POTENTIAL AND REALIZED REPRODUCTION IN A TROPICAL POPULATION OF PEROMYSCUS (RODENTIA)

Data from a laboratory colony of Peromyscus nudipes founded with indiv iduals trapped at 10-degrees-N latitude near Monteverde, Costa Rica, w ere compared with published and new data on the same population in the wild as a basis for assessing phenotypic plasticity in life-history c haracteristics. Mean litter size was almost identical in the wild and in the laboratory (2.8 +/- 0.1 and 2.9 +/- 0.2, respectively). In the laboratory, females matured at 6-8 weeks of age and males had matured by ca. 9-11 weeks of age. The available evidence suggests that first r eproduction is delayed in the wild relative to the laboratory. The fre quency with which litters were produced was much higher in the laborat ory than in the wild. Females averaged 7.4 +/- 0.8 litters/year in the laboratory, with a maximum of 11 litters/year, whereas females in the wild produced no more than 5 litters/year and may average about one-h alf that many. These results suggest that phenotypic plasticity in age at first reproduction and reproductive rate is high. In the wild, the se mice evidently realize only a small fraction of their reproductive potential. The difference apparently is due to delay of first reproduc tion and less-frequent production of litters in the wild, and not to d ifferences in litter size or the frequency of ovulation, mating, and c onception.