Nothing in an ecosystem lives alone

Word	What it means
Ecosystem	The living and non-living things in an area, and how they affect each other.
Biotic / abiotic	Living, or once living / non-living: sunlight, water, air, soil, temperature.
Producer / consumer	Makes its own food from sunlight, as plants and algae do / eats other living things. A herbivore eats plants, a carnivore animals, an omnivore both.
Primary / secondary / tertiary consumer	Eats producers / eats primary consumers / eats secondary consumers.
Scavenger / decomposer	An animal that eats dead animals it did not kill / a living thing, mostly bacteria and fungi, that breaks dead matter down into nutrients for the soil.
Food chain / food web	One path of who eats whom / all the food chains in an ecosystem, joined together.
Kilojoule (kJ)	A unit of energy.
Photosynthesis / respiration	How plants make sugar from carbon dioxide and water, using light / how every living thing releases the energy in sugar, using oxygen.
Symbiosis	Two species living closely together. Mutualism: both benefit. Commensalism: one benefits, the other is not affected. Parasitism: one benefits, the other — the host — is harmed.
Succession	The slow change in which living things fill an area: primary from bare rock, secondary where soil is left, as after a fire.
Population / quadrat	All the members of one species in an area / a square frame, often 1 m on each side, for counting a sample.
Invasive species	A species brought from somewhere else that spreads fast and harms the species already there.
Environmental impact assessment	A study, before a big project is built, of what it will change and how to reduce the harm.

People need food, water, shelter, energy and ways to get around, and all of them come from ecosystems. Clearing land grows food; damming a river stores water. Each does what it was meant to — and something else as well.

Worked: a highway through the mountains. The Trans-Canada Highway through Banff National Park was built for a fast, safe trip across the Rockies: that is the intended consequence. An unintended one: elk, deer, bears and wolves crossing it were hit by vehicles, and the road split their habitat in two. Parks Canada added fencing, with tunnels and tree-covered overpasses for wildlife, and where the fences went up, collisions with large animals dropped sharply. An environmental impact assessment tries to catch consequences like these before anything is built; the toolkit Intended and unintended consequences takes the idea through the whole course.

Biotic and abiotic together. Shade a pond — an abiotic change — and fewer algae grow, so everything that eats algae has less food. Change one factor and the living things follow.

willow → snowshoe hare → lynx

Read each arrow as “is eaten by”: it points the way the energy goes, from the food to the eater. The willow is the producer, the hare a primary consumer, the lynx a secondary consumer. Coyotes and great horned owls hunt hares too, and hares eat aspen and grass as well as willow, so real chains cross into a food web. More food sources make an animal safer: when hares are scarce, the lynx, which eats little else, goes hungry, while a coyote switches to mice or berries.

Where the energy goes. An animal uses most of the energy in its food just to stay alive — moving, keeping warm, growing — and that energy leaves its body as heat. Parts such as bones and fur are never eaten and go to decomposers. Only roughly a tenth ends up in the next eater.

Worked. The willows in a patch of forest store 30 000 kJ of energy in a year. Roughly how much reaches the lynx?

willows 30 000 kJ → hares roughly 3000 kJ → lynx roughly 300 kJ

So the forest can feed many hares but only a few lynx, and food chains rarely have more than four or five links: by then there is too little energy left to feed another level.

The water cycle. Water evaporates from lakes and leaves, condenses into clouds, falls as rain or snow, runs off or soaks in, and evaporates again.

photosynthesis: carbon dioxide + water + light energy → sugar + oxygen

respiration: sugar + oxygen → carbon dioxide + water + energy

The carbon cycle, simply. Plants take carbon dioxide from the air and build its carbon into sugar. Animals get that carbon by eating plants. Every living thing, plants included, returns carbon dioxide to the air by respiration, and so do decomposers as they break down the dead. Decomposers close the loop for nutrients too: the nitrogen in a fallen leaf can feed a new plant only once the leaf has been broken down.

Relationship	Who benefits	Example
Mutualism	Both	A bee gets nectar from a flower and carries its pollen to the next flower
Commensalism	One; the other is not affected	A robin nesting in a spruce tree
Parasitism	One; the host is harmed	Winter ticks feeding on a moose

Worked: which kind? A lichen is two living things in one. An alga makes food by photosynthesis and shares it; a fungus holds water and anchors both to the rock. Each gets something it could not get alone, so it is mutualism. For any pair, ask: does the first one gain? Is the second helped, harmed, or not affected at all?

Secondary succession: after a fire. When an Alberta forest burns, the soil and many roots survive. Fireweed and grasses come up within a year or two, and aspen sprout from their surviving roots. Many lodgepole pine cones stay sealed with resin until a fire's heat opens them. Over decades, white spruce grow up in the shade of the aspen and may eventually replace them.

Primary succession starts with no soil at all — bare rock left by a melting glacier, or a new lava flow. The first to grow there, the pioneer species, are usually lichens and mosses. As they grow and decay, and the rock slowly breaks apart, a thin soil builds up — over hundreds or thousands of years — and bigger plants move in.

Worked: estimating a population. A class wants to know how many dandelions grow in a 200 m² field. They drop a 1 m × 1 m quadrat at random five times and count what is inside: 4, 7, 3, 6 and 5.

mean = (4 + 7 + 3 + 6 + 5) ÷ 5 = 25 ÷ 5 = 5 per m²  →  5 × 200 = about 1000 dandelions

The quadrats must land at random: putting them where the dandelions look thickest would make the estimate far too high.

Invasive species. Zebra and quagga mussels, from eastern Europe, clog water pipes and crowd out native species in the lakes they reach. Alberta inspects boats coming into the province to keep them out, because the mussels can ride along on a boat or in water left inside it.

• Drawing food chain arrows backwards. The arrow points to the eater, the way the energy goes.
• Saying energy is recycled. Matter cycles; energy passes through once and leaves as heat.
• Calling a scavenger a decomposer. A raven eating a dead deer is a scavenger; the fungi and bacteria that break down what is left are decomposers.
• Calling commensalism mutualism. The spruce gains nothing from the robin.
• Calling regrowth after a fire primary succession. The soil survived, so it is secondary.
• Choosing where the quadrats go, or forgetting to multiply the mean by the whole area.