APES Unit 3.5 Population Growth and Resource Availability

Explain how resource availability affects population growth

Density-Dependent Factors vs. Density-Independent Factors

Influences an individual’s probability of survival

1. Density-Dependent: Based on population size

   1. ex. Biotic/Abiotic: Competition, Predation, Disease, Parasitism, Waste, Social/Physiological stress

   2. Toxic waste: Limiting factor (esp. dense pops)

   3. Stress → Infertility, reduced parental care, emigration

2. Density-Independent: At any population size

   1. ex. ~Abiotic: Natural disasters, weather/climate change, Anthropogenic events

*Both used for growth models

Exponential Growth Model

1. Estimates pop’s future size after given period of time based on biotic potential

   • J-shaped

     1. Small size = Small growth rate

     2. Population increase → more mature individuals → bigger growth rate

   • Grows at fixed rate

   • Density-Independent + Density-Dependent results

   • Moreso represents r-Selected Species: Resources =/= limiting

2. Stops growth when environmental limit is reached

   • Scarcity of resources

   • Increase in Parasites

   • Disease

   • Predators

3. Eventually reaches carrying capacity

Logistic Growth Model

Describes populations that are limited by carrying capacity

• S-Shaped: Exponential → Levels out

  1. ½ Carrying Capacity: Inflection point = slows down → stop growth

     • Pop constrained by resource availability

     • → Resources begin limiting pop growth

  2. Overshoot: Rapid growth → Less food for offspring

  3. Dieback: Major environmental consequence (ex. Overshoot) → large percentage of deaths

• Often K-Selected

• Density-Dependent Factors

Resource Bank Shrinkage: Habitats

Habitats are also Limiting Factors

• ex. Urban crowding, deforestation/logging

• ex. Sub-Saharan Africa: 177M → 657M in 50 years

1. Reduces land and water available to each individual