<b>Ecology</b>: Study of interactions among organisms and between organisms and their environment. <b>Biosphere</b>: All life on Earth + all parts where life exists (land, water, atmosphere, 8km above to 11km below ocean surface).

<b>Individual organism</b> → <b>Population</b> (same species, same area) → <b>Community</b> (different populations in area) → <b>Ecosystem</b> (community + physical environment) → <b>Biome</b> (similar climates, typical organisms) → <b>Biosphere</b>.

<b>Biotic</b>: Living components (animals, plants, bacteria, fungi). <b>Abiotic</b>: Non-living (sunlight, temperature, water, precipitation, soil, wind, humidity). Interact to shape ecosystem.

<b>Observation</b>: Identify species, behaviors, patterns. <b>Experimentation</b>: Test hypotheses, manipulate variables (greenhouse studies, field experiments). <b>Modeling</b>: Predict long-term/large-scale events, based on data.

<b>Habitat</b>: Physical location where organism lives (address). <b>Niche</b>: Organism's role in ecosystem (profession) - what it eats, when active, where lives, how interacts. <b>Fundamental niche</b> (potential) vs. <b>Realized niche</b> (actual with competition).

<b>Autotrophs</b>: Make own food. <b>Photosynthesis</b>: Use sunlight (plants, algae, cyanobacteria: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂). <b>Chemosynthesis</b>: Use chemical energy (deep-sea vent bacteria, sulfur compounds). Foundation of food chains.

<b>Herbivores</b>: Eat plants (primary consumers). <b>Carnivores</b>: Eat animals (secondary/tertiary consumers). <b>Omnivores</b>: Eat both plants + animals. <b>Scavengers</b>: Eat dead animals. <b>Detritivores</b>: Eat detritus (earthworms, crabs). <b>Decomposers</b>: Break down organic matter (bacteria, fungi).

Linear sequence showing energy transfer. Example: Grass (producer) → Rabbit (primary consumer/herbivore) → Fox (secondary consumer/carnivore) → Decomposers. Each step = <b>trophic level</b>.

Complex network of interconnected food chains. Shows multiple feeding relationships. More realistic than simple chains. Organisms often eat multiple things and are eaten by multiple predators.

<b>10% Rule</b>: Only ~10% of energy transfers to next trophic level (90% lost as heat from metabolism). <b>Biomass pyramid</b>: Total mass of living tissue decreases at higher levels. Limits food chain length to ~4-5 levels.

Efficiency of energy transfer between levels. Typically 5-20% (average 10%). Lost energy: respiration (heat), waste, incomplete digestion. Why top predators are rare.

<b>Decomposers</b> (bacteria, fungi): Break down dead organisms, return nutrients to soil. Essential for recycling. <b>Detritus</b>: Dead organic matter. Without decomposers, nutrients locked up in dead bodies.

Energy from chemical reactions (not sunlight). <b>Deep-sea vents</b>: Bacteria use H₂S + O₂ → organic compounds. Support entire ecosystems without photosynthesis. Also in hot springs, tidal marshes.

<b>Evaporation</b> (liquid → vapor), <b>Transpiration</b> (plants release water), <b>Condensation</b> (vapor → clouds), <b>Precipitation</b> (rain/snow), <b>Runoff</b> (flows to rivers/oceans), <b>Infiltration</b> (groundwater). Driven by solar energy.

<b>Photosynthesis</b>: CO₂ → organic compounds. <b>Respiration</b>: Organic → CO₂ (returns to atmosphere). <b>Decomposition</b>: Dead organisms → CO₂. <b>Combustion</b>: Burning fossil fuels/wood → CO₂. <b>Oceans</b>: Dissolve/release CO₂. <b>Sediments</b>: Long-term storage (fossil fuels).

<b>Nitrogen fixation</b>: N₂ → NH₃/NH₄⁺ (bacteria: Rhizobium in root nodules, cyanobacteria, lightning). <b>Nitrification</b>: NH₄⁺ → NO₂⁻ → NO₃⁻ (bacteria). <b>Assimilation</b>: Plants absorb NO₃⁻, make proteins. <b>Ammonification</b>: Dead organisms → NH₄⁺. <b>Denitrification</b>: NO₃⁻ → N₂ (back to atmosphere).

