Key Concepts of Population Growth Models to Know for AP Biology

Population growth models help us understand how species increase in number over time. They include exponential and logistic growth, influenced by factors like carrying capacity and density, which shape ecosystems and impact species survival in various environments.

1. Exponential growth model

   • Describes population growth in an ideal, unlimited environment.
   • Characterized by a constant rate of increase over time.
   • Results in a rapid increase in population size, often seen in newly colonized areas.

2. Logistic growth model

   • Accounts for environmental limitations on population growth.
   • Growth rate decreases as the population approaches carrying capacity.
   • Results in a more stable population size over time compared to exponential growth.

3. Density-dependent factors

   • Factors that affect population growth based on population size (e.g., competition, predation).
   • As population density increases, these factors can lead to decreased birth rates or increased death rates.
   • Examples include disease spread and resource availability.

4. Density-independent factors

   • Factors that impact population growth regardless of population size (e.g., natural disasters, climate).
   • Can cause sudden and drastic changes in population size.
   • Examples include hurricanes, droughts, and human activities.

5. Carrying capacity

   • The maximum population size that an environment can sustainably support.
   • Influenced by resource availability, habitat space, and environmental conditions.
   • Populations tend to stabilize around this capacity in the logistic growth model.

6. Intrinsic rate of increase (r)

   • The maximum potential growth rate of a population under ideal conditions.
   • Influenced by factors such as birth rates and death rates.
   • Higher r values indicate faster population growth.

7. J-shaped growth curve

   • Represents exponential growth where the population size increases rapidly.
   • Characterized by a steep upward slope, indicating unchecked growth.
   • Often seen in populations with abundant resources and few limiting factors.

8. S-shaped growth curve

   • Represents logistic growth where population growth slows as it approaches carrying capacity.
   • Characterized by an initial exponential phase followed by a plateau.
   • Reflects the balance between growth and environmental resistance.

9. K-selected species

   • Species that produce fewer offspring but invest more resources in raising them.
   • Typically found in stable environments where competition for resources is high.
   • Examples include elephants and humans.

10. r-selected species

    • Species that produce many offspring with little parental care.
    • Thrive in unstable or unpredictable environments where rapid population growth is advantageous.
    • Examples include insects and small rodents.