Population Growth & Resource Availability (College Board AP® Environmental Science): Study Guide

Environmental factors refer to the physical, biological, and chemical conditions of an environment that influence population dynamics

Key environmental factors include climate conditions and the availability of:

• food

• water

• shelter

• space

Population growth is directly tied to the availability of these resources

• When resources are abundant or sufficient, populations may grow

• When resources are scarce, growth slows or declines

For example:

• In deserts, the availability of water is a major limiting factor for plant and animal populations

• In tundra ecosystems, extreme cold limits plant growth and resource abundance

Resources are finite

• This means they are limited and can be exhausted (can be used up)

The resource base available to a population cannot support infinite growth due to its limited availability

• Example: Fisheries have finite fish populations that can be harvested sustainably

  • Overfishing depletes this resource base, threatening ecosystem balance and long-term food security

• On larger scales, finite resources include fossil fuels and freshwater supplies, which are critical for human survival

Renewable resources, while theoretically sustainable, can become finite when used faster than they regenerate

• Example: Forests are renewable, but excessive logging can lead to deforestation and long-term loss of biodiversity

When resources are abundant, populations can grow rapidly

• Abundant resources:

  • Reduce competition

  • Increase survival rates

  • Increase reproductive success

• Example: The abundance of food generated by modern agricultural systems supports human population growth.

Exponential growth is often observed when resources are temporarily plentiful, leading to a J-shaped population curve

• Example: Algal blooms occur in nutrient-rich waters, rapidly increasing algae populations until resources are depleted, causing the population to collapse

Resource abundance can also lead to overpopulation in certain species, resulting in ecological imbalance

• Example: Deer populations in areas without natural predators can grow excessively, leading to overgrazing and habitat degradation

When the resource base shrinks, populations face increased competition and stress, affecting their growth and survival

• Resource scarcity leads to:

  • Increased mortality: More individuals die due to lack of essential resources like food and water

  • Decreased fecundity: Reduced ability to reproduce due to insufficient food or habitat

  • Population decline: Growth slows and stabilizes at or below the carrying capacity, often fluctuating as resources are replenished or further depleted

• Example: Overgrazing by cattle can deplete grasslands, leading to soil erosion and reduced food availability for herbivores

Resource scarcity also creates unequal distribution:

• Stronger individuals or species outcompete weaker ones for limited resources

  • This leads to changes in population structure

  • Example: In drought conditions, plants with deeper roots may outcompete shallow-rooted species for water

Long-term scarcity can result in ecosystem collapse if critical resources are not replenished or restored

• Example: The collapse of the Easter Island civilization is often attributed to deforestation and unsustainable resource use, leading to societal and ecological decline