A population is a group of organisms of the same species. Like canaries in the coalmine, changes in populations of organisms can be important indicators of environmental changes.

Pollinator Survey in Creosote Shrubland at the Sevilleta National Wildlife Refuge, New Mexico


Larrea tridentata (Creosote Shrub) is a generalist plant that provides floral resources in the form of nectar and pollen to a wide variety of bee species. The aim of this study is to evaluate the extent of this interaction at the Sevilleta Creosote Shrubland. Specifically, bee individuals directly interacting with L. tridentata were captured in order to give an accurate description of the number of species dependent on Creosote for resources. 

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Rabbit Population Densities at the Sevilleta National Wildlife Refuge, New Mexico (1992-2004)


This study measured the population dynamics of black-tail jackrabbits (Lepus californicus) and desert cottontail rabbits (Sylvilagus auduboni) in the grasslands and creosote shrublands of McKenzie Flats, Sevilleta National Wildlife Refuge.  The study was begun in January, 1992, and continued quarterly each year.  Rabbits were sampled via night-time spotlight transect sampling along the roads of McKenzie Flats during winter, spring, summer, and fall of each year.  The entire road transect was 21.5 miles in length. Measurements of perpendicular distance of each rabbit from the center of the road were used to estimate densities (number of rabbits per square kilometer) via Program DISTANCE.  Results from 1992 to 2002 indicated that spring was the peak density period of the year, with generally steady declines through the year until the following spring. Evidence of a long-term "cycle" (e.g., the 11 year cycle reported for rabbits in the Great Basin Desert) did not appear in the Sevilleta rabbit populations.

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The purpose of the study was to assess the dynamics of rabbit populations in the grasslands and creosote shrublands of the Sevilleta NWR.  Rabbits are important herbivores in these habitats, and can influence NPP and plant species composition.  In turn, these animals also provide high-quality prey for many of the Sevilleta's mammal and reptile carnivores and birds of prey.  Density data on rabbits can be used to calculate herbivore pressure on the plant communities.

Data sources: 



When the samples were collected: The samples were collected in winter, spring, summer, and fall, of each year.  Rabbit populations were sampled during a single night during each of these four seasons per year.  Dates of collection varied in some years, but generally the sampling was conducted in January, April, July, and October.

Sampling Design: The rabbits were sampled along 21.5 miles of roadway that was broken up into four "legs" of varying lengths.

Leg A:  Black Butte southward to Five Points (5.7 miles).

Leg B:  Five Points eastward to the turnoff before Palo Duro Canyon (4.1 miles).

Leg C:  Palo Duro turnoff northward to the old McKenzie Headquarters site (6.1 miles).

Leg D:  McKenzie Headquarters site northwestward to Black Butte (5.6 miles).

Measurement Techniques: The rabbit surveys were conducted at night using spotlights. Surveys began one hour after sunset, when no trace of sunlight or dusk remained.  Beginning in 1998, samples were taken only during full-moon periods. A pickup truck was driven slowly (8-10 miles per hour) along the road of the 21.5 mile circuit.  Two (or more) observers stood in the bed of the pickup truck, and scanned the left and right sides (respectively) of the road with spotlights, while the driver kept watch for rabbits directly in front in the road.  During 1992, the spotlights were Q-Beam 500,000 candlepower spotting lights, with both flood and spot settings (spot settings were used during the rabbit sampling).  From 1993 through 1996, Q-Beam spotlights with 1,000,000 candlepower were used.  In 1997, new spotlights with 3,000,000 candlepower were used; these lights were set permanently on "flood", but illuminated well at distances previously reached by the spot settings of the less-powerful spotlights.  

In addition to the spotlights used by the standing observers in the bed of the pickup truck, two spotlights mounted on the pillar posts of the truck's cab were turned on and set for the roadsides ahead of the truck; these lights, coupled with the high-beam setting of the truck's headlights, illuminated the road in front of the truck for approximately 100 meters. When a rabbit was observed, one person's spotlight illuminated the spot at which the rabbit was first seen.  The second person's spotlight would track the rabbit, so that it was not counted twice.  A meter tape was walked out from the center of the truck bed (which equalled the center of the road) in a perpendicular direction from the road to the location at which the rabbit was first observed.  That distance was measured and recorded to the nearest meter.

