herbivores

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

Scaling of Recruitment with Seed Distribution and Colony Size in Pogonomyrmex spp. at the Sevilleta National Wildlife Refuge, New Mexico

Abstract: 

Ant colonies possess a “societal metabolism,” acquiring, transforming, and allocating resources through a network of foragers (Moses, 2005). Ant foraging- trail networks channel foragers to known food resources and away from competing colonies (Jun et al., 2003). Computer models suggest the spread of information occurs faster in larger colonies of harvester ants, genus Pogonomyrmex (Adler and Gordon, 1992), providing a possible mechanism of differentiation. Does the ability to utilize and share information scale super-linearly with a colony’s size? Within colonies, do foragers recruit more to denser sources of food, using information transfer to increase forager efficiency and harvest seed caches before competing colonies find them? To address these questions, we studied three sympatric species of Pogonomyrmex in central New Mexico that differ in average colony size: P. rugosus, P. maricopa, and P. desertorum. We hypothesized a) that across colonies recruitment to dense food resources scales positively with colony size, and b) that within colonies recruitment scales positively with seed density. We observed baited colonies for 1 hr, tracking the capture of dyed seeds arranged in piles of different densities and of native seeds. We generated a model of idealized effects of recruitment on foraging patterns and compared the output to our observations. We did not find support for hypothesis a, that recruitment scales positively with colony size, but did find support for hypothesis b, that recruitment does scale positively with increasing seed density. These findings highlight a key intersection between the metabolism of energy and of information.

Core Areas: 

Data set ID: 

235

Keywords: 

Purpose: 

To explore whether large ant colonies are "smarter" and how colonies use recruitment.

Methods: 

Experimental Design: Our experimental design consisted of testing potential differences in forager recruitment by baiting actively foraging colonies with dyed seeds arranged in different distributions (i.e. piles of different numbers of seeds) around each colony. Differences in the rate foragers collect seeds of different colors indicate potential differences in the rate foragers are recruited, by chemical pheromone trails, to piles of different sizes. We conduct these experiments on a number of colonies of three species of Pogonomyrmex that differ in average colony size, and then compare the rates those species retrieve seeds of different distributions.

Field Methods: We located actively foraging Pogonomyrmex colonies between 8 and 9am and distributed dyed millet seeds in a wide circular swath around each colony. We used 256 millet seeds of each color for P. rugosus and P. maricopy and 32 sesame seeds of each color for P. desertorum, which is smaller and has smaller colonies. For each color, we divided those seeds into piles as follows: red = 1 pile; purple = 4 piles; green = 16 piles; blue = "piles" of one seed each (i.e. scattered at random within the circular swath). We then sat near the nest entrance and recorded the seeds brought in by foraging ants. Using a Java program (SeedCounter) we recorded the color and time of each seed retrieved by the focal colony during an observation period of 1 to 1.5 hours. We generated seed uptake curves from this data.

Laboratory Procedures: We also developed an ant foraging simulation. Virtual ants start at a nest entrance at the center of a bounded lattice. The lattice contains 256 randomly distributed blue seeds and a single pile of 256 red seeds. A foraging ant searches at random until it collects a seed, then delivers it to the nest. To model patch fidelity, a successful forager returns to location it found its previous seed and begins a new random search.

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.

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.

Effects of Herbivores on Seed Banks of Grass and Shrublands at the Sevilleta National Wildlife Refuge, New Mexico (2004)

Abstract: 

Grazers and granivores have the potential to affect seed banks. Several studies have examined the impact of these herbivores on the aboveground vegetation, but few have looked at how they influence the seed bank. I asked whether both grazers and granivores alter the seed bank at the Sevilleta National Wildlife Refuge. Long-term experimental plots were installed in 1996 to exclude grazers and granivores from a grassland and shrubland. Soil samples were collected from these plots and seeds were germinated in a greenhouse. The grassland had significantly more species in its seed bank than the shrubland. Also, the seed bank composition differed significantly between the two sites. However, the number of species in the seed bank did not vary among herbivore treatments nor did total seed numbers vary among treatments at the grassland. At the shrubland, in contrast, plots that excluded both herbivores had fewer total seeds than control plots and plots where only grazers were excluded. Therefore, although herbivores play some role in the shrubland, herbivores do not reduce seed numbers at either site. Thus, seed bank size is not controlled by the consumption of seeds from these herbivores, but by some other factor (e.g. disturbance or abiotic events).

