AC

Unit 1: The Living World: Ecosystems

  • 1. The Living World: Ecosystems

    • Definition: Communities of living organisms interacting with their physical environment, encompassing both biotic and abiotic components.

      • Biotic Components: Living or once-living parts of an ecosystem (e.g., plants, animals, fungi, bacteria).

      • Abiotic Components: Non-living physical and chemical parts of an ecosystem (e.g., sunlight, water, soil, temperature, pH, nutrients).

    • Organism Interactions: Relationships between species within an ecosystem.

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

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

      • Parasitism: One species (parasite) benefits, the other (host) is harmed (e.g., ticks on mammals).

      • Predation: One species (predator) hunts and kills another (prey) for food (e.g., lion hunting zebra).

      • Competition: Species compete for limited resources, negatively affecting both (e.g., two species of birds competing for the same food source).

      • Resource Partitioning: Species divide a shared resource by specializing in different ways, such as using it at different times, different places, or consuming different parts of it, to reduce interspecific competition.

    • Energy Flow: Energy enters ecosystems primarily from the sun, is converted by producers, and flows through trophic levels.

    • Matter Cycling: Nutrients (e.g., carbon, nitrogen, phosphorus) cycle within and between ecosystems.

    2. Terrestrial Biomes

    • Definition: Large ecological areas on Earth's land surface, characterized by distinct climate conditions (temperature and precipitation) and their associated plant and animal communities.

    • Factors Determining Biomes: Mainly temperature and precipitation, which influence vegetation.

    • Key Biomes to Know:

      • Tundra: Cold, treeless, low-growing vegetation, permafrost. (e.g., Arctic)

      • Boreal Forest (Taiga): Cold, coniferous forests, relatively low biodiversity. (e.g., Canada, Russia)

      • Temperate Rainforest: Moderate temperatures, high precipitation, large trees. (e.g., Pacific Northwest)

      • Temperate Seasonal Forest: Moderate temperatures, distinct seasons, deciduous trees. (e.g., Eastern USA, Europe)

      • Woodland/Shrubland (Chaparral): Hot, dry summers; mild, rainy winters; fire-adapted shrubs. (e.g., California, Mediterranean)

      • Temperate Grassland: Cold, harsh winters; hot, dry summers; grasses. (e.g., Prairies, Steppes)

      • Tropical Rainforest: Warm, high precipitation, immense biodiversity, rapid nutrient cycling. (e.g., Amazon, Congo)

      • Tropical Seasonal Forest (Savanna): Warm, distinct wet and dry seasons, grasses, scattered trees. (e.g., Africa, Australia)

      • Subtropical Desert: Hot, extremely dry, sparse vegetation adapted to conserve water. (e.g., Sahara, Mojave)

    3. Aquatic Biomes

    • Definition: Ecological areas in water, characterized by salinity, depth, temperature, and water flow.

    • Freshwater Biomes:

      • Streams and Rivers: Flowing water, generally narrow, often originate from melting snow or groundwater. Organisms adapted to current.

      • Lakes and Ponds: Standing water, distinct zones (littoral, limnetic, profundal, benthic).

      • Wetlands: Saturated soil, emergent vegetation; highly productive (e.g., marshes, swamps, bogs). Critical for filtering pollutants, flood control, and habitat.

    • Saltwater Biomes (Marine):

      • Oceans: Largest biome, divided into zones based on depth and light penetration (photic, aphotic).

      • Coral Reefs: Warm, shallow, highly diverse; formed by coral polyps. Threatened by climate change and ocean acidification.

      • Estuaries: Areas where freshwater meets saltwater; highly productive, nurseries for many marine species. Tolerant of fluctuating salinity.

      • Intertidal Zone: Area between high and low tide lines; organisms adapted to harsh, changing conditions.

      • Mangrove Swamps: Coastal wetlands in tropical/subtropical regions, salt-tolerant trees. Provide habitat, protection from erosion.

    4. Carbon Cycle

    • Key Processes:

      • Photosynthesis: CO2 from atmosphere taken up by plant to create glucose

      • Respiration: Organisms release CO_2 back into atmosphere.

      • Decomposition: Decomposers break down dead organic matter, releasing carbon.

      • Combustion: Burning of fossil fuels or organic matter releases CO_2 and other carbon compounds.

      • Sedimentation: Burial of organic matter over millions of years forms fossil fuels (oil, coal, natural gas).

    • Major Reservoirs: Atmosphere (CO2), oceans (dissolved CO2, carbonates), rocks (limestone, fossil fuels), living organisms (biomass).

    • Human Impact: Burning fossil fuels, deforestation increase atmospheric CO_2, contributing to climate change.

