reptiles

Stress Response from Male-Male Competition in Varying Thermal Environments at the Sevilleta National Wildlife Refuge, New Mexico

Abstract: 

Environmental temperature influences virtually all aspects of organismal performance, including fitness. And since temperature varies throughout space and time, organisms must regularly compete for optimal thermal habitats, much as they do for other resources (e.g. territory, food, or females). However, competition for thermal resources imposes costs, often in the form of a stress response (i.e. increased corticosterone production). Elevated corticosterone promotes physiological and behavioral responses that can increase an organism’s chance of survival, but if left in an organism’s system for too long, it will reduce immunity, degenerate neurons, and lower fitness. Previous theoretical and empirical work indicates that, all else being equal, patchy thermal landscapes reduce the energetic cost of thermoregulation. Therefore, I hypothesize that lizards exposed to patchy distributions of preferred temperatures will have less stress (and thus lower levels of corticosterone) than those exposed to clumped distributions. Furthermore, patchily distributed resources are more difficult for territorial males to monopolize, and thus, subordinate males in patchy thermal landscapes should experience less stress than subordinate males in clumped thermal landscapes.

Additional Project roles: 

32
33

Data set ID: 

284

Core Areas: 

Keywords: 

Methods: 

Experimental design: Starting in the July of 2012, I will initiate this project as part of a continuing large-scale field study at Sevilleta LTER site in collaboration with PI Michael Angilletta’s Spatially Explicit Theory of Thermoregulation project. As in past research conducted in 2008, 2009 and 2011, I will use male Yarrow’s spiny lizard. This lizard thermoregulates accurately in the absence of predators14,15 and aggressively defends resources from conspecific males14,16.

Nine outdoor arenas (20 x 20 m), consisting of sheet metal walls and a canopy of shade cloth, will be used to manipulate the thermal environments. Among the arenas, three patterns of shade patches will be replicated three times each to generate distinct thermal landscapes (see Figure 1).  Lizards will be paired by size: large dominant (22-30 g) with a small subordinate (15-21 g). Each pair (n = 12) will be randomly assigned one of the thermal environments. Prior to each trial, males will be habituated to their arenas for 10 days. During this period, each male will be exposed to the thermal arena every other day (for a 24-h period) in the absence of a competitor (total of 5 days per animal). After the habituation period, males will be placed in arenas for a 4-day testing period. Males will spend two of these days in isolation and the other two in competition. Half the pairs will start the trial in isolation (solitary treatment), and the other half of the pairs will start the trial in competition (social treatment). A matched pair of lizards will be placed together in one arena, and the other two arenas will each have one individual (either small or large) placed into it.  After two days, all lizards will be captured and blood samples will be collected within three minutes (speed of collection is necessary to prevent handling stress from affecting plasma corticosterone levels17). Blood will be taken from the orbital sinus with a glass capillary tube and then taken back to the lab where the plasma will be obtained through centrifugation. Plasma will be stored at -80˚C for hormone assays18. After bleeding, solitary lizards will be placed together in one arena, and the previously paired individuals will be separated and split between the two remaining arenas. Thus, a completed habituation and observation set for six pairs (two pairs per type of thermal environment) will take 14 days. And 3 sets will be conducted per season giving a total of 18 pairs per season in each thermal environment (54 pairs in isolation and competition per season). Mixed modeling procedures in the statistical software R will be used to quantify the effects of competition and thermal patchiness on the corticosterone levels of lizards19.


 Fig. 1. Patterns of shade patches for arenas (each replicated 3x).

Linking Precipitation and C3 - C4 Plant Production to Resource Dynamics in Higher Trophic Level Consumers: Lizard Data (2005-2006)

Abstract: 

In many ecosystems, seasonal shifts in temperature and precipitation induce pulses of primary productivity that vary in phenology, abundance and nutritional quality.  Variation in these resource pulses could strongly influence community composition and ecosystem function, because these pervasive bottom-up forces play a primary role in determining the biomass, life cycles and interactions of organisms across trophic levels.  The focus of this research is to understand how consumers across trophic levels alter resource use and assimilation over seasonal and inter-annual timescales in response to climatically driven changes in pulses of primary productivity. We measured the carbon isotope ratios (d13C) of plant, arthropod, and lizard tissues in the northern Chihuahuan Desert to quantify the relative importance of primary production from plants using C3 and C4 photosynthesis for consumers.  Summer monsoonal rains on the Sevilleta LTER in New Mexico support a pulse of C4 plant production that have tissue d13C values distinct from C3 plants.  During a year when precipitation patterns were relatively normal, d13C measurements showed that consumers used and assimilated significantly more C4 derived carbon over the course of a summer; tracking the seasonal increase in abundance of C4 plants.  In the following spring, after a failure in winter precipitation and the associated failure of spring C3 plant growth, consumers showed elevated assimilation of C4 derived carbon relative to a normal rainfall regime. These findings provide insight into how climate, pulsed resources and temporal trophic dynamics may interact to shape semi-arid grasslands such as the Chihuahuan Desert in the present and future.

Data set ID: 

270

Additional Project roles: 

354

Core Areas: 

Keywords: 

Methods: 

Study site: 

This research was conducted on the Sevilleta LTER, located 100 km south of Albuquerque, New Mexico, which is an ecotonal landscape of Chihuahuan desert shrub and grasslands (Muldavin et al. 2008).  Data were collected from a 0.9 x 0.5km strip of land that encompassed a flat bajada and a shallow rocky canyon of mixed desert shrub and grassland dominated by the creosote bush (Larrea tridentata) and black grama grass (Bouteloua eriopoda). 

