Spatiotemporal Patterns in Nanoclimate

And

Behavior of the Lizard Gambelia wislizenii

 

Miku Gleason, Brenna Walker, Chase Carter,

Aliina Smith and Jennifer Henderson

 

Advisor: Dr. Roger Anderson

Western Washington University

Bellingham, WA 98225

 

 

Abstract

A major goal in ecology is to document and explain spatiotemporal patterns of distribution and abundance of organisms. The first phase of ecological research is to observe and describe where individuals are and when, with respect to environmental factors which motivate the organism.  Desert scrub habitats are relatively simple, tractable ecosystems and lizards are particularly tractable animals for ecological studies in desert scrubs.  Summer in the Great Basin Desert is a convenient time to study the Long-Nosed Leopard Lizard (Gambelia wislizenii) because only two of the four basic tasks are suspected to affect its spatiotemporal patterns: 1) acquiring and utilizing food, and 2) coping with the abiotic task of thermoregulation.  It is possible to produce an accurate thermal map of the habitat that is available to Gambelia wislizenii, thus enabling one to predict: a) where and when lizard activity is possible, b) when it is best for the lizards to be active (e.g., seek food), and c) when they must exclusively thermoregulate.

This study was designed to examine the spatiotemporal trends in 1) microclimate in Great Basin Desert Scrub, 2) nanoclimate among microhabitats and nanohabitats of three predominant mesohabitats of the Great Basin, 3) operative environmental temperatures of copper models, thereby enabling one to predict spatiotemporal patterns of Gambelia wislizenii, and 4) behavior of Gambelia wislizenii.  The study area is located in a 200 by 200 meter plot in the Alvord Basin at the northern extreme of the Great Basin Desert Scrub. The plot covers a range of mesohabitats (dominated by woody perennials); included among them are hardpan, sandy flat, and dune, all of which are found in an ecotone between a Basin Big Sage plant community upslope and the saline Greasewood plant community downslope.

 

Insolation, wind speed and air temperature within each mesohabitat in the study plot followed a clear and predictable spatiotemporal pattern. Daily patterns of direct solar radiation, substratum temperature in the open, and air temperature all showed very similar temperature parabolas, differing only in the timing of their peaks and troughs. Substratum temperature in the dappled/mixed shade varied with time of day, microhabitat, and nanohabitat because of the continuous change in the azimuth and declination of direct solar radiation, particularly where the sunlight strikes beneath the foliage-perimeter of the shrubs. The data provided by the copper models in this study can be directly applied towards predicting and explaining G. wislizenii spatiotemporal behavior patterns.  We can infer from the copper model temperatures and other temperature measures that at both cool ends of the daily activity period and during the heat of midday the G. wislizenii must behave in a manner consistent with careful thermoregulation.  

 

Large female G. wislizenii were relatively and consistently less active throughout the day as compared with the other size-sex classes.  One explanation for this activity difference may be differences among size-sex classes in modes of food acquisition. Large female G. wislizenii may use a long-wait ambush predation mode, spending relatively long periods in the dappled lighting under shrub foliage, lying-in-wait to ambush large, mobile prey such as lizards that may approach inadvertently.  In contrast, smaller G. wislizenii may use more short-wait ambush predation mode wherein they perform short visual scans of the foliage perimeters of shrubs, in search of grasshoppers, cicadas, and other large arthropods that reveal themselves by movement.

 

 

INTRODUCTION

 

There are four basic ecological tasks or challenges that an animal faces: 1) acquiring and utilizing food, 2) finding and acquiring mates, 3) avoiding and evading predators, and 4) coping with abiotic stresses and avoiding abiotic extremes.  In deserts, animals face a strong abiotic challenge via the spatiotemporal patterns of heat flow and the effects of heat flow on body temperatures.  Thus, how the animals cope with heat flow, such as using physiological and behavioral thermoregulation is especially important in small ectotherms that live in deserts.   Diurnally active lizards, for example, behaviorally regulate their body temperatures within narrow range of only a few degrees centigrade (Grant and Dunham, 1988; Muth, 1977).   Thermoregulatory behaviors include adopting specific postures that minimize or maximize exposure to solar radiation and selecting nanohabitats at some periods of the day that permit body temperatures to remain within a narrow range (Abts, 1976; Heath, 1965).

