Lesson 11 of 11 · 13 min
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Must-know facts
20 facts
- 01An ecosystem is a functional unit of nature: organisms interacting with each other and with their physical environment.
- 02Terrestrial: forest, grassland, desert. Aquatic: pond, lake, wetland, river, estuary. Man-made: crop field, aquarium.
- 03Structural features: species composition and stratification (trees on top, then shrubs, then herbs and grasses).
- 04Four functional aspects: productivity, decomposition, energy flow, nutrient cycling.
- 05Pond: phytoplankton and plants produce; zooplankton consume; fungi, bacteria and flagellates decompose.
- 06Productivity units: g m⁻² yr⁻¹ or kcal m⁻² yr⁻¹.
- 07GPP − R = NPP; NPP is what heterotrophs can use. Secondary productivity is the rate of new organic matter formed by consumers.
- 08Biosphere NPP about 170 billion tons dry weight a year; oceans, about 70 per cent of the surface, give only 55 billion tons.
- 09Decomposition steps: fragmentation, leaching, catabolism, humification, mineralisation.
- 10Lignin and chitin slow decomposition; nitrogen and sugars speed it; warm and moist favour it, cold and anaerobiosis inhibit it.
- 11The sun powers all ecosystems except deep-sea hydrothermal ones.
- 12PAR is under 50 per cent of incident sunlight; plants capture 2-10 per cent of PAR.
- 13Energy flow is unidirectional: sun → producers → consumers.
- 14Grazing food chain: grass → goat → man. Detritus food chain starts with dead organic matter.
- 15Aquatic: GFC is the main energy channel. Terrestrial: more energy flows through the DFC.
- 1610 per cent law: only 10 per cent of energy passes to the next trophic level.
- 17Standing crop: living biomass or number per unit area at a trophic level; dry weight is more accurate.
- 18Pyramid of number inverted for a single tree; pyramid of biomass inverted in the sea; pyramid of energy always upright.
- 19A sparrow is a primary consumer eating seeds and a secondary consumer eating insects.
- 20Pyramids ignore food webs, species at two levels, and saprophytes.
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Key terms
18 terms
- Ecosystem
- A functional unit of nature where organisms interact with each other and their physical surroundings.
- Stratification
- Vertical layering of species at different levels, such as trees, shrubs and herbs in a forest.
- Species composition
- The identity and number of plant and animal species in an ecosystem.
- Primary production
- Biomass made per unit area over a period by plants in photosynthesis.
- Gross primary productivity (GPP)
- Rate of production of organic matter in photosynthesis.
- Net primary productivity (NPP)
- GPP minus respiration losses; the biomass available to heterotrophs.
- Secondary productivity
- Rate of formation of new organic matter by consumers.
- Detritus
- Dead plant and animal remains, including fecal matter; the raw material of decomposition.
- Detritivore
- An organism such as the earthworm that breaks detritus into smaller pieces.
- Humus
- Dark, amorphous, colloidal matter that resists decay and stores nutrients.
- Mineralisation
- Release of inorganic nutrients as microbes break down humus.
- PAR
- Photosynthetically active radiation, under 50 per cent of incident sunlight.
- Saprotroph
- A decomposer that feeds by breaking down dead organic matter.
- Food web
- Interconnected food chains, including links between grazing and detritus chains.
- Trophic level
- An organism's place in a food chain based on its source of food.
- Standing crop
- Mass or number of living organisms at a trophic level at a given time.
- 10 per cent law
- Only about 10 per cent of energy passes from one trophic level to the next.
- Ecological pyramid
- Bars showing number, biomass or energy at successive trophic levels.