species interactions

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

Abstract: 

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. 

Core Areas: 

Data set ID: 

296

Keywords: 

Data sources: 

sev296_beesurvey_20150304.csv

Core Site Grid Seasonal Biomass and Seasonal and Annual NPP Data at the Sevilleta National Wildlife Refuge, New Mexico (2013 - present)

Abstract: 

Begun in spring 2013, this project is part of a long-term study at the Sevilleta LTER measuring net primary production (NPP) across three distinct ecosystems: creosote-dominant shrubland (Site C), black grama-dominant grassland (Site G), and blue grama-dominant grassland (Site B). Net primary production is a fundamental ecological variable that quantifies rates of carbon consumption and fixation. Estimates of NPP are important in understanding energy flow at a community level as well as spatial and temporal responses to a range of ecological processes.

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 in this dataset, 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. A third sampling at Site C is performed in the winter. Volumetric measurements are made using vegetation data from permanent plots (SEV289, "Core Site Grid Quadrat Data for the Net Primary Production Study") and regressions correlating species biomass and volume constructed using seasonal harvest weights from SEV157, "Net Primary Productivity (NPP) Weight Data."

Data set ID: 

291

Core Areas: 

Additional Project roles: 

433
434
435
436

Keywords: 

Methods: 

Data Processing Techniques to Derive Biomass and NPP:

Data from SEV289 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.

Data sources: 

sev291_coregridbiomass_20150818

Additional information: 

Other researchers involved with collecting samples/data: Chandra Tucker (CAT; 04/2014-present), Megan McClung (MAM; 04/2013-present), Stephanie Baker (SRB; 2013-present), John Mulhouse (JMM; 2013).

Pinon-Juniper (Core Site) Seasonal Biomass and Seasonal and Annual NPP Data for the Net Primary Production Study at the Sevilleta National Wildlife Refuge, New Mexico (2003-present)

Abstract: 

This dataset contains pinon-juniper woodland biomass data and is part of a long-term study at the Sevilleta LTER measuring net primary production (NPP) across four distinct ecosystems: creosote-dominant shrubland (Site C, est. winter 1999), black grama-dominant grassland (Site G, est. winter 1999), blue grama-dominant grassland (Site B, est. winter 2002), and pinon-juniper woodland (Site P, est. winter 2003). Net primary production is a fundamental ecological variable that quantifies rates of carbon consumption and fixation. Estimates of NPP are important in understanding energy flow at a community level as well as spatial and temporal responses to a range of ecological processes.

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 in this dataset, 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. A third sampling at Site C is performed in the winter. Volumetric measurements are made using vegetation data from permanent plots (SEV278, "Pinon-Juniper (Core Site) Quadrat Data for the Net Primary Production Study") and regressions correlating species biomass and volume constructed using seasonal harvest weights from SEV157, "Net Primary Productivity (NPP) Weight Data."

Data set ID: 

290

Core Areas: 

Additional Project roles: 

482
483
484
485

Keywords: 

Methods: 

Data Processing Techniques to Derive Biomass and NPP:

Data from SEV278 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.

Data sources: 

289_npppinjbiomass_20150824

Additional information: 

Other researchers involved with collecting samples/data: Chandra Tucker (CAT; 04/2014-present),  Megan McClung (MAM; 04/2013-present), Stephanie Baker (SRB; 10/2010-present), John Mulhouse (JMM; 08/2009-06/2013), Amaris Swann (ALS; 08/2008-present), Maya Kapoor (MLK; 08/2003 - 01/2005, 05/2010 - 03/2011), Terri Koontz (TLK; 02/2000 - 08/2003, 08/2006 - 08/2010), Yang Xia (YX; 01/2005 - 03/2010), Karen Wetherill (KRW; 02/2000 - 08/2009);  Michell Thomey (MLT; 09/2005 - 08/2008), Heather Simpson (HLS; 08/2000 - 08/2002), Chris Roberts (CR; 09/2001- 08/2002), Shana Penington (SBP; 01/2000 - 08/2000), Seth Munson (SMM; 09/2002 - 06/2004), Jay McLeod (JRM; 01/2006 - 08/2006); Caleb Hickman (CRH; 09/2002 - 11/2004), Charity Hall (CLH; 01/2005 -  01/2006), Tessa Edelen (MTE, 08/2004 - 08/2005).

