Biology Chapter 2.1: Ecosystems and Populations

2.1 Individuals, Populations, Communities, and Ecosystems

• Atmosphere: The layer of gases surrounding Earth.
• Hydrosphere: All water on Earth (oceans, lakes, glaciers, etc.).
• Lithosphere (Geosphere): The rocky part of Earth.
• Biosphere: All living organisms on Earth.
• Individual: A single organism within a species.
• Species: A group of organisms that can interbreed and produce fertile offspring.
• Population: A group of organisms of the same species living in the same area.
• Community: Different populations interacting in the same area.
• Ecosystem: A community of organisms and their physical environment, interacting as a system. Includes biotic (living) and abiotic (non-living) components.
• Habitat: The abiotic environment where an organism lives (e.g., temperature, sunlight).
• Niche: The role of an organism in its ecosystem, including interactions and environmental requirements (biotic and abiotic factors).
• Factors Affecting Populations: Abiotic factors (temperature, sunlight, pH, salinity, soil texture) and biotic factors (predators, diseases, food, competition).

2.2 Energy and Biomass in Ecosystems

• Energy Flow: Energy moves through food chains/webs from producers (autotrophs) to consumers.
• Trophic Level: A step in the food chain (e.g., producer, herbivore, carnivore). Energy decreases with each trophic level from heat loss.
• Decomposers/Detritivores/Saprotrophs: Organisms that break down dead organic matter, recycling nutrients.
  • Detritivores: Internal digesters, like worms.
  • Saprotrophs: External digesters, like mushrooms, release enzymes and absorb nutrients.
• Herbivores: Eat only plants.
• Carnivores: Eat only meat.
• Omnivores: Eat both plants and animals.
• Producers (Autotrophs): Use photosynthesis to convert sunlight into chemical energy.
• Predators: Hunt and kill prey for food (energy source).
• Parasites: Live on or inside a host and derive nutrients from it (energy source), often at the host's expense.
• Scavengers: Feed on dead animals and plants (energy source: carrion, decomposing organic matter).
• Productivity: Rate of energy or biomass production over time.
  • Gross Primary Productivity (GPP): Total energy captured by producers.
  • Net Primary Productivity (NPP): GPP minus energy used in respiration. (GPP - Respiration = NPP)
• Ecological Efficiency: Only about 10% of energy transfers to the next trophic level due to inefficient digestion, incomplete consumption, and heat loss.
• Biomass: Total mass of living organisms in an area (dry weight).
  • Methods of measurement: Drying and weighing, combustion (calorimetry for energy).
  • Extrapolation: Scaling up biomass from a small sample to a larger area.

2.3 Biogeochemical Cycles

• Carbon Cycle: Carbon moves between atmosphere, organisms, and Earth.
• Human Disruptions: Deforestation and fossil fuel burning disrupt the cycle, leading to climate change and ocean acidification.
• Carbon Sequestration: Capturing and storing CO₂ to reduce atmospheric levels.
  • Natural: Photosynthesis, soils, oceans.
  • Artificial: Carbon capture and storage (CCS).
• Carrying Capacity: Maximum population size an environment can sustain.
• Keystone Species: Species with significant impact on its ecosystem.
• Sinks: Systems absorbing more carbon than they release. E.g., a growing forest.
• Sources: Systems releasing more carbon than they absorb. E.g., burning fossil fuels.
• Stores: Systems maintaining balance, neither significantly absorbing nor releasing carbon. E.g., a mature forest.
•  The Three Laws of Thermodynamics: - First Law: Energy cannot be created or destroyed. - Second Law: Energy transformations are never 100% efficient. Some energy is lost as heat. - Third Law: As temperature approaches absolute zero, entropy approaches a minimum (irrelevant for this context).
• J-Curve (Exponential Growth): Rapid population increase without limits, unsustainable.
• S-Curve (Logistic Growth): Population growth slows and levels off at carrying capacity; represents real-world population dynamics of limited resources.

2.4 Pyramids of Numbers, Biomass and Productivity

•  Pyramid of numbers: The number of organisms at each trophic level in a food chain as a function of time (a.k.a Standing crop)

•  Pyramid of biomass: The biomass of organisms at each trophic level in a food chain at a specific point in time (a.k.a standing crop)

•  Pyramid of productivity: The flow of energy through trophic levels—energy generation rates at each level in a food chain. Always upright.

•  Variations in shape: Number, biomass, and productivity pyramids can invert depending on the specific ecosystem and its producers. This is because: - Different species at each level, or different time measurements have greatly varying populations.

• Bioaccumulation: Pollutants accumulating in a single organism.

• Biomagnification: Pollutants increasing in concentration as they move up the food chain.

Explore the intricate relationships between individuals, populations, communities, and ecosystems in this quiz. Dive into concepts like the biosphere, habitats, and ecological niches, and understand how these elements interact with both biotic and abiotic factors. Test your knowledge and grasp the foundational aspects of ecological science.