Core Areas: 

Data set ID: 

209

Keywords: 

Methods: 

Collecting and Processing soil samples

Soil samples were collected at each site for each treatment in both mid March and October in 2004 for a total of 720 samples(15 samples per treatment x 3 treatments per block x 4 blocks per site x 2 sites x 2 seasons). There are 30 points between vegetation subplots in each of the Small Mammal Exclosure Study plots. Fifteen of these points were randomly selected from each plot. Soil samples were taken using a square electrical box with dimensions of 10cm(length) x 10cm (width) x 2cm(depth). These soil samples were then stored in paper bags and labeled with a unique sample number, indicating the site, block, treatment, and sample point, using a sharpie marker. Soil samples were then taken to the University of New Mexicos greenhouse. Due to space constraints in the greenhouse, only half of the samples from each season could be censused at one time. Therefore, I randomly selected half of the samples from each plot for each census. Soil samples were spread in a thin layer over a soil mixture containing half sand and half Metromix 360 in 8 x 11 flats. Flats were arranged into eight blocks each containing one sample from each plot to minimize variance due to greenhouse location. Control flats of sand and Metromix 360(with no field soil) were also distributed in the eight blocks to account for any seeds that might have contaminated the sand. The samples were then watered using a sprinkler system three times a day for five-minute durations where the thermostat temperature ranged from 16 to 25 Celsius for seven weeks. All seedlings were counted and identified to species. These procedures were repeated for the remaining half of the soil samples for each season.

Data sources: 

sev209_seedbank_20111115

Maintenance: 

Metadata entered in Microsoft Access. 26 May 2009. tk

Quality Assurance: 

Data were visually assessed for any errors.

Additional information: 

Additional Information on the Data Collection Period

Soil samples were taken in mid March and October of 2004.

Additional Study Area Information

Study Area 1

Study Area Name: Five Points Grass Core Site

Study Area Location: Five Points is the general area which emcompasses the Black Grama Grassland (known as Five Points Grassland) and Creosote Core (Five Points Larrea) study sites and the transition between Chihuahuan Desert Scrub and Desert Grassland habitats. Both core sites are subject to intensive research activities, including measurements of NPP, phenology, pollinator diversity, and ground dwelling arthropod and rodent populations. There are drought rain-out shelters in both the Grassland and Creosote sites, as well as another set in the mixed ecotone with co-located ET Towers. The grassland Small Mammal Exclosure Study is located here, as well as many plots related to patch mapping and biotic transitions.

Elevation: 1616 m

Vegetation: Desert Grassland habitat is ecotonal in nature and the Black Grama Core site is no exception, bordering Chihuahuan Desert Scrub at its southern boundary and Plains-Mesa Grassland at its northern, more mesic boundary. There is also a significant presence of shrubs, dominantly broom snakeweed (Gutierrezia sarothrae), along with less abundant fourwing saltbush (Atriplex canescens), Mormon tea (Ephedra torreyana), winterfat (Krascheninnikovia lanata), tree cholla (Opuntia imbricata), club cholla (O. clavata), desert pricklypear (O. phaeacantha), soapweed yucca (Yucca glauca), and what are presumed to be encroaching, yet sparsely distributed, creosotebush (Larrea tridentata). Characteristically, the dominant grass was black grama (Bouteloua eriopoda). Spike, sand, and mesa dropseed grasses (Sporobolus contractus, S. cryptandrus, S. flexuosus) and sand muhly (Muhlenbergia arenicola) could be considered co-dominant throughout, along with blue grama (B. gracilis) in a more mesic, shallow swale on the site. Notable forb species included trailing four o’clock (Allionia incarnata), horn loco milkvetch (Astragalus missouriensis), sawtooth spurge (Chamaesyce serrula), plains hiddenflower (Cryptantha crassisepala), blunt tansymustard (Descurania pinnata), wooly plaintain (Plantago patagonica), globemallow (Sphaeralcea wrightii), and mouse ear (Tidestromia lanuginosa).

North Coordinate:34.3381
South Coordinate:34.3381
East Coordinate:106.717
West Coordinate:106.717

Study Area 2

Study Area Name: Rio Salado

Study Area Location: Rio Salado is about 3 km West I-25 just south of the Rio Salado. Site is accessed by taking San Acacia exit, going west and then taking the frontage road back north to the Sevilleta gate. After entering the refuge turn left after about .2 mi and take this road about 1.4 mi to a T in the road at the power lines. An earthen berm stops road travel here and the station is located about 300 m west on the blocked road.