<b>Weathering</b>: Rocks release phosphate (PO₄³⁻). <b>Absorption</b>: Plants take up from soil. <b>Food chain</b>: Passes through consumers. <b>Decomposition</b>: Returns to soil. <b>Sedimentation</b>: Washes to ocean, forms rocks. <b>No atmospheric component</b> (unlike C, N). Slow cycle.

<b>Law of the Minimum</b>: Nutrient in shortest supply limits growth. <b>Terrestrial</b>: Often nitrogen. <b>Aquatic</b>: Often phosphorus or nitrogen. Adding limiting nutrient increases productivity (can cause eutrophication).

<b>Size</b>: Number of individuals. <b>Density</b>: Number per unit area. <b>Distribution</b>: <b>Clumped</b> (groups, most common), <b>Uniform</b> (evenly spaced, territorial), <b>Random</b> (unpredictable, rare). <b>Age structure</b>: Proportion in each age group.

Population change = (Birth rate + Immigration) - (Death rate + Emigration). <b>Immigration</b>: Individuals moving in. <b>Emigration</b>: Individuals moving out. <b>Demography</b>: Study of population statistics.

<b>J-curve</b>: Accelerating growth when resources unlimited. <b>Equation</b>: dN/dt = rN (r = intrinsic rate of increase). Population doubles at constant intervals. Unsustainable long-term. Occurs after colonization or low density.

<b>S-curve</b>: Growth slows as approaches carrying capacity. <b>Carrying capacity (K)</b>: Maximum population environment can sustain. Growth rate highest at K/2. More realistic than exponential. <b>Equation</b>: dN/dt = rN(K-N)/K.

Maximum population size environment can support indefinitely. Determined by limiting resources (food, water, space, shelter). Varies with environmental conditions. Population fluctuates around K.

Effects depend on population density. <b>Competition</b> (for resources), <b>Predation</b> (more prey = more predators), <b>Disease/Parasitism</b> (spreads faster when crowded), <b>Stress</b>, <b>Waste accumulation</b>. Regulate populations near carrying capacity.

Effects regardless of density. <b>Weather</b> (drought, freeze, flood), <b>Natural disasters</b> (fires, hurricanes), <b>Seasonal cycles</b>, <b>Climate</b>. Can cause drastic population changes.

<b>r-selected</b>: Unstable environments. Many offspring, small size, little parental care, mature quickly, short lifespan (insects, mice, weeds). <b>K-selected</b>: Stable environments. Few offspring, large size, much parental care, mature slowly, long lifespan (elephants, whales, humans).

<b>Type I</b>: Low infant mortality, most die old (humans, large mammals, high parental care). <b>Type II</b>: Constant death rate throughout life (birds, rodents). <b>Type III</b>: High infant mortality, few reach adulthood (fish, insects, plants, many offspring).

<b>Negative feedback</b>: Density-dependent factors slow growth as population increases. <b>Oscillations</b>: Predator-prey cycles (e.g., lynx-hare). <b>Zero population growth</b>: Birth rate = death rate. Populations stabilize around carrying capacity.

<b>Competition</b> (-/-), <b>Predation</b> (+/-), <b>Herbivory</b> (+/-), <b>Mutualism</b> (+/+), <b>Commensalism</b> (+/0), <b>Parasitism</b> (+/-). Shape community structure and evolution.

<b>Interspecific</b>: Between different species for same resources. <b>Intraspecific</b>: Within same species (usually more intense). <b>Competitive exclusion principle</b>: Two species cannot coexist if they occupy identical niche. <b>Resource partitioning</b>: Species divide resources (different times, places, foods).

<b>Predation</b>: One organism kills/eats another. Drives evolution. <b>Prey defenses</b>: <b>Camouflage</b> (blend in), <b>Warning coloration</b> (bright = dangerous), <b>Mimicry</b> (Batesian: harmless looks dangerous; Müllerian: both dangerous look similar), <b>Physical</b> (spines, shells).

