Communities and Succession

1. Communities and Succession

2. Communities and Succession A community consists of all the plants and animals that occupy a particular area. The individual populations within a community interact with each other. The community is a constantly changing and dynamic unit, which passes through a number of stages from its origin to its climax. The transition from one stage to the next is called succession.

3. Climax community nothing

4. Have you ever seen something like this? How does it happen?

5. This is bare rock. Nothing lives here. Why?

6. Exposed. • No soil. • Absorbs and reflects heat. • Dry. • No nutrients.

7. How does succession work? A bare patch of ground will not stay bare. It will rapidly be colonized by a variety of plants. A recently cleared patch of ground The same ground 2 years later,

8. How Does Succession Work? There are 2 types of succession: PRIMARY- Plants grow where NO PLANTS HAVE GROWN BEFORE. SECONDARY- Plants grow where there has been a previous population. These will have been destroyed, eg: by fire

9. The 1st species to colonise are called PIONEER SPECIES. The “ultimate” species to colonise are called the CLIMAX COMMUNITY. Sand dune succession. The pioneer species is marram grass.

10. Pioneer species Pioneer species are often 'opportunist' species which are able to rapidly exploit a sudden new opening in ground plant cover. They must be able to grow quickly. They are usually short-lived. EXAMPLE: Mosses They are low growing, carpeting the ground and with little height. They then provide a microhabitat equivalent to a miniature forest for a variety of invertebrates such as mites and spiders. The moss also acts like a sponge when wet, in some cases providing a semi-aquatic microhabitat.

11. Looking again at our example….

12. Bare Ground Two Years Later No plant competition for light, space, nutrients or water. Soil mobile and liable to erosion and loss. A more extreme surface microclimate because the bare soil both absorbs and reflects heat more than soil covered in vegetation. A drier environment because there is no plant cover to hold moisture above ground and little humus to hold it in the soil. Lower nutrient levels in the soil. Intense plant competition for space and other resources. Soil bound by roots and plant cover. The plant cover provides a certain amount of ground insulation from extremes of temperature. There are now also a variety of microclimates within the vegetation. Plant cover and increasing humus levels help to retain water. The nutrient levels in the soil will have increased.

13. Bare Ground Two Years Later No plant competition for light, space, nutrients or water. Soil mobile and liable to erosion and loss. A more extreme surface microclimate because the bare soil both absorbs and reflects heat more than soil covered in vegetation. A drier environment because there is no plant cover to hold moisture above ground and little humus to hold it in the soil. Lower nutrient levels in the soil. Intense plant competition for space and other resources. Soil bound by roots and plant cover. The plant cover provides a certain amount of ground insulation from extremes of temperature. There are now also a variety of microclimates within the vegetation. Plant cover and increasing humus levels help to retain water. The nutrient levels in the soil will have increased.

14. Over time… • Undisturbed, an area will pass through a number of further different successional stages, each with its own characteristic mix of species. • Each new community will be better adapted to the changed environment which has been provided by the previous community. • Eventually, a climax or 'final' community is reached. At this point, the succession will not go any further. However, this does not imply that there will be no further change.

15. Succession Stages Grassland, small flowering plants. Grass, daisies Taller herbaceous plants. Willow herb, foxglove Bushes and shrubs. Hawthorn, bramble Fast growing trees. birch Larger, slow growing, stronger trees. oak

16. Application Task:Mount St Helens

17. Succession on a Hydrosere: Succession = change in the composition or structure of an ecological community. • A sere is a stage in the process of succession. • There are several examples of this: • bare rock - lithosere • bare sand - psammosere (as found on sand dunes). • Hydroseres – water • If the pond in your back garden is not dredged occasionally it will happen there in a few years.

18. Succession on a Hydrosere: CASE STUDY: Loch A’Mhuillin This is an ancient lake on the Isle of Arran that is gradually being colonised by vegetation.

19. Why is it being colonised? Inputs: Groundwater flow Hydrological Rivers Precipitation Surface run off Through flow Vegetation Sediment Outputs: River Evaporation Transpiration seepage The hydrological outputs outweigh the inputs= lake is drying up.

