Ap Environmental Science Unit 1
Gross & Net Primary Productivity
GPP: Total energy captured by producers through photosynthesis.
NPP: Energy available to consumers after respiration.
Equation: NPP = GPP − R
Why NPP matters: It determines the carrying capacity of ecosystems for consumers.
NPP is highest near the equator (tropics) and lowest near the poles and in deserts.
Productivity is influenced by light, temperature, precipitation, and nutrient availability.
Energy Flow & Trophic Levels
Trophic level: The position an organism occupies in a food chain (e.g., producer, herbivore, carnivore).
Energy pyramid (in words):
Sunlight provides energy to producers (plants, algae, phytoplankton), which capture energy through photosynthesis.
Primary consumers (herbivores) eat producers and gain about 10% of their energy.
Secondary consumers (carnivores) eat herbivores and receive only about 10% of the herbivores’ energy.
Tertiary consumers (top carnivores) eat secondary consumers but again receive only about 10% of that energy.
10% Rule: Only ~10% of energy passes to the next trophic level; the rest is lost to respiration, heat, and maintenance.
Carbon Cycle (Processes)
Largest reservoir: Ocean (dissolved CO₂ and carbonates).
Processes in words:
Photosynthesis: Plants, algae, and phytoplankton absorb CO₂ and turn it into glucose.
Respiration: Organisms break down glucose and release CO₂ back into the atmosphere.
Decomposition: Decomposers break down dead matter, releasing CO₂ or methane (CH₄).
Sedimentation & fossilization: Carbon gets stored in sediments or fossil fuels for millions of years.
Combustion: Burning fossil fuels releases stored carbon quickly as CO₂.
Key terms:
Modern carbon: Currently cycling through organisms, air, and oceans.
Fossil carbon: Stored for millions of years in coal, oil, and natural gas.
Nitrogen Cycle (Processes)
Largest reservoir: Atmosphere (78% nitrogen gas, N₂).
Processes in words:
Nitrogen fixation: Specialized bacteria or lightning convert N₂ gas into ammonia (NH₃) or ammonium (NH₄⁺), which plants can use.
Nitrification: Bacteria convert ammonia into nitrite (NO₂⁻), then nitrate (NO₃⁻). Nitrate is the main form plants absorb.
Assimilation: Plants absorb nitrate and incorporate it into proteins and nucleic acids. Animals get nitrogen by eating plants.
Ammonification: Decomposers break down organic matter (dead plants/animals, waste) into ammonia/ammonium.
Denitrification: Bacteria convert nitrate back into N₂ gas, returning it to the atmosphere.
Definition recap:
Nitrogen fixation = N₂ → NH₃/NH₄⁺
Nitrification = NH₃ → NO₂⁻ → NO₃⁻
Assimilation = NO₃⁻ → plant proteins
Ammonification = organic N → NH₃/NH₄⁺
Denitrification = NO₃⁻ → N₂ gas
Phosphorus Cycle (Processes)
Largest reservoir: Rocks and ocean sediments.
No atmospheric phase → phosphorus is naturally scarce.
Processes in words:
Weathering: Rocks release phosphate (PO₄³⁻) into soil/water.
Assimilation: Plants absorb phosphate; animals get it by eating plants.
Decomposition: Dead organisms release phosphate back into soil/water.
Sedimentation: Phosphate settles into ocean sediments, locked away long-term.
Definition: Phosphorus is a limiting nutrient — ecosystems often can’t grow unless phosphorus is available.
Hydrologic Cycle (Processes)
Largest reservoir: Oceans (97% of Earth’s water).
Processes in words:
Evaporation: Water from oceans/lakes turns into vapor.
Transpiration: Plants release water vapor from leaves.
Condensation: Water vapor forms clouds.
Precipitation: Water falls as rain, snow, sleet.
Runoff: Water flows across land into rivers/lakes.
Infiltration: Water soaks into soil, replenishing groundwater.
Definition: The hydrologic cycle is powered by the sun.
Biomes & Productivity
Biome: A large ecological area defined by climate, flora, and fauna.
High NPP biomes: Tropical rainforests, estuaries, wetlands.
Low NPP biomes: Deserts, tundra, open ocean (except upwellings).
Latitude/Altitude effect:
Low latitude (0°): Tropics → rainforests.
Mid-latitude (~30–60°): Temperate grasslands/forests.
High latitude (60°+): Polar tundra/ice.
Mountains mimic latitude with elevation (base: forest, top: tundra/ice).
Aquatic Ecosystems
Classification Factors
Salinity: The salt concentration of water.
