Kangaroo rats (Dipodomys spectabilis) are indigenous to the Chihuahuan desert. They construct sandy mounds that can be 30-40 meters in diameter. Kangaroo rats are classified as keystone species within drylands and have the ability to effect vegetation dynamics and erosional processes through their mound building activities. While it has been broadly established that kangaroo rats and their mounds can impact desert vegetation, few studies have explored this in a spatially explicit manner. Furthermore, little research has been done to understand the longevity and population dynamics of Kangaroo rat mounds over time. Here we use current and archival high-resolution imagery to map and quantify kangaroo rat mounds through time in the Jornada LTER. Specifically, we are interested in the spatial distribution, number, and size of Kangaroo rat mounds and how they interact with vegetation dynamics (shrub and herbaceous cover) through time. Here we use CORONA (1968, 2.8m resolution) and NAIP (2011, 1m resolution) imagery from the Jornada LTER to quantify the change in abundance of Kangaroo rat mounds in a 1 x 1 km area of the Jornada Experimental Range within the Chihuahuan Desert, north east of Las Cruces New Mexico. This area generally receives about 247 mm of rainfall annually and is dominated by mesquite shrublands interspersed with remnant black grama grasslands.
Results/Conclusions
This area of the Jornada Experimental Range underwent shrub encroachment during the time-period, with shrub density increasing from just 58 km-1 in 1968 to 510 km-1 in 2011. Preliminary results show that the density of the Kangaroo rat mounds have increased (by 23%, from 47 to 58 km-2), while the average mound size decreased (by 33%, from 176 m2 to 118 m2). The decreasing size of kangaroo rat mounds could indicate that there is increased intraspecific competition between Kangaroo rat colonies for food resources. Alternatively, some mounds may have become inactive, allowing ‘recolonization’ by neighboring herbaceous and woody vegetation. This explanation would be consistent with reports that Kangaroo rat populations decline with shrub encroachment. Our results do not allow clear inference of the relationship between shrub encroachment and the presence of Kangaroo rat mounds. However, based on other research at the Jornada where soil exposure and wind-blown sediments are associated with shrub encroachment, it is possible that the presence of Kangaroo rat mounds in 1968 may have facilitated mesquite shrub proliferation. Further research will determine the possible connections between Kangaroo rat mounds and surrounding features.