Ecosystems- F215

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Ecosystems

  • Ecosystem: any group of living organisms and non-living things that occur together with interrelationships between them. The components of an ecosystem include:

- Habitat: a place where an organism lives.

- Population: all the organisms of one species that live in the same place at the same time that can breed together.  

- Community: all the populations of different species that live in the same place at the same time.

Biotic factors are factors like food supply, predation and disease that can affect the living organisms.

Abiotic factors include soil pH, temperature, soil type etc.

Energy Transfer

Energy is lost at each trophic level through respiration, excretion. To measure the efficiency of energy transfer you can use pyramids of biomass, where the area of the bars is proportional to the dry mass. The gross primary productivity can also be used:the rate at which plants convertlight energt into chemical energy. 


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Succession

Succession: A directional change in a community of organisms over time.

This can occur after trauma to the land that destroys the current ecosystem, for example a volcanic eruption, or it can occur on sand dunes as the sea changes the land over time.

Primary succession: where land has been newly formed or exposed eg.Volcano, dropping sea level

Secondary succession: land has been cleared of plants but the soil remains eg. deforestation.

Stages of succession

1. Pioneer plants begin to colonise the area in the first seral stage. The abiotic conditions are harsh to only well adapted plants can live there.

2. The pioneer plants change the abiotic conditions and form basic soil,making the environment less hostile. This means more plants can survive here so over time a new ecosystem develops.

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Studying Ecosystems

Quadrats

A quadrat is a square frame that defines the sample area. You can measure two things:

- Distribution: Record the presence or absence or species/ individuals.

- Abundance:Estimate the number of individuals. You can use the ACFOR scale to describe the abundance of each species. 

With a quadrat you can also use a belt transect,  a line running across a habitat. Place a quadrat all along the side of the length of string. 

A line transect is very similar to a belt transect but without using the quadrats, instead you only count the vegetation touching the string.

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The Nitrogen Cycle

Saprotrophs: Bacteria and fungi involved in the decomposition of organisms.

- Saprotrophs secrete enzymes onto dead and waste material. These digest the material into small molecules,which are then absorbed into their body. These are then restored or respired.

Recycling nitrogen within an ecosystemThere are four different processes that involve bacteria:

Nitrogen Fixation: When nitrogen gas in the atmosphere is turned into ammonia by Rhizobium. Ammonia used by plants.Rhizobium found in the root nodules of leguminous plants.

Ammonification: When nitrogen compounds from dead organisms are turned into ammonium compounds by decomposers. Animal waste also turned into ammonium compounds.

Nitrification: When ammonium compounds in the soil are changed into nitrogen compounds to be used by plants. Nitrosomonas change ammonium compounds into nitrites, then Nitrobacter change nitrites into nitrates.

Denitrification: nitrates in the soil converted into nitrogen gas by denitrifying bacteria. Used for respiration in anaerobic conditions; when soil low in O2, nitrates conerted to make room.

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Carrying Capacity

Carrying Capacity: the maximum population size that can be maintained over aperiod of time in a particular habitat.

(http://scienceaid.co.uk/biology/micro/images/bacteriagrowth.png)

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Predation

Predation can act as a limiting factor on the size of a prey's population.

1. When the predator population increases,more prey are eaten.

2. The prey population decreases, leaving less food for the predator.

3. With less food, fewer predators can survive and their population size reduces.

4. With fewer predators, the number of prey increases. 

5. With more prey, the predator population increases.

In areas with high species diversity, this pattern isn't as obvious as predators have a choice of food sources.

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Competition

Competition occurs when resources are not present in adequate amounts to satisfy the needs of all the individuals who depend on these sources.

Intraspecific Competition

This occurs between individuals of the same species. When factors, like food supplies, become a limiting factor, individuals are competing for resources. Those best adapted will reproduce. 

The stationary phase is usually very stable, with only small fluctuations, This is because of competition:

- If the population size decreases, competition decreases so the population size increases again, and vice versa.

Interspecific Competition

This occurs when individuals of different species compete. This can effect both population size and distribution of a species in an ecosystem.

Competitive Exclusion Principle: when two species have exactly the same niche so one species dies out eg. Red squirrels and grey squirrels. 

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