Granivorous rodent populations in deserts are primarily regulated through precipitation-driven resource pulses rather than pulses associated with mast-seeding, a pattern more common in mesic habitats. We studied heteromyid responses to mast-seeding in the desert shrub blackbrush (Coleogyne ramosissima), a regionally dominant species in the Mojave–Great Basin Desert transition zone. In a 5-year study at Arches National Park, Utah, USA, we quantified spatiotemporal variation in seed resources in mast and intermast years in blackbrush-dominated and mixed desert vegetation and measured responses of Dipodomys ordii (Ord's kangaroo rat) and Perognathus flavescens (plains pocket mouse). In blackbrush-dominated vegetation, blackbrush seeds comprised >79% of seed production in a mast year, but 0% in the first postmast year. Kangaroo rat abundance in blackbrush-dominated vegetation was highest in the mast year, declined sharply at the end of the first postmast summer, and then remained at low levels for 3 years. Pocket mouse abundance was not as strongly associated with blackbrush seed production. In mixed desert vegetation, kangaroo rat abundance was higher and more uniform through time. Kangaroo rats excluded the smaller pocket mice from resource-rich patches including a pipeline disturbance and also moved their home range centers closer to this disturbance in a year of low blackbrush seed production. Home range size for kangaroo rats was unrelated to seed resource density in the mast year, but resource-poor home ranges were larger (P < 0.001) in the first postmast year, when resources were limiting. Blackbrush seeds are higher in protein and fat but lower in carbohydrates than the more highly preferred seeds of Indian ricegrass (Achnatherum hymenoides) and have similar energy value per unit of handling time. Kangaroo rats cached seeds of these two species in similar spatial configurations, implying that they were equally valued as stored food resources. Blackbrush mast is a key resource regulating populations of kangaroo rats in this ecosystem.
Caching Trials, Willow Flats
Each record represents a single cache made by a kangaroo rat that had collected seeds at a bait tray in the field. Kangaroo rats were allowed to visit the tray multiple times within a trial. Fluorescent powder on the seeds aided the observer in locating the caches. Datum: WGS84
Rodent Trapping, Salt Valley
Each record is a capture of a small mammal at Salt Valley, Arches National Park, Grand Co., Utah. Trapping was conducted in 15 sessions of 2 or 3 nights each.
Rodent Trapping, Willow Flats
Each record is a capture of a small mammal at Willow Flats, Arches National Park, Grand Co., Utah. Trapping was conducted in 11 sessions of 2 or 3 nights each.
Telemetry, Salt Valley
Location records for radiocollared Ord's kangaroo rats in Salt Valley, Arches National Park, Grand Co., Utah.
Telemetry, Willow Flats
Location records for radiocollared Ord's kangaroo rats at Willow Flats, Arches National Park, Grand Co., Utah. Because sample sizes were fairly small, these data were combined with trapping data from the same time period and geographic area to produce utilization distributions for kangaroo rats. Trapping data were drawn from the companion data set "Rodent Trapping, Willow Flats.csv".
Randomization procedure for niche overlap
To investigate possible competition between D. ordii and P. flavescens at Salt Valley, we calculated the observed niche overlap for all species–time period combinations. The 163 trap stations were considered the common resource, and we used the Czechanowski index (Feinsinger et al. 1981) as an estimate of niche overlap:
1.0 – 0.5 Ʃ │pi – ri│
where pi and ri represent the proportions of captures at trap station i for D. ordii and P.
flavescens, respectively. We then used a randomization procedure with 1000 trials to generate a distribution of niche overlap matrices to which the observed values could be compared (True BASIC program, S. Jenkins). The procedure generated random numbers of captures at each trapping station for each species-time period combination while keeping fixed the values of (1) the total number of captures at each station over all species-period combinations and (2) the total number of captures for each species-period combination over all stations. We could then answer the question of whether there was more or less between-species niche overlap observed within time periods (1997, 1998, and 1999-2001) than expected by chance by examining the probability of the occurrence of the observed niche overlap values relative to the distribution of values generated by the randomization procedure.
Randomization.csv
Food Preference Trials
Usable trials in a cafeteria-style design to determine a heirarchy of preference for Ord's kangaroo rats (Dipodomys ordii) selecting to eat 4 seeds which occur at high frequencies in the plant community at Arches National Park, Grand Co., Utah: Coleogyne ramosissima, Ephedra viridis, Cowania mexicana, Wyethia scabra. Compositional analysis was used to determine preference heirarchy.
Food Preference.csv
Home Range Habitat Areas, Salt Valley
Inputs for a test of the resource abundance hypothesis. We used the home range data for the mast year (1997) and the first post-mast year (1998) in separate analyses to examine the correlation between home range area and SMPA (seed mass per unit area). We also examined the effect of year on home range size and SMPA using ANOVA. Data were collected at Arches National Park, Grand Co., Utah.
