Unit 1 Beta

The Living World: Ecosystems: the one-page sheet

1.1 Introduction to Ecosystems

An ecosystem joins a community of species to the abiotic conditions around it. Species interact by predation (+/−), competition (−/−) and three kinds of symbiosis: mutualism (+/+), commensalism (+/0) and parasitism (+/−). Species that need the same resource can still coexist by resource partitioning, using it at different places or times.

An ecosystem is the living (biotic) and nonliving (abiotic) parts of an area and how they interact.
A population is one species in one area; a community is every population living and interacting there.
A habitat is where a species lives; its niche is its role: what it eats, when, where and under what conditions.
Symbiosis is a close, long-term relationship: mutualism (+/+), commensalism (+/0), parasitism (+/−). Predation is +/−, competition is −/−.

each gets less, so both are harmed: competition they overlap less: resource partitioning both species can live in the same community

ecosystem: All the living things in an area together with the nonliving parts (water, soil, light, air) and the ways they interact.
population: All the individuals of one species living in the same area at the same time.
community: All the populations of different species that live and interact in the same area.
species: A group of similar organisms that can breed with one another and produce fertile offspring.
habitat: The place where an organism or population lives, with the conditions it needs.
biotic: Living, or once living: the organisms of an ecosystem and the dead matter they leave. Plants, animals, fungi and bacteria are biotic factors.
abiotic: Nonliving: the physical and chemical parts of an ecosystem, such as temperature, sunlight, water, minerals and wind.
predation: An interaction in which one organism (the predator) kills and eats another (the prey). The predator benefits and the prey is harmed.
competition: An interaction in which organisms use the same limited resource, so each gets less and both are harmed. It can be between species or within one species.
symbiosis: A close, long-term relationship between two different species: mutualism, commensalism or parasitism.
mutualism: A relationship between two species in which both benefit (+/+), such as bees and the flowers they pollinate.
commensalism: A relationship in which one species benefits and the other is neither helped nor harmed (+/0).
parasitism: A relationship in which a parasite lives on or in a host and feeds on it, benefiting while the host is harmed (+/−), usually without being killed right away.
resource partitioning: Species that compete for a resource dividing it by place, time or food size, which reduces competition so they can coexist.
niche: The role of a species in its ecosystem: what it eats, where and when it is active, and the conditions and resources it needs.

1.2 Terrestrial Biomes

Terrestrial biomes are set mainly by temperature and precipitation. Tundra and taiga are cold; grassland, chaparral, deciduous forest and temperate rainforest are temperate; desert, savanna and tropical rainforest are warm. A climatograph shows monthly temperature and precipitation, so you can read a biome off it. Savannas are not deserts: they have a wet season and a dry season.

A biome is a large region with a typical climate and typical plants, found on several continents.
Temperature and precipitation together decide the biome; a climatograph shows both month by month.
Cold: tundra (with permafrost) and taiga. Temperate: temperate grassland, chaparral, temperate deciduous forest, temperate rainforest. Warm: desert biome, savanna, tropical rainforest.
Going up a mountain changes biomes in roughly the same order as going toward the poles, because it gets colder.

only some kinds of plants can grow there they decide which animals can find food and shelter end up with similar-looking biomes, even with different species

biome: A large region of the Earth with a typical climate and typical plants and animals, such as tundra, desert or tropical rainforest. The same biome can occur on several continents.
precipitation: Water that falls from the atmosphere as rain, snow, sleet or hail, usually measured in centimeters or millimeters.
climatograph: A graph of a place’s average temperature and precipitation for each month of the year, used to identify its biome.
tropical rainforest: A biome near the equator that is warm and very wet all year (often over 200 cm of rain), with dense, layered forest and soils poor in nutrients.
temperate deciduous forest: A temperate deciduous forest: a biome with warm summers, cold winters and rain through the year, whose broadleaf trees drop their leaves in fall.
temperate rainforest: A coastal biome with mild temperatures and very heavy rain from ocean air, with huge conifers, mosses and ferns.
taiga: The boreal forest: a cold biome of cone-bearing evergreen trees with long, snowy winters and short summers, just south of the tundra.
tundra: A cold, treeless biome with long winters, a short growing season, little precipitation and permafrost, found at high latitudes and on high mountains.
permafrost: Soil that stays frozen all year. It lies under the tundra, keeps roots shallow and stores large amounts of dead plant matter.
savanna: A tropical grassland with scattered trees, warm all year, with a wet season and a long dry season; fires and grazing keep it open.
temperate grassland: A biome of grasses and few trees with hot summers, cold winters and moderate precipitation, such as a prairie. Its deep soils are very fertile for farming.
desert biome: A biome that gets very little precipitation (usually under 25 cm a year), with plants that store water; it can be hot or cold.
chaparral: A shrubland biome with hot, dry summers and mild, rainy winters, where shrubs with small waxy leaves grow and fires are common.

