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Question

(a) List three density-dependent factors and three density-independent factors that can influence the population size of white-tailed deer. (b) Describe two ways that deer populations at low abundance can accelerate the process of ecological succession in a forest toward a climax stage. (c) Consider a region of temperate forest that contains 100,000 deer with a sex ratio of 3 females to 1 male, an infant mortality rate of 10, a crude birth rate of 40, and a crude death rate of 20. Only 10 percent of the females are able to reproduce. (i) Calculate population growth rate for white-tailed deer in this region. (ii) Calculate the number of deer that hunters would need to shoot in order to keep the deer population stable.

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a. Density-dependent factors: food resources, predation, disease, and suitable habitat. Density-independent factors: fires, storms, climate, and pollutants/contaminants.

b. Deer can expedite ecological succession by aiding in seed dispersal and consuming the shrub and grass species that compete with tree species for resources. The deer can also speed this process by consuming shade-intolerant pioneer tree species (e.g. pine, aspen, and cottonwood), thereby freeing up resources for the shade-tolerant tree species (e.g. spruce, oak, and cedar) that eventually dominate climax communities.

c. Given: 100,000 deer (sex ratio of 3 females to 1 male) 75,000 females (10 percent of females reproduce) 7,500 reproducing females 25,000 males Infant mortality rate = 10 (per 1,000 individuals) CBR = 40 (per 1,000 individuals per year) CDR = 20 (per 1,000 individuals per year)

i. Population growth rate = (CBR - CDR) / 10 = (40 - 20) / 10 = 2 percent

ii. If the deer population grows by 2 percent every year, hunters will need to kill 2 percent of the deer population each year to stabilize growth. 0.02 x 100,000 = 2,000 Therefore, hunters will need to kill 2,000 deer each year.

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