Freshwater: Low salinity (rivers, lakes, streams).
Brackish: Mix of salt and freshwater (estuaries, mangroves).
Marine: High salinity (oceans, seas).
Depth: How far light penetrates affects photosynthesis.
Photic zone: Sunlight reaches, allowing photosynthesis.
Aphotic zone: No light → no photosynthesis, organisms rely on detritus or chemosynthesis.
Flow: Movement of water.
Lentic systems: Still or slow-moving water (ponds, lakes, wetlands).
Lotic systems: Flowing water (rivers, streams).
Temperature: Changes with depth, latitude, and season; influences dissolved oxygen levels and biodiversity.
Freshwater Ecosystems
Lentic (still):
Examples: ponds, lakes.
Zones within lakes:
Littoral zone: near shore, shallow, plants rooted.
Limnetic zone: open water, light penetrates, phytoplankton.
Profundal zone: deep, dark, little oxygen.
Benthic zone: bottom sediments, decomposers.
Lotic (flowing):
Examples: rivers, streams.
Upstream: Fast flow, high oxygen, cooler temps, fewer nutrients.
Downstream: Slower flow, warmer, more sediments and nutrients, higher biodiversity.
Marine Ecosystems
Oceanic zones by depth:
Epipelagic zone (sunlight zone): Surface to ~200 m, enough light for photosynthesis, most marine life lives here.
Mesopelagic (twilight): 200–1,000 m, faint light, no photosynthesis.
Bathypelagic (midnight): 1,000–4,000 m, complete darkness, organisms use bioluminescence.
Abyssopelagic: 4,000–6,000 m, near freezing temps, high pressure.
Hadal zone: Deep ocean trenches below 6,000 m, extreme conditions.
Benthic division: Ocean floor zones (intertidal, continental shelf, abyssal plain, trenches).
Special Aquatic Ecosystems
Estuaries:
Where rivers meet the sea (freshwater + saltwater mix).
Very productive due to nutrient input and sunlight.
Critical nurseries for fish, birds, and shellfish.
Wetlands:
Areas saturated with water seasonally or permanently (swamps, marshes, bogs).
High NPP → biodiversity hotspots.
Provide ecosystem services: flood control, water filtration, carbon storage.
✅ Key Definitions Recap
Lentic: Still water ecosystem (lakes, ponds).
Lotic: Flowing water ecosystem (rivers, streams).
Photic zone: Sunlit layer where photosynthesis can occur.
Aphotic zone: Dark layer without photosynthesis.
Estuary: Transition area where freshwater meets saltwater.
Wetland: Land that is water-saturated, rich in biodiversity, and highly productive.
Terrestrial Biomes: Distinct ecological areas defined by similar climate, soil, and vegetation types, which include categories such as forests, grasslands, deserts, and tundras.
Classification Factors
Temperature and precipitation are the two biggest determinants of biome type.
Soil quality, flora (plants), and fauna (animals) are shaped by climate.
Latitude and altitude both affect biome distribution:
Latitude: Closer to the equator → warmer, wetter → tropical forests.
Altitude: Higher elevations mimic colder, higher-latitude biomes.
Tropical Rainforest
Climate: Hot, wet year-round.
Soil: Nutrient-poor (nutrients cycle quickly through biomass).
Flora: Broadleaf evergreen trees, vines, epiphytes.
Fauna: High biodiversity (insects, primates, birds, reptiles).
NPP: Very high (among the highest on Earth).
Savanna (Tropical Grassland)
Climate: Warm year-round with distinct wet and dry seasons.
Soil: Fertile with seasonal moisture.
Flora: Scattered trees, grasses, drought/fire-adapted plants.
Fauna: Large grazing mammals (zebras, antelope), predators (lions, hyenas).
NPP: Moderate to high.
Desert
Climate: Hot or cold, always very dry (<25 cm rainfall per year).
Soil: Often mineral-rich but low in organic matter.
Flora: Succulents (cacti), drought-resistant shrubs.
Fauna: Reptiles, rodents, nocturnal animals to avoid heat.
NPP: Very low.
Temperate Grassland (Prairie/Steppe)
Climate: Moderate rainfall, cold winters, hot summers.
Soil: Very fertile, thick topsoil.
Flora: Grasses, few trees.
Fauna: Bison, prairie dogs, burrowing animals, predators like wolves.
NPP: Moderate.
Temperate Deciduous Forest
Climate: Four distinct seasons, moderate rainfall.
Soil: Rich in nutrients due to seasonal leaf fall.
Flora: Deciduous trees (oaks, maples), shrubs, mosses.