1.3 Aquatic Biomes

Aquatic biomes differ mainly in salinity, depth, light, temperature and dissolved oxygen. Freshwater biomes include lakes (with littoral, limnetic, profundal and benthic zones), rivers and wetlands; marine biomes include estuaries, the intertidal zone, coral reefs and the open ocean. Plants and algae need the photic zone, and colder, moving water holds more oxygen.

Aquatic biomes are sorted by salinity, depth, light, temperature and dissolved oxygen: the freshwater biome (lakes, rivers, wetlands) and marine biomes (estuary, intertidal zone, coral reef, open ocean).
A lake has a littoral zone (shallow edge), limnetic zone (open sunlit water), profundal zone (deep, dark) and benthic zone (bottom).
Only the photic zone has enough light for photosynthesis; below it is the aphotic zone.
Estuaries, salt marshes and mangrove forests grow more life per square meter than almost anywhere on Earth: nutrients plus light plus shelter.

plants and algae grow only in the sunlit photic zone shallow, sunlit coastal water is very productive fish and other animals there have less oxygen to use

salinity: The amount of dissolved salt in water, often in parts per thousand (ppt). Freshwater is near 0 ppt and seawater about 35 ppt.
dissolved oxygen: Oxygen gas dissolved in water, in mg/L, which fish and other aquatic animals use. Cold, moving water holds more of it than warm, still water.
freshwater biome: An aquatic biome with very low salinity: lakes, ponds, rivers, streams and freshwater wetlands.
littoral zone: The zones of a lake: the littoral zone (shallow edge with rooted plants), limnetic zone (open sunlit water), profundal zone (deep water too dark for photosynthesis) and benthic zone (the bottom).
wetland: Land covered by shallow water or saturated with water for at least part of the year, such as a marsh or swamp. Wetlands store floodwater, filter pollutants and shelter wildlife.
estuary: The area where a river meets the sea and fresh and salt water mix. Rich in nutrients and sunlight, estuaries are nurseries for many fish and shellfish.
mangrove: A salt-tolerant tree that grows along tropical coasts and estuaries; mangrove forests hold sediment with their roots, protect shores from storms and shelter young fish.
coral reef: A structure built by colonies of coral animals in warm, clear, shallow seawater. Algae living inside the coral share food from photosynthesis in a mutualism.
intertidal zone: The intertidal zone: the strip of shore covered by water at high tide and exposed to air at low tide, where organisms must resist drying and waves.
open ocean: The deep water of the ocean away from the coast. It covers most of Earth, but each square meter grows little algae because nutrients are scarce at the sunlit surface.
photic zone: The upper layer of a body of water where enough light reaches for photosynthesis. Below it lies the aphotic zone, which is too dark.

1.4 The Carbon Cycle

Carbon cycles among the atmosphere, living things, soil, the ocean, sediments and rock, and fossil fuels. Photosynthesis removes CO2 from the air; respiration, decomposition and combustion return it. The ocean and growing forests act as carbon sinks. Burning fossil fuels moves slow-cycle carbon into the air far faster than sinks remove it, so atmospheric CO2 rises.

Carbon moves between reservoirs (air, living things, soil, ocean, rock, fossil fuels); each movement is a flux.
Photosynthesis removes CO2; cellular respiration, decomposition and combustion release it.
A carbon sink takes in more carbon than it releases (forests, the ocean); a carbon source releases more than it takes in.
The fast cycle (air, life, ocean surface) turns over in days to centuries; the slow cycle (sedimentation, rock, fossil fuels) takes millions of years.

