Study Notes on Ecology: Biotic and Abiotic Factors, Natural Selection

Influence of Environment on Population Dynamics

• The environment influences the population of organisms, including various factors and pressures.
• Key concepts covered in this lecture include biotic and abiotic factors.

Biotic Factors

• Definition:
    - Biotic factors refer to living components of an ecosystem.
    - Examples: Plants, animals, and microorganisms.
• Discussion Points:
    - In a visual example, living factors include:
      - Rats
      - Rabbits (two variations: brown and white)
    - Contextual recognition of plants as part of the biotic factors.

Abiotic Factors

• Definition:
    - Abiotic factors refer to non-living components of an ecosystem.
• Discussion Points:
    - Examples of abiotic factors in a visual example include:
      - Snow (cold temperatures, precipitation)
      - Influence on the living factors, such as bunny population.
    - The impact of abiotic factors on biotic factors includes:
      - Snow impacting fur density and color.
      - The ability of animals to survive varying snow conditions.

Interrelationship Between Biotic and Abiotic Factors

• Changes in abiotic factors can lead to shifts in living populations.
• Example discussed included:
    - Change in snow conditions affecting bunny populations.

Natural Selection Pressures

• Definition:
    - Natural selection pressures can show how certain characteristics and variations influence survival.
    - Changes in the population can occur before and after natural selection.
• Examples discussed include:
    - Peppered moth populations before and after the Industrial Revolution.

Types of Natural Selection

1. Stabilizing Selection

• Definition:
    - Stabilizing selection favors the average or common traits within a population.
• Key Example:
    - Robins that lay four eggs:
      - The norm for survival and reproductive success.
      - Higher survival rates for robins laying exactly four eggs; fewer for those laying too many (overcrowding) or too few (not sufficient).
• Visual Reference:
    - Graph showing the population shift from blue (original) to red (after selection).

2. Directional Selection

• Definition:
    - Directional selection occurs when one extreme of a trait is favored over others.
• Key Example:
    - Peppered moth populations:
      - Before industrialization: lighter moths had a higher population.
      - After pollution: darker moths increased due to better camouflage.
• Observations:
    - A clear increase in the dark moth population corresponds with environmental changes due to pollution.

3. Disruptive Selection

• Definition:
    - Disruptive selection favors extreme variations over intermediate traits.
• Key Example:
    - Rabbit populations:
      - Increased survival in gray and gray-white rabbits in a rocky environment.
      - Decreased survival for entirely white rabbits due to lack of camouflage.
• Conclusion:
    - A summary of the rise in populations of extreme traits and the decline of intermediates.

Conclusion

• Understanding concepts of stabilizing, directional, and disruptive selection is critical for examining survival and adaptation.
• Recognition of visual representations (graphs) related to each type of selection is essential for quizzes, particularly regarding how to identify and explain selection types based on examples.