Population Ecology: Key Concepts and Growth Models

age structure

Percentage of the population (or number of people of each sex) at each age level in a population.

asexual reproduction

Reproduction where a mother cell divides to produce two identical daughter cells (clones). Common in single-celled organisms.

biotic potential

Maximum rate at which a species' population can increase when no limits exist on growth.

carrying capacity (K)

Maximum population of a species that a habitat can support over a given period.

dieback

Sharp reduction in population size when numbers exceed the habitat's carrying capacity.

environmental resistance

All limiting factors that work together to limit population growth.

exponential growth

Growth where population size increases at a constant rate per unit time; produces a J-shaped curve.

intrinsic rate of increase (r)

Rate a population would grow if it had unlimited resources.

K-selected species

Species that produce few, large offspring and invest much time and energy to help them survive to adulthood.

linear growth

Growth that increases by a fixed amount each time period (e.g., 2, 4, 6, 8...).

logistic growth

Population growth that starts exponentially but slows as it reaches carrying capacity; S-shaped curve.

population density

Number of individuals of a population in a specific area or volume.

population dispersion

General pattern in which individuals are spaced throughout a habitat.

population distribution

Variation of population density across a geographic area (e.g., dense cities vs. sparse rural areas).

population dynamics

Factors that increase or decrease population size and affect age and sex composition.

population size

Total number of individuals in a population's gene pool.

r-selected species

Species that reproduce early, have many small offspring, and little parental care.

reproduction

Production of offspring by one or more parents.

sexual reproduction

Reproduction by combining gametes (egg and sperm) from both parents, creating offspring with mixed traits.

survivorship curve

Graph showing the number of survivors in different age groups for a species.

crude birth rate

Annual number of live births per 1,000 people in a population at midyear.

crude death rate

Annual number of deaths per 1,000 people in a population at midyear.

demographic transition

Theory that as countries industrialize, death rates fall first, followed by declines in birth rates.

emigration

Movement of people out of a geographic area.

family planning

Providing info and contraceptives to help people choose the number and spacing of their children.

fertility

The number of births that occur to an individual woman or within a population.

immigration

Movement of people into a country or area to live permanently.

infant mortality rate

Number of babies (per 1,000 births) that die before their first birthday.

life expectancy

Average number of years a newborn can expect to live.

population change

(Births + Immigration) − (Deaths + Emigration); the net population increase or decrease.

replacement-level fertility

Number of children a couple must have to replace themselves (usually 2.1 in developed, 2.5 in developing countries).

total fertility rate (TFR)

Average number of children a woman will have during her childbearing years (ages 15-44).