Comparison of Fine Scale Vegetative Parameters at Active and Inactive Gulf Coast Kangaroo Rat Burrow Sites
Bell, Meagan M.
The Gulf Coast kangaroo rat (Dipodomys compactus) is an endemic Texas species belonging to the family Heteromyidae. Many heteromyid species, especially kangaroo rats, are highly specialized nocturnal granivorous rodents with external fur lined cheek pouches, bipedal cursorial locomotion, and adaptations for arid and desert conditions. Despite being one of six Texas endemic mammals, few studies have been conducted on habitat requirements, movement, and basic ecology of the Gulf Coast kangaroo rat with no long-term research. From April 2016 to March 2017, I have seasonally monitored burrowing activity of Gulf Coast kangaroo rats and recorded vegetative parameters at 63 randomly selected sites on a working cattle and wildlife ranch located in Guadalupe County, Texas. Sites with active burrows or a history of occupancy were monitored monthly. Within a 10-m radius plot at each site and using the Daubenmire frame cover estimate technique, I recorded percent cover of the following cover classes: bare ground, standing dead vegetation, litter, living grass, and living forbs. Additionally, I identified to the lowest taxonomic level the dominant live green grass and forb species in each Daubenmire frame and recorded the height of the tallest live grass, live forb, and standing dead vegetation. Using a spherical densitometer, I determined the percent woody canopy coverage at each Daubenmire frame. Twenty-two of 63 sites were occupied. Using Nested ANOVA, I found significantly greater cover of litter, taller standing dead, and taller grass (p < 0.001) at unoccupied sites, while percent cover of forbs, percent cover of bare ground, and distance to the nearest woody canopy was significantly greater (p < 0.001) at occupied sites. Using AICc model selection, the favored logistic model to predict the probability of site occupancy was positively influenced by percent bare ground and forb coverage. Percent woody canopy cover, litter, and grass negatively affected this probability of Gulf Coast kangaroo rat occupancy. This model can aid with future efforts to determine areas to protect Gulf Coast kangaroo rats or other similar species. Comparing the dominant plants at occupied and unoccupied sites, I found greater percentages of plantain (Plantago spp.), rosette grass (Dichanthelium spp.), paspalum (Paspalum spp.), sand bur (Cenchrus spinifex), and hogwort (Croton capitatus) at occupied sites. Except for plantain, these large seeded species are known colonizers of disturbed habitats and which may offer rich food sources. Together, these results suggest Gulf Coast kangaroo rats select for open disturbed areas, supporting plants that produce relatively large seeds that are easily extracted from sandy soils.
Kangaroo rat, Ecology, Logistic regression, South Texas
Bell, M. M. (2017). <i>Comparison of fine scale vegetative parameters at active and inactive Gulf Coast Kangaroo Rat burrow sites</i> (Unpublished thesis). Texas State University, San Marcos, Texas.