Fauna: Deer, bears, small mammals, migratory birds.
NPP: Moderate to high.
Taiga (Boreal Forest/Coniferous Forest)
Climate: Cold, long winters; short, mild summers.
Soil: Acidic, nutrient-poor.
Flora: Coniferous trees (pines, spruces, firs).
Fauna: Moose, bears, wolves, migratory birds.
NPP: Moderate (lower than temperate forests).
Tundra (Arctic & Alpine)
Climate: Very cold, dry, long winters.
Soil: Permafrost, nutrient-poor.
Flora: Mosses, lichens, low shrubs.
Fauna: Caribou, arctic foxes, migratory birds.
NPP: Very low.
Zonation by Latitude and Altitude
Latitude:
0° (Equator): Tropical rainforests.
30° N/S: Deserts.
45–60° N: Temperate forests/grasslands.
60°+ N: Taiga, tundra.
Altitude (mountain “mini-biomes”):
Base: Tropical or temperate forest.
Mid-elevation: Temperate forest/grassland.
Higher: Taiga (coniferous forest).
Top: Tundra → ice/snow.
✅ Key Definitions Recap
Biome: A large ecological community defined by climate, plants, and animals.
Permafrost: Permanently frozen soil layer found in tundra.
Epiphyte: Plant that grows on another plant (common in rainforests).
Deciduous: Trees that shed leaves seasonally.
Coniferous: Cone-bearing, needle-leaved trees (pines, spruces).
Species Interactions
Predation
Definition: One organism (the predator) hunts, kills, and eats another organism (the prey).
Process in words: Predator locates prey → captures → consumes → gains energy/nutrients.
Examples:
Wolves hunting deer.
Owls eating mice.
Prey defenses (adaptations):
Camouflage: Blending with environment (chameleons, stick insects).
Mimicry: Looking like another species (viceroy butterfly mimics monarch).
Warning coloration: Bright colors signal toxicity (poison dart frogs).
Chemical defenses: Skunks spray, bombardier beetles release chemicals.
Behavioral strategies: Herding, playing dead, sudden displays (like eyespots)
Competition
Definition: Organisms compete for limited resources (food, space, mates, sunlight).
Types:
Intraspecific: Competition within the same species (e.g., two male deer fighting for mates).
Interspecific: Competition between different species (e.g., lions vs. hyenas for prey).
Principle of Competitive Exclusion:
No two species can occupy the same niche indefinitely.
One will outcompete the other unless they adapt.
Resource Partitioning (adaptation to competition):
Species use resources in different ways, times, or places to reduce conflict.
Example: Warbler birds feeding at different parts of the same tree.
Symbiosis
Definition: A close, long-term interaction between two species.
Types of Symbiosis:
Mutualism: Both benefit.
Example: Bees pollinating flowers (bee gets nectar, flower reproduces).
Example: Clownfish and sea anemones (protection + food scraps).
Commensalism: One benefits, the other is unaffected.
Example: Barnacles on whales (barnacles get transport, whale unaffected).
Example: Epiphytic plants growing on trees.
Parasitism: One benefits, one is harmed.
Example: Tapeworms in human intestines.
Example: Mistletoe extracting nutrients from trees.
Other Important Relationships
Keystone species:
Definition: Species with a disproportionately large impact on ecosystem structure.
Example: Sea otters eat sea urchins → protects kelp forests.
Indicator species:
Definition: Species that signal ecosystem health or stress.
Example: Amphibians (sensitive to pollution and habitat change).
Invasive species:
Definition: Non-native species that disrupt ecosystems, often outcompeting natives.
Example: Cane toads in Australia, zebra mussels in the Great Lakes.
✅ Key Definitions Recap
Predation: One benefits, one harmed (short-term killing).
Competition: Rivalry for resources (intra- vs interspecific).
Mutualism: Both benefit.
Commensalism: One benefits, other unaffected.
Parasitism: One benefits, one harmed (long-term dependence).
Resource partitioning: Division of resources to avoid competition.
Competitive exclusion: Two species cannot share the same niche indefinitely.
Keystone species: Essential to ecosystem balance.
Indicator species: Show ecosystem health.
Invasive species: Disruptive non-native organisms.
Symbiotic relationships: Interactions between species that benefit at least one party, including mutualism, commensalism, and parasitism. Biodiversity: The variety of life in an ecosystem, crucial for resilience and adaptability.
Ecosystem Sustainability
The ability of an ecosystem to maintain its functions and processes over time, ensuring that it continues to support diverse forms of life and provides essential services.