Tissue collection & sample preparation for stable isotope analysis:

From May to October of 2005 and 2006 we collected plant, lizard, and arthropod tissues for carbon stable isotope analysis. During mid-summer of 2005, we randomly collected leaf and stem samples from the 38 most abundant species of plants; these species produce over 90% of the annual biomass on our study site (see Appendix Table A).  Approximately 3.5 mg of plant material was then loaded into pre-cleaned tin capsules for isotope analysis.  

All animal research was conducted with the approval of the institutional animal care and use committee (UNM-IACUC #05MCC004).  Lizards were captured by hand using noose poles and by drift fence and pitfall trap arrays (Enge 2001) randomly scattered over a 0.5 km2 area.   Each lizard was toe clipped for permanent identification and snout-vent length (SVL), body mass (g) and sex were recorded.  For stable isotope analysis, we obtained a 50 μL blood sample from each lizard and only sampled individuals once in a two week period.  We acquired a total of 367 blood samples from 11 lizard species.  Blood samples were obtained by slipping a micro-capillary tube (Fisherbrand heparinized 50μL capillary tubes) ventral and posterior to the eyeball to puncture the retro-orbital sinus.   Before and after this procedure a local anesthesia (0.5% tetracaine hydrochloride ophthalmic solution, Akorn Inc.) was applied to the eye.  Blood samples were stored on ice and centrifuged within 24 hours to separate plasma and red blood cells.  For isotope analysis 15 μL of plasma were pipetted into a tin capsule, air dried, and then folded.  

Arthropods were captured bi-weekly from May through October of each year in pitfall traps (see above), as well as by hand and sweep netting. Individuals were frozen, lyophilized, ground into a fine powder and 0.5 mg samples were loaded into tin capsules for isotope analysis.

Stable isotope analysis:

Carbon isotope ratios of samples were measured on a continuous flow isotope ratio mass spectrometer (Thermo-Finnigan IRMS Delta Plus) with samples combusted in a Costech ECS 4010 Elemental Analyzer in the UNM Earth and Planetary Sciences Mass Spectrometry lab.  The precision of these analyses was ± 0.1‰ SD for δ13C.  A laboratory standard calibrated against international standards (valine δ13C -26.3‰ VPDB [Vienna Pee Dee Belemnite Standard]) was included on each run in order to make corrections to raw values. Stable isotope ratios are expressed using standard delta notation (δ) in parts per thousand (‰) as: δX = (Rsample /Rstandard – 1) x 1000, where Rsample and Rstandard are the molar ratios of 13C/12C of a sample and standard. 

Estimation of C3 and C4 carbon incorporation into arthropods and lizards:

We used d13C values of consumer tissues and a two-end-point mixing model to estimate the proportion of a consumer’s assimilated carbon that was derived from each plant photosynthetic type (Martinez del Rio and Wolf 2005):  

In this model p is the fraction of dietary C4 plant material incorporated into a sampled tissue. We chose to analyze the isotope composition of whole bodies for arthropods because this best reflects the diet of lizards.  For lizards we chose plasma because it has a rapid 13C turnover rate with an inter-specific retention time ranging from 25 to 44 days (Warne et al. 2009b). In the above model Δ is a discrimination factor, which is defined as the difference in isotope values between an animal’s tissues and food when feeding on an isotopically pure diet (DeNiro and Epstein 1978).  For our mixing model estimates we used discrimination (Δ13C) values resulting from a diet switch study for two species of lizards (Sceloporus undulatus, and Crotaphytus collaris) fed a diet of C4 raised crickets (Warne et al. 2009b).  We found the plasma of these lizards had a mean Δ13C = -0.2 ± 0.4‰ VPDB, while crickets fed a C4 based dog food had a Δ13C = -0.9 ± 0.4‰.  Reviews of stable isotope ecology have reported Δ13C values for arthropods ranging from -0.5 ± 0.3‰ (Spence and Rosenheim 2005) to 0.3 ± 0.1‰ (McCutchan et al. 2003).  Although variation in our assumed Δ13C values would affect proportional estimates of the C3 or C4 resources consumed, the observed trends would not change. 

Data analysis:  

To compare the seasonal isotope values of consumers between a spring C3 dominated and a summer C4 dominated ecosystem we present the mean δ13C (± SE) of each consumer species during the pre-monsoon (May, June and early-mid-July) and monsoonal periods for each year of this study.   We defined the monsoon period to begin with the first day of recorded monsoon rains in July (monsoon 2005 = July 25 to October 15; monsoon 2006 = July 6 to October 15).  The effects of seasonal and inter-annual primary production patterns on consumer resource assimilation (δ13C) were determined by two-way ANOVA using the PROC MIXED procedure (Littell et al. 2006) in SAS (SAS 1999).  To examine these effects in the lizard community as a whole, lizard species were treated as random effects in the PROC MIXED model.  In order to determine the significance of seasonal and year effects post-hoc analyses were conducted using Tukey-Kramer’s hsd test (Sokal and Rohlf 1995).  Prior to analysis the data were tested for homogeneity of variance and confirmed to meet the assumptions of ANOVA.

