ecosystems

Dynamic Earth GY4741 Notes

Ecosystems

  • Definition: Ecosystems are dynamic entities composed of the biological (biotic) community and the abiotic (non-living) environment.
  • Ecosystems interact with various factors which can be defined at different scales:
    • Regional Scale: Includes habitats such as peat bogs, sand-dunes, wetlands, mountain ranges, and estuaries.
    • Local Scale: Includes specific locations like hedgerows, streams, and fallen trees.
    • Controls: Various factors that influence ecosystems include:
    • Altitude
    • Exposure
    • Aspect
    • Slope
    • Rock type
    • Soil type
    • Drainage
    • Nutrient availability
    • Light
    • Grazing
    • Species density
    • Human activity

Ecosystem Structure

  • Biological Organisation Levels:
    1. Cells
    2. Organism
    3. Population
    4. Community
    5. Ecosystem
    6. Biosphere
  • Energy Flow through Ecosystems:
    • Inputs: Solar radiation from the sun
    • Outputs: Longwave radiation, heat, and various forms of energy transfer within the ecosystem.
  • Food Chain:
    • Describes the feeding hierarchy through which energy and nutrient transfer occurs.
    • Energy structures in a basic food chain may look like this:
    • 100,000 energy units ➜ Primary producers (plants)
    • 1,000 energy units ➜ Primary consumers (herbivores)
    • 100 energy units ➜ Secondary consumers (carnivores)
    • 10 energy units ➜ Tertiary consumers and so forth.
  • At least 3 trophic levels are required in an ecosystem which demonstrates the interdependence of organisms.

Food Webs

  • Represents the complex feeding relationships within ecosystems.
  • Ecological Pyramid: Illustrates the structure of food webs, showing how biomass is distributed among various trophic levels.
  • Real-life food webs are highly complex and illustrate the interconnectedness of organisms on the same level of the food chain.

Soil and Nutrient Cycling

  • Organic Matter: Refers to waste, residue, and metabolites from living organisms contributing to soil composition.
  • Soil Food Web Hierarchy:
    • First trophic level: Photosynthesizers (e.g., plants)
    • Second trophic level: Decomposing mutualists, pathogens, parasites, root-feeders, protozoa, including amoebae, flagellates, ciliates.
    • Third trophic level: Shredders and grazers.
    • Fourth trophic level: Predators.
    • Fifth & higher trophic level: Higher-level predators.
  • Trophic Level Dynamics:
    • Functional roles in nutrient cycling:
    • Decomposers recycle nutrients back into the soil, aiding plant growth.

Ecosystem Services

  • Provisioning Services:
    • Food, fresh water, wood and fiber, fuel.
  • Regulating Services:
    • Climate regulation, flood regulation, disease regulation, and water purification.
  • Cultural Services:
    • Aesthetic, spiritual, educational, recreational benefits.
  • Supporting Services:
    • Nutrient cycling, soil formation, primary production.
  • As per the Millennium Ecosystem Assessment (2005), natural systems provide humanity with essential ecosystem services.

Biodiversity and Species Concept

  • Species: Defined as an organisms' "kind" in Latin, grouping together organisms that are similar in morphology and physiology and can interbreed.
  • Biological Diversity: Encompasses genetic diversity, species diversity, ecosystem diversity, and biomass.
    • Estimated between 2 - 200 million species exist, with about 2 million described species.

Ecological Niche

  • Definition: The ecological niche of a species refers to its position in a community and its specific requirements regarding habitat resources and microclimatic conditions (such as climate, shelter, food, water).
  • Types of Niches:
    • Fundamental niche: The potential mode of existence, given the environment's abiotic conditions.
    • Realised niche: The actual mode of existence that includes competition from biotic factors.

Succession in Ecosystems

  • Defined as an orderly sequence of events where one community transitions to another, creating opportunities for successive communities to establish themselves (SERE).
  • Types of Succession:
    • Primary Succession: Occurs on newly formed substrates such as post-volcanic or post-glacial environments without pre-existing communities.
    • Secondary Succession: Occurs on soil that has been disturbed but where a pre-existing community can recolonize.

Ecosystem Stability and Fragility

  • Ecosystem Complexity: Many ecosystems possess complexity that provides robustness against various conditions.
    • The removal of key species, known as keystone species, can lead to vulnerabilities, secondary extinctions, food web fragmentation, and potential ecosystem collapse (e.g., species such as wolves, starfish, beavers, and oaks).

Population Dynamics

  • Populations vary over time and are subject to limits within ecosystems.
    • Carrying Capacity (K): Refers to the maximum number of individuals an environment can support, demonstrating that populations cannot exceed this limit.

Ecosystem Dynamics

  • Positive and negative feedback mechanisms determine ecosystem balance:
    • Natural Drivers: Weather patterns, seasons, and water availability influence productivity.
    • The responses of ecosystems, such as species numbers, density, and overall composition, can indicate overall health and stability.
  • The Earth as a dynamic entity raises philosophical inquiries regarding its ability to self-regulate, often linked to the Gaia theory.

Learning Outcomes

  • Appreciate the role of ecosystems in natural operations.
  • Describe various structures, functions, and processes within ecosystems.
  • Understand the continuous evolution of ecosystems influenced by numerous factors.
  • Recognize the impact of keystone species and the fragility of certain ecosystems.