Ecology Review: Food Chains & Webs, Relationships, Nitrogen & Carbon Cycles, Effects on Biodiversity

Key Concepts

• Ecology: Interactions between organisms and their environment.
• Food Chains & Food Webs: Flow of energy through an ecosystem.
• Trophic Levels: Position an organism occupies in a food chain.
• Energy Pyramid: Representation of energy at each trophic level.
• 10% Rule: Only about 10% of energy is transferred between trophic levels.
• Biodiversity: Variety of species and individuals in an area.
• Ecological Relationships: Interactions between species (predation, competition, symbiosis).
• Symbiosis: Organisms living together (parasitism, mutualism, commensalism).
• Nitrogen Cycle: Conversion of nitrogen into different forms for use by organisms.
• Carbon Cycle: Movement of carbon through the environment.
• Greenhouse Gas: Gases that trap heat in the atmosphere (e.g., carbon dioxide).
• Invasive Species: Non-native species that threaten biodiversity.
• Overharvesting: Unsustainable removal of species from an ecosystem.

1. Food Chains, Food Webs, and Energy Pyramids

• Food Chains: Start with producers (autotrophs like plants) that make their own food. Arrows indicate the direction of energy flow, pointing from what is eaten to the consumer. Consumers are classified as primary, secondary, tertiary, and apex consumers.
• Food Webs: More realistic representation of ecosystem interactions, showing multiple interconnected food chains. Reflects the biodiversity of the ecosystem.
  • Example: In a food web, a decrease in bird population can lead to an increase in grasshoppers (bird's prey) and a decrease in snakes (bird's predator).
• Energy Pyramids: Represent the amount of energy at each trophic level. Producers form the base, followed by primary, secondary, and tertiary consumers.
  • Trophic Levels: Producers are at trophic level 1, primary consumers at level 2, secondary consumers at level 3, and tertiary consumers at level 4.
  • 10% Rule: Only about 10% of energy is transferred from one trophic level to the next. The rest is lost as heat or remains in undigested material.
    • Example: If producers have 90,000 kilocalories, primary consumers get 9,000 kcal, secondary consumers get 900 kcal, and tertiary consumers get 90 kcal.

2. Ecological Relationships

• Predation: One organism (predator) eats another (prey).
• Competition: Organisms compete for resources.
• Symbiosis: Organisms living together.
  • Parasitism: One organism benefits, the other is harmed.
    • Example: Flea on a rabbit.
  • Mutualism: Both organisms benefit.
    • Example: Termites and microorganisms in their gut. Microorganisms break down wood for the termite, and the termite provides a home and food source for the microorganisms.
  • Commensalism: One organism benefits, the other is neither helped nor harmed.
    • Example: Barnacles on a whale.
    • Caveat: Commensalism can be dependent on different factors and may be more complex upon closer examination.
    • Example: Bats roosting in pitcher plants. Initially thought to be commensalism, it's actually mutualism because bat droppings provide nitrogen for the plant.

3. Nitrogen and Carbon Cycles

• Nitrogen Cycle:
  • Nitrogen is essential for amino acids (proteins) and nucleotides (nucleic acids).
  • Atmosphere is 78% nitrogen, but it needs to be "fixed" into usable forms.
  • Nitrogen Fixation: Nitrogen-fixing bacteria convert atmospheric nitrogen into ammonia (NH3) and ammonium (NH4+).
  • Nitrification: Nitrifying bacteria convert ammonia and ammonium into nitrites (NO2-) and nitrates (NO3-).
  • Ammonification: Decomposers convert nitrogen from dead organisms back into ammonia and ammonium.
  • Denitrification: Denitrifying bacteria convert nitrates and nitrites into nitrogen gas (N2).
• Carbon Cycle:
  • Carbon is a building block of life.
  • Carbon reservoirs: oceans, rocks, fossil fuels, living organisms, atmosphere (carbon dioxide).
  • Photosynthesis: Producers use carbon dioxide as an input.
  • Cellular Respiration: Plants and animals release carbon dioxide.
  • Decomposition stores carbon in sediment, which can eventually form fossil fuels.
  • Burning fossil fuels releases carbon dioxide, contributing to greenhouse gas emissions.
  • Carbon dioxide is a greenhouse gas that traps heat in the atmosphere.

4. Human Activity and Threats to Biodiversity

• Greenhouse Gas Emissions:
  • Burning fossil fuels releases carbon dioxide, trapping heat in the atmosphere.
  • Oceans absorb heat and carbon dioxide, leading to warming and acidification.
  • Coral Bleaching: Warming ocean temperatures cause coral to expel symbiotic algae, leading to coral bleaching and vulnerability.
• Destruction of Habitats:
  • Deforestation leads to soil erosion and runoff, affecting water bodies.
  • Unsustainable land development and dam construction disrupt aquatic habitats.
• Introduction of Invasive Species:
  • Invasive species are non-native species that threaten biodiversity.
  • Example: Formosan subterranean termites are "super" termites that consume plants rapidly and damage homes.
  • Example: Kudzu was introduced for erosion control but smothers native plants.
  • Example: Lionfish, introduced to the Atlantic, consume native fish and crustaceans, harming coral reefs.
• Overharvesting:
  • Overfishing can disrupt food webs.
  • Overharvesting in the pet trade can affect amphibian, bird, and reptile populations.

5. Protecting Biodiversity

• Biodiversity is critical for ecosystem stability, providing food, medicines, and clean water.
• Humans can positively affect biodiversity through:
  • Reforestation
  • Species conservation programs
  • Sustainable practices

6. Notable Quotes

• "Biodiversity is critical to the stability of ecosystems."

Conclusion

Ecology is the study of interactions within environmental systems. This video provides a review of key ecological concepts, including food chains, food webs, energy pyramids, ecological relationships, and nutrient cycles. It highlights the importance of biodiversity and the threats posed by human activities such as greenhouse gas emissions, habitat destruction, invasive species, and overharvesting. The video concludes by emphasizing the need for sustainable practices and conservation efforts to protect biodiversity and maintain healthy ecosystems.