If a rabbit was observed in the middle of the road, the distance was recorded as zero.  Beginning in January, 2000, perpendicular distances to the rabbits were taken with a laser range finder, with accuracies of less than 1 meter (accuracies were tested before field use and confirmed to be <1m).  Generally, rabbits within 100 meters of the road could be seen relatively clearly with all three types of spotlights. Other data recorded included (1) the odometer reading in miles from the beginning of the sample at Black Butte (odometers were reset to zero at the start of the sample), (2) whether the rabbit was on the Left or Right side of the road, and (3) the species of rabbit.  In addition, incidental data were recorded on weather conditions, presence of clouds and moon, and the time at which the survey was begun, along with the times at which each Leg was begun and finished.  Finally, the names of the people on the sampling crew were recorded.

Analytical Procedures: The perpendicular distance data were entered into Program DISTANCE to estimate the total density of rabbits in the study area. Values were computed as numbers of individuals per square kilometer In the analyses, if there were sufficient numbers of rabbits (>10 per leg), the difference legs were analyzed separately, and the resulting mean densities were estimated by averaging the four leg estimates.  In the results tables below, these instances are indicated by the category, "MEAN".  If sample sizes were too small to estimate the four legs separately, then all the rabbit observations were pooled together, and a density estimate for the entire 21.5 mile survey was calculated. These results are indicated by the category, "ALL".

Quality Assurance: 

The program DISTANCE command codes were as follows:











Stratum/label='DATE ENTERED HERE';






Est /key=uniform /adj=cosine  /select=sequential /criterion=AIC /monotone=weak;

Est /key=uniform /adj=hermite /select=sequential /criterion=AIC /monotone=weak;

Est /key=hnormal /adj=cosine  /select=sequential /criterion=AIC /monotone=weak;

Est /key=hnormal /adj=hermite /select=sequential /criterion=AIC /monotone=weak;


Density by sample;


Effects of Multiple Resource Additions on Community and Ecosystem Processes: NutNet Seasonal Biomass and Seasonal and Annual NPP Data at the Sevilleta National Wildlife Refuge, New Mexico (2008 - present)


Two of the most pervasive human impacts on ecosystems are alteration of global nutrient budgets and changes in the abundance and identity of consumers. Fossil fuel combustion and agricultural fertilization have doubled and quintupled, respectively, global pools of nitrogen and phosphorus relative to pre-industrial levels. In spite of the global impacts of these human activities, there have been no globally coordinated experiments to quantify the general impacts on ecological systems. This experiment seeks to determine how nutrient availability controls plant biomass, diversity, and species composition in a desert grassland. This has important implications for understanding how future atmospheric deposition of nutrients (N, S, Ca, K) might affect community and ecosystem-level responses. This study is part of a larger coordinated research network that includes more than 40 grassland sites around the world. By using a standardized experimental setup that is consistent across all study sites, we are addressing the questions of whether diversity and productivity are co-limited by multiple nutrients and if so, whether these trends are predictable on a global scale.

Above-ground net primary production is the change in plant biomass, represented by stems, flowers, fruit and and foliage, over time and incoporates growth as well as loss to death and decomposition. To measure this change the vegetation variables, including species composition and the cover and height of individuals, are sampled twice yearly (spring and fall) at permanent 1m x 1m plots within each site. Volumetric measurements are made using vegetation data from permanent plots (SEV231, "Effects of Multiple Resource Additions on Community and Ecosystem Processes: NutNet NPP Quadrat Sampling") and regressions correlating species biomass and volume constructed using seasonal harvest weights from SEV157, "Net Primary Productivity (NPP) Weight Data."

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Data Processing Techniques to Derive Biomass and NPP:

Data from SEV231 and SEV157 are used used to calculate seasonal and annual production of each species in each quadrat for a given year. Allometric equations derived from harvested samples of each species for each season are applied to the measured cover, height, and count of each species in each quadrat. This provides seasonal biomass for winter, spring, and fall.

Seasonal NPP is derived by subtracting the previous season's biomass from the biomass for the current season. For example, spring NPP is calculated by subtracting the winter weight from the spring weight for each species in a given quadrat. Negative differences are considered to be 0. Likewise, fall production is computed by subtracting spring biomass from fall biomass. Annual biomass is taken as the sum of spring and fall NPP.

