Effects of seed supplementation on a population of Merriam's Kangaroo rats (Dipodomys Merriami)

Includes bibliographical references (leaves 29-40)Temporal and spatial variability in food abundance plays an important role in population dynamics and the evolution of life histories. By observing responses to natural or experimental changes in food abundance we can gain key insights into the life-history strategy, adaptability, and possible future of populations under global climate change. I tested how food supplementation affected female survival and reproductive effort in a population of Merriam's kangaroo rat (Dipodomys merriami) at Theodore Payne Wildlife Sanctuary, Los Angeles County, California. Although my study occurred in a normal precipitation year (94. 7% of mean rainfall), it followed a two-year drought (22. 7 - 51.5% of mean rainfall), during which population densities steeply declined (from 61.1to7.6 individuals/ha) and seed caches were presumably depleted. Kangaroo rats were monitored at four sites through live trapping between August 2006 and November 2008. Supplemental seed was provided weekly at two of the four sites from February to June 2008 (breeding season) for all females and juveniles. During this supplementation period kangaroo rat densities on treatment plots (13.3/ha) were nearly twice as high as on control plots (7.5/ha), and females on treatment sites averaged 2.2 times more weaned offspring than control females. Despite similar survival rates of adult females during the supplementation period (91 % control vs. 92% treatment), five months after this period densities were nearly equal (9.0 vs. 7.6/ha, respectively), indicating that supplementation did not have a long-term effect. Seed resources appear to maintain population densities of kangaroo rats by limiting pre-weaning juvenile survival rather than increasing adult survival. This finding is consistent with a bet-hedging life history strategy. Although this strategy is advantageous when food supplies are unpredictable (as they were in my study), a prolonged drought can cause rapid population declines as females dramatically reduce reproductive effort. Such populations may be highly vulnerable to local extirpation as a consequence of extended droughts, which are predicted to become more frequent by climate change models for this region. As a widespread species, the decline of D. merriami could have significant consequences for the Mojave Desert ecosystem in which it occurs