Population Growth and Carrying Capacity

Population

A group of organisms of the same species living in the same geographical area at the same time.

Population change

Changes in the number of individuals in a population over time.

Births (B)

Add individuals to a population through reproduction.

Deaths (D)

Remove individuals from a population through mortality.

Immigration (I)

Addition of individuals into a population from other populations.

Emigration (E)

Movement of individuals out of a population into other populations.

Population gain mechanisms

Populations increase through births and immigration.

Population loss mechanisms

Populations decrease through deaths and emigration.

Ideal population growth conditions

Abundant food, no predators, no disease, no competition, optimal temperature and favourable environment.

Lag phase

Slow population growth due to few reproducing individuals and low population density.

Log phase

Exponential growth where population increases at biotic potential; birth rate exceeds death rate.

Diminishing growth phase

Growth slows due to increasing environmental resistance and competition for resources.

Stationary phase

Population stabilises as carrying capacity is reached; birth rate equals death rate.

Population growth rate

Change in number of individuals in a population per unit time.

Population size

Total number of individuals in a population.

Population density

Number of individuals per unit area.

Population growth

Change in number of individuals in a population over time (can be positive or negative).

Factors increasing population size

Adequate food, water, habitat space, disease resistance, low predation, high reproductive rate, stable abiotic conditions.

Factors decreasing population size

Limited food, water, space, disease susceptibility, high predation, low reproductive rate, unstable abiotic conditions.

Biotic factors (population)

Living factors such as predation, competition and disease affecting population size.

Abiotic factors (population)

Non-living factors such as temperature, rainfall and disasters affecting population size.

Density-dependent factors

Factors that affect population size depending on population density; include food availability, predation and disease.

Density-independent factors

Abiotic factors that affect populations regardless of size; include weather events and natural disasters.

Effect of density-dependent factors

Stronger effect when population density is high.

Effect of density-independent factors

Equal effect regardless of population size or density.

Biotic potential

Maximum rate of population growth under ideal conditions with unlimited resources.

Fecundity

Reproductive capacity of a species affecting biotic potential.

Factors affecting biotic potential

Age of reproductive maturity, litter size, number of reproductive events, survival rate of offspring.

Environmental resistance

Factors that limit population growth and prevent indefinite exponential increase.

Population growth limitation

Occurs because environmental resistance restricts survival and reproduction.

Population movement types

Birth, death, immigration and emigration (BIDE model).

Immigration in animals

Movement of individuals into a population from other populations.

Immigration in plants

Occurs mainly through seed or spore dispersal.

Emigration effect

Reduces population size as individuals leave the population.

Population equilibrium

Balance between births, deaths, immigration and emigration.

Carrying capacity

The maximum population size that can be sustained by a particular environment over a long period of time.

Environmental carrying capacity

The theoretical equilibrium population size at which a population stabilises when resources remain constant.

Sustainable population size

The maximum population that can be supported indefinitely without degrading the habitat or limiting future generations.

Overpopulation

Occurs when population size exceeds the carrying capacity of the environment.

Overshooting carrying capacity

Rapid population growth beyond carrying capacity, usually during exponential growth phase.

Boom-and-bust population

Population that grows rapidly (boom), overshoots carrying capacity, then crashes (bust).

Effect of overpopulation

Habitat degradation and reduction in carrying capacity.

Environmental limitation on population

Population growth is limited by resources such as water, space, nutrients and environmental conditions.

Factors affecting carrying capacity

Water availability, space, nutrients, and extreme weather events such as droughts, floods and temperature extremes.

Environmental resistance

Factors that prevent populations from exceeding carrying capacity by limiting growth and survival.

Biotic potential vs environmental resistance

Biotic potential increases population growth while environmental resistance limits it.

Population equilibrium

Balance between biotic potential and environmental resistance that maintains population size around carrying capacity.

Ester Boserup theory

Carrying capacity is not fixed and can increase due to human technology and innovation.

Technology and carrying capacity

Improvements in technology increase carrying capacity by increasing resource production.

Example of Boserup theory

Use of artificial fertilisers increases food production and supports larger populations.

Per capita consumption

Higher consumption levels reduce carrying capacity for a given population.

Key idea of Boserup

Population growth can drive technological innovation that increases resource availability.

Thomas Robert Malthus theory

Population increases exponentially while resources increase linearly, leading to eventual resource shortage.

J-shaped population growth curve

Exponential growth curve showing rapid increase in population size.

Resource limitation

Occurs when population growth exceeds availability of resources.

Carrying capacity in Malthus theory

Upper limit to population growth caused by resource limitation and environmental degradation.

Population collapse

If carrying capacity is exceeded, population size decreases due to lack of resources.

Sustainability (carrying capacity context)

Use of resources in a way that does not harm future generations or degrade ecosystems.

Human carrying capacity

More complex concept including environmental, cultural and social limits.

Impact on future generations

Overuse of resources reduces ability of ecosystems to support future populations.

Relationship between population and environment

Population growth must remain balanced with resource availability and environmental health.