 

Primary and venerable goals in ecological research are to document and explain spatiotemporal patterns of individuals and populations.   Observational-descriptive research of individuals within and among populations is a necessary precursor to any reliable experimental research. Desert lizards are particularly tractable field research animals because in the sparse scrub vegetation, they are easy to find, observe, and capture.  The Long Nosed Leopard Lizard (Gambelia wislizenii) is an abundant, tractable lizard in the Great Basin Desert Scrub in the Alvord Basin of southern Oregon. Gambelia wislizenii is bimodally active during its daily activity period in the post-reproductive season of early summer.  It is expected that the presumably narrow range of field-active body temperatures at which G. wislizenii regulates has an influence on its daily spatiotemporal patterns.  Moreover, an accurate thermal map of the habitat available vs. the habitat used by Gambelia wislizenii should help determine where and when it is possible for G. wislizenii to be active (e.g., seek food and mates) versus when they must exclusively thermoregulate. Information about the surrounding environment can be compared with lizard behavior to determine the optimal environmental temperatures for the lizard’s activity.  It would be useful to differentiate the influence of thermoregulation from the other three basic tasks on the nano-, micro- and mesohabitat use by Gambelia wislizenii and the lizard’s behavior in these “habitats,” (Anderson, 2006).  Strong correlation of spatiotemporal patterns in habitat use and behavior with any of the four basic autecological tasks will improve the chances of reaching an understanding of the relative influences of each of the four basic tasks on activity among individuals and among populations.

 

 

HYPOTHESES

 

Given that variation exists in all habitats, one would expect variation among the mesohabitats of Great Basin Desert Scrub in their thermal spatiotemporal patterns. Moreover, given that diurnally-active desert lizards thermoregulate relatively precisely, one would expect variation in the thermoregulation behavior of the desert-dwelling lizard Gambelia wislizenii to correlate with this spatiotemporal variation in temperatures. Thus, this study examined 1) the spatiotemporal microclimate trends within the three predominant mesohabitats of the Great Basin, 2) whether operative environmental temperatures of copper models can be used to predict microhabitat use by G. wislizenii, and 3) G. wislizenii behavior in these microhabitats and mesohabitats.

 

 

STUDY SITE

 

The study area is located in a 200 by 200 meter plot in the Alvord Basin at the northern extreme of the Great Basin Desert. The Great Basin desert scrub ecosystem comprises several large north-to-south trending basins which extend from southeast Oregon through sections of northeast and southeast California, and through much of Nevada, eastern Utah and western Idaho, with a gap between southeast Oregon and southwest Idaho (Sigler and Sigler, 1994). The Alvord Basin covers about 500 km2 and is surrounded by mountains and plateaus on all sides. The basin is located in the rain shadow of the Steen’s Mountain massif. This desert is classified as a high elevation desert (1215 m) and it frequently receives snow in the winter season (Larson and Larson, 1977). The study site is 3 km south of Borax Lake in Harney County Oregon. The plot covers a range of mesohabitats (dominated by woody perennials) on a gently sloping bajada; included among them are hardpan, sandy flat, and dune, all of which are found in an ecotone between a Basin Big Sage plant community upslope and the saline Greasewood plant community downslope (Rose, 2004, p.14).

 

 

MATERIALS AND METHODS

 

 

Weather station temperature measurements

 

For one week in early July 2005, 24 thermocouples, attached to a multiplexer of a portable weather station, were used to measure the temperatures of a variety of nanohabitats in the sandy flat mesohabitat; minute-by-minute temperatures were averaged once each 20 minutes (e.g., 0910 to 0930, 0930 to 0950, and 0950 to 1010 hrs).  Prevalent, representative microhabitats were used: two perennial plants Sarcobatus vermiculatus and Artemisia tridentata plants, and open sandy flat areas. Thermocouple probes were placed at the soil surface (substratum) in each cardinal direction, and midway between the stem base of each perennial plant and the foliage perimeter. Other thermocouples were placed: 25 cm above ground in the center foliage of each plant, and both at the soil surface and 10 cm below ground just north of the stem base in the presumptive coolest nanohabitats of the plant microhabitat.  Any thermocouple probe that had a chance of being exposed to air was painted white to improve the albedo and reduce heat absorption of direct sunlight by the probe.

 

 

Temperature measurements with hand-held units

 

To compare temperature trends among nanohabitats within a plant microhabitat and to compare similar microhabitats between the dune and hardpan environments, a medium-sized Greasewood (Sarcobatus vermiculatus) was selected for temperature observations in each mesohabitat. Thermocouple probes were placed in each cardinal direction at the base of each plant. Thermocouples wires were prepared with the same method as the weather station thermocouple wires. Wires were strung out to switch boxes situated in plastic containers and sheltered with separate containers when not in use. Wind speed, air temperature, and substratum temperatures were collected for each microhabitat in morning, afternoon and evening time periods. The air temperature was determined by attaching a single wire to the BARNANT 115 and maintaining the shaded temperature probe at two meters above ground.  The substratum temperature was measured by placing the single wire directly on the ground and covering it with a small patina of dust. Air and substratum temperatures collected by researchers (with infrared, thermocouple, and glass bulb mercury thermometers) on plot during other research activities were used to buttress observations in this study. The substratum temperatures measured with a cloacal thermometer were taken by gently resting the tip of the thermometer against the substrate and dusting the tip with a few particles of the local substratum. This process was repeated for measurements taken with the Barnant 115 thermocouple thermometer. The non-contact infrared thermometer measurements were taken by collecting readings from at least ten different locations within a 0.25 meter radius on level ground. The highest and lowest readings were removed (assuming inadvertent measures of substratum on tiny slopes) and the remaining temperatures (assumed to be on level ground) were then averaged and recorded.