Close, long-term interactions. <b>Mutualism (+/+)</b>: Both benefit (bees + flowers, lichen, mycorrhizae). <b>Commensalism (+/0)</b>: One benefits, other unaffected (barnacles on whales). <b>Parasitism (+/-)</b>: Parasite benefits, host harmed (tapeworms, ticks, mistletoe).

Species with disproportionately large impact on ecosystem relative to abundance. Removal causes major changes. Examples: Sea otters (control urchins), wolves (control herbivores), sea stars (control mussels). Maintain biodiversity.

Form major structural component of habitat. Create environment for other species. Examples: Coral (reefs), kelp (forests), trees (forest canopy). Usually abundant, high biomass.

<b>Primary succession</b>: Starts on bare rock/new land (glacial retreat, volcanic island). <b>Pioneer species</b>: Lichens, mosses. <b>Secondary succession</b>: After disturbance (fire, farming, logging), soil present. Faster than primary. <b>Climax community</b>: Stable end point, characteristic of climate.

<b>Species richness</b>: Number of different species. <b>Relative abundance</b>: Evenness of distribution. High biodiversity increases: ecosystem stability, productivity, resilience to disturbance. Highest in tropical rainforests, coral reefs.

<b>Biotic</b>: Producers, consumers (primary, secondary, tertiary), decomposers. <b>Abiotic</b>: Sunlight, temperature, water, soil, minerals, climate. Energy flows through (not recycled), matter cycles.

<b>Gross Primary Productivity (GPP)</b>: Total energy captured by producers. <b>Net Primary Productivity (NPP)</b>: GPP - respiration (energy available to consumers). <b>Standing crop</b>: Total biomass at given time. Highest in tropical rainforests, estuaries, coral reefs.

Determined by temperature + precipitation. <b>Tropical rainforest</b> (high temp, high rain, high diversity). <b>Temperate forest</b> (moderate temp, seasonal, deciduous trees). <b>Grassland</b> (moderate rain, periodic fire). <b>Desert</b> (low rain, extreme temps). <b>Taiga</b> (cold, conifers). <b>Tundra</b> (very cold, permafrost, low diversity).

<b>Freshwater</b>: Lakes (littoral, limnetic, profundal zones), rivers/streams, wetlands (filter water, biodiversity). <b>Marine</b>: <b>Photic zone</b> (sunlit, 0-200m), <b>Aphotic zone</b> (dark). <b>Intertidal</b> (tides), <b>Coral reefs</b> (high diversity), <b>Estuaries</b> (salt + fresh mix, high productivity), <b>Open ocean</b>.

Climate (long-term temperature + precipitation patterns) determines biome. <b>Latitude</b>: Tropical (equator) → temperate → polar. <b>Altitude</b>: Similar to latitude (higher = colder). <b>Rain shadow</b>: Mountains block moisture, desert on leeward side.

<b>Aquatic</b>: <b>Littoral</b> (shallow, near shore), <b>Limnetic</b> (open water, sunlit), <b>Profundal</b> (deep, no light), <b>Benthic</b> (bottom). <b>Terrestrial</b>: <b>Canopy</b> (treetops), <b>Understory</b> (shrubs/small trees), <b>Forest floor</b> (decomposition).

<b>Deforestation</b>: Clearing forests (agriculture, logging, development). <b>Urbanization</b>: Cities replace natural habitats. <b>Fragmentation</b>: Habitats broken into small patches (edge effects, reduced population sizes). Leading cause of species extinction.

<b>Air</b>: Smog, particulates, greenhouse gases (CO₂, CH₄), acid rain precursors (SO₂, NOₓ). <b>Water</b>: Sewage, chemicals, oil spills, thermal pollution, eutrophication. <b>Soil</b>: Pesticides, heavy metals, industrial waste. <b>Noise/Light</b>: Affects animal behavior.

<b>Greenhouse effect</b>: CO₂, CH₄, N₂O trap heat. <b>Global warming</b>: Average temp rising (~1°C since 1880). <b>Impacts</b>: Ice melting, sea level rise, extreme weather, range shifts, coral bleaching, extinction risk. <b>Causes</b>: Fossil fuel burning, deforestation.