Life is sustained by three major factors
One-way flow of energy from the Sun
Process in words: Sunlight enters Earth’s system → producers capture it through photosynthesis → energy moves through trophic levels (herbivores, carnivores, decomposers).
Energy cannot be recycled — once it is lost as heat, it is no longer available for biological work.
Example: Sunlight → grass → cow eats grass → human eats cow → most energy lost as heat at each step.
Cycling of nutrients (conservation of matter)
Matter moves repeatedly through biogeochemical cycles (Carbon, Nitrogen, Phosphorus, Water).
Nutrients are reused by different organisms over and over.
Example: Nitrogen cycles from atmosphere → soil → plants → animals → back to atmosphere through denitrification.
Gravity keeps the atmosphere in place
Gravity ensures gases (oxygen, carbon dioxide, nitrogen) remain near Earth’s surface for organisms to use.
Gravity also allows water to cycle (rain falls, rivers flow downhill, etc.).
Example: Without gravity, water vapor and gases would escape into space, and life as we know it could not exist.
Laws of Thermodynamics (Applied to Sustainability)
First Law (Conservation of Energy):
Energy cannot be created or destroyed.
In ecosystems: solar energy is transformed into chemical energy (glucose), then into kinetic energy (movement), heat, etc.
Example: A tree captures sunlight and stores it in wood. When burned, that energy is released as heat and light — but the total energy remains constant.
Second Law (Entropy):
Every energy transfer increases entropy (disorder); energy conversions are inefficient.
Explains why energy is lost as heat at each trophic level and why energy pyramids narrow at the top.
Example: Lions eat zebras, but most of the zebra’s energy is lost to heat and metabolism, not stored as lion biomass.
✅ Key Definitions Recap
Sustainability: The ability of ecosystems to maintain ecological processes over time.
One-way flow of energy: Energy moves through food chains/webs but cannot be recycled.
Nutrient cycling: Continuous reuse of matter (C, N, P, H₂O) in ecosystems.
Gravity in ecosystems: Keeps atmosphere and water in place, enabling cycles.
Entropy: Energy transfers increase disorder; explains heat loss in ecosystems.
Laws of Energy & Matter
First Law of Thermodynamics – Conservation of Energy
Definition: Energy cannot be created or destroyed; it can only change form.
Process in words:
Sunlight → converted by plants into chemical energy (glucose).
Herbivores eat plants → chemical energy converted into kinetic energy (movement), thermal energy (heat), etc.
The total amount of energy remains constant, but the form changes.
Example in ecology:
Plants photosynthesize sunlight into sugar.
Animals eat sugar for energy.
Energy changes form, but no new energy is created.
Second Law of Thermodynamics – Entropy
Definition: Every energy transfer increases disorder (entropy); some energy is always lost as unusable heat.
Process in words:
Each time energy moves up a trophic level, some energy is lost as heat.
This explains why energy pyramids narrow at the top — less energy is available to higher consumers.
Example in ecology:
A lion eats a zebra: most of the zebra’s energy is lost as heat or respiration, only a fraction goes into the lion’s biomass.
This loss explains why ecosystems can’t support many top predators.
Law of Conservation of Matter
Definition: Matter cannot be created or destroyed; it only cycles through forms.
Process in words:
Atoms (like carbon, nitrogen, phosphorus) are reused endlessly in biogeochemical cycles.
For example, carbon can exist as CO₂ in the atmosphere, glucose in a plant, muscle in an animal, and then soil organic matter after decomposition.
Example in ecology:
When wood burns, it doesn’t “disappear” — the carbon becomes CO₂, the minerals become ash, and energy is released as heat/light.
Ecological Implications
Energy vs. Matter:
Energy flows in one direction → sunlight → producers → consumers → heat (not recycled).
Matter cycles → elements like C, N, P, and H₂O move between organisms, atmosphere, water, and soil.
Why it matters:
Explains why ecosystems rely on constant energy input from the sun.
Explains why nutrient cycles (carbon, nitrogen, phosphorus, water) are essential to sustain life.
✅ Key Definitions Recap
First Law (Conservation of Energy): Energy is transformed, not created/destroyed.
Second Law (Entropy): Energy transfers are inefficient; disorder (heat loss) increases.
Law of Conservation of Matter: Matter cycles endlessly, never disappears.
Practical Exam Skills
Be able to:
Calculate percent change.
Apply experimental design (IV, DV, constants, control, hypothesis).
Interpret climatograms and energy pyramids.
Explain feedback loops:
Positive loop: amplifies change (e.g., melting ice → less albedo → more warming).
Negative loop: resists change (e.g., predator-prey population cycles).