. M., T. HO, AND C. A. CHRISTIE. 2012. The Chi-square test, often
used but more often misinterpreted. American Journal of Evaluation 3:448458.
FOWLER, N. L. 2005. An introduction to the vegetation and ecology of the
eastern Edwards Plateau (Hill Country) of Texas, Edwards Plateau Ecology.
Section of Integrative Biology, University of Texas, p. 1.
GIOVANNI, M. D., C. W. BOAL, AND H. A. WHITLAW. 2007. Prey use and
provisioning rates of breeding Ferruginous and Swainson’ hawk on the
southern great plains, USA. The Wilson Journal of Ornithology 4:558-569.
HENRY, E. 2009. Ecology, home range, and habitat selection of the Texas horned
lizard (Phrynosoma cornutum) in the southern high plains of Texas. Master’s
thesis, Texas Tech University, Lubbock, TX.
40
Texas Tech University, Tabea Malinowski, August 2014
KELLY, M. J., AND E. L. HOLUB. 2008. Camera trapping of carnivores: trap
success among camera types and across species, and habitat selection by
species, on Salt Mountain, Giles County, Virginia. Northeastern Naturalist
15:249-262.
MANASTER, J. 1997. Horned lizards. Texas Tech University Press, Texas.
MIDDENDORF, G. A., AND W. C. SHERBROOKE. 1992. Canid elicitation of
blood-squirting in a horned lizard (Phrynosoma cornutum). Copeia 2:519-527.
MIDDENDORF, G. A., AND W. C. SHERBROOKE. 2004. Responses of Kit foxes
(Vulpes macrotis) to antipredator blood-squirting and blood of Texas horned
lizards (Phrynosoma cornutum). Copeia 3:652-658.
MOUGEY, K. 2009. Radio transmitter mass: Impacts on home range, daily
displacement, and endurance in Texas horned lizards and bearded dragons.
Master’s thesis. Texas Tech University, Lubbock, Texas.
MUHKIN A., V. GRINKEVICH, AND B. HELM. 2009. Under cover of darkness:
Nocturnal life of diurnal birds. Journal of Biological Rhythms 3:225-231.
RICHARDSON, W. E., D. C. GRICE, AND L. A. PUTNAM. 1975. Soil survey of
Garza County, Texas. United States Department of Agriculture, Soil
Conservation Services.
SMITH, L. M. 2003. Playas of the Great Plains. p. 32, Figure 2.2., University of
Texas Press, Texas.
SHERBROOKE, W. C., AND J. R. MASON. 2005. Sensory modality used by
coyotes in responding to antipredator compounds in the blood of Texas
horned lizards. The Southwestern Naturalist 50:216-222.
SHERBROOKE, W. C. 2008. Antipredator responses by Texas horned lizards to
two snake taxa with different foraging and subjugation strategies. Journal of
Herpetology 42:145-152.
SHERBROOKE, W. C. 2003. Introduction to horned Lizards of North America.
University of California Press, California.
SHERBROOKE, W. C. 1991. Behavioral (predator-prey) interactions of captive
Grasshopper mice (Onychomys torridus) and horned lizards (Phrynosoma
cornutum and P. modestum). American Midland Naturalist 126:187-195.
41
Texas Tech University, Tabea Malinowski, August 2014
SHORT, H. L. 1979. Food habits of coyotes in a semidesert grass-shrub habitat.
Forest Service U.S. Department of Agriculture, Research Note 364 pp. 1-4.
SOISALO, M. K., AND S. M. C. CAVALCANTI. 2006. Estimating the density of a
jaguar population in the Brazilian Pantanal using camera-traps and capture–
recapture sampling in combination with GPS radio-telemetry. Biological
Conservation 129:487-496.
WHITE, P. J., K. RALLS, AND R. A. GARROTT. 1994. Coyote – kit fox interactions
as revealed by telemetry. Canadian Journal of Zoology 10:1831-1836.