Mega-Monsoon Experiment (MegaME) Vegetation Sampling Data from the Sevilleta National Wildlife Refuge, New Mexico (2014 - present)

Abstract: 

Shrub encroachment is a global phenomenon. Both the causes and consequences of shrub encroachment vary regionally and globally. In the southwestern US a common native C3 shrub species, creosotebush, has invaded millions of hectares of arid and semi-arid C4-dominated grassland. At the Sevilleta LTER site, it appears that the grassland-shrubland ecotone is relatively stable, but infill by creosotebush continues to occur.  The consequences of shrub encroachment have been and continue to be carefully documented, but the ecological drivers of shrub encroachment in the southwestern US are not well known.

One key factor that may promote shrub encroachment is grazing by domestic livestock. However, multiple environmental drivers have changed over the 150 years during which shrub expansion has occurred through the southwestern US. Temperatures are warmer, atmospheric CO2 has increased, drought and rainy cycles have occurred, and grazing pressure has decreased. From our prior research we know that prolonged drought greatly reduces the abundance of native grasses while having limited impact on the abundance of creosotebush in the grass-shrub ecotone. So once established, creosotebush populations are persistent and resistant to climate cycles. We also know that creosotebush seedlings tend to appear primarily when rainfall during the summer monsoon is well above average. However, high rainfall years also stimulate the growth of the dominant grasses creating a competitive environment that may not favor seedling establishment and survival. The purpose of the Mega-Monsoon Experiment (MegaME) is twofold. First, this experiment will determine if high rainfall years coupled with (simulated) grazing promote the establishment and growth of creosotebush seedlings in the grassland-shrubland ecotone at Sevilleta, thus promoting infill and expansion of creosotebush into native grassland. Second, MegaME will determine if a sequence of wet summer monsoons will promote the establishment and growth of native C4 grasses in areas where creosotebush is now dominant, thus demonstrating that high rainfall and dispersal limitation prevent grassland expansion into creosotebush shrubland. 

Data set ID: 

259

Core Areas: 

Additional Project roles: 

499
500
501
502

Keywords: 

Methods: 

Data Collection 

Vegetation and soil measurements are taken in the spring and fall each year. Spring measurements are taken in May when spring annuals have reached peak biomass for the growing season. Fall measurements are taken in either September or October when summer annuals and all perennial species have reached peak biomass for the growing season, but prior to killing frosts. Vegetation cover is measured to assess growth and survival of grasses and shrubs. Bare soil and litter covers are also measured to monitor substrate changes that occur within the plots.

One meter2 vegetation quadrats are used to measure the cover of all plants present in each m2.   There are 10 quads in each plot, checkered along on side of the plot.  There is a tag on one rebar of each quad with the representative quad number.  


General vegetation measurements 

The cover is recorded for each species of live plant material inside the quadrat.  Vegetation measurements are taken in two layers: a ground level layer that includes all grasses, forbs, sub-shrubs, and a litter and bare soil, and a “shrub” layer that includes the canopy of Larrea tridentata.  The purpose of this approach is to include Larrea canopies, while allowing the cover values of the ground level layer to sum to approximately 100%. The dead plant covers are not included in the measurement, thus the total amount may not equal 100%.  It is assumed that the remaining cover missing from the 100% is a combination of dead plant material.

 The quadrat boundaries are delineated by the 1 m2 PVC-frame placed above the quadrat.   Each PVC-frame is divided into 100 squares with nylon string.  The dimensions of each square are 10cm x 10cm and represent 1 % of the total quadrat area or cover.  The cover and height of all individual plants of a species that fall within the 1m2 quadrat are measured.  Cover is quantified by counting the number of 10cm x 10cm squares intercepted by all individual plants of a particular species, and/or partial cover for individual plants < 1%.