Data sources: 

sev270_lizard_isotope_20140216.txt

Capital Breeding and Allocation to Life History Demands are Highly Plastic in Lizards at the Sevilleta National Wildlife Refuge, New Mexico: Field Study

Abstract: 

The use of stored resources to fuel reproduction, growth and maintenance to balance variation in nutrient availability is common to many organisms. The degree to which organisms rely upon stored resources in response to varied nutrients, however, is not well quantified. Through stable isotope methods we quantified the use of stored versus incoming nutrients to fuel growth, egg and fat body development in lizards under differing nutrient regimes. We found that the degree of capital breeding is a function of an individual’s body condition. Furthermore, given sufficient income lizards in poor condition can allocate simultaneously to storage, growth, and reproduction, which allowed them to catch up to better conditioned animals. In a parallel, inter-specific survey of wild lizards we found that the degree of capital breeding varied widely across a diverse community. These findings demonstrate that capital breeding in lizards is not simply a one-way flow of endogenous stores to eggs, but is a function of the condition state of individuals and the availability of nutrients during both breeding and non-breeding seasons. Here we explore the implications of these findings for our understanding of capital breeding in lizards and the utility and value of the capital-income concept in general.

Data set ID: 

261

Core Areas: 

Keywords: 

Methods: 

Lizard Capture: 

For measures of capital breeding in wild lizards, females of seven species were caught April through July of 2008 under the approval of the University of New Mexico institutional animal care and use committee (UNM-IACUC #05MCC004).  The species captured were: Cophosaurus texanus, Crotaphytus collaris, Eumeces multivirgatus, Phrynosoma modestum, Sceloporus undulates consubrinus, Urosaurus ornatus, and Uta stansburiana.   Lizards deemed by palpation to be egg-bearing were returned to the lab, euthanized and reproductive tissues prepared for stable isotope analysis (see below).  

Stable isotope treatments:

After the lizards were euthanized liver, fat body, and thigh muscle samples were harvested, freeze dried and a 0.5 mg sample was placed into a pre-cleaned tin capsule (Costech, #041074, Valencia, CA) for stable isotope analysis.  Eggs and follicles were also harvested, their length and width measured and freeze dried.  All lipids were extracted from freeze dried and ground muscle and eggs/follicles by a 2:1 chloroform and methanol bath; lizard muscle had undetectable amounts of lipids.  The suspended lipids from eggs were pipetted into separate storage vials and air dried.  Lipids and lipid-free egg tissues were then loaded into tin capsules.  We measured the δ13C of each egg and follicle greater than 6mm in length (½ the length of shelled eggs and assumed to reflect reproductive allocation).  Our stable isotope methodology follows standard methods and our protocol is described in detail in Warne et al. (2010a, 2010b).  We report all isotope values in the standard delta notation (δX = (Rsample /Rstandard – 1) x 1000) in parts per thousand (‰) relative to the international carbon standard VPDB (Vienna Pee Dee Belemnite).  Measurements were conducted on a continuous flow isotope ratio mass spectrometer in the UNM Earth and Planetary Sciences Mass Spectrometry lab.  The precision of these analyses was ± 0.1‰ SD for δ13C based on long-term variation of the working laboratory standard (valine δ13C = -26.3‰ VPDB), samples of which were included on each run in order to make corrections to raw values obtained from the mass spectrometer. 

Essential to this study is the observation that differences in photosynthetic biochemistry inherent to C3- and C4-plants produces distinct differences in the d13C of their tissues, which can be used to trace the movement of nutrients through consumers (Hobson et al. 1997, O'Brien et al. 2000).  Because winter and summer monsoonal rains drive seasonally separated C3 and C4 plant production and resource flux in Chihuahuan Desert food webs (Warne et al. 2010b), we hypothesized that we could use natural variation in the δ13C of C3 and C4 resources to examine capital breeding in wild lizards. We predicted that during the late summer and early fall lizards would develop endogenous lipid stores (capital) from C4 derived sources because C4 plants (primarily grasses) comprise the bulk of primary production during this period.  We also hypothesized that reproduction in the spring (the income source) would be fueled by C3 plants associated with winter rains. We subsequently sampled female lizards of a variety of species during April through June 2008 to gauge the relative use of capital (C4) versus income (C3) resources for their first clutch of the season.  The lizards were collected from a mixed Creosote and gramma grassland. 

We used tissue d13C values and a standard two-end-point mixing model to estimate the proportion of endogenous fat or muscle (capital) and incoming insect-dietary sources used to provision eggs.  The mean δ13C value of insects feeding on C3 plants (-27.3‰) served as an income source (see Warne et al. 2010b).  The discrimination (Δ13C) values used in this model for muscle (-1.9‰) and fat bodies (0‰) were experimentally determined for S. undulatus (Warne et al. 2010a).  

