PPT 14

Ecology Overview

• Ecology: The science that studies interactions between organisms and their environments.

• Levels of Ecology:

  • Individual: Single organisms.

  • Population: A group of the same species.

  • Community: Different species interacting within an ecosystem.

  • Ecosystem: Communities interacting with their abiotic environment.

  • Landscape: Large-scale studies encompassing multiple ecosystems.

  • Biomes: Major ecological community types defined by climate, vegetation, and fauna.

  • Biosphere: The global sum of all ecosystems, impacting and being impacted by climate change.

Interactions in Ecosystems

• Abiotic Factors: Physical and chemical components of an ecosystem that affect living organisms.

  1. Temperature

     • Affects stability/structure of cells and biochemical reaction rates; organisms have a limited temperature range.

  2. Water

     • Essential in terrestrial habitats; determines biome distributions based on availability.

  3. Sunlight

     • Main energy source for most organisms; crucial for photosynthesis.

Additional Abiotic Factors

4. Nutrients: Essential for growth; includes nitrogen (N) and phosphorus (P).

5. Gases: Influence organism behavior and ecosystems, especially in aquatic systems.

6. pH: Affects nutrient availability (e.g., acidic soils).

7. Substrate Structure: Influences plant growth and water retention; varies between soil types and rock formations.

8. Disturbances: Events like droughts, floods, or human activities that drastically impact communities.

Habitat vs. Niche

• Habitat: The specific environment an organism resides in, including geographical and abiotic conditions (temperature, rainfall, salinity).

• Niche: The role an organism plays in its ecosystem, encompassing all interactions with biotic and abiotic resources.

Interspecific Competition: Case Study

• Experiment by Joseph Connell:

  • Studied interactions between barnacle species: Chthamalus stellatus (higher on rocks) and Balanus balanoides (lower).

  • Results:

    • Removing Balanus allowed Chthamalus to occupy a larger area, demonstrating competition's impact.

  • Conclusion:

    • Interspecific competition limits the realized niche of Chthamalus.

Competitive Dynamics

• Biotic Interactions:

  • Competition: Negative interaction where organisms exploit the same limited resources.

    • Types:

      • Intraspecific: Same species competition.

      • Interspecific: Different species competition.

      • Gause’s Principle: Two species competing for the same resource cannot coexist; slight advantages lead to exclusion.

  • Fundamental Niche: Potential niche without competition.

  • Realized Niche: Actual occupation and use of resources in a specific environment.

Ecosystem Engineers

• Species significantly altering their physical environment (e.g., beavers creating wetlands).

Predation Dynamics

• Predation: Interaction where one species consumes another; includes herbivory.

  • Strong selective pressures shape predator-prey relationships.

• Adaptations:

  • Predators develop enhanced senses and physical abilities (e.g., camouflage, hunting strategies).

  • Prey species develop defenses (e.g., hiding, alarm calls).

Keystone Species

• Keystone Predators: Species that enhance biodiversity by maintaining populations of competitive species (e.g., sea otters controlling sea urchin populations).

• Their absence can lead to drastic ecological shifts and reduced species diversity.

Defense Mechanisms

• Camouflage: Cryptic coloring aids in predator avoidance.

• Aposematic Coloring: Warning coloration to deter predators.

• Mimicry: Non-harmful species mimic harmful ones (Batesian mimicry) or two unpalatable species resemble each other (Müllerian mimicry).

• Parasitism: Relationship where one organism (the parasite) derives nourishment from another (the host), often harming the host.

Mutualism and Commensalism

• Mutualism: Both species benefit (e.g., cleaner fish/ sharks, anemone/ clown fish).

• Commensalism: One species benefits while the other is unaffected (e.g., egrets and water buffalo).

Population Ecology

• Populations can fragment into metapopulations, linking smaller populations through movement.

• Key Factors Influencing Population Size:

  • Birth rates exceeding death rates.

  • Immigration exceeding emigration.

• Density-Dependence: Interactions that affect population dynamics based on density, influencing factors such as competition and disease.

• Survivorship Curve: Graphical representation of the number of individuals surviving at different ages; can show different mortality patterns (early, late, or constant).