Ecosystems

• Producers convert light energy into chemical energy (GPP). Some of that is used up in respiration, and what's left (NPP) is stored as biomass and available to the rest of the food chain.
• Energy is lost at every trophic level — only around 10% passes from one level to the next. This is why food chains rarely have more than 4–5 levels.
• Ecology has a nested vocabulary: habitat → population → community → ecosystem. Each term builds on the one before it.
• Populations are shaped by biotic factors (living things — predators, competition, disease) and abiotic factors (non-living things — temperature, light, pH).
• A species' niche is its full "job" in the habitat. No two species can occupy exactly the same niche — one will always out-compete the other.
• Quadrats (frame and point) and transects (line and belt) are the tools used to measure abundance and distribution of species scientifically.
• Succession is the story of an ecosystem's life — from bare rock colonised by pioneer species, all the way to a stable climax community.

Think of a plant as a tiny solar-powered factory. Sunlight comes in, and the plant uses photosynthesis to turn that light energy into chemical energy — stored in sugars, and eventually in all the other molecules that make up the plant's body (its biomass). Organisms that do this conversion job are called producers.

But here's the catch: not all of that converted energy actually gets "saved" as new plant material. Just like your body burns some of the food you eat simply to stay alive (breathing, moving, keeping warm), a plant uses some of its own newly-made sugar for respiration — releasing energy to fuel its own cellular processes. That energy is spent, not stored, so it can't be passed on to anything that eats the plant.

This gives us two really important terms:

• Gross Primary Productivity (GPP) — the total rate at which the plant converts light energy into chemical energy (sugars) during photosynthesis. This is the "gross income."
• Net Primary Productivity (NPP) — what's left after the plant has paid its own "respiration bill." This is the energy actually stored as new biomass, and it's the only energy available to primary consumers (herbivores) and decomposers.

Roughly 90% of the energy converted during photosynthesis gets burned off in respiration — only about 10% typically ends up as new, storable plant biomass. This 90/10 split is the seed of a pattern you'll see again and again in this chapter.

How energy moves through a food chain

trophic level

biotic factors abiotic factors