 

 

iButton temperature measurements

 

Thermochron iButtons were placed on the substratum in three microhabitat types across the three predominant mesohabitats. The nanoclimates of the nanohabitats (weather conditions of microhabitat or nanohabitats, as opposed to the weather conditions of mesohabitats, typically known as the microclimates of mesohabitats) of four large A. tridentata and four large S. vermiculatus were selected for analysis with the iButtons. The specific iButton locations (nanohabitats) in the plant microhabitats were 1) deep shade center of each shrub, and 2) midway between the base and perimeter in each of the cardinal directions of each shrub, and the iButton in the open microhabitat, was placed on substratum surface about 1 m south of each shrub. The iButtons were programmed to record temperature once every ten minutes.

 

Copper model temperature measurements

 

Six copper models were constructed to reflect the three thermoregulation-relevant body positions for both sexes of Gambelia wislizenii, hence 3 models of males and 3 models of females.  Copper models were based on average snout-to-vent lengths (SVL) for each sex from a sample of the SVL measures of least 30 adults of each sex taken the previous year. The female models were constructed from copper tubing and glued together using epoxy. The male models were constructed from aluminum tubing and were glued together with epoxy.  Differences in heating between the copper and aluminum tubing were considered negligible due to the fact that they both heat up to the same final temperature. The males were constructed smaller than the females in accordance with the previous year’s data. Models were glued together using epoxy, spray-painted gray, and then hand-painted with a pattern of brown spots to imitate the natural reflectance of G. wislizenii. The thermocouple wire was inserted through a small hole drilled where the vent would be found on an average lizard. Thermocouples wires were prepared with the same method as the weather station thermocouple wires. Models were used to test sunlit thermal variance between body positions (BROS = body resting on substratum, FLEPOS = front legs extended, pelvis on substratum, and ALEBNTS = all legs extended, body not touching substratum) and to test average dappled/mixed shade temperature measurements of Sarcobatus vermiculatus microhabitat.

 

 

Focal observations of Gambelia wislizenii behavior

 

 G. wislizenii focal observations were performed on 11 non-consecutive days in early July 2005, and observations were confined to one of three time intervals each day. Morning observations were made from 8:30 to 11:30, afternoon observations from 12:00 to 16:30, and evening observations from 17:30 until about sundown (21:00). The target observation time was 25- 30 minutes per individual.  Observations were made from a minimum distance of 10 meters from the individual. One tool belt, one tape recorder, one walky-talky, one map board, two fishing rods, one clip board, and one set of binoculars was used per team. Tool belts were typically equipped with 1) a rapid-registering, thin-glass bulb mercury thermometer for measuring deep cloacal temperatures of lizards, 2) dental floss used as the noose material for noosing lizards, 3) scissors for cutting ends of the dental floss noose, 4) wind speed meter, 5) non-contact infrared thermometer, 6) pens and 7) a compass.  Teams of three or two people were assigned specific tasks during the observations. In a team of three, one person recorded audio observations, one person scribed and mapped and the third individual assisted in close range observations with the binoculars as well as performing video documentation on several occasions. In a team of two, one person scribed and mapped and the second person recorded on the tape recorder. Time was documented by the audio individual at each event during the observation. Lizard behaviors were verbally described and tape-recorded by an observer as they occurred. The individual scribing the map included the lizard’s route, noting both the lizards’ plot coordinates and the substrata and plant species used. Lizard body temperatures were taken at the end of each observation with a glass bulb mercury cloacal thermometer. Lizards were caught for temperature measurements by gently lassoing their neck with dental floss nooses attached to fiber glass fishing rods.

 

 

FIGURES

            

 FIGURE 1. Hourly averages for intensity of solar radiation on 5 days with clear skies in early July 2005
 
 

 

 


 FIGURE 2. Average hourly wind speeds for 5 days in July 2005

 
 
            

           

          

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 5.  Substratum temperatures in open dune microhabitats; data are hourly averages for 5 days of clear skies in early July 2005.

