Density dependence in roe deer population dynamicsKjellander, Petter
Density dependence on individual and cohort level was investigated experimentally in a twelve-year study on free living roe deer (Capreolus capreolus) population in Sweden. The deer were protected for 4 years, which caused density to increase from 9 to 36 deer/km2. Then density was reduced to 8 deer/km2by two seasons of intensive culling. After this the population has been allowed to recover. The study was based on radio telemetry with 382 marked deer. Food availability and browsing pressure was monitored by an exclosure study.
Density dependence was demonstrated in important components of demography, i.e. body weight, growth, fecundity and survival. I also found that negative effects of high density experienced during the first two years of life will affect the deer for the rest of their lives (cohort effects). Fecundity (ovulation), fawn/marked doe in fall and body weight were found to decrease in all age classes after the density increase. Likewise, body size decreased in age classes raised during the period with high density. Long-term consequences of early development on lifetime reproduction and survival were significant. Survival decreased in all age classes, also in the prime age animals. Lowest survival and strongest density effects were found in juveniles. The negative effect on survival persisted in all age classes at least for three years after peak density. I hypothesize that much of this time lag was a cohort effect coupled to lasting effects on body mass.
Male summer territory size decreased significantly with increasing population density, as did winter range size in both sexes. I suggest that much of the effect of deer density on winter home range size was coupled to the solitary behavior and social system of roe deer, with possible effects of dominance rank also outside the mating season. Further, no relationship was found between population density and the main winter food, standing bilberry (Vaccinium myrtillus) biomass, but a significant effect on the twig abundance was observed. Finally, I found indications of food limitation that might be both dampened and fortified by density independent changes in the environment.
Keywordscohort effect; demography; density dependence; lifetime reproduction; population limitation; predation; roe deer; survival; social system
Published inActa Universitatis Agriculturae Sueciae. Silvestria
2000, number: 154
Publisher: Department of Conservation Biology, Swedish University of Agricultural Sciences
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