Population Ecology of an Endemic Neotropical Island Rodent: Oryzomys bauri of Santa Fe Island, Galapagos, Ecuador

Abstract

SUMMARY (1) The rice rat Oryzomys bauri Allen is an endemic species restricted to the arid 2400 ha island of Santa Fe in the Galapagos Islands. Populations of 0. bauri in seven sites were studied over a 31-month period by mark-recapture methods. Population levels were relatively stable throughout the study. (2) Rat density was very significantly correlated with an index of quantity of vegetation, but was not correlated with number of vascular plant species. (3) Reproduction was restricted to the hot season, and occurred after arrival of the annual rains. Significant year-to-year variation in number of embryos was noted: more embryos per female occurred in a wet year than in a dry one. (4) Observed annual survivorship, a minimum estimate of true survivorship, was 3700, and did not differ significantly between females and males. Rates of disappearance did not differ significantly among study areas. (5) Male movements were significantly longer than female movements; recaptured animals moved very little between captures. (6) Compared to other Oryzomys populations, 0. bauri populations showed higher minimum survivorship and greater stability of population numbers. Oryzomys bauri may be converging on the population strategies used by desert Heteromyids.