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Texas Tech University, Tabea Malinowski, August 2014
CHAPTER III
TEXAS HORNED LIZARD THERMAL ENVIRONMENTS
Abstract
I measured temperatures at ten distinct locations in which Texas horned
lizards have been observed using iButtons. The purpose of this survey was to create
a thermal profile of horned lizard habitat and examine the thermal constraints of
their environments. Within the thermal environment of the Texas horned lizard,
thermal areas (microhabitats) with diverse mean temperatures were observed and
adaptations to their daily routine within their habitat were made.
Introduction
Texas horned lizards occur in North America and inhabit areas of Texas,
Kansas, Oklahoma, New Mexico, southern Colorado and southeastern Arizona in the
United States (Sherbrooke, 2003). They are adapted to desert environments and
inhabit open landscapes of arid and semiarid areas (Sherbrooke, 2003). The
prevailing vegetation type in this habitat is grassland-steppe, mixed with some
woody shrubs (Ludeke et al., 2005; Sherbrooke, 2003). High extinction risks occur
in species within arid environments, because of high outside temperatures, which
decrease the activity time periods of desert species (Lara-Resendiz et al., 2014). Due
to their recent and precipitous decline (Burrow et al., 2001), conservation and
preservation efforts have been implemented to preserve this charismatic species
(Burrow et al., 2001). Reptiles, which inhabit arid habitats, depend on a certain
thermal quality to stay active and regulate their internal body temperature (Lara43
Texas Tech University, Tabea Malinowski, August 2014
Resendiz et al., 2014). In particular, it is important to understand how horned
lizards select their habitats (Burrow et al., 2001). In their 2001 study, Burrow et al.
found that THL use areas of short vegetation cover as well as bare soil habitats for
foraging and thermoregulation throughout the entire day except in the afternoon.
THL engage in predictable behavioral patterns each day that are driven by
thermoregulatory needs (Heath, 1965). The thermal quality of microhabitats, which
THL occupies, was high in the morning and afternoon (Lara-Resendiz et al., 2014).
Lara-Resendiz et al., 2014 also found out, that the Texas horned lizard is efficient
and accurate in selecting the optimal microhabitat to regulate its internal body
temperature throughout the day. It stays active in the morning and afternoon to
forage for ants, but avoids the extreme heat around midday (Lara-Resendiz et al.,
2014). They leave their burrow early in the morning, when the ground temperature
reaches 19 C° and will wait for the first sun rays to initiate basking (Heath, 1965).
During the highest temperatures of the day, THL hides under stones, litter or shrubs
and trees to protect themselves from heat and to protect against predators (Burrow
et al., 2001). Conservation management should focus on creating a habitat that
contains a mosaic of woody vegetation, grassland with low vegetation height and
patches bare soil (Burrow et al., 2001).
Texas horned lizards have evolved adaptations to their dry and hot habitat,
where shade and water are scarce (Bogert, 1949). They regulate their internal
temperature through five different methods of thermoregulation (Heath, 1965).
Thermoregulation is the process of controlling the internal body temperature
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Texas Tech University, Tabea Malinowski, August 2014
(Soule, 1963). The temperature of its body influences an organism’s physiology,
development and behavior (Stevenson, 1984). Like other reptiles, horned lizards
are poikilothermic vertebrates (Sherbrooke, 2003). Poikilotherms vary their body
temperature with the temperature of the environment (Bogert, 1949). For many
poikilothermic reptiles maintaining an isothermic body temperature relative to the
environment requires movement throughout space multiple times per day
(Wheeler, 1986).
These methods, Texas horned lizards are using to regulate their internal
body temperature, are burrowing, shade-seeking, lying in the sun, changes in body
shape and movements of orientation (Heath, 1965). The range of body temperature
of THL was calculated in a study by Cowles and Bogert (1944). Their mean
temperature is 34.9 °C (max = 39.0 °C, min = 28.0 °C). This is a very broad active
temperature range and likely enabled THL to adapt to the harsh environments of
arid and semiarid desert regions.
Compared to the temperature ranges of other day-active desert lizards, Texas
horned lizards show one of the widest thermal tolerance ranges (Kour and
Hutchinson, 1970).
