AP Environmental Science
Advanced Placement Environmental Science aligned with the College Board CED: ecosystems, biodiversity, populations, Earth systems and resources, land and water use, energy, atmospheric and aquatic pollution, and global change.
Ämne: Biologi · Nivå: Gymnasium (16–19) · 413 kort
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- An ecosystem includes all the living (biotic) organisms in an area together with the nonliving (abiotic) components — water, air, soil, sunlight — and the interactions between them. Ecosystems range in scale from a rotting log to the entire biosphere.
- Producers (autotrophs) convert solar or chemical energy into chemical energy stored in organic molecules. Photoautotrophs (plants, algae, cyanobacteria) use photosynthesis; chemoautotrophs (e.g., hydrothermal-vent bacteria) oxidize inorganic compounds such as H₂S.
- Consumers (heterotrophs) obtain energy by eating other organisms. Primary consumers eat producers (herbivores); secondary consumers eat primary consumers; tertiary consumers eat secondary consumers. Decomposers break dead matter back into inorganic nutrients.
- The 10% rule states that only about 10% of the energy at one trophic level is incorporated into biomass at the next. The remaining ~90% is lost as heat (respiration), used for movement and metabolism, or not assimilated. This limits food chains to ~4–5 levels.
- Gross primary productivity (GPP) is the total amount of energy captured by producers via photosynthesis. Net primary productivity (NPP) = GPP − respiration losses. NPP represents the energy actually available to consumers.
- Tropical rainforests have the highest NPP among terrestrial biomes (≈2200 g C/m²/yr), driven by year-round warmth, abundant water, and intense sunlight. Estuaries and coral reefs are the most productive aquatic ecosystems; open ocean has low per-area NPP but is enormous in extent.
- The carbon cycle moves C between the atmosphere (CO₂), oceans (dissolved CO₂, carbonates), biosphere (organic compounds), and lithosphere (fossil fuels, limestone). Photosynthesis pulls CO₂ down; respiration and combustion release it back.
- Atmospheric CO₂ has risen from ≈280 ppm pre-industrial to ≈423 ppm in 2024, primarily from fossil-fuel combustion and deforestation. This is the largest and fastest rise in at least 800,000 years (per ice-core records).
- The nitrogen cycle: N₂ (78% of atmosphere) is inert. Nitrogen fixation by Rhizobium (legume roots) and cyanobacteria converts N₂ → NH₃/NH₄⁺. Nitrification (Nitrosomonas, Nitrobacter) oxidizes NH₄⁺ → NO₂⁻ → NO₃⁻. Denitrification returns NO₃⁻ → N₂.
- The Haber–Bosch process synthesizes ammonia (NH₃) from atmospheric N₂ and H₂ industrially — the basis of synthetic fertilizer. Humans now fix more nitrogen than all natural sources combined, driving eutrophication and nitrous oxide (N₂O) emissions.
- The phosphorus cycle differs from C and N cycles in that it has no significant atmospheric phase. P enters ecosystems primarily by weathering of phosphate rocks; mining of these rocks for fertilizer is the dominant human input to soils and waters.
- The hydrologic (water) cycle is powered by solar energy. Key fluxes: evaporation from oceans, transpiration from plants, condensation forming clouds, precipitation, surface runoff and infiltration into groundwater. About 97% of Earth's water is saltwater; <1% is accessible freshwater.
- A food web shows interconnected food chains in a community. Removing a keystone species (e.g., sea otters in kelp forests, gray wolves in Yellowstone) triggers a trophic cascade with disproportionate effects on community structure.
- Terrestrial biomes are defined largely by temperature and precipitation. Tropical rainforest: hot, wet year-round, high biodiversity. Desert: <25 cm precipitation/yr. Tundra: very cold, short growing season, underlain by permafrost. Taiga (boreal forest): cold winters, coniferous trees.
- Temperate grasslands (prairie, steppe) have hot summers, cold winters, moderate rainfall, and deep fertile soils that historically supported large grazers (bison) and have largely been converted to agriculture. Frequent fires and drought limit tree growth.