Additional information: 

 Study Area 1:  

*Study Area Name:  Socorro NM

*Study Area Location:  BLM land 11 miles south of Socorro, NM

*Study Area Description:  Mixed creosote and gramma grass shrubland

*GPS Coordinates:  

North Coordinate:  33°56'54.88"N

West Coordinate: 106°57'6.26"W

Study Area 2:  

*Study Area Name:  Tres pistoles 

*Study Area Location:  BLM land 13 miles east of Albuquerque, NM

*Study Area Description:  Mixed shrub and gramma grassland

*GPS Coordinates:  

North Coordinate:  35° 4'44.38"N

West Coordinate: 106°26'48.29"W

Capital Breeding and Allocation to Life History Demands are Highly Plastic in Lizards at the Sevilleta National Wildlife Refuge, New Mexico: Experimental Study

Abstract: 

The use of stored resources to fuel reproduction, growth and maintenance to balance variation in nutrient availability is common to many organisms. The degree to which organisms rely upon stored resources in response to varied nutrients, however, is not well quantified. Through stable isotope methods we quantified the use of stored versus incoming nutrients to fuel growth, egg and fat body development in lizards under differing nutrient regimes. We found that the degree of capital breeding is a function of an individual’s body condition. Furthermore, given sufficient income lizards in poor condition can allocate simultaneously to storage, growth, and reproduction, which allowed them to catch up to better conditioned animals. In a parallel, inter-specific survey of wild lizards we found that the degree of capital breeding varied widely across a diverse community. These findings demonstrate that capital breeding in lizards is not simply a one-way flow of endogenous stores to eggs, but is a function of the condition state of individuals and the availability of nutrients during both breeding and non-breeding seasons. Here we explore the implications of these findings for our understanding of capital breeding in lizards and the utility and value of the capital-income concept in general. 

Core Areas: 

Data set ID: 

260

Keywords: 

Methods: 

Lizard Capture and Maintenance:

Thirty two female prairie lizards (Sceloporus undulatus) were caught on Bureau of Land Management reserves near Albuquerque, NM during the last two weeks of July, 2007 and maintained in a room at the biology department of the University of New Mexico under the approval of the UNM-IACUC (#07UNM007).   Two lizards were housed per 20 gallon glass terrarium and were provided a sand substrate, as well as perch and shelter spaces built by stacked pieces of plywood and rock.  Lizards were kept on a 12 hour (light:dark) photoperiod and a temperature gradient was provided by a 100 watt heat lamp placed at one end of the terrarium and focused on the wood perch, which provided a stable heat gradient that ranged from 39 ± 1.7ºC at the perch to 26 ± 0.8ºC at the cool end of the tank.  Resulting mean daytime body temperatures were 36.3 ± 6.2ºC (n = 18).  An ultraviolet-B fluorescent light (ZooMed® UVB 10.0 fluorescent) was also provided for vitamin D synthesis. 

Experimental dietary treatments and reproduction:

S. undulatus were captured from a cottonwood woodland field site and paired by Snout Vent Length (SVL) and then randomly split into either a high (n = 16) or low nutrient treatment (n = 16).  The high nutrient diet consisted of seven crickets and two mealworms per week; similar to an ad libitum diet found by Angilletta (2001).  We estimated that a low nutrient diet reduced by ~30% of ad libitum (five crickets/week and one mealworm every other week) would reduce body condition and reflect the poor conditions experienced by lizards in the wild (see Ballinger 1977, 1979, Ballinger and Congdon 1980, Sinervo and Adolph 1994).   These low diet lizards were switched to the high diet after hibernation, referred to hereafter as the LH treatment (n = 16).   The high treatment prior to hibernation was split into a high diet post-hibernation (HH, n = 8) and a low treatment (HL, n = 8).  We did not have an LL treatment because we assumed that they would be in such low body condition that they would not reproduce.

The lizards were prepared for hibernation during November 2007 by gradually reducing the photoperiod to 7 hours per day, and were fasted for two weeks. Lizards were then placed in 27 liter plastic containers with a sandy substrate and wood shavings for burrowing on November 17, 2007 and maintained at 10.2 ± 3.1ºC.  The lizards were removed from hibernation on February 2, 2008. To induce reproduction, male prairie lizards that were maintained for a separate study were introduced for two weeks to the female terrarium in mid-February of 2008.  Reproduction was observed in numerous tanks (mounting and copulation), and signs of reproduction (bite marks) were apparent on all females. The female lizards were then palpated weekly to monitor egg development.  When eggs appeared to be nearly shelled or shelled, the lizards were euthanized via an intraperitoneal injection of sodium pentobarbital (using a dose of 60 mg/kg).   Two lizards were euthanized in late March following rapid development of shelled eggs.  All other lizards were euthanized during the last week of May 2008, at which time most were found to have either large follicles or shelled eggs. 

Stable isotope treatments:

After the lizards were euthanized liver, fat body, and thigh muscle samples were harvested, freeze dried and a 0.5 mg sample was placed into a pre-cleaned tin capsule (Costech, #041074, Valencia, CA) for stable isotope analysis.  Eggs and follicles were also harvested, their length and width measured and freeze dried.  All lipids were extracted from freeze dried and ground muscle and eggs/follicles by a 2:1 chloroform and methanol bath; lizard muscle had undetectable amounts of lipids.  The suspended lipids from eggs were pipetted into separate storage vials and air dried.  Lipids and lipid-free egg tissues were then loaded into tin capsules.  We measured the δ13C of each egg and follicle greater than 6mm in length (½ the length of shelled eggs and assumed to reflect reproductive allocation).  Our stable isotope methodology follows standard methods and our protocol is described in detail in Warne et al. (2010a, 2010b).  We report all isotope values in the standard delta notation (δX = (Rsample /Rstandard – 1) x 1000) in parts per thousand (‰) relative to the international carbon standard VPDB (Vienna Pee Dee Belemnite).  Measurements were conducted on a continuous flow isotope ratio mass spectrometer in the UNM Earth and Planetary Sciences Mass Spectrometry lab.  The precision of these analyses was ± 0.1‰ SD for δ13C based on long-term variation of the working laboratory standard (valine δ13C = -26.3‰ VPDB), samples of which were included on each run in order to make corrections to raw values obtained from the mass spectrometer. 