20. Succession on a hydrosere will happen relatively quickly. Loch A’Mhuillin has become overgrown with a succession of plant species.

21. Pioneer Species These colonise where no species has previously been. The first plant species to colonise Loch A’Mhuillin were floating aquatics. These simple plants can grow relatively easily in any pond or lake. They do not require stable soil. Since uncolonised land usually has thin, poor quality soils with few nutrients, pioneer species are typically very hardy plants, with adaptations such as long roots, root nodes containing nitrogen fixing bacteria, and leaves that reduce transpiration.

22. What happens next? The population of pioneer plants will increase, and some of them will die. Dead plants will begin to decompose and form soil. More complex plants (ie with simple roots) can then grow. A characteristic of these plants is that they produce huge numbers of seeds. They may live only one year, and spend the greatest part of their energy ensuring that offspring will arise the following year. Species of this kind are known as opportunist species. Grasses are a common example of opportunist species.

23. …and then? Plants continue to live and die, contributing to the soil that is forming. Eventually, the soil is able to support more complex plants Sun dew Bell Heather

24. Woody stemmed plants As the soil becomes deeper and more stable, more complex plants with deeper roots become established. gorse bracken rhododendrons

25. Climax Community In the final stages of succession, taller trees begin to grow. They, in turn, block out the sunlight needed by smaller trees and replace them. The final stage of ecological succession is known as a climax community. In Scotland, near the lake the typical climax community would be Scot’s Pine.

26. Gorse, rhododendron Mosses, sundew, bell heather bracken Floating aquatics grasses

27. An oak wood is a climax community About 4000 years ago much of Britain was a climax community of oak woodland. Most of this forest was cleared to allow for grazing and cultivation.

28. Questions. • What kind of problems would a pioneer species encounter? • Describe the kind of adaptations you might expect to see in a pioneer species in order to overcome these challenges. • Explain the difference between primary and secondary succession. • Early stages of ecological succession contain short-lived plants which devote enormous amounts of energy producing seeds. More mature communities do not need to do this. Why?

29. The diagram shows a profile along a transect showing succession on some coastal sand dunes. Point A B C D Index of diversity 1 2.3 5.4 6.1 a) What data must be collected in order to be able to calculate an index of diversity of plants at one of the points along the transect? (2) b) Suggest an explanation for the trend in diversity along the transect. (3)

30. Have you driven past areas like this? What is this type of community called?

31. Heathland The many heaths and grasslands in Britain that we refer to as “natural” are in fact the result of clearance and grazing. These are not true climax communities but sub-climax ones resulting from human activities. Because the normal succession has been artificially changed it is often referred to as a deflected succession and the resultant sub-climax is a plagioclimax.

32. In the process of succession, land on a newly formed volcanic island will be gradually colonised. Over time, changes in the composition of the plant and animal communities will occur until eventually no further change takes place. • What term is used to describe the final stable community at the end of a succession? (1) • Explain why one community is gradually replaced by another during succession. (2) • Describe how each of the following farming practices influences the process of succession. (total 3) • regular grazing by sheep • ploughing fields each year

33. The niche concept was investigated in some classic experiments in the 1930s by Gause. He used flasks of different species of the protozoan Paramecium, which eats bacteria. Conclusion: These two species of Paramecium share the same niche, so they compete. P. aurelia is faster-growing, so it out-competes P. caudatum.

34. In a second experiment: Conclusion: These two species of Paramecium have slightly different niches, so they don't compete and can coexist. It is important to understand the distribution: P. caudatum lives in the upper part of the flask because only it is adapted to that niche and it has no competition. In the lower part of the flask both species could survive, but only P. bursaria is found because it out-competes P. caudatum. If P. caudatum was faster-growing it would be found throughout the flask.

35. Rock Shore Ecology Discuss rocky shores as an example ecosystem. Explain how organisms have become adapted to suit the environmental conditions and to occupy a particular niche.

36. Rock Shore Ecology What are the physical problems with living on an exposed rocky shore? What are the “pay-offs”? Rocky shores havezoned communities.What are the zones on a rocky shore? What kinds of organisms live in each of these zones? Sketch a diagram showing the zonation and examples of the typical organisms that live there.