Vegetation cover measurements 

Cover measurements are made by summing the live cover values for all individual plants of a given species that fall within an infinite vertical column that is defined by the inside edge of the PVC-frame. This includes vegetation that is rooted outside of the frame but has foliage that extends into the vertical column defined by the PVC-frame.  Again, cover is quantified by counting the number of 10cm x 10cm squares intercepted by each species.  Do not duplicate overlapping canopies, just record the total canopy cover on a horizontal plane when looking down on the quadrat through the grid.

Larger cover values will vary but the smallest cover value recorded should never be below 0.1%.  When dealing with individual plants that are < 1.00%, round the measurements to an increment of 0.1.  Cover values between 1.00% and 10.00% should be rounded to increments of 1.0, and values > 10.00% are rounded to increments of 5.

Creosote 

Larrea tridentata canopy  is estimated using the portion of the canopy that falls within the quadrat.  The canopy edge is defined by a straight gravity line from the canopy to the ground (i.e. imagine a piece of string with a weight on the end being moved around the canopy edge).  ForLarrea seedlings the code LSEED is used and is a separate measurement from the Larrea canopy measurements. The cover measurement for LSEED is simply a count of individuals, not actual cover, as it is assumed that they would have a cover of < 1.00%.

Grasses 

To determine the cover of a grass clump, envision a perimeter around the central mass or densest portion of the plant excluding individual long leaves, wispy ends or more open upper regions of the plant.  Live tissue is frequently mixed with dead tissue in grass clumps. 

Forbs 

The cover of forbs is the perimeter around the densest portion of the plant.    Measure all foliage that was produced during the current season.

Cacti and Yucca 

The cover of cacti and yucca is made by estimating a perimeter around the densest portion of the plant and recorded as a single cover.  For cacti that consist of a cluster of pads or jointed stems (i.e., Opuntia phaecantha, Opuntia imbricata), estimate an average perimeter around the series of plant parts and record a single coverage measurement.

Vines 

Vine cover (and some forbs) is often convoluted. Rather than attempt to estimate cover directly, take a frequency count of 10X10X10cm cubes that the vine is present in. 

Seedlings 

As with other vegetation measurements, the smallest cover value for seedlings should never be <0.1%.  If the value of a seedling’s cover is less, round up to 0.1%.


Non-Vegetation cover measurements 

Materials other than vegetation that are measured in the drought plots include soil and litter.  

Soil 

Measure the cover of the area occupied by abiotic substrates.  Cover is quantified by summing the number of 10cm x 10cm squares intercepted by abiotic substrates.  Cover values < 10.00% should be rounded to increments of  and cover values > 10.00% should be recorded in increments of 5.  If there is no soil in the quadrat, record “SOIL” in the species column for that quadrat and record a “0” for cover.

Litter 

Measure the cover of the area occupied by litter, which is unattached dead plant material.  Cover is quantified by summing the number of 10cm x 10cm squares intercepted by abiotic substrates. Cover values < 10.00% should be rounded to increments of 1 and cover values > 10.00% should be recorded in increments of 5.  If there is no litter in the quadrat, record “LITT” in the species column for that quadrat and record a “0” for cover.


Clipping grass at Ecotone Site 

After measurements are taken at the Ecotone Site, grass is clipped down to the soil and removed from half of the quads in each plot. The goal is to assess the impact of competition on successful creosote seedling germination. The following quads, # 2, 4, 6, 7, and 10, get clipped in every plot at the ecotone site.


Water Addition 

The watering schedule varies based on seasonal rainfall. Our goal is to increase average monsoon precipitation (150mm) by 50%, so we shoot for a total of 225mm on the plots during the summer monsoon.

Data sources: 

sev259_megame_20161222.csv

Additional information: 

Additional Information on the personnel associated with the Data Collection:

Stephanie Baker 2014-present

Megan McClung 2014-present

Chandra Tucker 2014-present

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).