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Texas Tech University, Tabea Malinowski, August 2014
Questions
To improve conservation measurements and mitigate THL decline, there
should be increased focus on the habitat preferences of the Texas horned lizard
(Burrow et al., 2001). Information on the microhabitats (small-scale habitats;
Burrow et al., 2001) THL seeks out during the day, especially about the kind of
microhabitat (vegetation type, vegetation density and height, bare soil, shade, etc.)
will aid our understanding of how to create and/or protect a habitat in which THL
could survive the abiotic extremes of their harsh environment and also evade
predators. Furthermore I expect that Texas horned lizards prefer areas with a high
number of microhabitats (small-scale habitat for organisms) and that they play a
major role in the thermal physiology of THL (Burrow et al., 2001; Kour and
Hutchinson, 1970). I pose the following questions: What are the mean temperatures
at distinct locations within the THL habitat? Do the mean temperatures vary greatly
between the different distinct locations?
Hypotheses
I hypothesize that there are differences in the mean temperatures between
different vegetation- and landscape types within Texas horned lizard habitats. I
pose the hypothesis because different locations and different surfaces might warm
up faster or radiate solar heat over a longer period of time compared to other
locations within the THL home range. Exposed locations may warm up faster in the
morning, heat up rapidly during the extreme heat around midday, stay longer warm
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Texas Tech University, Tabea Malinowski, August 2014
due to radiation of stored heat in the evening, but cool down rapidly in the nights
due to their exposed characteristic. From the sun more protected locations may not
warm up so fast, but will stay cooler compared to exposed locations during midday
and also show a higher mean temperature within the nights due to protection from
cooling down through insulate structures like leaves.
Materials and Methods
Study Area
This work was conducted on the Beach Ranch, a privately owned cattle
ranch; approximately 26 km east of Post, Garza County, Texas. In the northwestern
part of the ranch are the foothills of the Caprock escarpment of the Llano Estacado,
which is located in the Southern Great Plains (Smith, 2003). The elevation of the
area is approximately 794 m above sea level (Richardson et al., 1975). In Garza
County around 48 cm of rain fall per year. Average seasonal temperatures range
from -2 °C to 35 °C, with the hottest temperatures occurring during THL active
periods in the spring and summer (Richardson et al., 1975). The soils are mostly
fine sandy loams or clay soils (Richardson et al., 1975). The most common
vegetation types are grassland prairie and desert shrubland (Richardson et al.,
1975). The dominant woody species in the area is mesquite (Prosopsis spp.). Other
typical plant species are blue grama (Bouteloua gracilis), buffalograss (Buchloe
dactyloides), broomweed (Amphiachyris dracunculoides), western ragweed
(Ambrosia psilostachya) and sideoats grama (Bouteloua curtipendula) (Fowler,
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Texas Tech University, Tabea Malinowski, August 2014
2005). Cholla (Opuntia imbricata) and prickly pear (Opuntia spp.) are also common
(Richardson et al., 1975).
Field Methods and Data Collection
I placed iButtons (N = 30; Embedded Data Systems, Lawrenceburg, Kentucky;
van Marken-Lichtenberg et al., 2006) at ten locations within the study site. The
distinct locations were observed places of Texas horned lizards that are available
refugia throughout the course of a day.
The iButtons were placed at the entry of an ant mound (N=3); 5 cm deep in
bare soil of an area without vegetation (N=3); on the exposed ground (without
vegetation cover), 1 m away from a dirt road (N=3); in dense vegetation (grassland)
in a randomly selected square of 1 m x 1 m with a vegetation cover>75% (N=3); in
the center of a yucca plant (Yucca spp.) of the size 40-60 cm height x 50-70 cm width
(N=3); on the top of an exposed stone of the size 20-30 cm height x 40-70 cm length
x 40-70 cm width (N=3); 20-30 cm above ground on the trunk of a mesquite shrub of
approximately 2-3 m height (N=3, Fig. 6); under (in the shadow) a mesquite shrub
(approx. 2 m high) 20-30 cm away from the trunk in a random direction (N=3); on
the bare ground (without vegetation cover) (N=3); and under a dead mesquite trunk
of the size 10-20 cm height x 30-50 cm length x 10-20 cm width (N=3).
iButtons were programmed to measure temperature every hour over the
span of 30 days (March 15– April 15, 2014). I then collected the iButtons and
downloaded the data to compare average temperatures of the ten microhabitats.