Additional information: 

Additional Information on the Data Collection Period

Species composition and net primary production was sampled semiannually (spring and fall) in 2007, 2008, and 2009. Soil was sampled and analyzed in the fall in 2007 and 2008. Plots were fertilized annually starting in 2008.

In August 2009, a wildfire burned all 40 of the NutNet plots causing no Fall 2009 vegetation measurements.

Special Codes for Vegetation Ids:

SPORSP- Unknown Sporobolus

SPSP- Unknown Sphaeralcea

UNKFO- Unknown Forb

Gunnison's Prairie Dog Restoration Experiment (GPDREx): Small Mammal Mark-Recapture Population Assessment within Grasslands at the Sevilleta National Widlife Refuge, New Mexico (2013-2014)


Prairie dogs (Cynomys spp.) are burrowing rodents considered to be ecosystem engineers and keystone species of the central grasslands of North America. Yet, prairie dog populations have declined by an estimated 98% throughout their historic range. This dramatic decline has resulted in the widespread loss of their important ecological role throughout this grassland system. The 92,060 ha Sevilleta NWR in central New Mexico includes more than 54,000 ha of native grassland. Gunnison’s prairie dogs (C. gunnisoni) were reported to occupy ~15,000 ha of what is now the SNWR during the 1960’s, prior to their systematic eradication. In 2010, we collaborated with local agencies and conservation organizations to restore the functional role of prairie dogs to the grassland system. Gunnison’s prairie dogs were reintroduced to a site that was occupied by prairie dogs 40 years ago.  This work is part of a larger, long-term study where we are studying the ecological effects of prairie dogs as they re-colonize the grassland ecosystem. With this project, we would like to further investigate the impact that Gunnison’s prairie dogs have on the landscape.  Gunnison’s prairie dog monitoring data has been collected from the beginning of the reintroduction project, but little information has been collected on how grassland species respond to the sudden presence of prairie dogs on the refuge.

This project will help determine if the prairie dog reintroduction has had positive impacts on the grassland ecosystem.  Prairie dogs benefit grasslands in many ways, but their role as ecosystem engineers directly impacts other species by creating new habitat that would not be present without prairie dogs.  We have documented physical landscape changes, but we have not specifically documented benefits to other grassland species.  This work will help determine if the reintroduced prairie dog populations on Sevilleta NWR are now acting as a keystone species in a grassland ecosystem by monitoring small mammal populations to see if species richness, diversity, and density are different on prairie dog colonized areas versus non-colonized areas.

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Trapping Location and Design:

Trapping will be done on the 16ha Prairie Dog Relocation Study Plots.  There are 4 of them- A, B, C, and D.  Each plot will have 169 traps placed in a grid covering 9 hectares. Using the vegetation quad map, there will be a trap placed at 1 meter to the north at each of the following vegetation plots 11-17, 20-26, 29-35, 38-44, 47-53, 56-62, 65-71.  This accounts for 49 of the traps.  There will also be a trap placed in between each veg plot, with rows running North/South, which accounts for 42 more of the traps.  Then making a complete row in between the North/South vegetation quad rows, will account for the remaining 78 traps. To locate the veg plots, each are marked with a rebar and short white PVC.  There is a numbered tag on each PVC corresponding to the map.

Flag each trap with a numbered pin flag to designate trap numbers.   This is important in ensuring that all traps are checked and closed each day.

Trapping Periods:

Trapping period will be one plot a week for 4 nights.

Trapping Procedure:

The traps are set each evening for four nights.  This entails setting and baiting the traps at a given locality on Monday afternoon, then checking the traps at dawn on Tuesday (night 1), Wednesday (night 2), Thursday (night 3), and Friday (night 4). Each trap is baited with a handful of steamed, crimped oats tossed into the trap after it is placed on the ground; a few oats are left outside the trap entrance to entice passers-by.  The ground needs to be smoothed out with a foot to make sure that the trap is level and not unbalanced.  

