4/17: In-Depth Notes on Soil Formation and Community Ecology (REC)(DOC)

Importance of Soil in Community Functionality

• The quality of soil greatly influences community stability and functioning.

• Understanding soil formation helps explain interactions between soil, vegetation, and animals.

Glacial History and Soil Formation

• Last Glacial Period (~18,000 years ago): Reached its peak, covering large areas, such as New York State.

  • Ice accumulation was hundreds of meters thick, impacting soil and vegetation.

  • Movement of glaciers not due to accumulation but due to malleability; ice pushed forward by gravity:

  • Performed a scouring action, stripping off topsoil and vegetation, leaving bedrock and loose materials like sand and gravel behind.

  • Recession (~12,000-13,000 years ago): Left barren landscapes; significant soil loss occurred during the ice advance.

Terms in Community Ecology

• Species Richness vs. Species Diversity:

  • Species Richness: The number of different species in an area (e.g., 75 species of insects).

  • Species Diversity: Includes both the number of species and their relative abundance.

• Succession: Changes in community structure over time:

  • Vegetative Succession: Change in plant communities over time is a major focus of ecological study.

Types of Succession

• Primary Succession:

  • Occurs in areas starting from bare substrate (no soil), such as post-glacial landscapes.

  • Example: Areas left after glaciers retreat develop soil through colonization by lichens, mosses, and eventually flowering plants.

• Secondary Succession:

  • Begins in areas where soil exists, often after disruptions like fires or floods.

  • More common due to frequent disturbances in ecosystems.

Case Study: Glacier Bay, Alaska

• Glacial retreat offers a natural laboratory for studying succession.

• Reveals predictable stages of vegetative growth:

  • Initial Stage: Bare rock → colonization by lichens → build soil.

  • Next Stages: Mosses → Herbaceous plants (e.g., fireweed) → shrubs → pioneer trees → climax forest species (e.g., hemlock).

  • Edaphic Changes: Soil properties improve over time (increased nitrogen, nutrient-rich soil).

Mechanisms of Succession

• Facilitation: Early species modify the environment, allowing later species to thrive.

• Tolerance: Some species continue to endure environmental conditions better than others.

• Inhibition: Certain species may limit the success of others, controlling community dynamics.

Community Stability

• A stable community is characterized by:

  • Species Richness: More species can provide system redundancy, thus adding resilience to community disruptions.

  • Co-evolutionary Relationships: Mutualisms contribute to the strength and resilience of communities.

  • Keystone Species: Species with significant but low biomass that control community structure and diversity (e.g., sea stars, alligators).

Keystone Species Study: Sea Stars

• Research by Robert Payne:

  • Demonstrated a decline in species richness in intertidal zones after removing sea stars.

  • Established that keystone species maintain balance by keeping prey populations low, preventing competitive exclusion among species within the community.

Conclusion

• Understanding soils, succession, community structures, and dynamic interactions reinforces insights into ecosystem stability and diversity.