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Ecological succession is taught in the note for Ecology. Read it below and look for the section on this topic.

Ecology

16 min read

Methods of studying ecology

Ecology is the study of organisms and their environment. To study a habitat, scientists sample. A quadrat is a frame placed at random to count plants in a small area. A transect is a line across a habitat along which quadrats are placed to show a gradual change. Mobile animals are sampled by pitfall traps, sweep nets or by capture–mark–recapture. Abiotic factors such as light, temperature, pH and moisture are measured with instruments.

Quadrats and transectsA quadrat is a square frame placed at random to count the plants or animals inside it, and the average is used to estimate the population of the whole area. A transect is a line across a habitat along which quadrats are placed at regular intervals to show how the community changes, for example from a river bank up the slope.quadrat 1 m²transect line with quadrats at equal spacingpopulation estimate = mean count per quadrat × (total area ÷ quadrat area)
Capture–mark–recapture: n₁ marked in the first sample, n₂ caught in the second sample, m of those already marked, N = the estimated population.
Worked exampleEstimating a population

In a pond, 40 fish are caught, marked and released. Later 50 are caught, of which 10 are marked. Estimate the population.

  1. Apply the formula.

Answer: About 200 fish.

Try itCapture–mark–recapture

Choose the numbers caught. See the estimated population.

Biodiversity

Biodiversity is the variety of living things, at the level of genes, species and ecosystems. A high biodiversity makes an ecosystem more stable. Simpson’s index measures it: D = 1 − Σ(n/N)², where n is the number of one species and N is the total. The index is high if there are many species with similar numbers.

A food webA food web where several food chains are linked. Grass and maize are producers. Grass is eaten by a grasshopper and a zebra, maize by a mouse and a grasshopper. The grasshopper is eaten by a bird, the zebra by a lion and the mouse by a snake. The eagle eats both the bird and the snake.GrassMaizeGrasshopperZebraMouseBirdLionSnakeEagleproducers at the bottom,top consumers at the top

Ecological succession

Succession is the gradual change in the community of a place over time. Primary succession starts on bare rock or new land with no soil: pioneers such as lichens and mosses colonise it, make soil, and are replaced by grasses, shrubs and finally trees, the climax community. Secondary succession starts where soil is already present, as after a fire or farming, and is faster.

Ecological successionA series of drawings showing how a community changes over time. Bare rock is colonised by pioneer species such as lichens and mosses, which help form soil. Grasses and herbs follow, then shrubs, and finally a stable climax community of trees. Each stage changes the environment so that the next can grow.Bare rockLichens, mossGrasses and herbsShrubsClimax foresttime
An ecological pyramidA pyramid with a wide base of producers, a smaller layer of primary consumers, a smaller layer of secondary consumers and a very small top of tertiary consumers. Each level has less energy and less biomass than the one below because only about ten percent of the energy is passed on, so there are fewer animals at higher levels.Tertiary consumersSecondary consumersPrimary consumersProducers (plants)Energy 10 kJ10 kJ100 kJ1 000 kJ10 000 kJ
The amber dot is the energy passed on. Most of the rest is lost as heat.

Conservation

Biodiversity is threatened by habitat loss, overhunting, pollution, invasive species and climate change. In situ conservation protects species in their natural habitat, in national parks, game reserves and marine parks. Ex situ conservation keeps them outside it, in zoos, seed banks and botanical gardens. Other methods are laws against poaching, reforestation, sustainable use and education of local communities.

MethodExamples in Tanzania
In situSerengeti, Ngorongoro, Mikumi and Selous national parks
Ex situSeed banks, botanical gardens, zoos
Community-basedWildlife management areas, village forest reserves
Check yourself Which tool is used to study change in a community along a slope?
Check yourself The first organisms on bare rock are called...
Check yourself A seed bank is an example of...

Key terms

Biodiversity
The variety of living things.
Succession
The gradual change of a community over time.
Climax community
The stable final community of succession.
Ex situ conservation
Protecting species outside their natural habitat.

Summary

  • Quadrats, transects and capture–mark–recapture are sampling methods.
  • Biodiversity is the variety of genes, species and ecosystems.
  • Succession goes from pioneers to a climax community.
  • Conservation may be in situ or ex situ.
Biodiversity Conservation methods