Gunnison’s Prairie Dog Use of Resource Pulses in a Chihuahuan Desert Grassland at the Sevilleta National Wildlife Refuge, New Mexico: Re-sight Scan Data

Abstract: 

Seasonal environments experience cyclical or unpredictable pulses in plant growth that provide important resources for animal populations, and may affect the diversity and persistence of animal communities that utilize these resources. The timing of breeding cycles and other biological activities must be compatible with the availability of critical resources for animal species to exploit these resource pulses; failure to match animal needs with available energy can cause population declines. Adult Gunnison’s prairie dogs emerge from hibernation and breed in early spring, when plant growth is linked to cool-season precipitation and is primarily represented by the more nutritious and digestible plants that utilize the C3 photosynthetic pathway. In contrast, summer rainfall stimulates growth of less nutritious plants using the C4 photosynthetic pathway. Prairie dogs should therefore produce young during times of increased productivity from C3 plants, while pre-hibernation accumulation of body fat should rely more heavily upon C4 plants.  If seasonal availability of high-quality food sources is important to Gunnison’s prairie dog population growth, projected changes in climate that alter the intensity or timing of these resource pulses could result in loss or decline of prairie dog populations.  This project will test the hypothesis that population characteristics of Gunnison's prairie dog, an imperiled grassland herbivore, are associated with climate-based influences on pulses of plant growth.

Data set ID: 

242

Core Areas: 

Additional Project roles: 

40
41

Keywords: 

Methods: 

Gunnison’s prairie dogs will be monitored at 6 colonies, with 3 colonies each occurring with the range of prairie and montane populations. Colonies for study within the prairie populations occur at Sevilleta National Wildlife Refuge (n = 3 prairie populations) and at Vermejo Park Ranch (n = 3 montane populations).  Live-trapping of prairie dogs will be conducted during 3 periods of the active seasons—following emergence (April), after juveniles have risen to the surface (mid-to-late June), and pre-immergence (beginning in August).  Trapping will occur for 3-day periods, following pre-baiting with open traps.  At capture, sex and body mass of each individual will be recorded.  Blood and subcutaneous body fat samples will be collected nondestructively for analysis of isotopic composition.  Prairie dogs will be marked with dye, and released on site immediately following processing.  After trapping periods at each site have concluded, population counts will be conducted during 2-3 re-sighting (or recapture) periods for each prairie dog colony.  Resighting observation periods will be ~3 hours in length, and consist of 2-6 systematic scans of the entire colony, beginning and ending from marked points outside of the colony boundary.  During each observation period, prairie dogs will be counted, recorded as marked or unmarked, and location on the colony noted.  

Vegetation cover and composition measurements will be collected (or obtained at Sevilleta, where such data is already being collected) during pre- and post-monsoon periods of the active season.  Total cover will be measured by plant species (or to genus if species is indeterminable). Total cover will be measured at 12 grid points per colony using Daubenmire frames (0.5 m x 0.5 m), and at 12 grid locations 200-800 m outside of each colony boundary.  Adjacent to each Daubenmire frame, a 20 cm x 30 cm sample of vegetation will be clipped and dried for determination of volumetric moisture content of vegetation.  

Primary productivity variables (cover, moisture content) will be tested for correlations to individual and population-level condition indicators in prairie dogs.  Carbon isotope ratios (δ13C) from prairie dog blood and fat samples will be analyzed on a continuous flow isotope ratio mass spectrometer.  The relative contribution of C3 and C4 plants to the diet of each individual will be determined based upon δ13C ratios for C3 and C4 plants in the study area and a 2-endpiont mixing model, and will be calculated for each individual animal, population and season.  Population estimates will be calculated using mark-resight estimates, and compared to maximum above-ground counts.  The influence of resource pulses on prairie dog population parameters will be tested by comparing the vegetation cover, moisture content, and ratio of total C3:C4 plant cover to the ratio of C3:C4 plants in prairie dog diets, population estimates, and juvenile:adult ratios as an index to population recruitment.   