Essential to this study is the observation that differences in photosynthetic biochemistry inherent to C3- and C4-plants produces distinct differences in the d13C of their tissues, which can be used to trace the movement of nutrients through consumers (Hobson et al. 1997, O'Brien et al. 2000).  The lizards were collected from cottonwood woodlands in which their diet was largely composed of C3-plant derived carbon, as evidenced by a baseline muscle δ13C of -25.1± 0.1‰ VPDB, near that of the mean value for C3 plants of -27.3 ± 0.04‰.  Prior to hibernation lizards were maintained on a diet composed of crickets (mean δ13C ± SEM for lipids = -22.5 ± 0.1‰ and lipid free carbon = -21.7 ± 0.1‰ VPDB, n = 16) raised on C3-plant derived dog food (Nutro® Natural Choice® large breed puppy lamb and rice formula) and mealworms (lipids = -26.3 ± 0.1‰ and lipid free = -24.35 ± 0.1‰ VPDB, n = 8) raised on bran meal.  Here we used the mathematical normalization model of Post et al. (2007) to determine the lipid-free δ13C values for these insects, assuming reported lipid contents of 13.8% for crickets and 32.8% for mealworms (Bernard and Allen 1997).  Maintaining lizards on a C3 diet prior to hibernation insured that their capital stores of fat bodies and muscle would have consistent carbon isotope values.  After hibernation the lizards were switched to a C4 based insect diet of crickets (lipids = -16.3 ± 0.1‰ and lipid free = -15.53 ± 0.1‰VPDB, n = 35) raised on a C4 - corn based dog food (Iams® Smart Puppy large breed formulaTM) and mealworms (lipids = -13.0 ± 0.3‰ and lipid free = -10.2 ± 0.2‰ VPDB, n = 9) raised on coarse ground cornmeal; which provided an ‘income’ diet with δ13C values distinct from the pre-hibernation C3 diet.   

We used tissue d13C values and a standard two-end-point mixing model to estimate the proportion of endogenous fat or muscle (capital) and incoming insect-dietary sources used to provision eggs.  Because crickets and mealworms had different δ13C values and the dietary treatments imposed on the lizards also consisted of differing quantities of feeder insects (high = 7 crickets + 2 mealworms/week; low = 5 + 0.5/week) we used a weighted mean to calculate the insect δ13C for each treatment in this model.   The weighted δ13C value for the high dietary treatment for C4 insect lipids was -15.6‰ and -14.3 for lipid free carbon; for the low treatment C4 insect lipids was -16‰ and -15‰ for lipid-free carbon.  The discrimination (Δ13C) values used in this model for muscle (-1.9‰) and fat bodies (0‰) were experimentally determined for S. undulatus (Warne et al. 2010a).  

Statistical analysis:

The effect of dietary treatment on the body condition of lizards was analyzed by repeated measures ANCOVA with treatment and stage of the experiment as fixed effects, individuals as random effects nested within treatment, and snout-vent length (SVL) as a covariate.  Body condition was estimated as the least squares (LS) mean of body weight (minus eggs) adjusted for SVL in this ANCOVA model; a method argued to be more statistically sound than other condition indices (Packard and Boardman 1988, García-Berthou 2001).  Treatment effects on SVL were similarly analyzed by repeated measures ANOVA.  Mauchly’s test was used to confirm that the assumption of sphericity for repeated measures analysis was valid, and epsilon corrections to the degrees of freedom were applied when necessary.   Dietary treatment effects on growth were measured by the specific growth rate of SVL (ln(SVL2/SVL1)/Δdays) for the pre- and post hibernation periods, and analyzed by one-way ANOVA.   Dietary treatment effects on reproductive effort, measured as relative clutch mass (RCM = clutch mass/body mass with no eggs) and clutch size were analyzed by one-way ANOVA.  The effect of dietary treatment on tissue δ13C values were similarly analyzed by one-way ANOVA.  Post-hoc comparisons of treatment effects during the four experimental stages were conducted using Tukey-Kramer’s HSD test.  Prior to all analyses the data were tested for homogeneity of variance and confirmed to meet model assumptions.  These analyses were performed in JMP® 8.0 (SAS Institute Inc., Cary, NC, 1989-2007).  All values are reported as mean ± SEM.

Keystone species have large impacts on community and ecosystem properties, and create important ecological interactions with other species.  Prairie dogs (Cynomys spp.) and banner-tailed kangaroo rats (Dipodomys spectabilis) are considered keystone species of grassland ecosystems, and create a mosaic of unique habitats on the landscape.