Each morning, traps are checked as follows:  the worker walks up and down the transects and closes open traps as you go along.  Traps are not reopened until the late afternoon/early evening, at which time additional bait is also put in.  When a closed trap is encountered, it is first checked to see if an animal is present by carefully and just slightly opening the door of the trap and looking inside.  Be aware that kangaroo rats can jump out while doing this, so use caution. Sometimes, although a trap may appear empty, a tiny rodent may be hiding under the treadle (especially in the large traps).  To check for this, one must reach into the trap and lightly push down the treadle.  If the treadle will not go down, there is likely a mouse underneath.  If no animal is in the trap, the trap is left closed until the afternoon. If a trap has an animal, the worker processes the animal at the stake and takes the relevant data.  While checking for animals on Friday morning (night four), traps are picked up, emptied of seed, and returned to storage boxes, ready for placement at another locality the following week.  Importantly, traps MUST BE counted as they are placed into storage boxes in order to insure that no traps (or animals) are left on the plot.  If rain falls on the baited traps, they may require cleaning and drying back at the field station before storage or use the following week.

Animal Processing:

Removing rodents from trap

For each capture, the trap number is recorded first.  Next, a given animal is shaken from the trap into a plastic gallon ziploc bag.  This is accomplished by wrapping the opening of the ziploc bag over the door end of the trap. Make sure that they bag is tight so the rodent can’t squeeze out between the bag and the trap.  Open the front door through the bag and lock open.  Roll the trap upside down and swing it in an arc downward.  As soon at the rodent enters the bag, close the bag off with your hand so the rodent cannot reenter the trap.  With kangaroo rats, you often do not need to shake the trap to get the animals out.  Instead, put the Ziploc bag on trap as normal and open trap door, but hold the trap angled upward instead of down and the rodent should come out on its own.  Hold tight on the bag though because sometimes they come out rather quickly.

If a trap is triggered, but appears empty, don’t assume there is no animal in trap.  Small species such as pocket mice can hide under the treadle.  Make sure and lightly press down on the treadle to make sure it goes all of the way down.  If not then there is most likely a rodent under treadle.  You can also open up the back door to look under treadle, but use caution as to not let rodent escape.

If another animal (lizard, bird, rabbit, prairie dog) is caught in the trap, they can simply be released.  However, make sure and mark on data sheet that the trap was closed due to bird/lizard/rabbit.  If you do find a trap that was triggered by wind or large animal and is in fact empty, make sure and mark on the datasheet that that trap number was triggered but empty.

Handling and Processing rodents

In the bag, the processor positions the rodent with its head in the corner of the bag.  Hold its head down with one hand from the outside of the bag, pressing gently on the back of the skull.  Then reach in the bag with the other hand and grasp the animal with the thumb and forefingers by the loose skin around the back of the neck and shoulders, and then remove it for inspection. 

First off check to see if the rodent is tagged or marked.  If it is then you will mark that individual as a recapture on data sheet.  After recording the ear tag number or other marking and the species of animal, it can be released.  If it is not marked, then it will need to be marked and processed.

Dipodomys spp, Onychomys spp, Neotoma spp, Peromyscus spp, and any other large species you may catch will be uniquely marked with one ear tag.  Ear tags should be placed at the very base of the ear on its interior edge (or the front of the ear).  Putting it on the external side or back of the ear allows the rodent to rip the ear tag off more easily, by scratching at it with its hind legs. 

Other species such as, Perognathus spp, Spermophilus spp, and other small rodents that have too small of ears to place an ear tag, will be marked with sequential individual numbers on their chest, using permanent markers.  A different color must be used for each night (blue for 1st night, black for 2nd night, and red for 3rd night).  Small rodents do not need to be marked the 4th night,  but large rodents do need to be ear tagged.  Start with number 1 and increase as necessary for catches.

Next, each animal is identified to species, sexed, and aged.  Specific measurements are taken only for those genera which required them for species identification:

            Peromyscus: Total length, tail, foot, ear;

            Onychomys:  Total length, tail, foot.

            Perognathus, and Reithrodontomys: Total length, tail.

All measurements are taken to the nearest millimeter using a plastic ruler.  The species is recorded by a 4-letter code that represents the first 2 letters of the genus and the first 2 letters of the species.

