communities and succession. a community consists of all the plants and animals that occupy a...
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Communities and Communities and SuccessionSuccession
Communities and Communities and SuccessionSuccession
Communities and Communities and SuccessionSuccession
Communities and Communities and SuccessionSuccessionA 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.
nothing Climax community
Have you ever seen something like this?
How does it happen?
This is bare rock.
Nothing lives here.
Why?
•Exposed.
•No soil.
•Absorbs and reflects heat.
•Dry.
•No nutrients.
How does succession work?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,
How Does Succession How Does Succession Work?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
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.
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.
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.
Pioneer speciesPioneer species
Looking again at our example….Looking again at our example….
Bare GroundBare Ground Two Years LaterTwo 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.
Bare GroundBare Ground Two Years LaterTwo 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.
Over timeOver 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.
Succession StagesSuccession StagesSuccession StagesSuccession StagesGrassland, 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
Application Task:Application Task:Mount St HelensMount St Helens
Succession on a Succession on a Hydrosere:Hydrosere:
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.
Succession = change in the composition or structure of an ecological community.
Succession on a Succession on a Hydrosere:Hydrosere:
This is an ancient lake on the Isle of Arran that is gradually being colonised by vegetation.
CASE STUDY: Loch A’Mhuillin
Why is it being colonised?Inputs:Inputs:
Groundwater flow
Hydrological Rivers
Precipitation
Surface run off
Through flow
Vegetation
Sediment
Outputs:Outputs:
River
Evaporation
Transpiration
seepage
The hydrological outputs outweigh the inputs= lake is drying up.
Succession on a hydrosere will Succession on a hydrosere will happen relatively quickly.happen relatively quickly.
Loch A’Mhuillin has become overgrown with a succession of plant species.
Pioneer SpeciesPioneer SpeciesThese 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.
What happens next?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.
…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
Woody stemmed plantsWoody stemmed plants
gorse
bracken
rhododendrons
As the soil becomes deeper and more stable, more complex plants with deeper roots become established.
Climax CommunityClimax CommunityIn 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.
Floating aquaticsgrasses
brackenMosses, sundew, bell
heather
Gorse, rhododendron
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.
Questions.1. What kind of problems would a pioneer species
encounter?
2. Describe the kind of adaptations you might expect to see in a pioneer species in order to overcome these challenges.
3. Explain the difference between primary and secondary succession.
4. 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?
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
S ea sh ore
0 3 0 00
H eig h tab o v eseash o re/m
1 0
A
B
C D
D is tan ce in lan d /m
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)
Have you driven past areas like this?What is this type of community called?
HeathlandHeathlandThe 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.
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.
(a) What term is used to describe the final stable community at the end of a succession? (1)
(b) Explain why one community is gradually replaced by another during succession. (2)
(c) Describe how each of the following farming practices influences the process of succession. (total 3)
i) regular grazing by sheep
ii) ploughing fields each year
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.
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.
Discuss rocky shores as an example ecosystem.Explain how organisms have become adapted to suit the environmental conditions and to occupy a particular niche.
Rock Shore EcologyRock Shore Ecology Rock Shore EcologyRock Shore Ecology
1. What are the physical problems with living on an exposed rocky shore?
2. What are the “pay-offs”?3. Rocky shores have zoned
communities.What are the zones on a rocky shore? What kinds of organisms live in each of these zones?
4. Sketch a diagram showing the zonation and examples of the typical organisms that live there.
Rock Shore EcologyRock Shore Ecology Rock Shore EcologyRock Shore Ecology