The Burden of Reproduction in Lizards: Changes in Respiratory Physiology Associated with Reduced Lung Volume at the Sevilleta National Wildlife Refuge (2007-2008)

Abstract: 

Previous morphological work on lizards suggests that the volume of growing eggs may result in a significant decrease in lung volume during gravidity. Iguanid lizard lungs are located within continuous thoracic and abdominal cavities and are highly distensible. Because of their distensible nature and lack of a diaphragm, both naturally occurring and introduced structures within the abdominal and thoracic cavities (i.e. organs, food, eggs) compress them and potentially reduce available lung volume for gas exchange. During reproduction, this decrease comes at a time of increased energetic demands, due to the cost of provisioning eggs and the physical burden of transporting the extra mass before laying. This means that females must increase the oxygen/carbon dioxide exchange with effectively smaller lung capacity than when they are not reproductive. Therefore, the way species compensate for this decrease affects performance, and ultimately the survival of individuals and their offspring.

Data set ID: 

211

Additional Project roles: 

308
309

Core Areas: 

Keywords: 

Purpose: 

This research has been focused on investigating how the burden of carrying eggs (gravidity) affects the respiratory physiology of two species of lizard, Crotaphytus collaris and Gambelia wislizenii. This work has been centered around two questions: 1) What is the respiratory response to morphological reductions in lung volume during reproduction in these two lizard species and, 2) Are these responses the same for two species of similar size and morphology but with differing activity levels?

Methods: 

Experimental Design:  

Lizards were housed outside in screen cages (LLL Reptile) to allow access to natural light and climatic conditions. Cages were outfitted with sand, wood and rock refugia, and one end of the cage was covered with 18 by 12” board to provide shade. Lizards were fed crickets every other day throughout the period of the study. Crotaphytus collaris were grouped as two females to every male and G. wislizenii as one male to every female, when possible, to provide mating opportunities for both species. Females estimated to be close to oviposition were placed in smaller cages filled with moist perlite to provide an appropriate substrate for laying. 

CO2 Production, Breathing Frequency and Tidal Volume Estimates:

Lizards were fasted for 48 hours prior to all measurements and placed in individual chambers in the dark at 33ºC for two hours to acclimate before recording. All procedures were performed between 2300 and 0400 during their normal resting phase, to minimize activity. We measured CO2 production using a flow-through respirometry system (Sable Systems, LI-COR). Following the recording of metabolic rate, tubing from each chamber was connected to a differential pressure transducer (Sable Systems), and breathing frequency and tidal (expired breath) volume were recorded. Tidal volumes were calibrated using a syringe to inject known volumes of air into an empty chamber and recording the resulting signal. Volumes approximating the lizards’ expected tidal volume range (from Templeton and Dawson 1963) were used for the calibration. The following day we recorded post-exercise tidal volumes (PETV) by placing an individual in a 3x2x3 plastic tub and encouraging the lizard to run for approximately one minute. Individuals who were reluctant to run were repeated placed on their back to force them to right themselves. These activities were used to induce active, forced breathing. Animals were immediately placed into chambers and tidal volume was recorded as above. PETV was measured at room temperature, which averaged 24.1 ± .12ºC (mean and SEM). Once all respiratory parameters were measured lizards were weighed, scanned with ultrasound imaging to determine reproductive stage (see Gilman and Wolf 2007 for procedures), fed, and returned to their respective cages. 

For analyses, females were placed into one of five categories, based on the size and stage off the eggs (early follicles, late-stage follicles, early egg, shelled egg, post laying). Statistical analyses were performed on non-gravid-mass-specific (when appropriate) values using Kruskal-Wallis and Mann-Whitney non-parametric tests and significance was determined as P<0.05. Tests of significance for CT estimates of lung volumes were performed using 2-sample and paired t-tests and Mann-Whitney non-parametric tests (P<0.05). 

Total Lung Volume:

We used Computed-Tomography (NanoSPECT/CT®) imaging to estimate lung capacity at two points during the reproductive cycle (gravid, post-laying) in four females (two of each species), and one point in the males. Two females and one male from each species were imaged. Individuals were fasted for 48 hours at 30 ºC and placed within cloth bags in a standard lab refrigerator for ~20 minutes and/or freezer for ~5 minutes until cool, to reduce activity. Lizards were then be taped to a cardboard restraint board with surgical tape (about the head body and limbs), to allow respiration but restrict other movement, and placed within a cloth bag on the imaging tray. Lung volume was estimated using the reconstructed CT data (NanoSPECT/CT, Bioscan, Washington, DC) by fitting 3-dimensional volumes to the interior of the lungs. A series of smaller volumes were fitted to the inside of the lungs and then summed to determine an estimate of total volume. Each sub-region spanned 8 slices of the reconstructed CT volume. Within each 8-slice sub-region, the estimation volume was drawn using a sum of the 8 slices as a guide. The region followed the border between the lungs and the body cavity of the subject. The axial length of each region was 3.6 mm (0.4 mm x 8).

Field methods: 

Lizards were hand-caught or noosed and placed in cloth bags for transport to the lab.

Data sources: 

sev211_lizardphys_20130412.txt

Instrumentation: 

* Instrument Name: CO2/H2O analyzer

* Manufacturer: LI-COR Biotechnology, Lincoln, NE

* Model Number: LI-7000

* Instrument Name: Respirometry Multiplexer, Universal Interface, Pressure Meter  

* Manufacturer: Sable Systems, Las Vegas, NV

* Model Number: V2.0, UI2, PT-100B 

*Instrument Name: Omega flowmeters, 

* Manufacturer: Omega Engineering, Inc., Stamford, CT

* Model Number: FL-3402C and FL-3403G

Quality Assurance: 

The range of data values were double-checked.