 
 
 

 

 

 

 

FIGURE 6.  Substratum temperatures in open harpan microhabitats; data are hourly averages for 5 days of clear skies in early July 2005.

 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Substratum north of S. vermiculatus root crown located in the dune
 

Substratum south of S. vermiculatus root crown located in the dune
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 7. Hourly averages for substratum temperatures under a mix of dappled shade and sun-shade edge of foliage of Sarcobatus vermiculatus (in each mesohabitat) for 5 days of clear skies in early July 2005.

 
 
 

 

 

 

 

 

 

 


                                                   

 

 

 

 

 

FIGURE 8. Hourly averages for substratum temperatures under a mix of dappled shade and sun-shade edge of foliage of Sarcobatus vermiculatus (in each mesohabitat) for 5 days of clear skies in

early July 2005.

 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 9.  Hourly averages for substratum temperatures under a mix of dappled shade and sun-shade edge of foliage of Artemisia tridentata (in sandy flats) for 5 days of clear skies in early July 2005.

 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 10. Hourly averages for temperatures of three nanohabitats at the microhabitat of the perennial shrub Artemisia tridentata for 5 days with clear skies in early July 2005

 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


FIGURE 11. Hourly averages for temperatures of three nanohabitats at the microhabitat of the perennial shrub Sarcobatus vermiculatus for 5 days with clear skies in early July 2005

 
 
 

 

 


FIGURE 12.  Variation in temperatures among copper lizard models of different a) lizard body positions, b) mesohabitats, and c) microhabitats.

 
 
            

   

 

    

 

               

FIGURE 13. Comparisons of temperatures of copper lizard models of different body positions as wind speed varies.

 
 
                       

           

 

 

 

FIGURE 14. Proportion of time spent moving by Gambelia wislizenii as related to sunlit substratum temperatures in open microhabitat.

 
 
 


           

 

 

FIGURE 15.   The inverse relationship of substratum temperature in sunlit microhabitat with the proportion the total time during focal observations that Gambelia wislizenii were observed to spend in that sunlit microhabitat.

 
 

 

            

FIGURE 16. Body temperatures of Gambelia wislizenii with respect to time and mesohabitat (Hardpan temperatures appear to be cooler in general, whereas sandy flat temperatures tend to be highest; note that scarcity of lizards midday resulted in few midday body temperatures.)

 
 
       

 

 

 

 

 

             

FIGURE 17.   The relative amount (%) of focal observation time that large female Gambelia wislizenii spent in motion as a function of sunlit substratum temperatures in open microhabitats during mornings in early July 2005.

(Note that the time spent moving appears to be relatively stable and low.)

 
 
 

 


           

 

FIGURE 18.   Comparisons among size-and-sex classes of Gambelia wislizenii for how much time they spend moving during morning (Data are shown as average percent of observation time spent in motion for each size-and-sex class from 8:30 to 11:30 hrs in the morning during early July. Large female lizards appear to be least active among all size-sex classes.)

 
 
             

 

       

 

 

 

 

            

FIGURE 19. Comparisons among size-and-sex classes of Gambelia wislizenii for how much time they spend moving during midday (Data are shown as average percent of observation time spent in motion for each size-and-sex class from noon to 16:30 hrs. Small females appear to be the most active among all size-sex classes.)

 

 
 
 

 

 


        

 

FIGURE 20. Comparisons among size-and-sex classes of Gambelia wislizenii for how much time they spend moving during early evening (Data are shown as average percent of observation time spent in motion for each size class from 17:30 until about sunset. Large males appear most active late in the day.)

 
 
            

 

 

 

 

 

 

 

RESULTS

 

 

I.  Spatiotemporal microclimate trends within the three predominant mesohabitats of the Great Basin

 

 

Diurnal air temperature, solar radiation and wind flow variation

 

Daily averages for insolation for sequences of 20 min periods throughout the day ranged from 0 LUX to 925 LUX, as measured by a pyranometer of an automated field weather station. Solar radiation peaked approximately at noon (Figure 1). 

 

Average air temperature for the sandy flat mesohabitat ranged from an average daily minimum of 13.2oC before sunrise (04:00-05:30 hrs) to an average daily high of 41oC at 17:00 hrs (Figure 2).

       

Wind speed recorded by the weather station confirmed field personnel’s direct observations of low wind in the morning and increased wind activity in the late afternoon. The weather station recorded an average modal low of 2.5 mph at 03:00 hrs and a high of 7.8 mph at 17:00 hrs (Figure 3).

