Population fluctuations and extinctions of small rodents in coastal southern California.

The population dynamics of three sympatric rodents, Microtus californicus, Mus musculus, and Reithrodontomys megatolis was studied at four sites in coastal southern California. The study was undertaken to determine the extent of local demographic diversity in rodent populations.The populations of all rodent species became extinct on one site, while on another site the populations fluctuated widely and on two other sites the populations remained relatively stable. The most common species, Reithrodontomys, exhibited differences in reproduction, age class structure, recruitment, and survivorship on the two sites which were monitored for relatively long terms. Immigration was the main source of new individuals entering the sites where the Reithrodontomys population was most persistent.On a local scale, some life history characteristics are affected in a density dependent fashion. When viewed on a global scale, the non-equilibrium nature of the rodent populations becomes clear.