Realm: Terrestrial
Climate: Temperate
Biome: Deserts and xeric shrublands
Central latitude: 34.200000
Central longitude: -106.430000
Duration: 20 years, from 1989 to 2008

16657 records

27 distinct species

Across the time series Dipodomys merriami is the most frequently occurring species

Methods

Permanent capture-mark-release trapping webs were usedto estimate density (number of animals per unit area) ofeach rodent species at each site. The method makes useof concepts from distance sampling. i.e.. point countsor line-intercept techniques. The method makes noattempts to model capture-history data. therefore it wasnot necessary to follow individuals through time(between sessions). Distance sampling methods allow forsighting or detection (capture) probabilities todecrease with increasing distance from the point orline. The modeling of detection probability as afunction of distance forms the basis for estimation.Trapping webs were designed to provide a gradient ofcapture probabilities. decreasing with distance from theweb center. Density estimation from the trapping web wasbased on three assumptions:1. All animals located at the center of the webwere caught with probability 1.0;2. Individuals did not move preferentially towardor away from the web center;3. Distances from the web center to each trapstation were measured accurately.Each web consisted of 12 trap lines radiating around acenter station. each line with 12 permanently-markedtrap stations. In order to increase the odds ofcapturing any animals inhabiting the center of a web.the center station had four traps. each pointing in acardinal direction. and the first four stations of eachtrap line were spaced only 5 m apart. providing a trapsaturation effect. The remaining eight stations in atrap line were spaced at 10 m intervals. The web thusestablished a series of concentric rings of traps. Trapsin the ring nearest the web center are close together.while the distances separating traps that form aparticular ring increase with increasing distance of thering from the web center. The idea is that the webconfiguration produces a gradient in trap density and.therefore. in the probability of capture. Three randomlydistributed trapping webs were constructed at each site.The perimeters of webs were placed at least 100 m apartin order to minimize homerange overlap for individualscaptured in the outer portion of neighboring webs.Measurement TechniquesEach site containing three webs was sampled for threeconsecutive nights during spring (in mid May or earlyJune) and summer (in mid July or early August for years1989 to 1993. then mid September to early October foryears 1994 through 2000). In that rodent populationswere not sampled monthly over the study period. there isno certainly that either spring or summer trapping timesactually captured annual population highs or lows. Basedon reproductive data in the literature. an assumptionwas made that sampling times chosen represent periods ofthe year when rodents have undergone. and wouldregister. 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 eachpermanent. numbered station (four in the center) on eachweb. for a total 444 traps over three webs. Traps werechecked at dawn each day. closed during the day. andreset just before dusk. Habitat. trap station number.species. sex. age (adult or juvenile). mass. bodymeasurements (total length. tail length. hind footlength. ear length). and reproductive condition (males:scrotal or non-scrotal; females: lactating. vaginal orpregnant) were recorded for each initial capture of anindividual. Each animal was marked on the belly with apermanent ink felt pen in order to distinguish it fromother individuals during the same trapping session. Thetrap station number for an initial capture related to aparticular trapping ring on a web and. therefore. to aparticular distance from the center of the web. The areasampled by a ring of traps was computed based oncircular zones whose limits are defined by pointshalfway between adjacent traps along trap lines; anadditional 25 m radius was added to the outer ring oftraps in order to account for homerange size ofindividuals caught on the outer ring.Analytical ProceduresArea trapped and number of individuals caught for eachring of traps was the basis for estimating theprobability density function of the area sampled. Theprogram DISTANCE produced the estimators used tocalculate density. Where sample size for a particularspecies and web was less than an arbitrarily chosenn=10. the number of individuals captured during thatsession was simply divided into the area of the web plusthe additional 25 m radius (4.9087 ha). This datasetincludes only the raw capture data. Unit of abundance = Count, Unit of biomass = Weight

Citation(s)

Friggens, M. (2008) "Sevilleta LTER Small Mammal Population Data", Albuquerque, NM: Sevilleta Long Term Ecological Research Site Database: SEV008. Available at: http://sev.lternet.edu/data/sev-8, accessed 2012.