Elevation: 1503 m

North Coordinate:34.296
South Coordinate:0
East Coordinate:0
West Coordinate:106.9267

Small Mammal Mark-Recapture Population Dynamics at Core Research Sites at the Sevilleta National Wildlife Refuge, New Mexico (1989 - present)

Abstract: 

This file contains mark/recapture trapping data collected from 1989-2012 on permanently established web trapping arrays at 8 sites on the Sevilleta NWR. At each site 3 trapping webs are sampled for 3 consecutive nights in spring and fall. Not all sites have been trapped for the entire period. Each trapping web consists of 145 rebar stakes numbered from 1-145. There are 148 traps deployed on each web: 12 along each of 12 spokes radiating out from a central point (stake #145) plus 4 traps at the center point. The trapping sites are representative of Chihuahuan Desert Grassland, Chihuahuan Desert Shrubland, Pinyon-Juniper Woodland, Juniper Savanna, Plains-Mesa Sand Scrub and Blue Grama Grassland.

Data set ID: 

8

Core Areas: 

Additional Project roles: 

517
518

Keywords: 

Methods: 

Sampling Design
Permanent capture-mark-release trapping webs were used to estimate density (number of animals per unit area) of each rodent species at each site. The method makes use of concepts from distance sampling, i.e., point counts or line-intercept techniques. The method makes no attempts to model capture-history data, therefore it was not necessary to follow individuals through time (between sessions). Distance sampling methods allow for sighting or detection (capture) probabilities to decrease with increasing distance from the point or line. The modeling of detection probability as a function of distance forms the basis for estimation. Trapping webs were designed to provide a gradient of capture probabilities, decreasing with distance from the web center. Density estimation from the trapping web was based on three assumptions:1. All animals located at the center of the web were caught with probability 1.0; 2. Individuals did not move preferentially toward or away from the web center; 3. Distances from the web center to each trap station were measured accurately. Each web consisted of 12 trap lines radiating around a center station, each line with 12 permanently-marked trap stations. In order to increase the odds of capturing any animals inhabiting the center of a web, the center station had four traps, each pointing in a cardinal direction, and the first four stations of each trap line were spaced only 5 m apart, providing a trap saturation effect. The remaining eight stations in a trap line were spaced at 10 m intervals. The web thus established a series of concentric rings of traps. Traps in the ring nearest the web center are close together, while the distances separating traps that form a particular ring increase with increasing distance of the ring from the web center. The idea is that the web configuration produces a gradient in trap density and, therefore, in the probability of capture. Three randomly distributed trapping webs were constructed at each site. The perimeters of webs were placed at least 100 m apart in order to minimize homerange overlap for individuals captured in the outer portion of neighboring webs.

Measurement Techniques

Each site containing three webs was sampled for three consecutive nights during spring (in mid May or early June) and summer (in mid July or early August for years 1989 to 1993, then mid September to early October for years 1994 through 2000). In that rodent populations were not sampled monthly over the study period, there is no certainly that either spring or summer trapping times actually captured annual population highs or lows. Based on reproductive data in the literature, an assumption was made that sampling times chosen represent periods of the year when rodents have undergone, and would register, significant seasonal change in density. During each trapping session, one Sherman live trap (model XLF15 or SFAL, H. B. Sherman Traps, Tallahassee, FL) was placed, baited with rolled oats, and set at each permanent, numbered station (four in the center) on each web, for a total 444 traps over three webs. Traps were checked at dawn each day, closed during the day, and reset just before dusk. Habitat, trap station number, species, sex, age (adult or juvenile), mass, body measurements (total length, tail length, hind foot length, ear length), and reproductive condition (males: scrotal or non-scrotal; females: lactating, vaginal or pregnant) were recorded for each initial capture of an individual. Each animal was marked on the belly with a permanent ink felt pen in order to distinguish it from other individuals during the same trapping session. The trap station number for an initial capture related to a particular trapping ring on a web and, therefore, to a particular distance from the center of the web. The area sampled by a ring of traps was computed based on circular zones whose limits are defined by points halfway between adjacent traps along trap lines; an additional 25 m radius was added to the outer ring of traps in order to account for homerange size of individuals caught on the outer ring.

Analytical Procedures
Area trapped and number of individuals caught for each ring of traps was the basis for estimating the probability density function of the area sampled. The program DISTANCE produced the estimators used to calculate density. Where sample size for a particular species and web was less than an arbitrarily chosen n=10, the number of individuals captured during that session was simply divided into the area of the web plus the additional 25 m radius (4.9087 ha). This dataset includes only the raw capture data.

