Patterns of Biodiversity

Lecture 18 - Patterns of Biodiversity

Overview of Today

  • Topics: What is Biodiversity?
    Biodiversity Metrics
    Patterns of Biodiversity
    Succession & Disturbance

  • Goals:

    • Quantify biodiversity

    • Understand factors shaping biodiversity patterns

What is Biodiversity?

  • Definition: "The variability among living organisms from all sources … this includes diversity within species, between species, and of ecosystems"

    • Source: UN Convention of Biological Diversity, 1992

Importance of Biodiversity

  • Historical examples of biodiversity impact:

    • Irish Potato Famine (1840s):

    • Genetic uniformity led to vulnerability to pests.

    • Lyme Disease:

    • More mammal diversity results in fewer Lyme disease hosts.

    • Coastal Ecosystems:

    • Mangroves, marshes, dunes, and coral reefs protect against natural disasters.

Characteristics of Diverse Communities

  • Diverse communities are:

    • More productive

    • Better able to withstand environmental stress

    • More stable from year to year

    • More resistant to invasive species

Quantifying Biodiversity

  • Key Metrics:

    • Abundance: Total number of organisms.

    • Richness: Number of species present.

    • Relative Abundance: Proportion of individuals per species.

Examples of Biodiversity Metrics

  • Abundance: 3 deer

  • Richness: 18 species

  • Relative Abundance Examples:

    • 1/6 deer, 1/9 ducks & beavers, 1/18 all others

Biodiversity Indices

  • Types of Diversity:

    • Alpha Diversity (α): Number of species in a habitat.

    • Beta Diversity (β): Local diversity in context of regional diversity.

    • Gamma Diversity (γ): Total number of species across habitats.

Diversity Metrics Examples

  • Calculating Alpha Diversity:

    • Habitat 1: α = 6

    • Habitat 2: α = 8

  • Calculating Beta and Gamma Diversity:

    • β = 4 unique species between habitats

    • γ = 9 total species combining both habitats

Factors Affecting Biodiversity

  • Evenness: The distribution of individuals among species.

    • Example: Two habitats with the same richness can differ in diversity due to abundance distribution.

Diversity Indices

  • Simpson's Index (D):

    • Accounts for both abundance and evenness

    • Higher values indicate a community dominated by fewer species.

  • Shannon-Weiner Index (H):

    • Sensitive to rare species; compares across similar ecosystems

    • Higher values suggest greater diversity.

Using Diversity Indices

  • When to Use D vs. H:

    • Simpson’s D: Best for statistical analysis, poor for ecology.

    • Shannon’s H: Better for ecosystems with even species representation.

Detecting Species

  • Methods:

    1. Direct Observation: Visual or auditory detection.

    2. Physical Sampling: Trapping species.

    3. Passive Detection: Using technology like camera traps.

    4. Molecular Methods: Detecting DNA in environmental samples.

    5. Community Surveys: Engaging with local communities for detection data.

Patterns of Biodiversity

  • Biodiversity distribution is uneven globally.

  • Latitudinal Gradient:

    • More rich and diverse ecosystems found in tropical regions.

Why is There a Latitudinal Gradient?

  • Geographical Area Hypothesis:

    • Larger areas (equatorial regions) host more species.

  • Species-Energy Hypothesis:

    • Increased solar energy in tropics enhances primary productivity.

  • Climate Stability Hypothesis:

    • Stable climates allow greater specialization and longer evolutionary time.

Impact of Elevation on Biodiversity

  • Species richness typically declines as elevation increases.

Ecosystem Change & Disturbance

  • Disturbances can create opportunities for diversity by changing habitat structures.

  • Intermediate Disturbance Hypothesis:

    • Moderate disturbances foster biodiversity by allowing less competitive species to thrive.

Ecological Succession

  • Types of Succession:

    • Primary Succession: Occurs on barren land (e.g., post-volcanic eruptions).

    • Secondary Succession: Follows disturbances that leave soil intact (e.g., after forest fires).

Climax Community

  • The stable and self-sustaining community at the final succession stage.

    • Can persist for long durations unless disturbed.

Study Questions

  • What are the three types of biodiversity?

  • Benefits of ecosystems from biodiversity?

  • Definitions of species abundance, richness, and evenness?

  • Main methods of calculating biodiversity?

  • What influences biodiversity patterns?

  • Effects of elevation and disturbances on biodiversity?

  • Understanding primary and secondary succession?