Population dynamics Births Deaths Births and immigration add individuals to a population. Deaths and emigration remove individuals from a population. Figure 53.3 Immigration Emigration

Patterns of dispersion within a population’s geographic range (a) Clumped (b) Uniform Figure 53.4 Patterns of dispersion within a population’s geographic range (c) Random

Survivorship curves for squirrels shows relatively constant death rate 1,000 100 Number of survivors (log scale) Females 10 Males Figure 53.5 Survivorship curves for male and female Belding’s ground squirrels 1 2 4 6 8 10 Age (years)

Survivorship Curves Number of survivors (log scale) 1,000 I 100 II 10 Figure 53.6 Idealized survivorship curves: Types I, II, and III III 1 50 100 Percentage of maximum life span

Variation in the size of seed crops in plants (a) Dandelion Figure 53.9 (b) Coconut palm

2,000 = 1.0N 1,500 = 0.5N Population size (N) 1,000 500 5 10 15 Exponential Growth Model 2,000 dN = 1.0N dt 1,500 dN = 0.5N dt Population size (N) 1,000 500 Figure 53.10 Population growth predicted by the exponential model 5 10 15 Number of generations

The J-shaped curve of exponential growth characterizes some rebounding populations 8,000 6,000 Elephant population 4,000 2,000 Figure 53.11 Exponential growth in the African elephant population of Kruger National Park, South Africa 1900 1920 1940 1960 1980 Year

Logistic Growth model Exponential growth 2,000 = 1.0N 1,500 K = 1,500 dN = 1.0N dt 1,500 K = 1,500 Population size (N) Logistic growth 1,000 dN 1,500 – N = 1.0N dt 1,500 Figure 53.12 Population growth predicted by the logistic model 500 5 10 15 Number of generations

The growth of laboratory populations fits an S-shaped curve which hovers around the Carrying Capacity of the area. 1,000 180 150 800 120 Number of Paramecium/mL 600 Number of Daphnia/50 mL 90 400 60 200 30 Figure 53.13 How well do these populations fit the logistic growth model? 5 10 15 20 40 60 80 100 120 140 160 Time (days) Time (days) (a) A Paramecium population in the lab (b) A Daphnia population in the lab

Percentage of juveniles producing lambs Decreased reproduction at high population densities 100 80 60 Percentage of juveniles producing lambs 40 Figure 53.16 20 200 300 400 500 600 Population size

Territoriality (a) Cheetah marking its territory (b) Gannets Figure 53.17 (b) Gannets

50 2,500 Wolves Moose 40 2,000 30 1,500 Number of wolves Changes in predation pressure can drive population fluctuations 50 2,500 Wolves Moose 40 2,000 30 1,500 Number of wolves Number of moose 20 1,000 10 500 Figure 53.19 Fluctuations in moose and wolf populations on Isle Royale, 1959–2006 1955 1965 1975 1985 1995 2005 Year

Number of hares (thousands) Number of lynx (thousands) Snowshoe hare 160 120 9 Figure 53.20 Population cycles in the snowshoe hare and lynx Lynx Number of hares (thousands) Number of lynx (thousands) 80 6 40 3 1850 1875 1900 1925 Year

Human population growth 7 6 5 4 Human population (billions) 3 2 The Plague Figure 53.22 Human population growth (data as of 2006) 1 8000 B.C.E. 4000 B.C.E. 3000 B.C.E. 2000 B.C.E. 1000 B.C.E. 1000 C.E. 2000 C.E.

Age-structure pyramids for the human population of three countries Rapid growth Slow growth No growth Afghanistan United States Italy Male Female Age Male Female Age Male Female 85+ 85+ 80–84 80–84 75–79 75–79 70–74 70–74 65–69 65–69 60–64 60–64 55–59 55–59 50–54 50–54 45–49 45–49 40–44 40–44 35–39 35–39 30–34 30–34 25–29 25–29 20–24 20–24 Figure 53.25 Age-structure pyramids for the human population of three countries (data as of 2005) 15–19 15–19 10–14 10–14 5–9 5–9 0–4 0–4 10  8 6 4 2 2 4 6 8 10  8 6 4 2 2 4 6 8 8 6 4 2 2 4 6 8 Percent of population Percent of population Percent of population

K = carrying capacity Population size (N) dN K – N = rmax N dt K Review: Population Growth Curve K = carrying capacity Population size (N) dN K – N = rmax N dt K Number of generations

You should now be able to: Define and distinguish between the following sets of terms: density and dispersion; clumped dispersion, uniform dispersion, and random dispersion; life table and reproductive table; Type I, Type II, and Type III survivorship curves; semelparity and iteroparity; r-selected populations and K-selected populations. Explain how ecologists may estimate the density of a species.

Explain how limited resources and trade-offs may affect life histories. Compare the exponential and logistic models of population growth. Explain how density-dependent and density-independent factors may affect population growth. Explain how biotic and abiotic factors may work together to control a population’s growth.