Data sources: 

sev008_rodentpopns_20161027

Instrumentation: 

 

Sherman live traps: model XLF15 or SFAL, H. B. Sherman Traps, Tallahassee, FL

Maintenance: 

Trap sets require care and cleaning as well as proper storage. Otherwise, webs are made up of durable rebar and aluminum tags which only need repair if disturbed. Tools used in the field - scales and rulers, pouches, trap bags and ziplock supply must be maintained on hand at SevFS for trapping events.

Additional information: 

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

Sevilleta Field Crew Employee History

Chandra Tucker April 2014-present, Megan McClung, April 2013-present, Stephanie Baker, October 2010-Present, John Mulhouse, August 2009-June 2013, Amaris Swann, August 25, 2008-January 2013, Maya Kapoor, August 9, 2003-January 21, 2005 and April 2010-March 2011, Terri Koontz, February 2000-August 2003 and August 2006-August 2010, Yang Xia, January 31, 2005-April 2009, Karen Wetherill, February 7, 2000-August 2009, Michell Thomey, September 3, 2005-August 2008, Jay McLeod, January 2006-August 2006, Charity Hall, January 31, 2005-January 3, 2006, Tessa Edelen, August 15, 2004-August 15, 2005, Seth Munson, September 9, 2002-June 2004, Caleb Hickman, September 9, 2002-November 15, 2004, Heather Simpson, August 2000-August 2002, Chris Roberts, September 2001-August 2002, Mike Friggens, 1999-September 2001, Shana Penington, February 2000-August 2000.

*In fall 2013, the Grassland Core site was not able to be trapped due to government shutdown. 

Desertification/Bureau of Land Managment (BLM) Transects at the Sevilleta National Wildlife Refuge, New Mexico (1976,1986,1996)

Abstract: 

Responses of plant communities to mammalian herbivores vary widely, due to variation in plant species composition, herbivore densities, forage preferences, soils, and climate. In this study, we evaluated simultaneous changes in 11 plant assemblages on the 100,000 ha Sevilleta National Wildlife Refuge (SNWR) in central New Mexico, USA, over a 20-yr period following removal of the major mammalian herbivores (livestock and prairie dogs) in 1972-1975. Thirty study sites were established in 1976 within and outside of the SNWR, and these sites were resampled in 1986 and 1996 using line transect methods. At the landscape scale, repeated measures ANOVA of percentage cover measurements showed no significant overall net changes in total perennial plant basal cover, either with or without herbivores present; however, there was an overall increase in annual forbs and plant litter from 1976 to 1996. At the site scale, significant changes in species composition and dominance were observed both through time and across the SNWR boundary; each plant assemblage exhibited varying degrees of change, with sites dominated by Bouteloua eriopoda (black grama grass) being the most dynamic and sites dominated by Scleropogon brevifolius (burro grass) being the most persistent. Species-specific changes also were observed across multiple sites: B. eriopoda cover increased while Gutierrezia sarothrae (a small, short-lived shrub) greatly decreased. The non-uniform, multi-directional changes of the different plant assemblages acted to prevent detection of overall changes in perennial vegetation at the landscape level. Some plant assemblages displayed significant changes after removal of herbivores, while others appeared to respond primarily to climate dynamics. Certain species (e.g., G. sarothrae) that were not preferred by livestock or prairie dogs showed overall declines during drought periods, while other preferred species (e.g., B. eriopoda) exhibited widespread increases during wetter periods regardless of herbivore presence. Therefore, the vegetation dynamics cannot be attributed solely to removal of mammalian herbivores, and in some cases can be explained by short- and long-term fluctuations in climate. These results emphasize the variety of responses of different plant assemblages to mammalian herbivores under otherwise similar climatic conditions, and illustrate the value of site- and landscape-scale approaches to understanding the impacts of plant-herbivore interactions.

Core Areas: 

Data set ID: 

109

Additional Project roles: 

297
298
299
300
301

Keywords: 

Purpose: 

This data set contains observations of vegetation change in the Sevilleta National Wildlife Refuge of central New Mexico, USA, from 1976 to 1996 following the removal of all livestock and prairie dogs in 1972-75. Specifically, we addressed the following: (1) Would the removal of the two "keystone" mammal herbivores (livestock and prairie dogs) have significant effects on plant species composition or cover at the landscape level? (2) Would the various site-specific plant assemblages within the region exhibit similar changes through time and/or to herbivore removal? (3) What are the influences of species-specific dynamics in changing the landscape and site plant assemblages? (4) What are the relative roles of herbivory and climate dynamics in influencing vegetation change at both landscape and site-level scales?