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Texas Tech University, Tabea Malinowski, August 2014
Statistical Analysis
I measured the temperature at three replicates of ten microhabitats on the
Beach Ranch via iButtons over a time period of 30 days. After collecting the
iButtons, I conducted a one-way ANOVA to compare the temperature means of the
different treatments. The dense vegetation treatment was excluded from analysis
due to lost iButtons.
I used analysis of variance (ANOVA) and Tukey multiple comparisons tests to
compare average temperatures between the selected areas. The ANOVA was
conducted using the statistical program JMP® Software (Statistical Discovery™ SAS,
Cary, New York). ANOVA is a procedure that is used to detect differences among
three or more sample means (Heiberger and Neuwirth, 2009). The graphs were
constructed using Sigmaplot (Systat Software, San Jose, California).
Results
Ant mounds had the highest mean temperature and yucca had the lowest
mean temperature within the ten different locations (Table 3). The Tukey-Kramer
HSD test was able to sort the means in four different groups (A, B, C and D). Only the
treatments yucca and ant mound were only in one of the four different groups (ant
mound: group A; yucca: group D) and are therefore variant from the other means,
which means they are significantly different from each other (Fig. 7).
The daily temperature curve of the 10 distinct locations fit a cubic function
(R² = 0.595983; Fig. 8; Fig. 9-18). The highest temperature during the day can be
49
Texas Tech University, Tabea Malinowski, August 2014
observed at around 0300 p.m. in the afternoon and the lowest at around 0600 a.m.
in the early morning. The temperature cools down in the late afternoon (0600 p.m.)
and begins to warm up in the late morning (0900 a.m.). This pattern was predictable
based on local weather observations and held for all the microhabitats examined.
Discussion
The locations we examined were selected, in part, due to historic
observations of Texas horned lizards in similar microhabitats. My hypothesis that
there are differences in the mean temperatures between different vegetation and
landscape types within Texas horned lizard habitats was supported. Many of these
locations differ significantly in their mean temperatures (e.g., 16.23 °C, yucca; 19.57
°C, ant mound).
It was unexpected that ant mounds had the highest mean temperatures of all
treatments. On the surface, ant mounds appear similar to bare ground; further
examinations of these differences are warranted. A possible explanation for this
observation might be that harvester ants (Pogonomyrmex spp.), which are
herbivorous and consume high-energy plant seeds carry the plant material into their
mound (Crist and MacMahon, 1991). During decomposition of these plant materials,
heat arises and warm up the mound, which lies in the ground (MacKay and MacKay,
1985). The process of decomposition could explain the high mean temperature of
the treatment ant mound (Jenkinson, 2006).
My second hypothesis that the average temperatures are the highest during
midday and the lowest during the night in all of the different microhabitats was also
50
Texas Tech University, Tabea Malinowski, August 2014
supported. As expected, the daily temperatures of the nine treatments (Table 4)
follow a predictable pattern with a cubic or sine curve best representing the daily
temperature cycles. Low temperatures generally occurred at night and in the early
morning, and high temperatures occurred around noon. The resulting daily
temperature curve fits with our knowledge of the Texas horned lizard daily activity
patterns (Fig. 19) and results in a thermal profile, where THL burrow themselves in
the soil over night and in the early morning to avoid the low temperature at night
and are most active during the daytime hours (Heath, 1965). They are able to
regulate their internal body temperature in seeking out different microhabitats
throughout the day. In a study of Lara-Resendiz et al., 2014, they found out that
horned lizards are efficient and accurate in selecting the adequate microhabitat to
regulate its internal body temperature throughout the day. Horned lizards stay
active in the morning and afternoon to forage for ants, but avoid the extreme heat
around midday (Lara-Resendiz et al., 2014). Texas horned lizards are active
thermoregulators, who follow a predictable pattern each day to regulate their
internal body temperature efficiently and maintain it in the optimal and preferred
range by using the existence of microhabitats (Lara-Resendiz et al., 2014).
