This experiment was conducted at three sites, each with a
grassland-to-shrubland ecotone. Two of the sites, JER Pasture 9 and
JER Pasture 12A, occur on the USDA Agricultural Research Service
Jornada Experimental Range. One site, CDRRC Pasture 3, is located on
New Mexico State University’s Chihuahuan Desert Rangeland Research
Center. Climate is arid to semi-arid, with long-term (90-year) mean
annual temperature of 15C and mean annual precipitation of 250 mm,
over half of which occurs in summer (July–September).
Sites were chosen to contain 3 distinct habitat types (or “ecotone
positions”): grassland, ecotone, and shrubland. Within each habitat
type of each site, a 300m x 100m rectangular trapping area was
established. Trapping locations were arranged as a 16 x 6 grid within
the trapping area with 20m spacing between traps, yielding 96 traps
per habitat and 288 traps per site for a total of 864 trapping
locations for the entire study. The trapping area encompasses the
quadrats assessed for plant cover in data package
knb-lter-jrn.210262001, which was used to calculate annual net primary
productivity estimates available in data packages
knb-lter-jrn.210262004 and knb-lter-jrn.210262005.
Livetrapping was conducted annually over 4 consecutive nights using
Sherman model XLKR live traps baited with a seed mix. Traps were set
in late afternoon/early evening and checked the following morning. Ear
tags were affixed to rodents with ears large enough to support them.
Rodents too small to affix ear tags were given a unique ID which was
labeled on their ventral side with a permanent marker. Blue permanent
markers were used on rodents trapped on the first night, black on the
second night, and red on the third night. No permanent markers were
used on rodents caught on the fourth night, but ear tags were still
administered if possible. In addition to tagging/marking, rodents were
weighed, identified to species, and assessed for sex, reproductive
status, and maturity status. This dataset includes only the first
capture of each individual each year on a habitat type within a site
(a relative abundance index).
From 2004 to 2007, livetrapping occurred mostly during July. From 2008
to 2018, when the project had become part of long-term sampling by
Jornada Basin LTER program, livetrapping occurred during October. The
three habitat types within each site were trapped during the same
week.
Observations in the dataset may have missing tags for several reasons,
including: 1) rodents caught on the fourth night whose ears were too
small for an ear tag, 2) rodents who escaped before an ear tag could
be read, 3) rodents who escaped before an ear tag could be affixed,
and 4) observer error. Reasons 2-4 may also apply to observations with
missing values for Sex, Rep, and Status.
Also available are measures of rodent biomass in data package
knb-lter-jrn.210262010.
