Ecology and Human Population Dynamics: Species, Growth, and Demographic Models Save Groups

Generalist species

Species that can live in a wide range of habitats and eat a variety of foods; adaptable to changing environments (e.g., raccoons, cockroaches).

Specialist species

Species that thrive in specific habitats and have narrow diets; sensitive to environmental changes (e.g., koalas, pandas).

Difference between generalists and specialists

Generalists have broad niches and adapt easily; specialists have narrow niches and are more vulnerable to change.

K-selected species

Large, few offspring, high parental care, long lifespan, stable environments, high competition (e.g., elephants, humans).

r-selected species

Small, many offspring, little parental care, short lifespan, unstable environments, low competition (e.g., mice, insects).

Biotic potential

The maximum reproductive rate of a population under ideal environmental conditions.

Invasive species characteristics

Usually r-selected; reproduce quickly and thrive in disturbed ecosystems.

Survivorship curve

A graph showing the survival rate of a cohort from birth to the oldest age reached.

Type I survivorship curve

High survival early in life, die off in old age (K-selected, e.g., humans).

Type II survivorship curve

Constant death rate throughout life (e.g., birds, reptiles).

Type III survivorship curve

Many die young, few survive to adulthood (r-selected, e.g., fish, insects).

Carrying capacity (K)

The maximum population size that an environment can sustain indefinitely with available resources.

What happens if population exceeds carrying capacity?

Resources deplete → death rate rises → population declines back to or below K.

Logistic growth curve

S-shaped curve showing population growth that slows as it approaches carrying capacity.

Population growth and resources

When resources are abundant, growth accelerates; when limited, growth slows or declines.

Limiting factors of population growth

Resource availability and environmental constraints that cap population size.

Age structure diagram

Graph showing the distribution of ages in a population; reveals growth trends.

Rapid growth age structure shape

Pyramid shape — many young individuals.

Stable population shape

Column shape — roughly equal age groups.

Declining population shape

Inverted pyramid — fewer young individuals.

Total Fertility Rate (TFR)

Average number of children a woman is expected to have in her lifetime.

Replacement level fertility

2.1 children per woman — keeps population stable.

Factors affecting TFR

Age at first childbirth, education, healthcare, access to family planning, and government policies.

Infant mortality rate

Number of infant deaths per 1,000 live births; affected by healthcare and nutrition.

Human population growth factors

Influenced by birth rate, death rate, infant mortality, family planning, education, and nutrition.

Density-independent factors

Natural events (storms, fires, droughts) that limit population regardless of size.

Density-dependent factors

Resource-related limits like food, water, disease, or space that intensify with population size.

Rule of 70

Doubling time (years) = 70 ÷ growth rate (%).

Earth's carrying capacity

The maximum number of humans Earth can sustain with available resources.

Demographic Transition Model (DTM)

Describes changes in birth and death rates as a country develops economically.

Stage 1: Pre-industrial

High birth & death rates → slow population growth.

Stage 2: Transitional

Death rates drop, birth rates remain high → rapid growth.

Stage 3: Industrial

Birth rates decline → growth slows.

Stage 4: Post-industrial

Low birth & death rates → stable or declining population.

Developing country characteristics

High infant mortality, many children in the workforce.

Developed country characteristics

Low infant mortality, higher education, smaller families, longer life expectancy.