Communties Flashcards
What is a community?
-A community is the sum total of all the populations in a particular area
-It can be thought of as the biotic component of the ecosystem (interactions between autotrophs and heterotrophs)
What is an ecosystem?
An ecosystem us the community plus its physical environment, so is therefore made up from both biotic and abiotic components
What is succession?
-The changes overtime in an ecosystem
-It involves changes in the communities present as well as in the abiotic environment
What is primary succession?
When a new area of land, which has not previously been colonised, is colonised for the first time
What name do we give to the species that are first to arrive during primary succession?
Pioneer species
Why are lichens (algae + fungus) ideal pioneer species?
They are able to tolerate desiccation and can grow in cracks on bare rock (attaching via hairs called hyphae). They are typical “r-strategists”
How does a young or embryonic soil form in primary succession?
The lichens and weathering degrade the rock forming embryonic soil, which accumulates in crevices as the lichens die and decompose. The trapped minerals and moisture create a very thin soil, soon suitable for mosses
How does this young soil deepen and become richer in nutrients?
The lichens and mosses die and decompose causing debris containing water and minerals to accumulate further and deeper the soil
How are the larger plants like grasses, ferns and flowers able to colonise the area?
The deepening soil, now becoming richer in organic matter (like nitrates) from decomposition, allows plants with root systems to become established. Roots help to break up rock, further again.
As primary succession continues, what predictable changes typically occur over time?
-soil depth and fertility increase
-plant biodiversity increases (may decrease slightly later on)
-plant height and biomass increases
-communities become more complex with more food webs
-abiotic environment becomes less hostile
What name do we give to each stage of succession?
Each stage is called a sere
What is the climax community?
This is the stable end stage of succession which is in equilibrium with the environment.
(In the UK , its is often made up of deciduous forest, with trees such as oak and ash, which have an understorey of shrubs and beneath that a herb and ground layer of plants, mosses, fungi etc)
What are the biotic and climatic climax communities?
-The climax community occurs when the composition of species in the final community has been determined by climate
-The biotic climax community occurs when the composition of the species present in the final community has been determined by biotic factors
What is secondary succession?
Secondary succession is the series of community changes which take place on a previously colonised, but disturbed or damaged habitat (by fire, flooding, wind damage etc)
Why is secondary succession faster than primary succession?
The soil is already formed containing plant seeds and also regenerative paths of plants, as well as soil organisms like detritivores and nitrifying bacteria
