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Continuation of Community Ecology

Overview of the Lecture

  • Topic: Community Ecology
  • Agenda: Continued discussion of community, exam results, and introduction to ecosystem ecology.
Exam Results
  • Total participants: 43
  • Exam breakdown:
    • Total points possible: 70
    • Average score: 40.1
    • Median score: 40
    • Maximum score: 58
    • Minimum score: 20
  • Adjustments made: Added 10 points to scores, resulting in an average adjusted score of approximately 72%, consistent with previous year.
  • Grade distribution: Histogram reflects a bell-shaped curve with additional failing grades (four extra F's).
  • Anticipation of improvement in future exams as students adjust their study habits.
  • Source of questions: Various sources including test banks related to OpenStax materials.

Community Ecology

Overview of Major Interactions
  • Major species interactions discussed include:
    • Commensalism
    • Parasitism
    • Mutualism
    • Predation
    • Competition
  • Importance of data collection to describe communities and identify parameters for comparison.
Importance of Community Ecology
  • Understanding community health based on species diversity (decrease in diversity may indicate peril).
  • Use of indicator species (e.g., amphibians) to signal ecosystem distress or improvement.

Species Diversity

Variety & Definition
  • Total cataloged species: Over 1 million, primarily insects.
  • Classification requirements: A species must be published and have a type specimen in a museum. Examples include:
    • T. Rex specimen in the Carnegie Museum.
  • The majority of identified species are insects (~1 million), followed by:
    • Animals: 250,000
    • Plants: 250,000
    • Fungi, bacteria, protists, and archaea also included in biodiversity discussions.
Measurement of Diversity
  • Species diversity can be assessed through:
    • Richness: The count of unique species present in an area.
    • Example of measuring richness: Studying birds to find a diversity of 5 species with numerous individuals.
    • Evenness: The relative abundance of species in a community.
  • The density of species often relates to latitudinal gradients, with higher diversity near the equator.
  • Combination of richness and evenness yields Diversity Indices (e.g., Shannon index), to quantify biodiversity.
Specific Examples of Microbial Diversity
  • Microbial diversity measured against soil pH levels, ideally peaked around neutral pH (~7).

Ecological Relationships

Productivity and Biodiversity
  • Question raised: Does high productivity lead to higher diversity or vice versa?
    • Conclusion from long-term studies suggests increased diversity correlates with higher productivity and ecosystem robustness.
  • Summary of agricultural experiments indicating recovery from disturbance in more diverse plots, linking diversity to stability.
Habitat Size and Impact on Diversity
  • Larger habitats support higher species diversity.
  • Introduces Island Biogeography Theory, developed by MacArthur and Wilson, considering:
    • Size of habitat: Larger areas have lower extinction rates.
    • Proximity to other land masses: Closer islands have increased immigration rates due to easier access.
  • Application of habitat patterns to land preservation strategies (e.g., Costa Rica’s approach).
Fragmentation of Habitats
  • Fragmentation results from human activity (e.g., urban development), causing significant ecological challenges.
  • Consequences observed in large predators unable to thrive in fragmented spaces (e.g., reintroduction challenges with wolves).
  • Increased edge-to-area ratio leads to higher risk for species requiring large, uninterrupted habitats.

Trophic Structure

Introduction to Trophic Levels
  • Definition of trophic levels:
    • Autotrophs: Primary producers that convert sunlight into energy (e.g., plants).
    • Primary Consumers: Herbivores feeding on autotrophs.
    • Secondary and Tertiary Consumers: Carnivores and higher-level consumers in the food chain;
  • Recognition that food chains are simplifications of much more complex food webs.
Bottom-Up and Top-Down Controls
  • Bottom-Up Control: Energy availability at lower trophic levels influences diversity and productivity.
  • 10% Law: Only approximately 10% of energy is transferred to each successive trophic level (loss through metabolism and waste).
Biomagnification Example
  • The case study of DDT pollution illustrates how chemicals can be magnified through trophic levels, affecting apex predators disproportionately.
  • Overview of how pollutant concentrations can rise despite low initial levels due to the 10% law.

Ecological Succession

Types of Succession
  • Primary Succession: Occurs on surfaces where no soil exists (e.g., post-volcanic environments).
    • Slow process, starts with pioneer species (e.g., lichens, mosses) and builds up through stages (herbaceous plants to perennial vegetation to forests).
  • Secondary Succession: Follows disturbances where soil remains, such as forest fires or agricultural reversion.
  • Importance of understanding succession for managing ecological recovery and resource utilization.