CH 52 Community Ecology

Community Ecology Overview

I. Definition of Community

  • Community: All the species that inhabit a particular area.

  • Community Ecology: Examines interactions between populations within a community.

II. Species Diversity

  • Species Richness: Number of different species in a community.

  • Relative Abundance: Percentage representation of each species in the community.

III. Measuring Diversity

  • Community Examples:

    • Community 1:

      • A: 25%

      • B: 25%

      • C: 25%

      • D: 25%

    • Community 2:

      • A: 80%

      • B: 5%

      • C: 5%

      • D: 10%

    • Diversity is measured as heterogeneity across communities.

IV. Species Interactions

  • Populations may be linked through various types of interspecific interactions:

    • Competition (-/-): Detrimental to both species due to limited resources.

    • Predation (+/-): One species benefits while the other is harmed. This includes parasitism.

    • Mutualism (+/+): Both species benefit from the interaction.

    • Commensalism (+/0): One species benefits while the other is unaffected.

V. Competition and Niche

  • Competition: Occurs when resources are limited.

  • Ecological Niche: The sum total of resources used by an organism, including its role in the environment.

  • Competitive Exclusion Principle: Two species with identical niches cannot coexist.

    • Examples:

      • Chthamalus and Balanus under varying tidal conditions.

VI. Resource Partitioning

  • Similar species coexist by differentiating their ecological niches.

    • Evidence shows character displacement among species on different islands.

    • Example: Beak depth variation in G. fortis and G. fuliginosa based on sympatric vs. allopatric populations.

VII. Predation Dynamics

  • Types of Predation:

    • Carnivory, Herbivory, Parasitism.

  • Defenses against Predation:

    • For Plants: Behavioral, coloration, mechanical, and chemical defenses.

    • For Animals: Similar types of defenses as plants.

VIII. Mimicry in Predator-Prey Relationships

  • Batesian Mimicry: Harmless species mimicking harmful ones.

  • Müllerian Mimicry: Unpalatable species resembling each other; both benefit from the protection provided by shared warning colors.

IX. Other Predatory Relationships

  • Parasites and Pathogens: Parasites derive nourishment from hosts and can be endoparasites or ectoparasites.

  • Parasitoidism: A specific type of parasitism where the parasite eventually kills the host.

X. Commensalism and Mutualism

  • Commensalism: One species benefits and the other is unaffected.

  • Mutualism: Both species benefit from the interaction.

XI. Coevolution

  • Coevolution: Reciprocal evolutionary adaptations of two interacting species; the evolution of one species exerts selective pressure on another.

XII. Trophic Structure of Communities

  • Energy flow depicted through the food chain from photosynthetic sources to herbivores, carnivores, and decomposers.

    • Trophic Levels: Includes producers, primary consumers, secondary consumers, and tertiary consumers.

  • Dominant Species: Highest abundance or biomass; their removal can change community structure.

  • Keystone Species: Have a regulating effect on other species; significant impact when removed.

  • Foundation Species: Change environmental conditions, affecting community structure.

XIII. Community Models

  • Bottom-Up vs. Top-Down Models: Discuss how nutrient levels versus predation shape community structures.

    • Bottom-Up: Nutrients control community organization.

    • Top-Down: Predation controls community dynamics.

XIV. Disturbance and Community Dynamics

  • Disturbances (fires, weather, human activities) play a role in maintaining community equilibrium.

  • Ecological Succession: Transition in species composition over time.

    • Primary Succession: Begins in lifeless areas.

    • Secondary Succession: Follows disturbance where soil remains intact.

XV. Biogeography and Biodiversity

  • Biodiversity: Measures species number and their relative percentages.

  • Biogeography: Patterns and relationships of species distribution.

    • Key factors influencing biodiversity include area size and geographic isolation.

  • Species-Area Curve: Quantifies species number by geographic area.

XVI. Island Biogeography

  • Study of factors affecting species diversity based on island size and isolation.

  • Immigration rates and extinction rates impact diversity in isolated habitats.

XVII. Conclusion

  • Understanding community ecology involves examining interactions among species, the impact of predation, competition, and the influences of human activity and ecological succession.