succession
life processes at the biosphere
-all species may have a stage in their lifecycle when movement to colonise new habitats can take place
-this is essential to avoid extinction
-when it colonises an area it will change the Habitat, making it suitable for other new species as well
-pioneer species: good at spreading and germinating in bare soil / unoccupied habitat
-seres:
-each sere has a prefix based on its starting conditions:
-water - hydrosere
-bare rock - lithosere
-sand - psammosere
-the process of change in a sere is called ecological succession
-ecological succession stages:
-the pioneer species makes the area more suitable for other species so new colonizers appear and may outcompete them
-they also change the conditions
-a final community is then reached that remains dominant as long as conditions do not drastically change
-this is the climax community
-the species that make up this community are based on the climate so it can be referred to as the climatic climax community
-rainfall and temperature are critical for determining a biome
-sere: the sequence of stages in ecological succession during which and uncolonized habitat reaches a climax community
-plagioclimax community:
-when human activity deflects the climax community so the natural climax community does not have time to reform and a new community develops
-a long-term balance between succession and human activities causes plagioclimax activities that don't change such as grassland / moorland
-secondary succession:
-if the activity that caused plagioclimax communities stop secondary succession will eventually re-establish the climax community
-takes place faster than primary succession - less delays for species colonisation
succession process
-psammosere - sand:
-1) plant nutrients not readily available
-2) as some succeed in colonizing the sand is stabilized and nutrients are added
-3) sequence of changes in the community of a species will establish the same climax community in a hydro / lithosere
-lithosere - bare rock:
-1) initial abiotic conditions harsh and unsuitable
-2) simple autotrophs arrive - lichens and algae
-3) dead organic matter and rock fragments accumulates
-4) mosses colonise and thin soil builds up
-5) grasses and ferns can then colonise
-6) as larger plants colonize and layers of soil form abiotic conditions become less harsh
-7) seedlings of the less hardy plants can survive in the nutrient containing soil in the shade of other plants
-8) pollinating insects colonize so flowering plants follow
-9) once soil is deep enough trees can colonize
-10) turns out quite similar to hydrosere as they form in the same climates
-hydrosere - freshwater:
-1) first to colonize - single-celled algae from the soil
-2) birds and flying insects bring in spores and seeds for algae and plants
-3) lake edges colonised by rooting plants - reeds and lilies
-4) the more plants that colonise -> more food and shelter for animals to colonise
-5) plants grow and die filling the lake with organic matter
-6) water becomes shallower so rooted plants can survive
-7) emerged species with leaves above water -> shade submerged species
-8) sediments keep filling the lake and open water recedes -> less aquatic species
-9) soil accumulates and can support larger plants and trees that can survive in waterlogged soil
-10) transpiration removes more water -> drier soil -> supports more plants
-11) larger trees create a canopy -> inhibits small plant growth
-12) community is dominated by the largest trees with other trees living in or around them
-13) few of original species are still present