Reptile Populations at the Sevilleta National Wildlife Refuge, New Mexico (1989-1990)

Abstract: 

Reptile populations were sampled in spring and summer in various habitats: grassland, creosote shrubland, pinyon-juniper woodland, cottonwood forest, subalpine forest, and subalpine meadow. On 18 sites mark-release methods were used; on 12 sites, all animals were kept for museum specimens. Museum specimen preparations included skulls, whole skeletons, and alcohol preservations; all specimens had tissue samples (liver, heart) taken for ultra-cold preservations for genetic analyses; some were karyotyped. All museum specimens were checked for internal parasites.

Data set ID: 

9

Core Areas: 

Additional Project roles: 

52

Keywords: 

Methods: 

Livetrapping of lizards and snakes on the Sevilleta was done by using pitfall traps connected with drift fences.  A pitfall trap consisted of two large ( 10) cans connected end to end resulting in a trap approximately 44 cm deep and 15 cm in diameter.  The traps were inserted into the ground so the tops are flush.  Two pitfalls were placed into the ground approximately 6 meters apart and connected with a 12 cm tall aluminum flashing fence.  The fence guided the reptiles into the pitfall traps.

There were 24 pitfall traps per web (12 sets) totaling 120 per site. Seventy-two of these were for mark and recapture studies, while the remaining 48 werefor the collection of museum specimens.

The pitfalls were covered with aluminum flashing lids that sit approximately 2.5 cm off the ground.  The lids provided complete shade and protection from precipitation.  The trap floors were also punctured to permit drainage if necessary.

The pitfall traps were opened for three weeks at a time, and were checked every two or three days by a crew of two to five.  At the end of the three weeks they were closed by covering the openings with a square ceramic tile, 20 cm per side.  The edges of the tiles were then covered with dirt as an extra safeguard against penetration. All pitfalls were checked for the presence of animals by removing the aluminum lids and visually inspecting each trap's interior.  Lizards found in the traps on the collection webs were removed from the traps, placed in plastic bags with an adequate supply of air, and transported to the lab for processing.  Lizards found in pitfalls on mark-recapture webs were removed by hand, then identified to species level, checked for previous capture and individual identification marks, measured, weighed and sexed.  The lizards were toe-clipped with no more than two toes cut per foot, and the longest toes on the hind feet left intact.

All snakes were identified to species level, and non-venomous snakes were measured and weighed but not marked because so few are captured. Venomous snakes were removed from pitfalls by the head animal technician using a "snake stick" which enabled the user to handle snakes safely without injury to the snake.

All lizards and snakes are released at the exact location of capture.

Data sources: 

sev009_reptilepopn_09072011.txt

Additional information: 

This data set was obtained from the Mac computer of Howard Snell, Asst. Professor at UNM. All data from years 1989 and 1990, were entered by him or his assistants. As 1989 and 1990 data sets were in separate files, they have been merged together as one file in this data set. The format was changed to "rdb" format in order to allow the data set to be used on the Sevilleta system. File begin edit: May 28, Michelle L. Murillo: changing to rdb format.File end edit: May 28, Michelle L. Murillo.

Note: holder, measurer, recorder taken out, can be found on original data sheets.

Pino Gate Prairie Dog Study at the Sevilleta National Wildlife Refuge, New Mexico: Mound-Scale Lizard Data (2000-2002)

Abstract: 

Keystone species have large impacts on community and ecosystem properties, and create important ecological interactions with other species. Prairie dogs (Cynomys spp.) and banner-tailed kangaroo rats (Dipodomys spectabilis) are considered keystone species of grassland ecosystems, and create a mosaic of unique habitats on the landscape. These habitats are known to attract a number of animal species, but little is known about how they affect lizard communities. Our research evaluated the keystone roles of prairie dogs and kangaroo rats on lizards at the Sevilleta National Wildlife Refuge in central New Mexico, USA. We evaluated the impacts of these rodents on lizard communities in areas where prairie dogs and kangaroo rats co-occurred compared to areas where each rodent species occurred alone. Our results demonstrate that prairie dogs and kangaroo rats have keystone-level impacts on these lizard communities. Their burrow systems provided important habitats for multiple lizard species, especially the lesser earless lizard (Holbrookia maculata). At the landscape-scale, the total number of lizards was two-times greater on the where both prairie dogs and banner-tailed kangaroo rats co-occurred than where only kangaroo rats occurred.

Data set ID: 

177

Core Areas: 

Keywords: 

Data sources: 

sev177_pdoglizardmound_01312006.txt

Methods: 

Experimental Design

Mound-scale plots: To evaluate lizards associated with mound disturbance patches and rodent burrow systems, we established replicate mound-scale plots with paired "non-mound" control plots. The mound and non-mound plots were spatially intermixed within each landscape-scale plot. Lizards were sampled around 10 kangaroo rat mounds on the Krat plot, 10 prairie dog and 10 kangaroo rat mounds on the Pdog+Krat plot, and on paired non-mounds located 10 m away from sample mounds, in areas with minimal rodent disturbance.

Sampling Design

Lizards were visually sampled along strip transect lines established through each mound-scale plot. Strip transects on the mound-scale plots measured 1 m x 5 m.