Non-native species introduced to new area. Often lack natural predators/parasites. <b>Impacts</b>: Outcompete natives, alter habitats, disrupt food webs, cause extinctions. Examples: Zebra mussels, kudzu, cane toads, Asian carp. Prevention: biosecurity, quarantine.

Harvesting organisms faster than they can reproduce. <b>Overfishing</b>: Cod, tuna population collapse. <b>Overhunting</b>: Passenger pigeon (extinct), whales (endangered). <b>Poaching</b>: Elephants (ivory), rhinos (horns). Unsustainable resource use.

<b>Cultural eutrophication</b>: Excess nutrients (N, P from fertilizer runoff, sewage) enter water. <b>Process</b>: Algal bloom → blocks sunlight → algae die → decomposition uses O₂ → <b>hypoxia/dead zones</b> → fish/organisms die. Major problem in lakes, coastal areas.

<b>Bioaccumulation</b>: Toxins build up in organism over time. <b>Biomagnification</b>: Toxin concentration increases up food chain. Top predators most affected. Examples: DDT (egg shell thinning in eagles), Mercury (fish consumption warnings), PCBs. Fat-soluble toxins persist.

<b>Stratospheric ozone (O₃)</b>: Blocks UV radiation. <b>CFCs</b> (chlorofluorocarbons from refrigerants, aerosols) break down ozone. <b>Ozone hole</b>: Over Antarctica. <b>Effects</b>: Increased UV → skin cancer, cataracts, crop damage. <b>Montreal Protocol</b>: Banned CFCs, ozone recovering.

<b>Causes</b>: SO₂ + NOₓ from fossil fuel combustion → H₂SO₄, HNO₃ in atmosphere. pH < 5.6. <b>Effects</b>: Damages forests (leaches nutrients from soil), acidifies lakes (kills fish/amphibians), corrodes buildings. <b>Solutions</b>: Scrubbers on smokestacks, catalytic converters, renewable energy.

<b>Soil erosion</b>: Tree roots hold soil, removal causes erosion. <b>Species loss</b>: Habitat destruction, extinction. <b>Climate</b>: Less CO₂ absorption, more CO₂ release (burning/decomposition). <b>Water cycle disruption</b>: Less transpiration, altered rainfall. <b>Indigenous displacement</b>.

Science of protecting biodiversity. <b>Goals</b>: Prevent extinctions, preserve habitats, restore ecosystems. <b>Strategies</b>: Protected areas, captive breeding, reintroduction programs, habitat corridors, legislation (Endangered Species Act, CITES).

<b>Renewable</b>: Replace at/faster than use rate (solar, wind, forests, fisheries if managed). <b>Non-renewable</b>: Finite supplies (fossil fuels, minerals). <b>Ecological footprint</b>: Land/water needed to support lifestyle. <b>Sustainability</b>: Meeting needs without compromising future generations.

Active restoration of degraded ecosystems. <b>Examples</b>: Wetland restoration, reforestation, stream restoration, removing invasive species. <b>Reintroduction</b>: Return species to former range (wolves to Yellowstone, condors). <b>Bioremediation</b>: Use organisms to clean pollution.

Areas with high species richness + endemism (species found nowhere else) + threat level. <b>Criteria</b>: >1,500 endemic plant species, >70% habitat loss. <b>Examples</b>: Madagascar, tropical Andes, Caribbean, Philippines. Conservation priorities. ~36 hotspots globally.

<b>National parks</b>, <b>Wildlife reserves</b>, <b>Marine protected areas (MPAs)</b>, <b>Wilderness areas</b>. Preserve habitats, prevent development. <b>Challenges</b>: Insufficient size, isolated (need corridors), enforcement, human-wildlife conflict. ~15% of land, ~7% of ocean protected.

Human population ~8 billion, growing. <b>Demographic transition</b>: High birth/death → high birth/low death (rapid growth) → low birth/death (stable). <b>Carrying capacity</b>: Uncertain for humans (technology extends but finite). <b>Resource consumption</b>: Developed nations use disproportionate share. Need sustainable practices.