Succession and communities

Define succession and climax community

succession is the changes in species composition and structure of a community overtime

this can reach a climax community = A stable community that has reached equilibrium so no net changes occur.

What is primary succession

The changes in a species composition and structure of a community overtime where the env hadn’t previously been colonised eg. bare rock

What is a sere and the stages

A sere is the sequence of succession and changes to the species and communities

Seral stages are each stage of this and its the changes in the env making it more suitable for species and to reach equilibrium and climax community. eg. xerosere in dry conditions

explain a sere for primary succession on a bare rock

1. The bare rock becomes colonised by lichens and algae - pioneer species (the first species to colonise an env) to create a pioneer community

2. Weathering by lichens causes the rock to breakdown and decompose into soil

3. Spores in wind spread seeds so moss grows

4. Taller grasses outcompete moss and plants that can be adapted in direct sunlight and low qual soil win to dominate - heather

5. animals include mites, ants and spiders and foxes and insects

6. through spreading of seeds and growth of shrubs, the soil develops as more plants means more decomposition so more minerals. Humus also develops to increase moist soil

7. larger well adapted plants like small trees can grow but biodiversity limited below as sunlight restriction

8. Taller trees - beech and oak outcompete these and a climatic (depending on climate) climax community is made

Explain what occurs at a climatic climax community

• high biodiversity

• long living trees and plants

• complex food web

• equilibrium between GPP and respiration

• equilibrium between growth and decay

• equilibrium between sunlight and decay

• equilibrium between minerals returned and uptake

What is secondary succession

This is the more common type which is the recolonization of an env. by changes to the species composition and community structure overtime that had been damaged by fire etc.

Its lots quicker and easier because

• bulbs, seeds and spores may remain

• other organisms may help

• humus, soil density and minerals remain

What is deflective succession and disclimax community

Where humans have effected the natural proccess of ecological succession

Disclimax is the effect of this as it is nearly climax community but humans have prevented it from reaching this by

1. cattle and sheep grazing - prevents more than grasses and shrubs growing like trees

2. farming - all species except one rae removed

3. deforestation - removes trees

4. Grouse shooting - grouse are bred for shooting however they only use young heather for building their nests so every 12 years the heather is burnt to allow the secondary succession to occur and seeds are regenerated

Explain heather development as a type of secondary succession

1. pioneer

2. building

3. mature

4. degenerate

Give of of the factors affecting succession

Migration - the arrival of spores, seeds and organisms as non'-native species through immigration may alter the community and soil

Give of of the factors affecting succession

Competition 2 types

1. Interspecific competition - competition between individuals of different species in the same niche as no 2 species can occupy the same one and they compete for basic things like food etc.

2. Intraspecific Competition is Competition of individuals of the same species and is always density dependent as the pop increases the resources in that niche decrease so its survival of the fittest

Competition occurs in all seral stages

The research to support this came from Gause who cultured 2 bacteria in yeast food sources and found that when grown seperately they showed their own one step curves but together one outcompeted the other and continued the curve whilst the other died

‘competition exclusion theory’ - two organisms in the same env. occupying the same niche one will outcompete the other and the other will die.

Explain a final factor effecting succession

Facilitation

This is positive interactions by altering the env. to increase resource availability, refuge from physical stress, predation and competition through mutualism and commensalism. that causes an independence between a community. It can be weak or strong and long but still important

Mutualism - a relationship/interdependence between 2 organisms where both benefit from it

eg. bees and pollinators and birds taking insects from trees

Commensalism - A loose relationship/interdependence between 2 organisms where one isn’t affected and the other benefits

eg. canopy and shrubs below or squirrel and tree for protection