Ecological Tolerance and Disturbances

Ecological Tolerance Niche

  • Some species possess a greater ability to tolerate disturbances and various environmental conditions.
  • These species are considered more adaptable to changing circumstances.

Effects of Changing Conditions/Disruptions

  • A discussion on what can happen as a result of changing conditions or disruptions is introduced.
  • Example: The 'Akiapōlā'au' bird, which is endemic to Hawaii, is noted as the only bird in Hawaii that fills the woodpecker niche.
  • Such species inhabit specific forested habitats with narrow tolerance ranges.

Natural Disruptions to Ecosystems

  • Natural disturbances affect ecosystems at varying scales of time and space.
  • Disturbance:
    • Defined as an event that has drastic impacts on environmental conditions.
    • Results in changes to the composition, structure, or function of a community or ecosystem.

Short-Term Disturbances

  • Acid Rain:

    • Lowers the pH of rainfall, negatively impacting some plants and aquatic organisms.
    • Changes occur slowly; amphibians are particularly sensitive to pH shifts.
      • -

  • Chemical Reaction Leading to Acid Rain:

    • ext{H}2 ext{O} + ext{CO}2
      ightarrow ext{H}2 ext{CO}3 (Carbonic Acid)
    • Natural acidity is further contributed by the oxides of nitrogen and sulfur (NOx and SO2).

  • Other short-term disturbances include:

    • Hurricanes
    • Tornados
    • Forest fires
    • These events have varying intensities and ecosystems can recover in a relatively short period ranging from years to decades.

Long-Term Disturbances

  • Climate as a Long-Term Change:

    • Changes over extended periods due to various factors.
    • Solar Radiation:
      • Changes in the amount of energy the Earth receives, e.g., observable changes during sunset activities (short-term) and Milankovitch cycles (long-term).

  • Atmospheric Composition:

    • Changes in CO2 levels influence climate and ecosystem dynamics.

Ecological Succession

Key Terms

  • Resistance:

    • The ability of an ecosystem to remain largely unchanged when subjected to disturbances.

  • Resilience:

    • The capacity of an ecosystem to bounce back and return to its original state after a disturbance.

  • Facilitation:

    • Describes the process by which pioneer or early successional species modify the environment, making it more habitable for other species.
    • Example: Nitrogen-fixing species add nitrogen to the soil.

  • Inhibition:

    • Describes conditions created by certain species that render the environment inhospitable for others.
    • This can occur through competition (resource dominance) and allelopathy (toxic substance production preventing the growth of other plants).
    • Examples include Sumac and Black Walnut trees.

Case Study: Mt. Saint Helens

  • Virginia Dale studied ecological succession after the eruption at Mt. Saint Helens, Washington.

Community and Ecosystem Dynamics

Return to Original State

  • Do communities or ecosystems always revert to the same state following disturbances?
    • The answer is No.

Desertification

  • Defined as the process wherein a grassland becomes desert-like due to significant disturbances (e.g., overgrazing).
  • Climate change can exacerbate this process (e.g., observed in Spain and the Amazon).

Keystone Species

  • Removal of a keystone species can have significant impacts on the ecosystem.
    • Leads to a Trophic Cascade:
    • Disruption in trophic levels (the hierarchical levels in an ecosystem based on feeding relationships).

Indicator Species

  • Species that are very sensitive to changes in their environment or habitat and thus serve as indicators of ecological health.
    • Example: Amphibians are particularly sensitive to changes in water quality.

Types of Ecological Succession

Primary Succession

  • Occurs in environments with no pre-existing soil; all life is absent initially.
    • Causes include volcanic eruptions, severe flooding, landslides, and glacial retreats.

Secondary Succession

  • Characterized by a disturbance where soil remains intact and some organisms might still survive, such as worms.
    • Causes include forest fires, agricultural abandonment, tornadoes, hurricanes, and flooding (depending on soil integrity).

Pioneer Species

  • Defined as the first plants or animals to colonize in post-disturbance environments.

  • Typically, they are easily dispersed and non-woody (herbaceous).

  • Resilience allows them to survive harsh conditions.

    • Primary Succession:
    • Species such as lichens and mosses that can establish on exposed rocks and are crucial in breaking down rocks through both chemical and physical erosion processes (e.g., freezing and thawing of water).

  • Once established, colonization by woody shrubs begins, followed by shade-intolerant trees (such as pine and cedar), eventually leading to the growth of dominant trees in the mature forest (including oak, hickory, and maples).

Conclusion

  • Various factors shape how ecosystems respond to disturbances, and these responses can have long-term implications for biodiversity and ecological stability.
  • Understanding ecological tolerance, succession, and the role of different species is essential for conservation efforts and ecosystem management.