The Texas horned lizard seeks out different locations (microhabitats) during
the day and night to regulate its internal body temperature (Fig. 20; Fig. 21). THL
shows a bimodal activity pattern each day with active periods during the morning
and the afternoon (Lara-Resendiz et al., 2014). They find refuge buried in the soil or
lying in the shade of shrubs from the lethal surface temperatures around midday
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Texas Tech University, Tabea Malinowski, August 2014
(surface temperature > 40°C; Lara-Resendiz et al., 2014). Within the nine
treatments (microhabitats) we were able to find optimal and not so optimal
locations for THL during the course of the day.
At nights, the warmest locations are within the center of a yucca plant or in
the soil. Due to this reason Texas horned lizards burrow themselves in the soil for
protection against predators and against heat loss in the nights. Locations like on a
stone and on a road, cool down rapidly during the night, resulting in that THL would
lose a lot of their internal body heat (Fig. 20). During the morning, THL burrow
itself out of the soil and starts basking in the sun to warm up and start foraging.
Good locations to warm up are on the road or in the open ranchland. Locations like
in the soil or under trunk are not a good choice, because start to warm up late in the
day (Fig. 20). Around noon, temperatures get incredible hot and THL seek for cool
and shady places to avoid the extreme heat. In the case locations like on the bare
ground or on a stone heat up extreme, so THL avoid these locations. Cool places to
stop THL from heating up to strong are within the center of a yucca plant or in the
soil (Fig. 21). After the temperatures cool down in the afternoon, THL leave the
shady places or burrows itself out of the soil to forage again for ants. In the
afternoon THL seeks for places which are warm enough to keep foraging. Good
locations would be on a stone or on the road, because they warmed up in the
extreme heat over noon and are able to store the heat and keep warm until then
evening. Locations within a yucca plant or in the shadow of vegetation might be
already to cool for THL to stay active and to forage for ants (Fig. 21).
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Texas Tech University, Tabea Malinowski, August 2014
Ectotherms like THL depend on the distribution and availability of
microhabitats throughout their home range to efficiently regulate their internal
body temperature and in order to perform their daily activities, which include
foraging, reproduction, etc.; high temperatures restrict the daily activities of horned
lizards (Lara-Resendiz et al., 2014). To maintain the preferred internal body
temperature and stop overheating or cooling down, thermoregulation is necessary
(Lara-Resendiz et al., 2014). The ten different locations represent microhabitats of
the Texas horned lizard; these microhabitats offer ample variation in temperature to
allow THL to thermoregulate via location shifting throughout the day. Future work
should examine mean temperatures in summer months, when lizards are most
active. Additionally, expanding the number of locations and iButtons could prove
interesting.
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Texas Tech University, Tabea Malinowski, August 2014
TABLE 3--Means for one-way ANOVA for the distinct locations
Treatment
Mean
ANT MOUND
BARE GROUND
ON MESQUITE
ON STONE
ROAD
SHADOW
SOIL
UNDER TRUNK
YUCCA
19.5655
18.2470
17.2286
18.8561
18.4448
17.5344
18.9288
17.7171
16.2304
Std Error Lower 95% Upper 95%
0.38310
0.38310
0.38310
0.38310
0.38310
0.38310
0.38310
0.38310
0.38310
54
18.814
17.496
16.478
18.105
17.694
16.783
18.178
16.966
15.479
20.316
18.998
17.980
19.607
19.196
18.285
19.680
18.468
16.981
Texas Tech University, Tabea Malinowski, August 2014
TABLE 4--Temperatures (°C) of the distinct locations (30 March 2014)
Time:
00:00:00
01:00:00
02:00:00
03:00:00
04:00:00
05:00:00
06:00:00
07:00:00
08:00:00
09:00:00
10:00:00
11:00:00
12:00:00
13:00:00
14:00:00
15:00:00
16:00:00
17:00:00
18:00:00
19:00:00
20:00:00
21:00:00
22:00:00
23:00:00
00:00:00
Ant
mound: Soil:
Bare
ground:
Stone: Trunk: Road: Shadow:
under
