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Ecosystems are made up of all the biotic and abiotic feature that interact in a particular area. Ecosystems are
always changing, sometimes slowly and sometimes quickly. Succession is the term used to describe these changes.
One example of succession is when bare rock or other
barren land is first colonised. This may occur as a result of:
·A glacier retreating and depositing rock
·Sand being piled into dunes, by wind or sea
·Volcanoes erupting and depositing lava
·Lakes or Ponds being created by land subsidising
·Silt and mud being deposited at river estuaries
The first stage of this type of succession is the colonisation
of an inhospitable environment by organisms called
Pioneer species have special features;
·The production of vast quantities of wind- dispersed seeds or spores so they can easily reach isolated situations
such as volcanic islands.
·Rapid germination of seeds on arrival as they do not require a period of dormancy
·The ability to photosynthesise, as light normally available but other food is not. They are therefore not
dependant on animal species.
·The ability to fix nitrogen from the atmosphere because, even if there is soil, it has few or no nutrients.
·Tolerance to extreme conditions.
Succession takes place in stages. At each stage, certain species can be identified that change the environment so
that it is more suitable for other species to live. The new species then out compete the species that are already
living in the area, so that a new community is formed.
EXAMPLE; Lichens can survive in areas that have very hostile conditions. They are a pioneer species. They can
grow on bare rock. In time the rock base will ware away, leaving dirt or sand. Lichens then die and decompose,
adding nutrients, this dirt can then support a community of small plants. Mosses are the next stage of succession
followed by ferns. This cycle continues until there is a thick layer of soil, that is rich with nutrients. The abiotic
features are change allowing a community to develop, in the UK the most likely final community is a thick forest.
Climax community- Stable community that has a balanced equilibrium of species with few, if any, new species
replacing those that have become established. This community has animals, and plants.
Animals- Animals also undergo similar changes, mostly determined by plant types available for food and habitats.
During succession a number of common features emerge-
·Non living environment becomes less hostile- for example, soil forms, nutrients are plentiful and plant provide
shelter from the wind. This leads to;
·A greater number and variety of habitats- that in turn can produce;
·Increased Biodiversity- as different species occupy these habitats. This is very evident in the early stages, reaching
a peak in mid-succession, and decreasing as the climax community is reached. Decrease is due to dominant
species out competing pioneer and other species, leading to their elimination from the community. With
increased biodiversity comes;
·More complex food webs- leading to;
·Increased biomass- Especially during mid succession.
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Conservation of habitats
Conservation is the management of the earth's natural resources in such a way that maximum use of them can be
made in the future. It involves human action to maintain ecosystems and biodiversity. It includes careful
management of existing resources and reclamation of those already damaged by human activities.
Three main reasons for conservation;
· Ethical- Other species have occupied the earth for far longer than we
have and should be allowed to co exist with us.…read more