C4.1 Communities [IB Biology SL/HL]

C 4.1: Populations and Communities

Definition of Community

• A community includes all biotic factors (populations) in an ecosystem, interacting with each other.

• Example: Various populations of corals and fish in a reef ecosystem.

Intraspecific Relationships

• Intraspecific: "Within" the same species.

  • Types of Relationships:

    • Competition:

      • Organisms compete for resources like food, territory, mates (animals); light, pollinators, soil nutrients (plants).

      • Crucial for natural selection; individuals with advantageous traits thrive.

    • Cooperation:

      • Mutual benefits among same species. Examples include huddling for warmth, group hunting, defense strategies (e.g., schooling in fish).

Interspecific Relationships

• Interspecific: "Between" different species.

  • Types of Relationships:

    1. Herbivory:

       • Primary consumers eat primary producers (e.g., aphids on plants).

    2. Predation:

       • One species kills and eats another (e.g., hawk eating a mouse).

    3. Interspecific Competition:

       • Different species compete for the same resource (e.g., different barnacles on a rock).

    4. Mutualism:

       • Both species benefit from the interaction (e.g., hummingbird pollinating a flower).

    5. Parasitism:

       • Parasite lives on or in a host, harming it without usually killing it (e.g., tapeworms).

    6. Pathogenicity:

       • A pathogen (e.g., bacteria, fungus, virus) lives in a host, causing harm (e.g., potato blight causing plant death).

Examples of Mutualism

• Pea Plant & Rhizobium Bacteria:

  • Nodules on roots provide protection and carbohydrates for bacteria, while bacteria fix nitrogen for the plant.

• Mycorrhizae & Orchids:

  • Orchids offer carbohydrates through photosynthesis; mycorrhizae absorb nutrients from soil, benefiting both.

• Zooxanthellae & Corals:

  • Algae live in coral, providing carbohydrates and oxygen; coral provides shelter and carbon dioxide for photosynthesis, showcasing interdependence.