The Effect Of Supplemental Food On The Life History Traits And Demography Of A Population Of Peromyscus Mexicanus
A population of Peromyscus mexicanus, inhabiting a wet tropical forest was provided with a high quality food supplement for one year (Experiment 1). Unfed and fed populations were compared to assess the effect of food addition on the reproductive and developmental characteristics of females and young, and to assess the effect of food addition on population dynamics. In a 6-month post-treatment period (Experiment 2), the response to food cessation was assessed.;Females on fed areas produced their first litter at an earlier age than unfed females in the 8-month rainy season but not in the 4-month dry season. Among pre-reproductive females, fed animals were more likely to survive to produce their first litter than unfed animals. Regardless of season, litter failure was twice as frequent among unfed females (29%-55% on unfed areas compared to 15%-32% on fed areas, in Experiment 1 and Experiment 2 respectively). The size of successful litters at weaning did not vary with food addition (x = 1.7) but weaned litters were smaller than litters at birth (x = 2.7). Fed females did not breed more frequently than unfed females. On both fed and unfed areas, females produced approximately 2 litters before disappearing from the study grid. Among females from whom lifetime reproductive success could be estimated, females on fed areas weaned twice as many offspring as unfed females. Juvenile survival was not influenced by food addition. Overall, 40% of the females and 26% of the males born on the study grids, were present on grids as adults. Weight and parity had little influence on reproductive patterns.;Population density did not vary significantly with food addition although increased juvenile recruitment resulted in slight density increases on fed areas. Adult and subadult recruitment rates did not vary with food addition. Home range size did not vary with food addition. In other studies, home range size decreased in response to food addition and immigration increased. Compared to other Peromyscus populations, density of this population was high and home range sizes were small. Density dependent aggression is suggested as a possible reason for the absence of a home range and immigration response in this study. Survival was also unaffected by food addition.;Females responded rapidly to a cessation of food supplementation. Females bred later and litter failure was more frequent on post-food than fed areas. Patterns on post-food areas were similar to those on an unfed control grid. Reproductive and demographic responses to food addition in Experiment 2 were similar to responses in Experiment 1 with two exceptions. Population density declined on all grids, regardless of food addition. Adult immigration increased on fed areas relative to unfed areas possibly due to reduced social stress resulting from density declines.
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