Sex and reproductive status is then determined by examination of the genitalia (lactating/vaginal/pregnant/scrotal).  Look for enlarged scrotum, enlarged nipples, or an enlarged vaginal opening.  If none of these are apparent, then the rodent is non-reproductive. Females will still have visible nipples when non-reproductive.

ADULT MALES reproductive status:

-Scrotal (ST): the scrotum can be fully enlarged or partially enlarged.

- Non-reproductive (N)

ADULT FEMALES reproductive status:

-Vaginal (V): in estrus; vagina is obviously swollen and looks large and puckered, vaginal plug can be present or absent

-Pregnant (P):  heavier weight, can palpate babies

-Lactating (L): nipples (at least one) reddish and/or enlarged

-Non-reproductive (N)

Before releasing the individual, it is then weighed to the nearest gram, using a Pesola scale clipped to the base of the animal’s tail.   Larger animals can easily get off of scale so it is easier to put them back in the bag and weigh them inside the bag.  Make sure and weigh bag after rodent is released and subtract from first weight to get actual weight of rodent.

Animals which perished during captivity on plots are noted in the comments on field data sheets as 'D.I.T' (Dead In Trap).

Data sources: 


Additional information: 

This data is collected each summer, starting in 2013, by an student in the Sevilleta LTER Research Experience for Undergraduates Summer Program.  Ear tagging started taking place in the summer of 2014.

Data Collector History

Ty Werdel 2013

Betsy Black & Andrew Velselka 2014

Gunnison's Prairie Dog Restoration Experiment (GPDREx): Population Dynamics within Grasslands at the Sevilleta National Widlife Refuge, New Mexico


Prairie dogs (Cynomys spp.) are burrowing rodents considered to be ecosystem engineers and keystone species of the central grasslands of North America. Yet, prairie dog populations have declined by an estimated 98% throughout their historic range. This dramatic decline has resulted in the widespread loss of their important ecological role throughout this grassland system. The 92,060 ha Sevilleta NWR in central New Mexico includes more than 54,000 ha of native grassland. Gunnison’s prairie dogs (C. gunnisoni) were reported to occupy ~15,000 ha of what is now the SNWR during the 1960’s, prior to their systematic eradication. In 2010, we collaborated with local agencies and conservation organizations to restore the functional role of prairie dogs to the grassland system. Gunnison’s prairie dogs were reintroduced to a site that was occupied by prairie dogs 40 years ago.  This work is part of a larger, long-term study where we are studying the ecological effects of prairie dogs as they re-colonize the grassland ecosystem.

Data set ID: 


Additional Project roles: 


Core Areas: 



Experimental Design

Four replicate paired 16 ha plots were established in spring 2010. Each pair consists of a treatment plot with prairie dogs (reintroduced), which are plots B and D and a control plot with no prairie dogs (plots A and C). The closest distance between adjacent plots, either within a block or between blocks, is 200 m (Figure 1). The treatment and control within each pair were randomly assigned. Each plot is a 400x400 m on 9x9 grid array with systematically located sample locations for 81 vegetation quadrats. There are also 4 more plots, E and H are control plots and F and G are treatment plots. F and G have been equipped with artificial burrows and are release sites. However, E and H were not set up to do vegetation quads.

Trapping Period

Prairie dogs will be sampled using capture-recapture methods in the summer (3rd week of June) each year and spring (last week of March) and fall when possible.

Pre-baiting Procedure

Set 150 traps within each 300m x 300m trapping area. Place traps in pairs near active burrows at least 4 days prior to trapping. At this time trap doors should be wired open (make certain all traps are properly wired open) with bait trailing from the outside into the back of (or through) the trap. Traps should be baited with sweet feed. Make sure that all traps are functioning properly by testing the trap door sensitivity and adjusting with pliers if needed. Pre-bait traps every morning for 3 days total. All pairs of traps should be numbered with one pin flag for each pair (1-75). All trap pairs should also be GPSed by their number and have maps made for ease of locating traps during trapping.

