6.1 Notes

Population Distribution and Abundance

  • Population: A group of interbreeding individuals occupying a specific area at the same time.

    • Defined by natural boundaries (e.g., species in a lake) or human-created boundaries (e.g., national parks).

Key Concepts

  1. Population Distribution:

    • The size, shape, and location of the area occupied by a population.

  2. Population Abundance:

    • The total number of individuals within a specific area.

  3. Population Density:

    • The number of individuals per unit area.

  • Population Ecology:

    • The study of factors affecting population size and changes over time and space.

Niche Concept and Distribution Patterns

  • Niche:

    • The role of a species in its environment which includes interactions with both biotic and abiotic factors.

      • Habitat Requirements (Grinnell, 1917): Factors like temperature, water availability, food, and shelter.

      • Functional Role (Elton, 1927): Roles like predator or primary producer.

      • Interrelationships (Hutchinson, 1957): Includes factors that affect growth, survival, and reproduction.

  • Fundamental Niche:

    • The potential habitat of a species without biotic interactions.

  • Realized Niche:

    • The actual niche limited by biotic interactions such as competition and predation.

Examples of Niche Dynamics

  • Barnacles example:

    • Fundamental niches overlap, but competition reduces the realized niche for certain species (e.g., Chthamalus vs. Balanus).

Population Distribution Patterns

  • Studied at various scales; examples include the distribution patterns of kangaroos in Australia.

Climate and Distribution

  • Climate affects distribution directly (e.g., temperature, precipitation) and indirectly through food production, habitat availability, and interactions among species.

Types of Distribution Patterns

  1. Random Distribution:

    • Occurs with neutral interactions; individuals have equal chances of being anywhere in the area.

  2. Clumped Distribution:

    • Individuals grouped in patches, often due to social behavior or resource concentration.

  3. Regular (Uniform) Distribution:

    • Individuals are evenly spaced, often due to territoriality or competition for scarce resources.

Population Density

  • Defined as the number of individuals per unit area or volume.

  • Smaller organisms generally have higher densities than larger organisms.

Rarity and Extinction Risk

  • Factors Affecting Rarity:

    1. Geographic range (extent of occurrence)

    2. Habitat tolerance (broad vs. narrow)

    3. Local population size (large vs. small)

  • Species like the House Sparrow are common; others like the Northern Spotted Owl are rare and more vulnerable to extinction.

Causes of Extinction

  • Common Reasons:

    • Habitat loss, competition, climate change, disease, and human activities.

  • Case Study: Passenger Pigeon:

    • Once abundant, the population drastically declined due to over-hunting and habitat destruction.

    • Last known individual died in 1914, highlighting the impacts of neglecting conservation.

Conservation Efforts

  • The Endangered Species Act (ESA) was established to protect endangered species and habitats in the U.S.

  • Examples of successful recoveries, such as the California Condor and Bald Eagle, showcase the importance of conservation measures.

Notes prepared from lecture material and biotic interactions relevant to ecological studies.