Rodent community dynamics as mediated by environment and competition in the San Joaquin Desert

We studied a rodent community in the San Joaquin Desert of California, United States, from 1993 to 2016. Using biannual trapping on a 144-trap plot, we found that mice of various species were rarely caught in appreciable numbers in contrast to many other studies of rodent communities in arid North America. Most captures were made of 3 species of kangaroo rats: giant kangaroo rat (Dipodomys ingens), Heermann's kangaroo rat (D. heermanni), and San Joaquin kangaroo rat (D. nitratoides). The site was dominated by D. ingens, which, in many years, was the only kangaroo rat captured. Precipitation varied extremely across the study period with 2 periods of high rainfall and 2 periods of well-below-average rainfall. The rodent community seems to have been responding to both bottom-up control and the competitive dominance of D. ingens. In particular, our trapping showed 2 complete cycles of abundance of D. ingens, from very high numbers to crashes with either no or only 2 individuals caught during a session. In both cases, the species recovered after these crashes in abundance. Although we found some D. ingens living to 4–5 years, and D. heermanni and D. nitratoides living up to 3 years, annual survivorship estimates were low compared with other studies of kangaroo rats. Other studies, however, were of much shorter duration and therefore may have missed eventual downturns in population abundances. Dipodomys ingens is a protected species, and from a conservation standpoint, our data indicate that populations can be highly resilient even in the face of high environmental variability.