Instrumentation: 

*Instrument Name: Continuous flow isotope ratio mass spectrometer

*Manufacturer: Thermo-Finnigan IRMS  Delta Plus 

*Instrument Name: Elemental Analyzer

*Manufacturer: Costech

*Model Number: ECS4010

Additional information: 

Other Field Crew Members: Talbot, William; Duran, Ricardo; Gilbert, Eliza; Donovan, Michael; Nichols, Erv; Sevilleta LTER prairie dog field crew led by Koontz, Terri; Sevilleta NWR prairie dog field crew led by Erz, Jon.

Tissue samples are analyzed for stable carbon isotope ratios in stable isotope laboratory operated by Dr. Zachary Sharp and Dr. Nicu-Viorel Atudorei of the Department of Earth and Planetary Sciences, University of New Mexico.

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.

Gunnison's Prairie Dog Use of Resource Pulses in a Chihuahuan Desert Grassland at the Sevilleta National Wildlife Refuge, New Mexico: Capture Data

Abstract: 

Seasonal environments experience cyclical or unpredictable pulses in plant growth that provide important resources for animal populations, and may affect the diversity and persistence of animal communities that utilize these resources. The timing of breeding cycles and other biological activities must be compatible with the availability of critical resources for animal species to exploit these resource pulses; failure to match animal needs with available energy can cause population declines. Adult Gunnison’s prairie dogs emerge from hibernation and breed in early spring, when plant growth is linked to cool-season precipitation and is primarily represented by the more nutritious and digestible plants that utilize the C3 photosynthetic pathway. In contrast, summer rainfall stimulates growth of less nutritious plants using the C4 photosynthetic pathway. Prairie dogs should therefore produce young during times of increased productivity from C3 plants, while pre-hibernation accumulation of body fat should rely more heavily upon C4 plants. If seasonal availability of high-quality food sources is important to Gunnison’s prairie dog population growth, projected changes in climate that alter the intensity or timing of these resource pulses could result in loss or decline of prairie dog populations. This project will test the hypothesis that population characteristics of Gunnison's prairie dog, an imperiled grassland herbivore, are associated with climate-based influences on pulses of plant growth.

Data set ID: 

241

Core Areas: 

Additional Project roles: 

37
38
39

Keywords: 

Methods: 

Gunnison’s prairie dogs will be monitored at 6 colonies, with 3 colonies each occurring with the range of prairie and montane populations. Colonies for study within the prairie populations occur at Sevilleta National Wildlife Refuge (n = 3 prairie populations) and at Vermejo Park Ranch (n = 3 montane populations). Live-trapping of prairie dogs will be conducted during 3 periods of the active seasons—following emergence (April), after juveniles have risen to the surface (mid-to-late June), and pre-immergence (beginning in August). Trapping will occur for 3-day periods, following pre-baiting with open traps. At capture, sex and body mass of each individual will be recorded. Blood and subcutaneous body fat samples will be collected nondestructively for analysis of isotopic composition. Prairie dogs will be marked with dye, and released on site immediately following processing. After trapping periods at each site have concluded, population counts will be conducted during 2-3 re-sighting (or recapture) periods for each prairie dog colony. Resighting observation periods will be ~3 hours in length, and consist of 2-6 systematic scans of the entire colony, beginning and ending from marked points outside of the colony boundary. During each observation period, prairie dogs will be counted, recorded as marked or unmarked, and location on the colony noted. Vegetation cover and composition measurements will be collected (or obtained at Sevilleta, where such data is already being collected) during pre- and post-monsoon periods of the active season. Total cover will be measured by plant species (or to genus if species is indeterminable). Total cover will be measured at 12 grid points per colony using Daubenmire frames (0.5 m x 0.5 m), and at 12 grid locations 200-800 m outside of each colony boundary. Adjacent to each Daubenmire frame, a 20 cm x 30 cm sample of vegetation will be clipped and dried for determination of volumetric moisture content of vegetation. Primary productivity variables (cover, moisture content) will be tested for correlations to individual and population-level condition indicators in prairie dogs. Carbon isotope ratios (δ13C) from prairie dog blood and fat samples will be analyzed on a continuous flow isotope ratio mass spectrometer. The relative contribution of C3 and C4 plants to the diet of each individual will be determined based upon δ13C ratios for C3 and C4 plants in the study area and a 2-endpiont mixing model, and will be calculated for each individual animal, population and season. Population estimates will be calculated using mark-resight estimates, and compared to maximum above-ground counts. The influence of resource pulses on prairie dog population parameters will be tested by comparing the vegetation cover, moisture content, and ratio of total C3:C4 plant cover to the ratio of C3:C4 plants in prairie dog diets, population estimates, and juvenile:adult ratios as an index to population recruitment.