Trapping Procedures

On the morning of the first trapping day, well before sunrise, the wire should be removed from the traps and the traps then set and baited to capture animals. This can also be done the day before trapping begins. Prairie dogs should be trapped for 3 consecutive mornings.Each morning of trapping, make sure that the traps are all opened well before sunrise, so animals are not disturbed by human activity. This is very important. Traps should only be left opened during the early morning period, until about 10:00 or 11:00 am, depending on the weather conditions and time of year. Prairie dog activity declines by 10:00-11:00, so even if the weather conditions are fine for continued trapping, trap success after this time will decline. Traps should be collected by around 9:00 am, depending on the weather conditions and time of year, and all trapped animals should be brought to a common processing station. The team walks the plot to make sure and check every trap for dogs. As dogs are found trapped, a piece of masking tape is attached to the front of the trap, labeled with the trap number so that that animal can be released where it was trapped. Animals at the processing site should be kept at all times in the shade and carrots should be given to provide moisture during the heat and stress. Once animals have been processed they should be released into their burrow, at the location of their capture. All traps should then be closed for the day. To make sure all are closed, one person should close all the traps from one of the plots and mark the number on the GPS sheet to note the trap has been closed. This can also be done as a team effort, but traps need to be checked twice to make sure they are all closed.

Data sources: 


The Sevilleta Gunnison’s Prairie Dog (Cynomys gunnisoni) Relocation project examines keystone consumer (herbivore) effects on grassland in concert with ecological restoration of a “species of greatest conservation need in New Mexico” (NMG&F Comprehensive Wildlife Conservation Strategy, 2007).

Gunnison's Prairie Dog Restoration Experiment (GPDREx): Vegetation Cover Data from the Sevilleta National Wildlife Refuge, New Mexico (2011 - present)


Prairie dogs (Cynomys spp.) are burrowing rodents considered to be ecosystem engineers and keystone species of the central grasslands of North America. Yet, prairie dog populations have declined by an estimated 98% throughout their historic range. This dramatic decline has resulted in the widespread loss of their important ecological role throughout this grassland system. The 92,060 ha Sevilleta NWR in central New Mexico includes more than 54,000 ha of native grassland. Gunnison’s prairie dogs (C. gunnisoni) were reported to occupy ~15,000 ha of what is now the SNWR during the 1960’s, prior to their systematic eradication. In 2010, we collaborated with local agencies and conservation organizations to restore the functional role of prairie dogs to the grassland system. Gunnison’s prairie dogs were reintroduced to a site that was occupied by prairie dogs 40 years ago.  This work is part of a larger, long-term study where we are studying the ecological effects of prairie dogs as they re-colonize the grassland ecosystem.

Data set ID: 


Core Areas: 

Additional Project roles: 




Experimental Design

Two replicate paired 16 ha plots were established in spring 2010. Each pair consists of a treatment plot with prairie dogs (reintroduced), which are plots B and D and a control plot with no prairie dogs (plots A and C).  There are 4 other plots (E,F,G, and H) but they are not set up to do vegetation sampling. 

Sampling Periods

 Baseline vegetation sampling occurred at the end of April 2010. A second sampling was done at the end of September 2011.  There was no other vegetation sampling until September 2013, at which time it will be collected consistently every spring and fall. 

Field Procedures 

Percent live plant canopy cover and height of live foliage of all plant species are measured using 0.25 m2 vegetation sampling quadrats at the end of the growing season each spring (late April) and late summer (early September).  The 50x50 cm vegetation measurement frame has a string grid which partitions the frame into 25, 10x10 cm squares. One quarter of a 10x10 cm grid cell equals 1% cover. Therefore each 10x10 cm cell has a 4% cover value. Vegetation measurements range from 0.1 to 100%. A cover of 0.1 represents a plant species trace occurrence on the quad. The next smallest measurement is 1%, or ¼ of a 10x10 cm grid cell. Cover is measured to the nearest 1% for 1-10% cover and to the nearest 5% for 10-100% cover. Total cover for a particular plant species is measured by counting the number of 10x10 cm cells occupied by the foliage canopy, multiplying that value by 4 and rounding to the nearest 5% for total cover greater than 10%. Typical maximum plant canopy height for each species is also measured to the nearest centimeter.

