3.1-3.5 APES Notes

Outline of Main Topics

1. Generalists vs. Specialists

1.1 Definitions and Survival Traits

1.2 Ecological Tolerance

2. Reproductive Strategies

2.1 K-Selected Species

2.2 r-Selected Species

3. Population Dynamics

3.1 Carrying Capacity (K)

3.2 Population Characteristics

3.3 Growth Factors

4. Predator-Prey Relationships

5. Survivorship Curves

6. Growth Models and Prediction

Detailed Summary

1. Generalists vs. Specialists

1.1 Definitions and Survival Traits

• Specialists are species with a narrow ecological niche, meaning they have specific requirements (e.g., food needs such as bamboo) and are more vulnerable to extinction due to limited adaptability to new conditions.

• Generalists possess a wider ecological niche, allowing greater adaptability. They have broad food requirements and can thrive in various environments, making them less prone to extinction and more frequently invasive.

1.2 Ecological Tolerance

• The tolerance range indicates the conditions under which species can survive. Specialists tend to have a restricted range, while generalists can thrive under a broader array of conditions.

2. Reproductive Strategies

2.1 K-Selected Species

• These species produce few offspring with a high degree of parental care.

• They have longer lifespans and take longer to reach sexual maturity, resulting in a low biotic potential and slow population growth.

• Examples include most mammals and birds, which are more susceptible to environmental changes or invasions.

2.2 r-Selected Species

• Characterized by high reproductive rates, these species produce many offspring with little to no parental care.

• They tend to mature quickly and thus have a high biotic potential leading to rapid population growth. Examples include insects and fish.

• r-selected species are often more suited to rapidly changing environments and are more likely to become invasive due to their quick reproduction.

3. Population Dynamics

3.1 Carrying Capacity (K)

• Carrying capacity refers to the maximum number of individuals an ecosystem can support based on available resources (food, water, habitat).

• Populations may overshoot this capacity, leading to resource depletion and subsequent die-offs.

3.2 Population Characteristics

• Key population characteristics include:

  • Size (N): Total number of individuals in a specific area at a given time.

  • Density: Number of individuals per area, impacting competition and disease spread.

  • Distribution: How populations are spaced (random, uniform, clumped).

  • Sex Ratio: The balance of males to females affects breeding success.

3.3 Growth Factors

• Density-Dependent Factors: These include resource competition and disease, influencing populations primarily when they reach a certain size.

• Density-Independent Factors: Natural disasters affect populations regardless of their size.

4. Predator-Prey Relationships

• Hare and lynx populations illustrate the dynamic balance in predator-prey interactions:

  • As hare populations increase, lynx populations rise due to increased food.

  • Subsequent hare population declines due to predation lead to reduced lynx numbers.

5. Survivorship Curves

• Survivorship curves illustrate population survival rates over time, classified into three types:

  • Type I (K-selected): High survivorship in early and middle life, steady decline in old age (e.g., humans).

  • Type II: Constant mortality risk throughout life (e.g., birds).

  • Type III (r-selected): High mortality in early life, survival improves for those who reach adulthood (e.g., fish and plants).

6. Growth Models and Prediction

• Biotic Potential (r): The maximum growth an organism can achieve without limiting factors, often leading to exponential growth.

• Logistic Growth Model: Describes populations that grow rapidly and then slow as they approach carrying capacity, resulting in an S-shaped curve.

• Both growth models help predict population sizes over time, accounting for factors like births, deaths, immigration, and emigration.