 

Sunlit substratum temperatures in open areas of sandy flat, hardpan and dune

 

Average temperature trends for sunlit substratum in the sandy flat followed a characteristic parabola, peaking near 13:00 hrs for the weather station thermocouple thermometer and, slightly later, near 14:00 hrs for the iButtons and hand-held thermometers (Figure 4). Although the daily low substratum temperatures recorded depended on how early they were typically performed, all measurement methods ranged 13.8 - 20.0oC for the earliest recordings, verifying relatively cool conditions if a lizard were to be active at those times. The averages for daily high substratum temperatures recorded for all measurement methods ranged 48.4 -55.6 oC, although wind-protected locations could reach highs of 63.0oC (Figure 4). Sunlit substratum temperature trends in the dune and hardpan environments displayed similar patterns, but at different levels.  The peak substratum temperature on the dune was slightly higher than on the sandy flat by several degrees, whereas the peak temperature of hardpan substratum averaged several degrees lower than the substratum of sandy flats (Figures 5 and 6).

 

 

 

Microclimate of dappled/mixed shade at Sarcobatus vermiculatus

 

Putative soil surface (substratum) temperatures measured by iButtons (essentially the soil-air interface) within the north and south nanohabitats under the S. vermiculatus foliage (in the sandy flats), with the iButtions placed midway between base and plant perimeter, measured maximum temperatures about 1 hour later (6:00 hrs) than did either the soil-surface thermocouple of the weather station or the various hand-held temperature recording devices that measured substratum temperatures adjacent to the copper models locations (Figure 8). Moreover, the single thermocouple probe that measured substratum temperature for the weather station recorded lower substratum temperatures than did the iButtons.  Another notable difference between iButton measurements and other devices (weather station thermocouples and various hand-held units) was the shape of the temperature curve.  The parabolic pattern of the iButton temperatures dropped slightly during the midday high temperature period while weather station thermocouples and the hand-held units did not show the midday drop (Figure 8).  North and south-side S. vermiculatus substratum nanohabitats both displayed surprisingly similar temperature trends. As a general trend, north-side substratum was only slightly cooler than south-side substratum—by about 3-4oC (Figure 8).

 

Putative soil surface (substratum) temperatures measured by iButtons within the east and west nanohabitats under the S. vermiculatus on all three mesohabitats displayed relatively little variation (44oC-48oC) within mesohabitat type (Figure 9).  The west-side substratum under S. vermiculatus located in the sandy flat, however, displayed a relatively higher temperature peak of 58oC. In general, the temperatures were slightly lower than the north-side and south-side substratum temperatures relative to each mesohabitat type.  The nanohabitats of east-side and west-side substrata under the shade of foliage of S. vermiculatus had noticeably different temperature trends with respect to time. In contrast to north-side and south-side iButtons, west-side iButtons recorded peak temperatures at approximately the same time as the weather station/hand-held devices (10:00). East-side iButtons conversely recorded peak temperatures 1 hour (5:00 hrs) later than the weather station thermocouples and hand-held thermometers (4:00 hrs) (Figure 9).

 

 

 Comparisons of temperatures in two microhabitats: Sarcobatus vermiculatus and Artemisia tridentata

 

In the sandy flat mesohabitat, the putative soil surface (substratum) temperatures measured under S. vermiculatus foliage midway between base and plant perimeter and under A. tridentata foliage midway between base and plant perimeter, displayed relatively similar temperature trends, although A. tridentata nanohabitats were generally several degrees centigrade warmer than the corresponding nanohabitats under S. vermiculatus (Figures 8 and 9). The lag time between the other temperature gauges and iButton peak temperature recordings in A. tridentata reflected a similar timing with the north and south iButtons of S. vermiculatus.   The temperature patterns were virtually opposite of the S. vermiculatus east and west temperature parabolas,  with a 1 hour lag time for westerly iButtons and very little lag time for easterly (Figures 8 and 9).

 

Sub-surface soil temperatures (-10cm) just north of the root-crown of S. vermiculatus in the sandy flat peaked (28.6oC) at about 05:00hrs, and reached a trough (12.5oC) at 16:30 hrs (Figures 10 and 11). Similarly, soil temperatures at -10cm under A. tridentata peaked at 4:00 (30.7oC) and troughed at 17:00 (13.4oC).  Daily average for air temperature in S. vermiculatus foliage (+25cm above substratum) varied relatively little, with a low of 17.4 to a high of 24.8oC; Artemisia foliage temperatures ranged from 17.2oC to 25.3oC.  Substratum (soil surface) temperatures just north of the stem base of Artemisia had a daily low of 15.1oC and a daily high of 39.6oC; similar nanohabitat locations for Sarcobatus varied daily from 15.4-37.2oC (Figures 10 and 11).