Instrumentation: 

Instrument Name: Continuous flow isotope ratio mass spectrometer Manufacturer: Thermo-Finnigan IRMS Delta Plus Model Number: Instrument Name: Elemental Analyzer Manufacturer: Costech Model Number: ECS4010

Additional information: 

Field Crew: Hayes, Chuck; Talbot, William; Duran, Ricardo; Gilbert, Eliza; Donovan, Michael; Nichols, Erv; Sevilleta LTER prairie dog field crew led by Koontz, Terri; Sevilleta NWR prairie dog field crew led by Erz, Jon.

The Effect of Kangaroo-Rat Activity on Plant Species Composition at the Sevilleta National Wildlife Refuge, New Mexico (1999)

Abstract: 

Our objective was to evaluate the effects of kangaroo rat mounds on species diversity and composition at a semiarid-arid grassland ecotone. We expected that source populations of plants occurring on kangaroo rat mounds have important influences on the species composition of vegetation at the landscape scale, and that these influences differ by grassland type. Our study was conducted at the Sevilleta LTER in New Mexico, where a grassland type dominated by Bouteloua gracilis, a shortgrass steppe species, and a grassland type dominated by B. eriopoda, a desert grassland species, meet to form patches across the landscape.

Four 0.4 ha plots were sampled for species diversity and composition in a regular 7m x 7m grid in each grassland type. Kangaroo rat mounds were also mapped and sampled for vegetation measures in four areas of 1.6 ha in each type. The landscape scale abundance of many subordinate species was increased significantly by populations occurring on kangaroo rat mounds in both grassland types. However, the area affected by the burrowing activity of kangaroo rats was twice as large in the B. eriopoda dominated grassland type. Furthermore, dominant plants on mounds in the B. eriopoda type were also abundant in off-mound areas whereas dominant plants on mounds in the B. gracilis type were not as abundant off-mound. These results indicate that the presence of mounds in the B. gracilis dominated type is creating islands of plant communities that are distinct from the rest of the grassland. Therefore, the occurrence of certain plant species in this grassland type may be intimately associated with the disturbance regime at this ecotone. This study demonstrates that effects of small burrowing animals may facilitate the coexistence of species at this ecotone.

Data set ID: 

169

Additional Project roles: 

225

Core Areas: 

Keywords: 

Methods: 

Experimental Design - We selected eight stands, four dominated by Bouteloua eriopoda and four by Bouteloua gracilis (stands were marked with A1, A2, A3, A4 in the data set for the Bouteloua eriopoda type, and U1, U2, U3, U4 for Bouteloua gracilis type). Study areas were selected using aerial photos to ensure that they were located in well-defined black grama- or blue grama-dominated belts.  Study areas were 126 m x 126 m in size and were placed so that they contained a randomly selected, average-sized, and recently abandoned kangaroo rat mound in the center.

Field Methods - In each patch type, we mapped all kangaroo-rat mounds and measured their size within the four 1.6 ha (126 m x 126 m) areas (total areas = 8). We classified each mound as active, recently abandoned, or old according to the level of small mammal activity. We noted the dominant and co-dominant plant species on each mound (i.e. species with at least 5% relative cover). In the center of each 1.6 ha plot, we estimated canopy cover (visual cover estimation) by species in 100 2m2 quadrats arranged in a regular 7 m x 7 m grid centered on a randomly selected and recently abandoned mound. Each grid covered a 63 m x 63 m area in the centre of the 1,6 ha stands. For each quadrat, we noted its location as being on a mound proper, at the edge of a mound, or in the off-mound vegetation.

Data sources: 

sev169_krat_03072012
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