Chapter 4: Population Ecology

Wood

4.1 Population DynamicsI. Population Characteristics

92

II. Population-Limiting Factors 94

III. Population Growth Rates 97

I. Population CharacteristicsA. Population Density

i. The number of organisms per unit of area.

B. Spatial Distributioni. Dispersion the pattern

of spacing of a population.

ii. 3 patterns of dispersiona) Uniform

b) Clumped

c) Random

C. Population Rangesi. A species might not be

able to expand its population range because it cannot survive the abiotic conditions found in the expanded region.

II. Population-Limiting Factors

A. There are two categories of limiting factors—density-independent factors and density-dependent factors.

B. Density-Independent Factors

i. Any factor in the environment that does not depend on the number of members in a population per unit area is a density-independent factor.

Ex) Weather, fires, pollution, and natural disasters

C. Density-Dependent Factors

A. Any factor in the environment that depends on the number of members in a population per unit area is a density-dependent factor.

Ex) Disease, parasites, competition, and predation.

III. Population Growth RatesA. The population growth

rate (PGR) explains how fast a given population grows.

B. The natality of a population is the birthrate in a given time period.

C. Mortality is the death rate.

D. Exponential Growth Modeli. Exponential growth

occurs when the growth rate is proportional to the size of the population.

ii. Also known as a “J-Curve”

iii. All populations grow exponentially until some limiting factor slows the population’s growth

E. Logistic Growth Modeli. The population’s growth

slows or stops following exponential growth, at the population’s carrying capacity.

ii. Also known as a “S-Curve”

iii. A population stops increasing when the number of births is less than the number of deaths, or when emigration exceeds immigration.

iv. Emigration is people moving out of a population.

v. Immigration is people moving into a population.

F. Carrying Capacityi. The maximum number of

individuals in a species that an environment can support for the long term is the carrying capacity.

ii. Carrying capacity is limited by the energy, water, oxygen, and nutrients available.

G. Reproductive Patternsi. Species of organisms

vary in the number of births per reproduction cycle, in the age that reproduction begins, and in the life span of the organism.

R-strategist vs. K-strategist• An r-strategist is

generally a small organism.

• Short life span

• Produces many offspring

A k-strategist is generally a larger organism.

Long life span

Produces few offspring

4.2 Human PopulationI. Human Population

Growth p.100

II. Zero Population Growth p. 104

III. Age Structure p. 104

IV. Human Carrying Capacity p. 105

I. Human Population GrowthA. The study of human

population size, density, distribution, movement, and birth and death rates is demography.

B. For thousands of years, environmental conditions kept the size of the human population at a relatively constant number below the environment’s carrying capacity.

C. Humans have learned to alter the environment in ways that appear to have changed its carrying capacity.

D. Although the human population is still growing, the rate of its growth has slowed.

E. Population trends can be altered by events such as disease and war.

F. Human population growth is not the same in all countries.

II. Zero Population GrowthA. Zero population growth

(ZPG) occurs when the birthrate equals the death rate.

B. The age structure eventually should be more balanced with numbers at pre-reproductive, reproductive, and post-reproductive ages being approximately equal.

III. Age StructureA. A population’s age

structure is the number of males and females in each of three age groups:

i. Pre-reproductive stage

ii. Reproductive stage

iii. Post-reproductive stage

IV. Human Carrying Capacity

A. Scientists are concerned about the human population reaching or exceeding the carrying capacity.

B. An important factor is the amount of resources from the biosphere that are used by each person.