    5. Nitrogen Cycle

    • Key Processes:

      • Nitrogen Fixation (N. Fix): Atmospheric N2 converted to ammonia (NH3) by bacteria (e.g., in legumes) or lightning. N2\rightarrow NH3

      • Nitrification: Ammonia (NH3) converted to nitrites (NO2^-$) and then nitrates (NO3^-$) by bacteria. NH3\rightarrow NO2^-\rightarrow NO3^-

      • Assimilation: Plants absorb nitrates (NO3^-$) or ammonia (NH3) from soil to build proteins and nucleic acids.

      • Ammonification: Decomposers convert organic nitrogen (from dead organisms/waste) back to ammonia (NH_3).

      • Denitrification: Nitrates (NO3^-$) converted back to atmospheric N2 gas by bacteria under anaerobic conditions. NO3^-\rightarrow N2

      • FNAAD

    • Major Reservoir: Atmosphere (78% N_2​).

    • Human Impact: Fertilizers (e.g., Haber-Bosch process), runoff leads to eutrophication; burning fossil fuels creates NO_x​ (air pollution, acid rain).

    6. Phosphorus Cycle

    • Key Processes:

      • Weathering: Phosphate (PO_4^{3-}​) released from rocks.

      • Absorption/Assimilation: Plants absorb dissolved phosphate from soil or water.

      • Decomposition: Decomposers return phosphate to soil/water from dead organic matter.

      • Sedimentation: Phosphate can settle out of water to form new rocks.

      • WADS

    • Major Reservoir: Sedimentary rocks; no significant atmospheric component.

    • Limiting Nutrient: Often limits primary productivity in ecosystems, especially aquatic ones.

    • Human Impact: Mining for fertilizers, runoff leads to eutrophication of aquatic systems.

    7. Hydrologic (Water) Cycle

    • Key Processes:

      • Evaporation: Liquid water to water vapor.

      • Transpiration: Evaporation of water from plant leaves.

      • Condensation: Water vapor to liquid water (cloud formation).

      • Precipitation: Water released from clouds (rain, snow).

      • Infiltration: Water soaking into the ground.

      • Runoff: Water flowing over land surface.

      • Sublimation: Solid water (ice) to water vapor.

    • Major Reservoirs: Oceans, ice caps/glaciers, groundwater, lakes, atmosphere.

    • Human Impact: Paving impervious surfaces (increased runoff, reduced infiltration), deforestation (reduced transpiration), diverting water, polluting water bodies.

    8. Primary Productivity

    • Gross Primary Productivity (GPP): Total amount of solar energy that producers (e.g., plants) capture via photosynthesis over a given amount of time.

    • Net Primary Productivity (NPP): GPP minus the energy lost by producers through respiration (R_p​).

      • Formula: NPP=GPP-R_p

      • They may combine this with trophic levels and 10% rule!!!

    • Measurement: Expressed in units of energy per unit area per unit time (e.g., kcal/m^2/year) or biomass per unit area per unit time (e.g., g\ C/m^2/year).

    • Factors Affecting NPP: Sunlight, water, nutrients, temperature.

    • Relationship to Biodiversity: High NPP often supports higher biodiversity.

    9. Trophic Levels and Energy Flow

    • Trophic Levels: Steps in a food chain or food web, representing the position an organism occupies based on its feeding habits.

      • Producers (Autotrophs): Convert solar energy into chemical energy (e.g., plants, algae). Base of the food chain.

      • Primary Consumers (Herbivores): Eat producers (e.g., deer, rabbits).

      • Secondary Consumers (Carnivores/Omnivores): Eat primary consumers (e.g., wolves, bears).

      • Tertiary Consumers (Carnivores/Omnivores): Eat secondary consumers (e.g., hawks, sharks).

      • Decomposers/Detritivores: Break down dead organic matter at all trophic levels, recycling nutrients (e.g., bacteria, fungi, earthworms).

    • Energy Transfer (10% Rule): Only about 10% of the energy from one trophic level is transferred to the next; the rest is lost primarily as heat during metabolic processes. This limits the number of trophic levels.

    • Biomagnification/Bioaccumulation: Increasing concentration of toxins through successive trophic levels.

    10. Food Chains and Food Webs

    • Food Chain: A linear sequence showing how energy is transferred from one organism to another, illustrating who eats whom.

      • Example: Grass \rightarrow Rabbit \rightarrow Fox

    • Food Web: A complex, interconnected network of food chains in an ecosystem, showing multiple feeding relationships. More realistic than a simple food chain.

    • Interdependence: Disruptions to one part of a food web can have cascading effects on other species.

    11. Ecological Succession

    • Definition: The gradual process of change and development that occurs in an ecosystem over time.

    • Primary Succession: Occurs in an area previously devoid of life and soil (e.g., newly formed volcanic rock, exposed glacial retreat). Pioneer species (lichens, mosses) colonize first, gradually forming soil.

    • Secondary Succession: Occurs in an area where an existing community has been removed by a