Ecosystems and sampling

Word	Meaning	Example
Habitat	The place where an organism lives	The meadow
Population	All the organisms of one species in an area	All the daisies
Community	All the populations of different species in an area	Daisies, worms, beetles, blackbirds…
Ecosystem	A community plus the non-living parts: soil, water, light, temperature	The whole meadow, living and not
Niche	The role of a species: what it eats, where it lives, what it does	Dung beetles recycle dung

Different species can co-exist in one habitat because they have different niches: blue tits feed among the twigs, woodpeckers on the trunk. Every organism matters: producers make the food, pollinators help plants reproduce and decomposers recycle nutrients.

Sampling with quadrats. You cannot count every plant in a big area, so you count a sample. Place quadrats at random, using random numbers as coordinates on a grid, so the sample is not biased. Use plenty of them. Then estimate = mean number per quadrat × number of quadrats that fit in the area. A 200 m² meadow with a mean of 4 daisies per 1 m² quadrat holds about 4 × 200 = 800.

Abiotic and biotic factors. Abiotic factors are the non-living parts of an ecosystem: light, temperature, water, wind, and the minerals and acidity of the soil. Biotic factors are living: food, predators, competitors, grazers and disease. A change in either can change which species live in a habitat, and how many.

The seasons change the abiotic factors. In a British wood, bluebells grow early in spring and make their food before the trees are in full leaf; the trees drop their leaves in autumn; swallows fly south when the flying insects run out, and hedgehogs hibernate. Plants and animals are adapted to cope.

To see how living things change across an area, such as from a shady hedge into an open field, use a transect: lay a tape and sample at regular points along it, and measure a physical factor such as light. Other kit: sweep nets for insects in long grass, and pitfall traps for animals that walk along the ground.