environmental studies

Introduction to Populations in Ecology

  • Review of ecosystems, species, and populations.

  • Ecosystems consist of nested systems from individual organisms to the biosphere.

Concept of Populations

  • Population Definition: A group of individuals of the same species living together in a particular area.

    • Example: Human populations can be analyzed at different scales (e.g., globally, regionally, locally).

  • Population sizes fluctuate over time due to various environmental conditions:

    • Access to resources (water, food).

    • Response to environmental stressors like storms.

Fluctuations in Population Sizes

  • Populations are not stable; they fluctuate over time due to:

    • Environmental conditions like storms affecting seabirds, which showed increased mortality rates due to inability to recover from successive storms.

  • Tipping points exist when stressors accumulate to a level that drastically affects population sizes.

    • Example: Mass die-offs of species can occur due to dramatic environmental changes.

Human Impact on Ecological Systems

  • Human activities lead to ecological problems, particularly impacting biodiversity and population stability:

    • Human-made biomass (techno-mass) now outweighs natural biomass.

    • Current extinction events are significantly higher than the natural background extinction rate.

    • Mass Extinction: The sixth mass extinction event in recorded history is currently ongoing.

  • Factors contributing to extinction:

    • Increased resource consumption.

    • Urban development and habitat destruction.

    • Cumulative effects of minor changes across different ecosystems.

Background Rate of Extinction

  • Average background extinction rates provide context for current rates:

    • Approximately 10% of species lost over one million years.

    • In the past century, over 400 vertebrate species lost (typically takes 10,000 years).

    • Graphs illustrate extinction trends over millions of years.

Ecological Research and Observations

  • Current observations highlight significant declines in amphibian populations (over 40% globally threaten).

  • Various factors causing declines:

    • Outbreaks of diseases (e.g., fungal infections causing large-scale losses).

    • Habitat loss and degradation.

    • Climate change affecting biodiversity and species interactions.

Population Dynamics and Ecological Principles

  • Connection to previously discussed concepts:

    • Carrying capacity and limiting factors (abiotic and biotic).

    • Populations exhibit two main growth patterns:

      • J-Curve: Exponential growth followed by a crash (minimal competition, optimal conditions).

      • Example: Mold growing exponentially on food until resources are depleted.

      • S-Curve: Logistic growth that stabilizes around the carrying capacity due to environmental resistance.

Biotic Potential and Environmental Resistance

  • Biotic Potential: Maximum capacity of a species to reproduce under ideal conditions.

    • Varies between species (e.g., fruit flies vs. humans).

  • Environmental Resistance: Factors that limit population growth, creating a balance with biotic potential:

    • Access to water, food, predators, diseases influence carrying capacity.

Succession in Disturbed Ecosystems

  • Disturbances can modify ecosystems, influencing population sizes and species composition.

    • Primary Succession: Starts from a lifeless area (e.g., after a volcanic eruption).

    • Secondary Succession: Starts from existing vegetation after disturbances (e.g., after a forest fire).

  • Disturbances can play a critical role in ecosystem health:

    • Some species are adapted to thrive in frequently disturbed environments.