Field Method

Lizards were sampled by walking slowly along each transect. Individuals were counted and identified to species. Lizards were sampled thoughout the spring and summer from spring 2000 through spring 2002.

Additional information: 

Additional Information on the personnel associated with the Data Collection / Data Processing

Field Crew Member: Julie McIntyre

Additional Study Area Information

Study Area Name: Pino Gate

Study Area Location: The study site was located near the base of the Los Pinos mountains and directly adjacent to the nothern fencline of the SNWR at Pino Gate

Elevation: 1600 m

Vegetation: Burrograss (Scleropogon brevifolius), sand dropseed (Sporobolus ryptandrus), and black grama (Bouteloua eriopoda) were the dominant vegetation.

Soils: Deep clayey loam soils

Geology: On an upper bajada slope, in a broad swale

Climate: Long-term mean annual precipitation is 243 mm, about 60% of which occurs during the summer. Long-term mean monthly temperatures for January and July are 1.5°C and 25.1°C, respectively.

Site history: Historically, prairie dogs were common throughout the area, but were exterminated by the early 1970’s (John Ford, United States Department of Agriculture Wildlife Services, personal  communication). Gunnison’s prairie dogs began to re-colonize the study site from adjacent private land in 1998. During our study, the colony occurred within a 5 ha area, near the base of the Los  Piños Mountains in an area with deep clayey loam soils. The site has been long inhabited by kangaroo rats, and represents typical northern Chihuahuan Desert grassland.

North Coordinate:34.406954
South Coordinate:34.406954
East Coordinate:106.606269
West Coordinate:106.606269

Pino Gate Prairie Dog Study at the Sevilleta National Wildlife Refuge, New Mexico: Landscape Plot Lizard Data (2001-2002)

Abstract: 

Keystone species have large impacts on community and ecosystem properties, and create important ecological interactions with other species. Prairie dogs (Cynomys spp.) and banner-tailed kangaroo rats (Dipodomys spectabilis) are considered keystone species of grassland ecosystems, and create a mosaic of unique habitats on the landscape. These habitats are known to attract a number of animal species, but little is known about how they affect lizard communities. Our research evaluated the keystone roles of prairie dogs and kangaroo rats on lizards at the Sevilleta National Wildlife Refuge in central New Mexico, USA. We evaluated the impacts of these rodents on lizard communities in areas where prairie dogs and kangaroo rats co-occurred compared to areas where each rodent species occurred alone. Our results demonstrate that prairie dogs and kangaroo rats have keystone-level impacts on these lizard communities. Their burrow systems provided important habitats for multiple lizard species, especially the lesser earless lizard (Holbrookia maculata). At the landscape-scale, the total number of lizards was two-times greater on the where both prairie dogs and banner-tailed kangaroo rats co-occurred than where only kangaroo rats occurred.

Core Areas: 

Data set ID: 

173

Additional Project roles: 

340
341

Keywords: 

Data sources: 

sev173_pdoglizardplot_01312006.txt

Methods: 

Sampling Design

The landscape-scale plots were 180 m x 180 m. Lizards were visually sampled along strip transect lines established along each gridline of the landscape-scale plots, using a 5 x 5 grid array. Strip transects on the landscape-scale plots measured 1 m x 30 m.

Methods & Experimental Design

Landscape-scale plots: We compared lizards on plots occupied by: 1) both species (Pdog+Krat plot); 2) only kangaroo rats (Krat plot); and 3) both species, but where prairie dogs inhabited one half of the plot and kangaroo rats inhabited the other half (Transition plot).

Field Methods

Lizards were sampled by walking slowly along each transect, and individuals were counted and  identified to species. Lizards were always sampled in the morning between 9:00 - 11:00 am. Lizards were sampled throught the springand summer from spring 2000 through late summer 2002.

Maintenance: 

These metadata were obtained from Ana Davidson in a Word File. The data are in an Excel file that accompanies the metadata. -- KLV 1/31/2006

Additional information: 

Additional Information on the personnel associated with the Data Collection / Data Processing

Field Crew Member: Julie McIntyre

Additional Study Area Information

Study Area Name: Pino Gate

Study Area Location: The study site was located near the base of the Los Pinos mountains and directly adjacent to the nothern fencline of the SNWR at Pino Gate

Elevation: 1600 m

Vegetation: Burrograss (Scleropogon brevifolius), sand dropseed (Sporobolus ryptandrus), and black grama (Bouteloua eriopoda) were the dominant vegetation.

Soils: Deep clayey loam soils

Geology: On an upper bajada slope, in a broad swale

Climate: Long-term mean annual precipitation is 243 mm, about 60% of which occurs during the summer. Long-term mean monthly temperatures for January and July are 1.5°C and 25.1°C, respectively.

Site history: Historically, prairie dogs were common throughout the area, but were exterminated by the early 1970’s (John Ford, United States Department of Agriculture Wildlife Services, personal  communication). Gunnison’s prairie dogs began to re-colonize the study site from adjacent private land in 1998. During our study, the colony occurred within a 5 ha area, near the base of the Los  Piños Mountains in an area with deep clayey loam soils. The site has been long inhabited by kangaroo rats, and represents typical northern Chihuahuan Desert grassland.

North Coordinate:34.406954
South Coordinate:34.406954
East Coordinate:106.606269
West Coordinate:106.606269

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