Ecology II - Population Dynamics and Ecosystem Functions Notes

Logistic Growth

  • Concept: Populations typically grow to their carrying capacity (K) and then stabilize.
  • Curve: This growth pattern is represented by a sigmoid (S-shaped) curve.
  • Overshoot Behavior: Populations may exceed K and then decline or fluctuate around it.

Predator-Prey Dynamics

  • Example: Northern Canada’s biota, specifically snowshoe hares and lynxes.
  • Cycle Description:
    • Hare population increases, providing more food for lynxes.
    • Lynx numbers grow as a result but eventually lead to overpredation of hares.
    • This causes hare numbers to decline, leading to a lower lynx population, allowing hare numbers to rebound.
  • Observational Point: Lynx populations typically peak after hare populations due to the food supply relationship.

Competition in Ecosystems

  • Resource Competition:
    • Plants compete for sunlight; taller trees overshadow shorter ones, limiting their growth.
    • Example: The creosote bush (Larea tridentata) efficiently extracts water and creates "dead zones" around its roots.
  • Niche Concept:
    • Niche: The specific environmental conditions required for a species to thrive.
    • Fundamental vs. Realized Niche:
      • Fundamental niche: All conditions for potential existence.
      • Realized niche: Actual conditions due to competition.

Competitive Exclusion and Resource Partitioning

  • Competitive Exclusion Principle: One species may eliminate another when niches overlap.
  • Resource Partitioning:
    • Species adapt to share a niche by utilizing different resources or habits.
    • Example: Bird species in Canadian conifer forests use different tree spaces/insects for feeding.

Biomass and Energy Transfer

  • Trophic Levels:
    • Primary Producers: Generate energy through photosynthesis.
    • Primary Consumers: Consume producers directly.
    • Secondary Consumers: Feed on primary consumers.
    • Tertiary and Quaternary Consumers: Feed on secondary and tertiary consumers respectively.
  • Pyramid Scheme:
    • Energy and biomass decrease at each trophic level due to metabolic inefficiencies.
    • Average ecological efficiency: 10% of the biomass at one level is converted to the next.

Trophic Pyramid Representation

  • Biomass Representation:
    • Each trophic level depicted as a bar in a stacked diagram, demonstrating size reduction.
  • Biological Magnification:
    • Toxins like DDT or mercury accumulate and become more concentrated higher up the food chain, affecting top consumers.

Cycling in Ecosystems

  • Decomposers: Break down organic matter, returning atoms to the ecosystem.
  • Carbon Cycle:
    • Photosynthesis removes CO2; respiration returns it to the atmosphere.
    • Additional inputs from fires and geological activities, while some CO2 is sequestered in the oceans and corals.

Greenhouse Effect and Climate Change

  • Mechanism: The atmosphere traps heat reradiated from the Earth, warming it.
  • Historical Insights:
    • Principle established in 1896 by Svante Arrhenius; Keeling's observations (1958) of CO2 levels at Mauna Loa confirmed the cycle and upward trend in atmospheric CO2.
  • Consequences of Increased CO2:
    • While the greenhouse effect is useful for maintaining temperature, excessive CO2 leads to global warming with adverse effects on human life and the environment.

Fossil Fuels and Climate Impact

  • Carbon Burial: Ancient organisms retain carbon when buried, forming fossil fuels over millions of years.
  • Consequences of Fossil Fuel Combustion: Releases ancient carbon back into the atmosphere, increasing atmospheric CO2 and enhancing the greenhouse effect, exacerbating climate change.