Data sources: 

sev109_blmtransects_02252000.txt

Methods: 

Study Design

This study takes advantage of a series of events during the mid-1970's that coincided to create a unique opportunity for evaluating multi-scale responses of plant communities to the removal of keystone mammalian herbivores. The Sevilleta NWR, a 100,000 ha former Spanish land grant and cattle ranch containing a wide range of vegetation communities, was created in December, 1973. The Sevilleta land grant had been heavily grazed by cattle since the late 1800's, and prairie dogs had been present even earlier. As part of its new "wildlife reserve" status, the entire refuge was fenced and all livestock were removed during 1974-75. In summer 1972, coincidentally just prior to the creation of the SNWR, rangeland pest control agents eradicated virtually all prairie dogs through an intensive poisoning campaign. Livestock and prairie dogs remained in areas outside the SNWR. Since 1973, the SNWR has been without livestock and prairie dogs, although prairie dogs have just recently begun to return to portions of the refuge.

These events created a unique situation in which to evaluate the roles of keystone mammalian herbivores on different vegetation communities that (1) were subjected to similar climatic dynamics (i.e., all sites experienced the same high and low rainfall periods), (2) were formerly grazed at high densities by the same species of mammalian herbivores, and (3) were released and protected from grazing during the same time periods.

In 1976, range scientists of the United States Bureau of Land Management (BLM) established and sampled 30 "range trend plots" (described below) in and around the SNWR to monitor the influences of cattle grazing on the vegetation; however, the plots were never resampled by the BLM. In 1986, ecologists from the University of New Mexico's Technical Applications Center resampled the sites. In 1988, the SNWR became the main study site of the Sevilleta Long-Term Ecological Research program (LTER); as part of this LTER program, in 1996 we returned to the sites for a 20-yr sample. These samples over two decades allowed us to evaluate the changes in plant cover and species composition at both a landscape scale (SNWR and bordering regions) and at individual sites representing multiple plant assemblages.

Vegetation Sampling

Study sites (n=30) are widely distributed and encompass a variety of plant assemblages. Biomes represented included desert, grassland, shrub-steppe, and woodlands. A line transect was established at each site by BLM range scientists in 1976; transects are 30.48 m (100 ft) in length and marked with permanent steel stakes at each end of the transect. The transects are sampled with a "line loop" technique (Parker 1951), a modification of the line point method. Instead of a point, a steel loop with an inner diameter of 1.91 cm (0.75 inch) is used. At every 0.305 m (1 foot) interval of the measuring tape, the loop is placed on the ground and the contents inside the loop recorded. Perennial plants in the loop are identified, and if two species were present, both are recorded. Overhanging shrub canopies are counted, but perennial grasses and forbs are recorded only if the base or stem fell inside the loop. It is important to note that this method does not include measurements of plant height and canopy cover for grasses and forbs, and thus prevents an assessment of plant assemblage architectural changes through time or across the SNWR fence lines.

Annual forbs are classified as "litter" in the August 1976 data set (as per BLM field methods). The 1986 measurements were conducted in January-March when annual forbs were dead, and hence were also categorized as "litter"(perennial plants were still present and easily identifiable). The 1996 samples were collected in August, near the peak of the growing season. Although we identified every plant to species, for consistency of comparisons we also pooled annual forbs and litter in our analyses. If no plants were present, the point was recorded as soil, rock, or litter. Rock or litter need to occupy at least the opening of the loop to be counted. Soil is recorded if no plants are present and the loop is not occupied by rock or litter.

We have located 29 of the original 30 transects, and resampled 28 of the still-existing sites. Photographs and GPS locations were taken of the transects for documentation and comparison with photographs taken in 1976.

Plant codes in the following data file correspond to the old Sevilleta plant code list.

Maintenance: 

File created 15 August 1996 by Dan Ryerso.n2/18/00 Metadata added to data files by Robert Parmenter.

Additional information: 

When the Samples/Data were Collected

August, 1976; Winter of 1986, August 1996, August 2006.

