Index of Diversity Nature of Environment Explanation Low valueUnfavourable (eg desert, Arctic tundra, upper seashore) Few species present, often small populations Generally abiotic factors determine species present Usually unstable ecosystems High valueFavourable (eg tropical forest, temperate woodland, lower seashore) Many species present, usually large populations Generally biotic factors determine species present Usually stable ecosystems

Ecological Succession

Media Film Watch the following film and TAKE NOTES tut_vid_3.mov

Ecological Succession Ecological succession is the directional change in the composition of species that occupy a given area through time It involves initial colonisation and establishment of pioneer plant species, followed by their replacement with other species until a relatively stable community is formed Occurs because, through the processes of living, growing and reproducing, organisms interact with and affect the environment within an area, gradually making it more suitable for other species

Succession is directional Different stages in a particular habitat succession can usually be accurately predicted These stages, characterised by the presence of different communities, are known as 'seres' Each sere is a less hostile environment than the previous The seres are not totally distinct from each other Ecological Succession

Primary Succession A type of ecological succession that occurs in an area where there were no organisms initially

Secondary Succession A type of ecological succession that occurs in an area where an existing community has been severely cleared by disturbance

Fixed dunes (very little sand visible) Mobile dunes (lots of visible sand) An Example of Succession- Sand Dune Ecosystem

Dune building High winds move sand along beach Sand is dropped and builds up on debris left at high tide forming small wind breaks Sand piles up further in these areas as wind speed drops locally This provides a bigger wind break and more sand piles beginning the process of dune building

Pioneer Stage (Sere 1) Little organic matter Sand does not retain water and dries out rapidly High concentration of sodium and calcium (from sea spray) Soil nutrients in short supply

Pioneer Stage Plants Portland Spurge Euphorbia portlandica Intolerant of being buried by sand Tolerant of salt Able to colonise bare sand Unable to stabilize the dunes Species include sea spurge and sea holly

Yellow Dune Stage (Sere 2) Organic matter staring to build up Less spray from the sea water Some areas shielded from the wind Sand will continue to deposit Environmental conditions slowly improving

Yellow Dune Plants Marram Grass (Ammophila breviligulata) stabilizes the sand Leaves grow vertically so can withstand more sand deposits Leaves have waxy coating to retain water Leaves often rolled to reduce exposed surface area, reducing transpiration and water loss Deep vertical root system and extensive horizontal root network helps to stabilize the sand

Grey Dune Stage – Sere 3 Humus layers are building up, retaining some moisture but water is scarce in summer months Sand is no longer being deposited Developing soil will be lime rich (from crushed sea shells) or acidic Wind speed is considerably lower

Grey Dune Plants Heather (Calluna vulgaris) Pyramidal Orchid (Anacamptis pyramidalis) Grey-green lichens (Peltigera, Cladonia) will colonize the dune extensively, combining with accumulating humus to give the dune sand a characteristic dirty grey colour. Other larger plants are able to take advantage of the improving conditions

Dune Scrub Stage- Sere 4 Build-up of humus from previous stages has produced a sandy soil, capable of supporting pasture grasses and bushes Soil now retains moisture and contains more nutrients (ie nitrates) although rain may leach Na and K ions from the soil Almost no bare sand is now visible Environment is less harsh and abiotic factors (ie competition) begin are shaping species composition

Dune Scrub Plants Bushes will develop on the tops and in the hollows of the dunes. These will include: Hawthorn, Crataegus monogyna, Elder, Sambucus, Brambles, Rubus and Sea Buckthorn. Sea Buckthorn (Hippophae rhamnoides) has often been introduced onto dunes to help stabilize them. It has nitrogen fixing root nodules and thrive even on nutrient- poor young dunes.

Climax Community- Sere 5 Climax communities are those that tend to remain stable for relatively long periods of time Even in the absence of tree planting, the dunes will eventually develop into woodland, the final stage This does not however, imply that there will be no further change. When large organisms such as trees, die and fall down, then new openings are created in which secondary succession will occur.

There has been an increase in species diversity from the sparsely populated, unstable dunes at the beginning of succession to the fixed, more stable dune community populated by shrubs and flowering plants

Sub-climax community Sometimes succession does not proceed all the way to a climax community, often prevented by mans activities or other factors: Rabbits May heavily crop the vegetation and expose bare soil Droppings may add nutrients to the sand Other plants, typical of waste ground, may colonize these bare patches

By this time, the dung has been transformed into humus and nutrients and has been recycled back into the soil. The holes clearly visible in the cow pat have been made by the animals which have colonized it. Succession occurs on many different timescales It may take hundreds of years for a climax woodland to develop, while the succession of invertebrates and fungi within a single cow pat may be over within as little as 3 months.

Pioneer species Climax Community Harsh Environment High Diversity Low Diversity Less Harsh Environment Bare Rock Sere 1 Sere 2 Sere 3 Sere 4 Sere 5 FernsLichensMossesShrubsTrees Stages of succession- bare rock example

How do we study succession? We are unable to study succession in situ as the process takes place of many years However, many ecosystems exhibit all the stages of succession Therefore we can walk through different areas of a particular ecosystem and observe the different stages as we progress, using distance as a surrogate for time

Transects Starting from the strand line a line is established at right angles to the shore. A tape is set down along the line of the transect. The vegetation can be sampled at intervals along the line by using a quadrat