 

 

II. Copper model operative environmental temperatures

 

 

Averaged copper model temperature measurements

 

Copper lizard model temperatures placed in the open microhabitats of the sandy flat mesohabitat reached 35oC by 08:30 hrs (Figure 3).  Temperatures of the models were over 41oC in the same microhabitats by 10:30 hrs.  Thus, one would expect to see G. wislizenii moving about in the open areas beginning at 08:30 hrs and most likely through 11:00 hrs.  Hence, based on copper lizard model temperatures, it is likely that G. wislizenii are restricted to dappled/mixed shade and full shade during the high midday temperatures.  Temperature measurements of copper lizard models in sunlit and dappled/mixed shade nanohabitats (at ground level) of plant microhabitats were generally higher than those measured by thermocouples (input to weather station) and iButtons placed in the same types of nanohabitats.  Moreover, temperatures of copper lizard models and iButtons peaked about 1 hr later than the weather station peak (Figure 5).  In the open microhabitats of the sandy flat mesohabitat, the peak temperature of copper lizard models was 54.8oC at 14:00 hrs, (Figure 3). After about 17:30 hrs, the copper model temperatures in the open microhabitats of the sandy flat mesohabitat were at or below 41oC, thus based on these operative temperatures as measured by the models, by 17:30 hrs the G. wislizenii should be seen frequently in these open microhabitats (Figure 3).

 

 

Sunlit thermal variance between copper model body positions

 

When comparing the variances in temperature between the different body position models it is apparent that in the open sunlit microhabitats, the models representing the body position where the lizard has its body resting on the substratum (BROS) become much warmer than either the FLEPOS (front legs extended and pelvis on substratum) or the ALEBNTS model (all legs extended with body not touching the substratum) (Figure 12). The open sunlit substratum reached the highest temperatures among all microhabitats and nanohabitats, and all three models showed distinctly different increasing temperature trends as substratum temperatures rose.  Differences among models in temperature can be attributed to the amount of body contact with the substratum.  Note that the greater average temperatures of the sandy flat areas produced the larger temperature differences between model types (Figure 12). 

 

The effects of the wind on the models can also be seen in Figure 13. The BROS model, lying flat on the ground was affected much less by the wind fluctuation in the sandy flat areas, while the other two types of models showed similar variation between the temperatures on sandy flat-open and sandy flat-protected (just leeward of shrub) locations (Figure 13).

 

 

 

III. Focal observations of Gambelia wislizenii behavior

 

 Although relatively few Gambelia wislizenii were seen at midday when temperatures were highs, those lizards that were seen appeared to be moving a lot (Figure 14). Most lizards were seen when sunlit substratum temperatures ranged between 45-49oC; a slight increase in time spent moving appeared to accompany rising ambient temperatures (Figure 14).

 

The G. wislizenii decreased the amount of time they spent in the sun as the substratum temperatures increased (Figure 15).  This inverse relationship is consistent with the findings of Tanner and Krogh (1974). Leopard lizard body temperatures ranged lower in the hardpan areas than for dune and sandy flat (Figure 16). Throughout the morning and evening time periods, lizard body temperatures range from about 36.0 oC to as high as 42.0 oC.

 

Large female G. wislizenii seem to move at relatively low and constant rates throughout the day (Figure 17). Their activity level is generally lowest among size-sex classes (Figure 18, 19 and 20). Small females apparently are more active than large females, and with respect to activity levels, small females tend to behave more like small males. Small females, however, are the most active size-sex class during the heat of midday.   Males, regardless of body size, appear to be bimodal in activity, with peaks during morning and evening activity periods, and the trough in activity during the heat of midday (Figure 18, 19 and 20).

 

 

 

DISCUSSION

 

 

I.  Comparisons of spatiotemporal trends in microclimates among the three predominant mesohabitats of the Great Basin Scrub in the Alvord Basin

 

Solar radiation, wind speed and air temperature within each mesohabitat of this portion of the Alvord Basin follows a clear and predictable spatiotemporal pattern. Incoming solar radiation, substratum temperature in the open, and air temperature all show very similar temperature parabolas, differing only in the timing and amplitude of their peaks and troughs.  Based on the ambient environmental temperatures, one would expect to find G. wislizenii being relatively inactive, perhaps thermoregulating in the dappled and full shade of a larger perennial plant during the peak temperatures of midday, and occupying burrows from about 19:30-08:00 hrs (inactivity period).

 

 Substratum temperature in the dappled/mixed shade varies with time of day, microhabitat, and nanohabitat because of the continuous change in the azimuth and declination of incoming solar radiation, particularly where the sunlight strikes beneath the foliage-perimeter of the shrubs.  Differences in plant physiognomy between S. vermiculatus and A. tridentata appear to affect the consistency of the shading effect of the foliage appears to vary slightly. That is, a deeper and more consistent shade may be produced by greasewood (S. vermiculatus).  If so, it a reasonable speculation is that 1) greater and spatially more even branching in the volume of foliage that comprises the above ground vegetation and 2) shorter distance between the underside of the foliage volume and substratum in S. vermiculatus may produce the more consistent shading.   The sun-shade patterns and the temperatures in patches of sun and shade of various sizes under small and large shrubs of both species yet need to be documented before the effects of the thermal environments under these shrubs on lizards can be understood. 