carbon is stored in plants and the animals that eat them CO2 returns to the air CO2 builds up in the atmosphere faster than sinks can take it back

carbon cycle: The movement of carbon among the atmosphere, living things, soil, the ocean, sediments and rock, and fossil fuels, by processes such as photosynthesis, respiration, decomposition, combustion and sedimentation.
reservoir: A place where an element such as carbon is stored for a time, such as the atmosphere, the ocean, soil, living things or rock.
flux: The movement of a substance from one reservoir to another, often given as an amount per year.
carbon sink: A reservoir that takes in more carbon than it releases, such as a growing forest or the ocean. A carbon source releases more carbon than it takes in.
photosynthesis: The process in which plants, algae and some bacteria use light energy to turn carbon dioxide and water into sugar, releasing oxygen.
cellular respiration: The process in which living things break down sugar with oxygen to release energy, giving off carbon dioxide and water.
decomposition: The breakdown of dead matter and wastes by decomposers, which releases carbon dioxide (or methane where oxygen is scarce) and returns nutrients to the soil.
decomposer: An organism, mostly bacteria and fungi, that breaks down dead matter and wastes, returning nutrients to the soil and carbon to the air.
carbon dioxide: CO2, a gas made of one carbon and two oxygen atoms. It is taken in by photosynthesis and released by respiration, decomposition and combustion.
methane: CH4, a gas made of one carbon and four hydrogen atoms, released by decomposition without oxygen (swamps, rice paddies, landfills), by cattle and from natural gas.
fossil fuel: Coal, oil or natural gas: the remains of ancient organisms buried and changed by heat and pressure over millions of years. They store carbon from the slow part of the carbon cycle.
combustion: Burning: a fuel reacts with oxygen and releases energy, carbon dioxide and water. Burning fossil fuels or wood moves stored carbon into the atmosphere.
sedimentation: The settling of particles, such as shells and dead matter, to the bottom of water, where over long times they can harden into sedimentary rock such as limestone.

1.5 The Nitrogen Cycle

Nitrogen’s largest reservoir is N2 gas in the air, which most organisms cannot use. Bacteria fix it into ammonium, nitrifying bacteria turn ammonium into nitrate, plants assimilate nitrate, decomposers return ammonium by ammonification, and denitrifying bacteria in low-oxygen soil return N2 to the air. Nitrogen often limits plant growth, and excess fertilizer nitrate leaches into water.

The atmosphere (78% N2) is the main reservoir, but most living things cannot use N2.
Nitrogen fixation (bacteria, lightning, industry) makes ammonium; nitrification makes nitrate; assimilation brings it into living things; ammonification returns ammonium; denitrification returns N2 to the air.
Nitrogen is often the limiting nutrient on land, which is why fertilizer raises crop yields.
Nitrate dissolves and is not held by soil, so extra nitrate is lost by leaching into streams and wells.

ammonium enters the soil plants take up nitrate and build proteins (assimilation) ammonium returns to the soil, and denitrifying bacteria send some nitrate back to the air as N2

nitrogen cycle: The movement of nitrogen among the atmosphere, soil, water and living things through nitrogen fixation, nitrification, assimilation, ammonification and denitrification.
nitrogen fixation: The conversion of N2 gas from the air into ammonia or ammonium that living things can use, by bacteria (in soil and in legume root nodules), by lightning, or by industry making fertilizer.
nitrification: The conversion by soil bacteria of ammonium into nitrite and then nitrate, the form most plants take up.
assimilation: The uptake of nitrate or ammonium by plant roots and its use to build proteins and DNA; animals assimilate nitrogen by eating plants or other animals.
ammonification: The release of ammonium into the soil by decomposers as they break down nitrogen in wastes and dead organisms.
denitrification: The conversion by bacteria in low-oxygen soil or water of nitrate back into N2 gas, which returns to the atmosphere.
ammonium: NH4+, a form of nitrogen made by nitrogen fixation and ammonification. Plants can take it up, and its positive charge helps soil particles hold it. Ammonia (NH3) is the related gas.
nitrate: NO3−, the form of nitrogen made by nitrification that most plants take up. It dissolves easily and is not held by soil, so it leaches into water.
limiting nutrient: The nutrient in shortest supply compared with what organisms need, so it limits growth; adding it increases growth. Nitrogen and phosphorus are common limiting nutrients.
fertilizer: A substance added to soil to supply nutrients, mainly nitrogen, phosphorus and potassium, so plants grow more.
leaching: The washing of dissolved substances, such as nitrate, down through the soil by water, toward underground water and streams.