Trunk:
Yucca:
11.5
10.75
11.25
11.25
10.5
12.25
11.5
11.25
12
16.25
22
27.75
33.25
36
37.5
34.25
31.5
30.5
28.5
25.5
22.75
21.25
20.25
19.5
18.75
11.67
9.16
11.33
11.33
10.67
12.67
10.83
10
15
19.33
21.83
25.17
27.67
30.17
30.67
30
30.67
29
27.5
25.67
23.5
22.17
21.17
20.67
19.83
11
10.16
10.83
10.66
10.16
11.33
10.5
10.66
14.5
19.83
24.83
30.16
33.66
35.66
35.66
36.5
37.16
31.33
30.33
24.66
21.83
20.5
19.5
18.83
18
15.83
14.83
14
13.83
13.5
13.17
13.17
12.33
12.67
14.67
17.17
20.5
23.67
26.17
28.33
29.5
29.5
29.5
27.67
25.67
24
22.5
21.5
20.67
20
4.5
2.75
7.25
8
7.25
9.25
5.5
4.5
14.5
20.75
23.75
28.75
36.5
38.5
41.25
39.25
37.75
27
32.25
25
21.5
20
19
18.5
18
12.33
11
11
10.17
10
11
9.33
9.66
12.33
17.67
21.67
25.67
31.33
35
37.83
37.83
39.5
35
31.83
27.33
24
21.83
20.5
19.5
19
11
9
11.33
11.16
9.33
13
11.83
9.66
14.66
20.33
20.83
26.83
28.83
31.83
35.5
33.83
34.5
31.16
28.5
26
23
22
20.5
20.16
19.16
11.3
10.2
10.8
10.8
10
12
10.8
9.67
11.2
18
23.3
28.2
32
34.8
36.2
36.3
35.2
34
29.5
25.5
22.2
20.5
19.5
19
18
10.5
10.16
11
10.83
10.5
11.5
10.83
11
15.66
22.66
28
31.66
36.5
34.5
34.16
32.66
33.16
28.5
26.33
23.5
21
19.66
18.83
18.33
18
Mean
temperature:
19.5
18.9
18.2
18.8
17.2
18.4
17.5
17.7
16.2
Max.
temperature:
51.6
38.5
54.7
47.1
45.5
52.7
42.6
47.7
41.8
Min.
temperature:
-1.5
5.6
-5.7
-1.3
-4.6
-3.5
-2.5
-2.5
-3.5
55
Texas Tech University, Tabea Malinowski, August 2014
FIG. 6—Ibutton on a mesquite trunk
56
Texas Tech University, Tabea Malinowski, August 2014
FIG. 7--Mean temperatures of distinct locations within the THL habitat
57
Texas Tech University, Tabea Malinowski, August 2014
FIG. 8—Representative daily temperature curve of the mean temperatures of the
distinct locations (30 March 2014; mean of temperature across all
microhabitats)
58
Texas Tech University, Tabea Malinowski, August 2014
FIG. 9—Representative daily temperature curve of the temperatures of the 9
different distinct locations (30 March 2014)
59
Texas Tech University, Tabea Malinowski, August 2014
FIG. 10—Representative daily temperature curve of the temperatures of the
treatment: Ant mound (30 March 2014)
60
Texas Tech University, Tabea Malinowski, August 2014
FIG. 11—Representative daily temperature curve of the temperatures of the
treatment: In soil (30 March 2014)
61
Texas Tech University, Tabea Malinowski, August 2014
FIG. 12—Representative daily temperature curve of the temperatures of the
treatment: On a stone (30 March 2014)
62
Texas Tech University, Tabea Malinowski, August 2014
FIG. 13—Representative daily temperature curve of the temperatures of the
treatment: On the ground (30 March 2014)
63
Texas Tech University, Tabea Malinowski, August 2014
FIG. 14—Representative daily temperature curve of the temperatures of the
treatment: On the road (30 March 2014)
64
Texas Tech University, Tabea Malinowski, August 2014
FIG. 15—Representative daily temperature curve of the temperatures of the
treatment: In the shadow (30 March 2014)
65
Texas Tech University, Tabea Malinowski, August 2014
FIG. 16—Representative daily temperature curve of the temperatures of the
treatment: On a trunk (30 March 2014)
66
Texas Tech University, Tabea Malinowski, August 2014
FIG. 17—Representative daily temperature curve of the temperatures of the
treatment: Under a trunk (30 March 2014)
67
Texas Tech University, Tabea Malinowski, August 2014
FIG. 18—Representative daily temperature curve of the temperatures of the
treatment: In a yucca plant (30 March 2014)
68
Texas Tech University, Tabea Malinowski, August 2014
FIG. 19—Representative daily temperature curve of the mean temperatures of the
distinct locations (30 March 2014; mean of temperature across all
microhabitats) combined with the daily routine of the Texas horned lizard
69
Texas Tech University, Tabea Malinowski, August 2014
FIG. 20-- Representative daily temperature curve combined with the lizards
behavior in the night and morning
70
Texas Tech University, Tabea Malinowski, August 2014
FIG. 21-- Representative daily temperature curve combined with the lizards
behavior at noon and in the afternoon
71
Texas Tech University, Tabea Malinowski, August 2014
Literature Cited
BOGERT, R. B. 1949. Thermoregulation in reptiles, a factor in evolution.
