POPULATION DYNAMICS OF NOCTURNAL DESERT RODENTS: A NINE YEAR STUDY.

Abstract

Demography of nocturnal desert rodents was monitored for nine years. Three dissimilar areas were sampled with three distinct trapping configurations and time regimes. All three areas contained similar rodent species. Increased plant growth and seed production resulting from variations in rainfall seemed to have the most profound effect on both rodent densities and species composition. Deviations from the bimodal rainfall pattern occurred in the latter parts of 1972, 1977, and 1978 and early 1973, 1978, and 1979. During these times there was a 2-4 fold increase in rainfall. This pattern produced "desert blooms" in the spring of 1973, 1978, and to some extent 1979. In addition, 1972 and 1978 were years of high rainfall. The reaction of the rodents to the increased plant production was rapid and dramatic. Heteromyid numbers increased approximately six fold with some species increasing twelve fold within a matter of five months. The smaller heteromyids, Perognathus amplus and P. penicillatus, were the first to increase substantially, while the larger rodents reached peak populations in the following year. The resulting population crash that followed the high densities was as dramatic as the increase. Neotoma albigula populations did not increase substantially after the first rainfall phenomenon but did so dramatically after the second period of aberrant rains. The densities of N. albigula remained high long after the heteromyid populations decreased to "normal" levels. The three areas were found to be dominated by different species while the overall rodent densities in the three areas were very similar within the same time frame.