 

 

II. Copper model operative environmental temperature

 

 

Averaged copper model temperature measurements

 

 The copper models absorbed heat via conduction and radiation from the soil, foliage, and air. The time lag of the temperatures recorded for copper lizard models and iButtons relative to the air and substratum temperatures measured by the weather station are readily apparent in Figure 4. The iButtons, however were recording temperature nearer the substratum and midway between base and perimeter of the perennial, hence the iButtons measured nanohabitat temperatures (e.g., nanohabitat and nanoclimate) of dappled lighting, whereas the copper models measured a mix of sun-shade edge and dappled lighting conditions nearer the plant perimeter.  As a general trend, however, it appears that the data from the copper lizard models data correlated with the iButton data. These spatiotemporal similarities may be because both the iButtons and copper models were integrating temperature from around them as well as the incoming heat waves.

 

 

 

Variation in temperatures among copper models with different body positions exposed to varying sunlight levels and wind speeds.  

 

Comparisons of temperatures of the different lizard copper model body positions in open microhabitats, exposed to full sunlight, and under varying levels of exposure to showed consistent differences among models.  These results corroborate the findings of Muth’s study of thermoregulation postures of Callisaurus draconoides (Muth, 1977), a common prey species of G. wislizenii in the Mojave and Sonoran Deserts (Parker and Pianka, 1976). Temperature changes in the models were similar under the same changes of lighting and wind. For example, all models reached a trough in temperature at a about two minutes after the peak wind speed, and all slowly began to rise in temperature as the wind speed declined. The predictable differences in model temperature with model location, and the tightly correlated changes among models with changes in wind and sunlight conditions lend support to the hypotheses that to remain within the upper and lower limits of body temperature throughout the daily activity period, then an individual Gambelia wislizenii must 1) vary its spatiotemporal use among microhabitats and nanohabitats, and 2) actively thermoregulate at some times of the day.

 

 

Copper model applications in predicting G. wislizenii spatiotemporal activity

 

The data provided by the copper models in this study can be directly applied towards predicting and explaining G. wislizenii spatiotemporal behavior patterns. This confirms earlier, seminal work with copper model (Bakken 1992).  And similar to a study of thermoregulation in another lizard, (Bauwens et. al., 1996), a modestly strong inference from the preliminary results of this study is that in the heat of the day (1:30 - 3:30 hrs) G. wislizenii must thermoregulate exclusively.  Similarly, in at the very extremes of the daily activity period, it would be expected that thermoregulatory warming by basking would be the only viable activity.  Hence in the interim periods when temperatures are less extreme, one would expect a mix of thermoregulation and other activities.  Indeed, there may be periods of the mid-morning and late afternoon when most microhabitats are thermally equable for G. wislizenii, and it can be expected that nearly all of the behavior occurring during these equable conditions would be related to the other basic autecological tasks, such as food acquisition and mate selection.  More comprehensive documentation of the lizard’s behavior and its thermal environment (with copper models) is required before firm conclusions can be made about how these lizards spend their waking hours.

 

 

 

III. Focal observations of Gambelia wislizenii behavior

 

Smaller lizards with smaller body volume relative to body surface area than larger lizards can warm more quickly in the morning sun, thereby perhaps becoming active earlier in the day than larger lizards.  This same phenomenon, however, may cause an inverse relationship of body size and rate of overheating when venturing into the sunlit open areas in late morning and midday.  That is, larger lizards may be able to stay within the normal range of field-active body temperature when walking quickly enough across the hot substratum of sunlit areas in the open, whereas the smaller individuals may tend to overheat when crossing those same open areas (Waldschmidt, 1980).  Hence, high temperatures may cause the trough in activity for all size-sex classes except for the large females, which are the largest body-size class of lizards (Lappin and Swinney, 1999).  The activity level of large females is relatively low all day, however, and, moreover, small female females remain relatively active.  It is theorized that mature females are the largest size-sex class because of selective pressure to produce large young (Tanner and Krogh, 1974).  Hence, higher activity by females during late morning and early afternoon may be related to the need for greater energy needs than in males.  The activity level of arthropods in late morning (Rose, 2004) is apparently not so low that short-wait ambushing is unprofitable.  It can be inferred that the low activity level of large females throughout the morning is not influenced by the need to thermoregulate, but the activity level may be because it the large females are focused on food acquisition, and use long wait ambushing predation behavior for the majority of the morning when its lizard prey (Whitaker and Maser, 1981) are active.