- Aquatic ecosystems are classified by salinity and depth. Freshwater: lakes (with limnetic, littoral, profundal zones), streams, wetlands. Marine: estuaries (where rivers meet sea), intertidal, neritic (over continental shelf), pelagic (open ocean), benthic (sea floor).
- Wetlands (swamps, marshes, bogs) provide flood control, water purification, nutrient cycling, and habitat for >40% of species. They store carbon in saturated peat soils — draining wetlands releases CO₂ and methane.
- Lake stratification: in summer, warm low-density water (epilimnion) sits over a thermocline above cold dense bottom water (hypolimnion). Spring/fall turnover mixes layers and redistributes oxygen and nutrients — critical for productivity.
- Biodiversity is measured at three levels: genetic diversity (variation within a species), species diversity (number and abundance of species — richness + evenness), and ecosystem diversity (variety of ecosystems in a region).
- Ecosystem services are benefits humans receive from ecosystems. Provisioning: food, water, timber. Regulating: climate, water purification, pollination. Supporting: soil formation, nutrient cycling. Cultural: recreation, spiritual, aesthetic.
- Island biogeography theory (MacArthur & Wilson, 1967): species richness on an island depends on island size and distance from the mainland. Larger islands hold more species (lower extinction); islands closer to mainland have higher immigration rates.
- Habitat fragmentation breaks contiguous habitat into smaller patches, which act like islands: reduced area + isolation → fewer species. Edge effects (light, wind, predators) penetrate small patches, further reducing usable interior habitat.
- Ecological tolerance is the range of abiotic conditions (temperature, pH, salinity, moisture) within which a species can survive. Species near the limits of their tolerance are most vulnerable to environmental change. Stenotopic species have narrow tolerance; eurytopic species are wide.
- Ecological succession is the predictable change in community composition over time. Primary succession starts on bare rock (lava flow, retreating glacier) and begins with lichens and mosses. Secondary succession follows a disturbance where soil remains (fire, abandoned farm).
- Pioneer species (lichens, mosses, weeds, fireweed) colonize disturbed or barren areas, modify soil and microclimate, and facilitate arrival of later successional species. They typically have r-selected traits: small size, fast growth, high seed output.
- A climax community is the relatively stable end-stage of succession, historically thought to be deterministic but now seen as dynamic and disturbance-shaped (e.g., fire-maintained grasslands and pine forests).
- Resilience is an ecosystem's ability to recover after disturbance; resistance is its ability to withstand disturbance without changing. High biodiversity generally increases both. Loss of redundancy (multiple species playing similar roles) reduces resilience.
- Adaptations are inherited traits shaped by natural selection that improve fitness in a given environment. Behavioral (migration, hibernation), physiological (antifreeze in arctic fish), and morphological (thick fur, succulent leaves) categories overlap in real organisms.
- Generalist species (raccoons, coyotes, cockroaches) thrive on a wide range of resources and habitats; they cope well with environmental change. Specialists (giant pandas, koalas, pygmy three-toed sloths) depend on narrow resources and are vulnerable to disruption.
- K-selected species (elephants, whales, oak trees, humans) produce few offspring, invest heavily in parental care, mature slowly, and live near the environment's carrying capacity (K). Recovery from population crashes is slow.
- r-selected species (insects, mice, dandelions, most fish) produce many offspring with little parental care, mature quickly, and have boom-bust populations. They are good colonizers and pioneer-succession species but vulnerable to overharvest if r drops.
- Survivorship curves plot number of survivors vs age. Type I (humans, large mammals): low juvenile mortality, most die old. Type II (many birds, small mammals): constant mortality across life. Type III (most fish, invertebrates, plants): very high juvenile mortality, few reach adulthood.
- Exponential growth (dN/dt = rN) produces a J-shaped curve. It is unsustainable and observed when populations are small, in new habitat, after disturbance, or in invasive species' early phase. Bacteria and r-selected pioneers approximate this growth.