Data sources: 


Additional information: 

More information about who is involved with the samples/data:

Terri Koontz 2010

Amaris Swann 2011

John Mulhouse 2011

Stephanie Baker 2011-present

Megan McClung 2013-present

Chandra Tucker 2014-present

Study Site Information: 

The SevLTER Prairie Dog Project 16 ha study plots are located east of the Blue Grama Core site at the foothill of the Los Pinos Mountains and along Test Well Road. It is a grassland dominated by blue grama grass, with associated grass species consisting of black grama, galleta, purple three-awn, sand muhly, and dropseed. Yucca and Cholla cactus are the dominant shrubs at the site.

Water Potential Data From Pinyon-Juniper Forest at Sevilleta National Wildlife Refuge, New Mexico


This dataset consists of profiles of soil water potential measured via in situ thermocouple psychrometers located within a rainfall manipulation experiment in a piñon-juniper woodland. The sensors are centrally located within 40 m x 40 m water addition, water removal, infrastructure control, and ambient control plots. The profiles are installed under each of ten target piñon and juniper trees (five of each species) which were also used for other physiological measurements, as well as at five intercanopy areas. The raw sensor output (in μV) has been temperature-corrected and individual calibration equations applied.

Background: This sensor array is part of a larger experiment investigating the mechanisms of drought-related mortality in the piñon-juniper woodland. Briefly, one hypothesis is that, during periods of extended, very-negative, soil water potential (“drought”) trees experience xylem tensions greater than their threshold for cavitation, lose their hydraulic connection to the soil, dessicate and die. A second hypothesis is that in order to avoid this hydraulic failure, trees restrict water loss via reduction in stomatal conductance which also limits the diffusion of CO2 for photosynthesis, and eventually may starve to death depending on the drought duration. 

The goal of the project is to apply drought stress on an area significantly larger than the scale of individual trees to determine whether hydraulic failure or carbon starvation is a more likely mechanism for mortality under drought conditions. The cover control treatment replicates the microenvironment created under the plastic rainfall removal troughs (slightly elevated soil and air temperatures and relative humidity) without removing ambient precipitation. The water addition treatment is intended to simulate 150% of the 30-yr average rainfall via n = 6 19-mm super-canopy applications during the growing season (April-October). More details on the experiment can be found in Pangle et al. 2012 Ecosphere 3(4) 28 (http://dx.doi.org/10.1890/ES11-00369.1). These three treatments, in addition to an ambient control with no infrastructure, are applied to three replicated blocks, one on relatively level terrain, one on a southeast-facing slope, and one on a north-facing slope. The soil psychrometers were installed in the southeast-facing block only, to measure the effectiveness of the treatments on plant-available soil moisture.

For the purposes of comparing soil water potential under various cover types (piñon, juniper, intercanopy), it should be noted that significant tree mortality has occurred on Plot 10. As described below, on 5 August 2008 the site was struck by lightening and many of the soil psychrometers were rendered inoperable. At approximately the same time, four of the five target piñon trees in the southeast-facing drought plot (Plot 10) started browning and it was discovered that they had bark beetle (Ips confusus) galleries and were infected with Ophiostoma fungi. By October 2008 those trees (T1, T2, T4, and T5) had dropped all their needles. Therefore the psychrometers buried under them were no longer located “under trees” after that time. By June 2009 the remaining target piñon (T3) died. By March 2010, one of the target juniper trees (T10) had died. At the time of this writing (April 2011) it is anticipated that more of the juniper trees on P10 will die during this year. 

Data set ID: 


Additional Project roles: 


Core Areas: 



Methods:  Within Plots 9-12 of the larger PJ rainfall manipulation experiment, thermocouple psychrometers (Wescor Inc., Logan, UT, USA) were installed. Soil psychrometers profiles were placed under each of the initial ten target trees in each plot, and at the same five intercanopy areas that were instrumented to measure soil and air temperature and soil volumetric water at 5 cm depth. Each profile consisted of sensors at (1) 15 cm; (20) cm; and (3) as deep as could be augered and installed by hand, generally 50-100 cm depth. Sensors were calibrated with four NaCl solutions of known water potential before field deployment.

Sensors are controlled via a Campbell Scientific CR-7 datalogger (Campbell Scientific, Logan, UT, USA). The datalogger takes measurements every 3 h but soil water potential does not change that fast and the daytime measurements are generally unusable because of thermal gradients between the datalogger and the sensors, therefore the data presented here are only the 3:00 AM timepoints.