1.6 The Phosphorus Cycle

Phosphorus is stored mostly in rock and ocean sediments and has no significant gas phase, so it cycles slowly. Weathering releases phosphate, plants take it up, animals eat plants, and decomposers return it to the soil. Rain carries phosphate on soil into water, where it settles as sediment. Phosphorus often limits growth in fresh water, so extra phosphate makes algae grow.

The main reservoirs are rock and ocean sediments; the phosphorus cycle has no significant gas phase, so it is slow.
Weathering releases phosphate; plants take it up; decomposers return it; sedimentation stores it.
Phosphorus builds DNA, ATP, cell membranes, bones and teeth.
Phosphate is often the limiting nutrient in fresh water, so extra phosphate (fertilizer, detergents, wastewater) makes algae grow fast.

phosphate enters the soil decomposers return phosphate to the soil when they die it settles as sediment and returns to land only when rock is uplifted, over millions of years

phosphorus cycle: The movement of phosphorus among rock, soil, water, sediments and living things. It has no significant gas phase, so it is slow; weathering, uptake, decomposition and sedimentation move it.
weathering: The breakdown of rock into smaller pieces and dissolved minerals by water, ice, temperature changes, chemical reactions and living things. It releases phosphate and other nutrients into soil.
phosphate: The form of phosphorus (PO4 with a negative charge) that plants take up and that makes up DNA, ATP, cell membranes, and bones and teeth. It clings to soil particles.

1.7 The Hydrologic (Water) Cycle

The water cycle moves water among the ocean, air, land, ice and groundwater. The sun drives evaporation and transpiration; vapor condenses into clouds and falls as precipitation; on land it runs off to rivers or infiltrates to recharge aquifers. Almost all water is salty ocean water, and most freshwater is ice or groundwater. Paving increases runoff and reduces recharge.

The hydrologic cycle is driven by the sun (evaporation, transpiration) and gravity (precipitation, runoff, infiltration).
About 96.5% of Earth’s water is in the ocean; most freshwater is ice or groundwater, and lakes and rivers hold a tiny share.
An aquifer is porous rock or sediment that holds groundwater; deep aquifers refill very slowly.
Pavement and cleared land mean less infiltration and more runoff: more floods and less groundwater recharge.

water vapor rises into the air clouds form and precipitation falls runoff feeds rivers; infiltration refills groundwater in aquifers

hydrologic cycle: The water cycle: the movement of water among the ocean, atmosphere, land, ice, living things and groundwater by evaporation, transpiration, condensation, precipitation, runoff and infiltration.
evaporation: The change of liquid water into water vapor, powered by the sun’s energy; most of it happens at the ocean surface.
transpiration: The release of water vapor from plants, mostly through small openings in their leaves. Evaporation and transpiration together are called evapotranspiration.
condensation: The change of water vapor into liquid droplets as air cools, which forms clouds, fog and dew.
runoff: Water from rain or snowmelt that flows over the land surface into streams, rivers and lakes instead of soaking into the ground.
infiltration: The soaking of water from the land surface down into the soil and rock, which refills groundwater.
groundwater: Water that fills the pores and cracks in soil and rock below the surface; it moves slowly and supplies wells and springs.
aquifer: An underground layer of porous rock or sediment, such as sand, gravel or sandstone, that holds groundwater and lets it flow to wells.

1.8 Primary Productivity

Primary productivity is the rate at which producers capture energy by photosynthesis. Gross primary productivity (GPP) is the total; producers use part of it in respiration (R); the rest, net primary productivity, NPP = GPP - R, becomes plant matter that animals can eat. Productivity is highest where light, water, warmth and nutrients are all plentiful.

Producers (autotrophs) make their own food by photosynthesis.
Primary productivity is the rate producers capture energy, in units such as kcal/m²/yr or g/m²/yr.
$\text{NPP} = \text{GPP} - \text{R}$ , so $\text{GPP} = \text{NPP} + \text{R}$ .
Productivity is highest where light, water, warmth and nutrients are all plentiful (rainforests, wetlands, estuaries, reefs) and lowest in deserts, tundra and the open ocean.

that total rate is gross primary productivity (GPP) that energy is lost as heat NPP is the energy available to the animals that eat plants

producer: An organism that makes its own food from light (or chemicals) and simple substances, such as a plant, alga or photosynthetic bacterium; also called an autotroph.
primary productivity: The rate at which producers capture energy and build organic matter by photosynthesis in an area, such as kcal per square meter per year.
gross primary productivity: Gross primary productivity: the total rate at which producers capture energy by photosynthesis, before any is used for their own respiration.
net primary productivity: Net primary productivity: GPP minus the energy producers use for their own respiration (NPP = GPP - R). It is the energy stored as new plant matter and available to the animals that eat plants.