- Logistic growth (dN/dt = rN(K−N)/K) produces an S-shaped curve as the population approaches carrying capacity K. Growth slows as resources become limiting; population stabilizes around K.
- Carrying capacity (K) is the maximum population size an environment can sustainably support given available resources — food, water, shelter, space. Exceeding K leads to resource depletion, increased mortality, and a population crash (overshoot).
- Density-dependent limiting factors intensify with population size: competition, disease, predation, parasitism, waste accumulation. Density-independent factors affect populations regardless of size: weather, fire, flood, volcanic eruption.
- Age-structure pyramids reveal a population's growth trajectory. A broad base of young people (pre-reproductive) signals rapid growth (Nigeria, Pakistan). A column shape signals stability (Sweden). A top-heavy shape signals decline and aging (Japan, Italy).
- Total fertility rate (TFR) is the average number of children a woman bears in her lifetime. A TFR of ≈2.1 (replacement-level fertility) holds population stable, accounting for childhood mortality. Global TFR fell from ≈5 in 1950 to ≈2.3 in 2024.
- The demographic transition model has four stages. Stage 1: high birth + high death, slow growth (pre-industrial). Stage 2: death rate falls, birth stays high, rapid growth. Stage 3: birth rate falls, growth slows. Stage 4: low birth + low death, stable. Some models add stage 5: birth < death, decline.
- Factors that reduce TFR: education of women, urbanization, women in the workforce, access to contraception, higher household wealth, lower infant mortality (parents need fewer births), and delayed marriage. These are correlated with the demographic transition.
- Doubling time for an exponentially growing population is approximated by the Rule of 70: t ≈ 70 / (% annual growth). A 2% growth rate doubles in ≈35 years; 1% in 70 years. Useful for back-of-the-envelope population and economic calculations.
- World population reached ≈8.1 billion in 2024, projected by the UN to peak around 10.3 billion in the 2080s before slowly declining. Most future growth is in sub-Saharan Africa; many wealthy nations (Japan, S. Korea, Italy) are already losing population.
- Plate tectonics: Earth's lithosphere is divided into rigid plates that move on the plastic asthenosphere. Convergent boundaries cause subduction (Andes, Cascades) or collision (Himalayas). Divergent boundaries create new crust (Mid-Atlantic Ridge). Transform boundaries slide past each other (San Andreas Fault).
- Volcanic eruptions release ash, CO₂, SO₂, and H₂S. Large eruptions cause short-term cooling — e.g., Mount Pinatubo 1991 ejected ≈20 Mt SO₂, forming stratospheric aerosols that lowered global temperature by ≈0.5 °C for ≈1 year.
- Soil forms slowly through weathering of parent rock plus accumulation of organic matter. CLORPT mnemonic: Climate, Organisms, Relief (topography), Parent material, Time control soil characteristics. Forming an inch of topsoil takes hundreds to thousands of years.
- Soil horizons (top to bottom): O (organic litter), A (topsoil, dark, rich in humus), E (eluviation/leaching zone), B (subsoil, accumulation of clay and minerals), C (weathered parent material), R (bedrock).
- Soil texture is the proportion of sand, silt, and clay. Loam (≈40% sand, 40% silt, 20% clay) is ideal for most agriculture — holds water and nutrients while draining and aerating well. Sand drains too fast; clay is poorly drained and dense.
- Soil erosion strips fertile topsoil by wind and water. The 1930s American Dust Bowl, driven by drought + plowing of native grasslands, removed >850 million tons of topsoil. Conservation practices: contour plowing, terracing, no-till, cover crops, windbreaks.
- A watershed (drainage basin) is the land area where all precipitation drains to a single outlet — a river, lake, or ocean. The Mississippi River watershed covers ≈40% of the contiguous US; activities anywhere in it eventually affect the Gulf of Mexico.
- Earth's atmosphere has four main layers. Troposphere (0–12 km): weather happens here, contains ≈75% of mass. Stratosphere (12–50 km): contains ozone layer, temperature rises with altitude. Mesosphere (50–85 km): coldest. Thermosphere (85–600 km): auroras, ISS orbit.