POPULATIONS AND ENVIRONMENT

Dynamic Ecosystems – Remember it! & Test it!

Dynamic Ecosystems – Remember it! & Test it!

  • Natural change within an ecosystem is known as succession.
  • Primary succession is where an ecosystem begins with an environment in which there are no species, like bare rock.
  • The first colonisers are usually lichen.
  • Moses can grow on lichen and a thin layer of soil forms.
  • Pioneer species can take root on the thin soil and encourage more soil production.
  • Secondary success is where there are a few species.
  • Herbaceous plants can then take root and are followed by larger plants.
  • Trees grow more slowly but their size eventually kills of the shrubs and encourages shade-tolerant species.
  • Once the climax community is reached succession stops.
  • Each stage is known as a seral stage and together they’re known as a sere.
  • Human kept landscapes, like gardens and farmland, are artificial climaxes or plagioclimaxes.
  • Conservation of a habitat usually involves managing succession. This ensures particular habitats are preserved.
  • Evidence-based conservation management involves collecting and analysing data on past conservation activities and then using this to make decisions.

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TEST IT!

1. A group of ecologist studied three abandoned crop fields over a period of 60 years. They noted the following trends:
i. The soil nitrate concentration rose
ii. The percentage cover of bare soil decreased
iii. The number of woody plants rose
iv. The number of small annual plants decreased

a) Explain why the soil nitrate concentration changed.

b) The coloniser and pioneer plants have different characteristics. For example, pioneer seeds germinate better with fluctuating temperatures. Why is this is an advantage?

c) What would be the advantage for a plant that colonised 50 years before to photosynthesis best at low light intensities?

2. An ecosystem is not a fixed entity: it is in fact, constantly changing over time.

  1. Give an example for each of the following:
    1. pioneer
    2. herbaceous plant
    3. What is the difference in habitat in which pioneers and herbaceous plants can grow?
    4. Explain what a climax community is.
    5. What kind of community is a garden known as?

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ANSWERS

a) There was an increase in dead organisms which increased the amount of humus and decomposition. This led to an increase in nitrification and nitrogen fixation.

b) The temperatures in bare soil fluctuate and at the start of succession there’s more bare soil and few plants.

c) These plants will survive in shady conditions, produced when the taller plants grow and block out the sunlight.

2.

a) Answers include:
i. ferns, grasses
ii. dandelions, goose grass
b) Pioneers can grow in thin soil while herbaceous need more soil in which to grow their roots.

c) A food web composed of numerous trophic levels and comprised of a complexity of interactions at which succession stops.

d) An artificial climax/ plagioclimax