 

Even with the trough in their activity during midday, both the males and the smaller adult females maintained a relatively high average level of activity throughout the day when compared to the activity of large females. The greater rates of movements of the small adults may be short-wait ambush predation on arthropods on and under shrubs (e.g., walk to near the perimeter of a shrub, and visually search the perimeter foliage for telltale movement of grasshoppers and cicadas) (Parker and Pianka, 1976; Steffen, 2002; Rose 2004).

 

The data from the copper models and the sun-shade patterns and substratum and above ground temperatures associated with sun and shade under perennials must be considered preliminary.  Similarly, the low sample sizes for each size-sex class for each period of the day render the behavioral results suggestive, but not definitive.  Moreover, a careful examination of arthropod prey captured by Gambelia wislizenii, relative to the availability of those prey has yet to be performed.  The results of the work on lizard behavior in relation to its thermal environment in the Alvord Basin, however, is a firm foundation, providing the understanding needed for the next round of research endeavoring to document, explain, and understand the spatiotemporal patterns of desert reptiles.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Literature Cited

 

 

Abts, M. L. 1976. Thermal ecology and movement in the leopard lizard, Gambelia wislizenii. Unpublished MA Thesis. Portland State University, Portland, OR.

 

Anderson, R.A. 2006, in press. Food acquisition modes and habitat use in Lizards: questions from an integrative perspective.  In S. Reilly, D.B. Miles, and L.D. McBrayer, eds.  Foraging Modes in Reptiles: Concepts and Controversies; Oxford University Press.

 

Bakken G.S. 1992. Measurement and application of operative and standard operative procedures in ecology. Am Zool 32:194-216.

Bauwens, D., P.E. Hertz, and A, Castilla. 1996. Thermoregulation in lacertid lizard: the relative contributions of distinct behavioral mechanisms. Ecology 77: pp 1818-1830.

Grant, B. and A.E. Dunham. 1988. Thermally imposed time constraints on the activity of the desert lizard sceloporus merriami. Ecology: 69: pp 167-176.

 

Larson, P. and L. Larson. 1977. A Sierra Club Naturalist’s Guide to the Deserts of the

            Southwest. Sierra Club, San Francisco, California.

 

Lappin, A.K. and E. J. Swinney. 1999. Sexual dimorphism as relates to natural history of leopard lizards (Crotaphytidae: Gambelia). Copeia 1999:649-660

 

Muth, A. 1977. Body temperatures and associated postures of the zebra-tailed lizard, Callisaurus draconoides. Copeia 1: 122-125.

 

Muth, A. 1977. Thermoregulatory postures and orientation to the sun: a mechanistic evaluation for the zebra-tailed lizard, Callisaurus draconoides. Copeia 4: 711-715.

 

Parker, W. S. and E. R. Pianka. 1976. Ecological observations on the leopard lizard (Crotaphytus wislizenii)in different parts of its range. Herpetologica 32: 95-114.

 

Rose, E.L. 2004. Foraging behavior in Gambelia wislizenii the long-nosed leopard lizard, in Harney County, Oregon. Unpublished MS thesis, Western Washington University, Bellingham, WA

 

Sigler, J.W. and W.F. Sigler. 1994. Fishes of the Great Basin and the Colorado Plateau: past and present forms. In K.T. Harper, L.L. St. Clair, K.H. Thorne, and W.M. Hess (eds.), Natural History of the Great Basin and the Colorado Plateau, pp 163-208.  University Press of Colorado, Niwot, Colorado.

 

Steffen, J. E. 2002. The ecological correlates of habitat use for he long nose leopard lizard, Gambelia wislizenii, in southeast Oregon. Unpublished MS thesis, Western Washington University, Bellingham, WA.

 

Tanner, W. W. and J. E. Krogh. 1974. Ecology of the leopard lizard, Crotaphytus wislizenii at the Nevada test site, Nye county, Nevada. Herpetologica 30:63-72.

 

Tanner W. W and J E. Krogh. 1974.Variations in activity as seen in four sympatric lizard species of southern Nevada. Herpetologia 30: 303-308.

 

Heath, J. E. 1965. Temperature regulation and diurnal activity in horned lizards. University of California Publications in Zoology 64:97-136.

 

Waldschmidt, S. 1980. Orientation to the sun by the Iguana lizards Uta stansburiana and Sceloporus undulatus: hourly and monthly variations. Copeia 3: 458-462.

 

Whitaker, J and C. Maser. 1981. Food habits of seven species of lizards from Malheur county, southeastern Oregon. Northwest Science 55: 202-208.