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

Employee History for Sevilleta Field Crew: Mike Friggens, 1999-September 2001;Karen Wetherill, February 7, 2000-Present; Terri Koontz, February 2000-August 2003, August 2006-Present; Shana Penington, February 2000-August 2000;Heather Simpson, August 2000-August 2002; Chris Roberts, September 2001-August 2002; Caleb Hickman, September 9, 2002-November 15, 2004; Seth Munson, September 9, 2002-June 2004; Maya Kapoor, August 9, 2003- January 21, 2005;Tessa Edelen, August 15, 2004-August 15, 2005; Charity Hall, January 31, 2005-January 3, 2006; Yang Xia, January 31, 2005-Present; Michell Thomey, September 3, 2005-August 2008; Jay McLeod, January 2006-August 2006;Amaris Swann, August 25, 2008-Present

Additional Study Area Information

The study was conducted on rangelands within and adjacent to the SNWR, Socorro County, New Mexico. Elevations of the study sites ranged from 1400 to 1870 m. Annual precipitation records of Socorro, New Mexico (30 km south of SNWR) from 1973 to 1996 ranged from a minimum of 150 mm to a maximum of 367 mm. The average annual precipitation during the first decade of this study (1976--1986) was 266 mm, and in the second decade (1986--1996) was 245 mm. During 1976, precipitation was slightly below average and had been preceded by a year of high precipitation. Precipitation in 1985, prior to the 1986 sample, also had been above average. Measurements taken in 1996 followed a 2-yr period of low precipitation, but the summer monsoons of 1996 produced above-average moisture. Mean monthly temperatures ranged from 2.7C during January to 24.3C in July.

Site Location Description

Table 1. Locations, soils, and commuity classification of study sites Community type is defined by species composition in 1996. Of the original 30 transects established in 1976, only 28 were resampled in 1996. Site #3 was not found, and Site #24 had been destroyed by road construction.

Location Predominant
Transect Latitude Longitude Soil Type Species
_____________________________________________________________________________________________
01 34 24' 37" 106 55' 49" Turney loam Burrograss
02  34 24' 47" 106 55' 43" Turney loam Burrograss
04 34 25' 45" 106 55' 27" Turney loam Burrograss
05 34 26' 02" 106 59' 47" Nickel-Caliza very gravelly sandy Galleta grass loam
06 34 25' 10" 107 01' 07" Nickel-Caliza very gravelly sandy Blue grama grassloam
07 34 15' 46" 106 56' 55" Armijo-Glendale-Bluepoint Galleta grass association
08 34 15' 05" 106 56' 01" Arizo-Riverwash complex Black grama grass
09 34 13' 46" 106 55' 40" Arizo-Riverwash complex Broom dalea
10 34 13' 29" 106 55' 37" Arizo-Riverwash complex Broom dalea
11 34 13' 27" 106 56' 44" Nickel-Caliza very gravelly sandy Broom dalea loam
12 34 13' 17" 106 47' 08" Bucklebar sandy clay loam Burrograss
13 34 11' 49" 106 48' 28" Barana loam Burrograss
14 34 13' 09" 106 47' 20" Bucklebar sandy clay loam Galleta grass
15 34 11' 48" 106 48' 44" Barana loam Black grama grass
16 34 24' 35" 106 32' 16" Sedillo-Clovis association Blue grama grass
17 34 23' 16" 106 31' 05" Ponciano very bouldery clay loam Black grama grass
18 34 24' 11" 106 40' 07" Turney loamy sand Black grama grass
19 34 24' 08" 106 40' 08" Turney loamy sand Galleta grass
20 34 24' 14" 106 40' 21" Turney loamy sand Black grama grass
21 34 24' 12" 106 40' 22" Turney loamy sand Black grama grass
22 34 23' 42" 106 40' 40" Turney loamy sand Black grama grass
23 34 21' 00" 106 37' 22" Sedillo-Clovis association Blue grama grass
25 34 20' 15" 107 00' 59" Armijo-Glendale-Bluepoint Saltbush/dropseed association grass
26 34 20' 17" 107 01' 09" Armijo-Glendale-Bluepoint Saltbush/dropseed association grass
27 34 20' 20" 107 01' 31" Armijo-Glendale-Bluepoint Saltbush/dropseed association grass
28 34 15' 55" 106 43' 52" Campana Yesum association Burrograss
29 34 16' 18" 106 44' 56" Elbutte-Courthouse Variant-Rock Galleta grass outcrop complex
30 34 16' 07" 106 44' 05" Campana Yesum association Black grama grass

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