1.9 Trophic Levels

Trophic levels sort organisms by how they get energy. Producers (level 1) make food from light; primary consumers (herbivores, level 2) eat producers; secondary and tertiary consumers eat the levels below; an apex predator is at the top. Omnivores feed at more than one level. Arrows point from food to eater, so a change at one level ripples to the others.

A trophic level is an organism’s position in the feeding sequence: producers are 1, primary consumers 2, secondary 3, tertiary 4.
Herbivores eat producers; carnivores eat animals; omnivores eat both and feed at more than one level.
An apex predator is at the top with no natural predators as an adult.
Arrows point from food to eater, the direction energy moves.

they form trophic level 1 they form level 2 they form levels 3 and 4, up to an apex predator

trophic level: An organism’s position in a feeding sequence: producers are level 1, primary consumers level 2, secondary consumers level 3, tertiary consumers level 4.
consumer: An organism that gets energy by eating other organisms (a heterotroph). Primary consumers eat producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers.
herbivore: An animal that eats plants or algae (a primary consumer). A carnivore eats animals; an omnivore eats both plants and animals.
apex predator: A predator at the top of its feeding sequence, with no natural predators as an adult, such as a wolf, orca or eagle.

1.10 Energy Flow and the 10% Rule

Energy enters ecosystems through producers and flows one way, up the trophic levels. At each step about 90% is used for life processes and lost as heat, so only about 10% passes on: multiply by 0.10 for each step. This explains energy pyramids, the small number of trophic levels and why eating at a lower level feeds more people. Energy is not destroyed; it leaves as heat.

The 10% rule: about 10% of the energy at one trophic level reaches the next. Multiply by 0.10 for each step up.
The first law of thermodynamics: energy is not created or destroyed. The second law: every transfer turns some into heat, so no transfer is 100% efficient.
An energy pyramid always narrows going up; biomass pyramids usually do too.
Transfer efficiency = energy at the higher level ÷ energy at the lower level × 100.

that energy leaves as heat and cannot be passed on that energy goes to decomposers instead about 10% is available to the next level up, so energy shrinks at every step

10% rule: The rule of thumb that about 10% of the energy at one trophic level is passed to the next; the rest is used for life processes and lost as heat.
biomass: The total mass of living (or recently living) organisms in an area, often measured as dry mass in grams per square meter.
energy pyramid: A diagram of the energy at each trophic level, which always narrows going up because energy is lost as heat at each step. A biomass pyramid shows mass and a pyramid of numbers shows counts of organisms.
first law of thermodynamics: The laws of energy. The first law: energy is not created or destroyed, only changed in form. The second law: each energy transfer turns some energy into heat that is less useful, so no transfer is 100% efficient.
efficiency: The share of energy put in that comes out in a useful form: useful output ÷ input × 100. Ecological efficiency is the share of energy passed from one trophic level to the next, about 10%.

1.11 Food Chains and Food Webs

A food chain follows one path of energy from producers to top consumers; a food web shows all the overlapping chains in an ecosystem. Arrows point from food to eater. Decomposers and detritivores recycle nutrients from every level. Because organisms are linked, a change in one population spreads: prey increase when predators decline, and the effect can reach plants several links away.

A food chain is one path of who eats whom; a food web is all the linked chains in an ecosystem.
Arrows point from food to eater, the way energy and matter move.
Decomposers and detritivores break down dead matter from every level and return nutrients to producers.
Webs with many links are usually more stable: consumers can switch food when one species declines.

food chains link into a food web its predators switch to other prey, and its prey increase species two or three steps away can change too

food chain: A single sequence of organisms, each eaten by the next, showing one path that energy and matter take from producers to top consumers.
food web: All the interconnected food chains in an ecosystem, showing that most organisms eat and are eaten by several species.
detritivore: An organism, such as an earthworm, millipede or crab, that eats detritus (dead organic matter) and breaks it into smaller pieces, speeding decomposition.