Every fact in the three ecosystem lessons is listed here with where it comes from. The numbers in [brackets] on the lesson pages link to this list.
How we rate sources
High: space agencies (NASA), peer-reviewed open textbooks (OpenStax, Rice University) and professional scientific societies (American Physical Society).
Medium-high: reputable science news reporting directly on a primary document.
Medium: single-author essays and popular history sites. We only use these for history details, and never on their own: each one is paired with a second source.
Wikipedia was not used as a source. Numbers are rounded (for example 9.8 m/s² for Earth's gravity). The text was drafted with help from AI (Claude) and then checked against these sources. Corrections: hello@echoesof.science.
Where the facts are simplified or less certain: the '10% rule' is an average [2]; real transfer efficiencies vary, and in the Silver Springs study the efficiency between the first two trophic levels was about 14.5% [3]. The Yellowstone wolf story is simplified: the researcher quoted by The Wildlife Society says the first ten years matched predictions well, but later bears, cougars and bison made the picture more complicated, and outside the park people remain the main influence [4]. A sealed bottle garden is a model of an ecosystem, not a perfect copy: it still needs light from outside and sometimes a little water [5].
All sources
[1] Ecosystem
National Geographic Education · Reliability: Medium-high
Type: Educational publisher (encyclopedic entry)
An ecosystem is a geographic area where plants, animals and other organisms, as well as weather and landscape, work together to form a bubble of life. Ecosystems contain biotic (living) factors such as plants, animals and other organisms, and abiotic (non-living) factors such as rocks, temperature and humidity. Every part of an ecosystem depends on every other part, directly or indirectly. Ecosystems can be very large or very small; tide pools are complete, tiny ecosystems. The five main types of biome are desert, aquatic, tundra, grassland and forest. A change in temperature often affects what plants grow; animals that depend on the plants must adapt, move or perish. Some ecosystems can be restored after damage. A keystone species helps define an entire ecosystem.
National Geographic Education · Reliability: Medium-high
Type: Educational publisher (article)
The initial source of energy for almost every ecosystem on Earth is the Sun. Producers make their own food by converting solar energy, mostly by photosynthesis; plants are the main producers on land and phytoplankton in the ocean. Primary consumers (herbivores or omnivores, e.g. grasshopper, zooplankton) eat producers; secondary consumers (e.g. mouse, herring) eat primary consumers; higher levels include snake, cod, hawk and killer whale. On average only 10% of the energy at one trophic level is passed on to the next; this limits the number of trophic levels. Much energy escapes as heat during respiration, some food is indigestible and leaves as waste, and some organisms die without being eaten. Decomposers break down waste and dead matter. Energy pyramid steps get smaller going up because energy is lost at every level.
[3] Biology 2e, 46.2 Energy flow through ecosystems
OpenStax (Rice University) · Reliability: High
Type: Peer-reviewed open university textbook
Autotrophs are critical for all ecosystems. In the Silver Springs (Florida) study, gross primary productivity was 20,810 kcal/m²/yr, of which 13,187 kcal/m²/yr were used for respiration or lost as heat. The trophic level transfer efficiency between the first two trophic levels was about 14.48%. After four to six energy transfers there is not enough energy left to support another trophic level. Pyramids of energy are always upright.
[4] Study documents wolves' role in transforming Yellowstone
The Wildlife Society · Reliability: Medium-high
Type: Professional society for wildlife scientists (news article on a study)
After wolves returned to Yellowstone, elk became scarce where wolves concentrated; wolves helped restore willows, cottonwoods and aspens, and returning willows supported beavers and yellow warblers. The researcher, Mark Boyce, calls the first effect a behavioural trophic cascade. After about 10 years things became more complicated (bears eating elk calves, returning cougars, more bison); whether wolves can control bison is unknown, and outside the park humans are the dominant influence.
A terrarium is a miniature garden or ecosystem in a glass or plastic container. In a sealed container humidity stays high and moisture is re-circulated, so it needs watering only a few times a year. Small slow-growing foliage plants, miniature ferns and mosses suit sealed terrariums. Put a drainage layer of washed gravel in the base, then potting compost. Plants need bright, indirect light for at least six hours a day; keep out of direct summer sun and away from heat. Light condensation shows there is just enough water; no condensation means it may need water; too much can rot plants.
Used in: Ages 10–11 (experiment); Ages 10–11 (quiz)
Ground vegetation in two contrasting areas of woodland or grassland is compared by random sampling of both areas or along a transect, using quadrats, recording the number of individuals of each species or an estimate of abundance. For many statistical tests, 10–30 samples are needed in each area. Safety: long sleeves and trousers (brambles, nettles, ticks), sturdy footwear, watch for branches and uneven ground, do not work alone.
Used in: Ages 15–16 (experiment); Ages 15–16 (quiz)