Introduction to ecosystem
Biosphere: The part of the Earth and it's atmosphere that is inhabited by living organisms.
Within the biosphere there are numbers of different ecosystems. These have distinctive features that affect the organisms living there.
A habitat is the place with a distinct set of conditions where an organism lives.
For example in a pond habitat there will organisms who live on the surface of the water, such as skaters, those who are anchored to the bottom of the pond and those who float or swim in the water.
Each of these places have particular conditions in which the organisms that live there can survive in and are adapted to.
Within a habitat there may be tiny microhabitats, again each with distinct conditions. For example, the underside of a stone will be different to the upper side.
Within a habitat there will be several to many populations.
A population is a group of individuals of the same species found in an area.
The various populations sharing a habitat or an ecosystem make up a community.
A niche is the way in which an organism exploits its environment. If two organisms live in the same habitat and share the same niche, in that they will have the same food source, the same time of feeding, the same shelter site and so on, they will compete with eachother.The better adapted will eventually out-compete the other species, as two species are only able to share the same habitat if they occupy different niches.
Living organisms live in a part of the atmosphere called the biosphere
which contains numerous ecosystems
within which there are many different habitats.
In these are several populations
which share the same area to make up a community.
Non-living or physical factors:
- Solar energy input - affected by latitude, season, cloud cover, and changes in the Earth's orbit. Light is vital in photosynthesis, flowering and sometimes germination.
- Climate - Rainfall, wind exposure and temperature over a along period of time.
- Topography - altitude (which affects climate) slope, aspect (direction the land faces) and drainage.
- Oxygen availability - particularly important in aquatic systems. For example fast-flowing streams are often better oxygenated than stagnant pool.
- Edaphic - connected with the soil, and include soil pH and mineral salt availability (affected by geology). Other factors include soil texture, e.g. sandy and clay soils have different characteristics with pros and cons.
- Pollution - can be of the air, water or land.
- Catastrophes - are infrequent events that disturb conditions considerably, such as earthquakes, floods, volcanic erruptions and fires.
- Competition - For resources like food, light, shelter, water and space can be interpecific (between species) or intraspecific (within species).
- Grazing, Predation and Parasitism - are all relationships between two organisms where one benefits at the others expense.
- Mutualism - A relationship in which both partners benefit.
Biotic factors are usually density dependent - The effects are related to the size of the populaton relative to the area available. (the larger the population density, the greater the competition for food, space and so on.
Abiotic and Biotic factors summary
Biotic and abiotic factors can both interlink in affect the survival of organisms.
An example of this is if poor weather reduces the survival rate of one animal species this will have a knock on affect on the survival abilities of their predators.
If pH of soil is changed this may affect the survival of bacteria and therefore the rate of decomposition and material recyling.
Anthroprogenic factors are those arising from human activity. They can be either abiotic or biotic.
The landscapes of Britain wouls still be largely wooded were it nto for deforestation, moor-burning and grazing.
Grazing of may be seen as just abiotic, however the removal of natural predators, such as wolves, and use of fertilisers in agricultural grazing is the results of human action.
Primary succession starts in newly formed habitats where there has never been a community before. This may occur, for example on a bare rock.
Unless prevented succession can then continue until thousands of years later, a relatively stable community is established.
Primary succession continued...
The pioneer phase:
Pioneer species are the first to colonise. They are the only organisms that can survive in the harsh conditions of a lack of soil, water and nutrients.
The pioneers start to break up the surface and change it just enough to making it suitable enough for other organisms to be able to survive there. Wind blown moss spores may begin to grow.
Primary succession continued... (2)
The mosses build up more organic matter int he soil which can then hold water. This enables seeds of small, shallow rooted plants to establish.
A conditions improve seeds from larger, deeper rooted plants begin to grow. They compete with existing smaller plants, and eventually out-compete.
This occurs until, eventually a community of tall plants and trees is reached. This stable climax community often remains unchnged unless conditions in the habitat change.
As sucession continues the number of niches increases, as does the number of species present - however it is not unusual for a climax community to have lower biodiversity than preceding stages of succession.
Primary succession continued... (3)
A climax community without trees:
There are some ecosystems, such as that of the tundra and moss bogs in northern Scotland, where the climax community is not a forest or woodland.
An example is an area within Shetland called the Keen of Hamar. It is a large area of bare, stony soil on a hill, on which succession is not occurring. This has been explained as being possible due to the properties of the soil and underlying rock, which are sandy and so will be at risk of drought after a few days of no rain. It does, however, have high biodiversity including rare species.
Secondary succession occurs on bare soil where an exisitng community has been cleared, for example in a ploughed feild or after a forest fire.
Bare soil does not remain bare for long if left, uninterferred. Some seed species will be lying dormant in the soil (a seed bank) and other will be rought by the wind or animals.
Groundsel is an example of an adapted pioneer species:
- Seeds widely dispersed by the wind.
- Rapid growth.
- Short life cycle.
- Abundant seed production.
Pioneer species like Groundsel can't compete with slower growing specie such as grases. However it succeeds by getting in quickly, growing rapidly and flowering within a few weeks.
A community that remains stable only because human activity prevents succession from running its course is called a deflected succession.
An example would be sheep grazing in Britain, which prevents many grasslands from developing into woodlands.
Many habitats, such as chalk grassland need to be actively managed, by grazing, mowing or burning, in order to prevent succession that would result in a loss or change in biodiversity.