Inv. 14/15 Ecology Study Guide

Levels of Organization

• Individual: A single organism of a species. Example: One deer in a forest.
  
  

• Population: A group of individuals of the same species living in the same area and interacting. Example: A herd of deer in a forest.
  
  

• Community: All the different populations of organisms living and interacting in an area. Example: Deer, trees, birds, and insects in a forest.
  
  

• Ecosystem: The community of organisms in an area along with their non-living (abiotic) environment. Example: A forest with deer, trees, birds, soil, water, and sunlight.
  
  

• Biome: A large geographic area with similar climate, plants, and animals. Example: A temperate deciduous forest.
  
  

• Biosphere: The part of Earth where life exists, including all biomes and ecosystems. Example: Earth’s land, water, and atmosphere supporting life.

Energy Flow in Ecosystems

• 10% Energy Rule: Only 10% of energy is passed to the next trophic level; the rest is lost as heat.
  
  

• Trophic Levels:
  
  

  • Producers (Autotrophs): Convert sunlight into energy (e.g., plants, algae).
    
    

  • Primary Consumers (Herbivores): Eat producers.
    
    

  • Secondary Consumers (Carnivores/Omnivores): Eat herbivores.
    
    

  • Tertiary Consumers (Top Predators): Eat secondary consumers.
    
    

• Decomposers (Bacteria, Fungi): Break down dead organisms, recycling nutrients.
  
  

• Detritivores (Earthworms, Crabs): Eat decomposing organic matter, recycling nutrients.
  
  

• Food Chain: Linear flow of energy in an ecosystem.
  
  

• Food Web: Shows multiple feeding relationships and energy flow in an ecosystem.
  
  

Biogeochemical Cycles and Ecosystem Stability

• Carbon Cycle:
  
  

  • Photosynthesis absorbs CO₂; respiration, decomposition, and combustion release it.
    
    

  • Disruptions (e.g., fossil fuel burning) lead to climate change.
    
    

• Nitrogen Cycle:
  
  

  • Nitrogen-fixing bacteria convert atmospheric nitrogen into usable forms.
    
    

  • Decomposers and bacteria help recycle nitrogen into the soil.
    
    

  • Excess nitrogen (fertilizers) can cause eutrophication in water systems.
    
    

• Nutrient Availability:
  
  

  • Low nutrients → limited growth and biodiversity.
    
    

  • Excess nutrients → algal blooms and ecosystem disruption.
    
    

Ecological Relationships

• Mutualism: Both species benefit (e.g., bees pollinating flowers).
  
  

• Commensalism: One benefits, the other is unaffected (e.g., barnacles on whales).
  
  

• Parasitism: One benefits, the other is harmed (e.g., tapeworms in intestines).
  
  

• Predation: One organism hunts and consumes another (e.g., wolves and deer).
  
  

• Competition: Two species compete for the same resources, affecting survival.
  
  

• Keystone Species: Species that have a disproportionate effect on ecosystem stability (e.g., sea otters controlling sea urchin populations).
  
  

Ecological Succession and Community Changes

• Primary Succession: Occurs on bare rock, no soil present (e.g., after a volcanic eruption).
  
  

• Pioneer Species: First to colonize an area (e.g., lichens, mosses).
  
  

• Secondary Succession: Occurs in disturbed areas with existing soil (e.g., after a wildfire).
  
  

• Climax Community: A stable, mature ecosystem that develops over time.
  
  

Population Growth and Carrying Capacity

• Exponential Growth (J-Curve): Rapid increase in population when resources are abundant.
  
  

• Logistic Growth (S-Curve): Growth slows as it reaches carrying capacity.
  
  

• Carrying Capacity: Maximum number of individuals an environment can support.
  
  

• Limiting Factors:
  
  

  • Density-Dependent: Competition, predation, disease (increase with population size).
    
    

  • Density-Independent: Natural disasters, climate changes (affect populations regardless of size).
    
    

Key Takeaways for Test Questions

• Levels of Organization: Life is organized in a series of groupings.

• Ecological Pyramids: Show energy, biomass, and numbers at each trophic level.
  
  

• Predator-Prey Relationships: Populations cycle in response to one another.
  
  

• Effects of Disruptions: Changes in food webs, loss of biodiversity, altered biogeochemical cycles.
  
  

Succession and Stability: Ecosystems recover over time, but human actions can slow or prevent recovery.