Note that on 5 August 2008 the site was struck by lightening. Many of the soil psychrometers were destroyed by ground current, with the worst damage on the drought and cover control plots where the metal support posts for the infrastructure may have helped to propagate ground current. Some of those sensors were eventually replaced but in the case of the infrastructure plots we were limited to installing new sensors between the plastic troughs because it was impossible to auger under the plastic. Therefore, while the original installation was random with regard to the pattern of plastic domes and troughs, the replacement installation was exclusively outside the plastic and the data may therefore be biased towards wetter microsites.


Instrument Name: thermocouple psychrometer with stainless steel screen

Manufacturer: Wescor, Inc, Logan, UT, USA

Model Number: PST-55

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


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.

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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).

Fungal Thermophile Survey at the Sevilleta National Wildlife Refuge, New Mexico


Biological soil crusts (BSCs) are complex assemblages of fungi, lichens, bacteria, mosses and green algae that stabilize surface soils and manage and traffic photosynthate, nutrients and water to diverse microbial and producer communities in arid environments worldwide.  In Sevilleta grasslands, BSCs occupy much of the open space between clumps of vegetation and vary substantially in terms of structure. 

BSCs have important biological and physical roles.  They have been termed ‘mantles of fertility’ because of their general importance in biogeochemical cycling and net primary production in arid ecosystems.  It has been proposed that BSCs play a role in the rapid movement of N, C and water from open areas to plants (see below).  BSCs stabilize soils, and physical and chemical disturbances of BSCs lead to topsoil loss and dust storms.  BSCs are therefore critical components in efforts to understand implications of both climate change and physical disturbance.  Related to this, it has been suggested that BSC diversity can be used to inform conservation policies.

BSCs have been the subject of several previous Sevilleta LTER studies.  Green et al. showed that stable-isotope carbon and nitrogen could be transferred bi-directionally between BSCs and adjacent plants.  This led Collins et al. to propose that fungal hyphae provide connections between plant roots and BSCs that allow for transport between the two, a proposal known as the “fungal loop hypothesis.”  Porras-Alfaro et al. have surveyed the diversity of fungi in BSCs from Sevilleta grasslands using molecular methods.  We have also shown that thermophilic fungi are common in BSCs (unpublished results), a result that is not unexpected given the high summer temperatures attained in Sevilleta surface soils.  Yet, many questions remain regarding the organisms present in BSCs, their biological roles and how long it takes for BSCs to re-establish after disturbance.  Long-term, we are interested in the types of fungi present in BSCs and in how fungi function in transporting nutrients between BSCs and adjacent plants.  We are also interested in the extent to which specific fungi provide structure to BSCs and in how they help protect from stress agents such as desiccation.  We are interested in the extent to which fungi might help BSCs tolerate high summer soil temperatures, which often reach ≥ 60C.  We therefore have a special interest in thermophilic fungi present in the BSCs.  To date, little has been done to actually culture fungi from Sevilleta BSCs, hence the need for the current study.  

In summary, BSCs are one of the most important features of aridland ecosystems and form a critical interface between physical and biological domains.  Understanding the roles of BSCs in protecting soil structure, and in the cycling of carbon, water and nitrogen, is fundamental to aridland ecology.  The work proposed here continues efforts to characterize the specific fungi associated with Sevilleta BSCs.  It is a modest but important step toward addressing the long-term goals mentioned above.

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For each sampling site and sampling period a small amount of surface crust (approx. one teaspoon per sample) was taken from each of 10 locations at approximately 1 meter intervals across a transect.  Samples were transported back to the laboratory in plastic bags.

On rare occasions, a larger sample of 0.5 liter volume or less may have been removed at one or two sampling stations.

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Data was collected at: LTER PJ site (N 34 23’ 08.7” W 106 31’ 27.0”), a sand dune above the railroad tracks near the Sevilleta wetlands (N34 18' 06.5"  W106 51' 14.1"), gypsum outcroppings (N34 12' 40.5"  W106 45' 35.5"), grasslands near the Sev LTER warming and monsoon sites (N34 21' 34.3" W106 41' 29.4" and N34 20' 38.1"  W106 43' 34.5"), and the Rio Grande Bosque (N34 19'45" W106 51'40").



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