Evolution 3:195-211.
BURROW, A. L., R. T. KAZMEIER, E. C. HELLGREN, AND D. C. RUTHVEN.
2001. Microhabitat selection by Texas horned lizards in southern Texas. The
Journal of Wildlife Management 65:645-652.
COWLES, R. B., AND C. M. BOGERT. 1944. Thermal Tolerance. Bulletin of the
American Museum of Natural History 83:261–296.
CRIST, T. O., AND J. A. MACMAHON. 1991. Foraging patterns of Pogonomyrmex
occidentalis (Hymenoptera: Formicidae) in a shrub–steppe ecosystem: The
roles of temperature, trunk trails, and seed resources. Environmental
Entomology 20:265-275.
FOWLER, N. L. 2005. An introduction to the vegetation and ecology of the
eastern Edwards Plateau (Hill Country) of Texas, Edwards Plateau Ecology.
Section of Integrative Biology, University of Texas, page 1.
HEATH, J. E. 1965. Temperature regulation and diurnal activity in horned
lizards. University of California Press, California.
HEIBERGER, R. M., AND E. NEUWIRTH. 2009. R through Excel pp. 165-191.
Berlin, Germany.
JENKINSON, D. S. 2006. Studies on the decomposition of plant material in soil.
European Journal of Soil Science 17:280-302.
LARA-RESENDIZ, R. A., T. JEZKOVA, P. C. ROSEN, AND F. R. MENDEZ-DE LA CRUZ.
2014. Thermoregulation during the summer season in the Goode´s horned
lizard Phrynosoma goodei (Iguania: Phrynosomatidae) in Sonoran Desert.
Amphibia-Reptilia 2:161-172.
LUDEKE, K., D. GERMAN, AND J. SCOTT. 2005. Texas vegetation classification
project: interpretive booklet for phase I, Texas Parks and Wildlife Department
and Texas Natural Resources Information System.
72
Texas Tech University, Tabea Malinowski, August 2014
MACKAY, W., AND E. MACKAY. 1985. Temperature modifications of the nest of
Pogonomyrmex montanus (Hymenoptera: Formicidae). Southwestern
Naturalist 30:307-309.
RICHARDSON, W. E., D. C. GRICE, AND L. A. PUTNAM. 1975. Soil survey of
Garza County, Texas. United States Department of Agriculture, Soil
Conservation Services.
SMITH, L. M. 2003. Playas of the Great Plains. p. 32, Figure 2.2., University of
Texas Press, Texas.
SHERBROOKE, W. C. 2003. Introduction to horned Lizards of North America.
University of California Press, California.
VAN MARKEN-LICHTENBELT, W. D., H. A. M. DAANEN, L. WOUTERS, R.
FRONCEZEK, R. J. E. M. RAYMANN, N. M. W. SEVERENS, AND E. J. W. VAN
SOMEREN. 2006. Evaluation of wireless determination of skin temperature
using iButtons. Physiology and Behavior 88:489–497.
73