Biology A2- Global Warming and Succession


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Global Warming

Global Warming:  Term used for rapid increase in global temperature in the last century. Its  type of climate change- significant change in weather 

Evidence 1= Temperature records

Since 1850, temp around the world measured with thermometers

Gives reliable but short-term record

Evidence 2= Dendrochronology (tree rings)

Most trees produce one ring in their trunks for every year

Thickness of ring depends on the climate- warmer weather = thicker ring

Count the rings and see what the weather was like in what year

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Global Warming

Evidence 3= Pollen in Peat Bogs

Can be used to show how temperature has changed over thousands of years:

1. Pollen is often preserved in peat bogs (acidic wetland areas)

2. Bogs can accumulate in layers- age of preserved pollen increases with depth

3.Take cores from peat bogs and extract pollen grains from different aged layers. They then identify the plant species the pollen came from and to see what plants were sucessful.

4. If they find pollen from plnts similar to now, then the climate was similar

5. As plant species vary with climate, so the pollen will vary with climate.

6. So an increase in pollen from a plant thats successful in warm weather would show an increase in temperature. 

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Greenhouse Gases

Carbon dioxide:

More fossil fuels like coal, natural gas and petrol are burnt, releasing CO2. 

Also increased by destruction of natural sinks (store carbon to keep it out of atmosphere). e.g. trees are big sink storing carbon as organic compounds. CO2 released when trees are burnt, or when decomposers break down the organic compounds and respire them. 

Atmospheric methane:

Increasing levels because more methane is being released into the atmosphere

E.g. More fossil fuels are being extracted, there's more decaying waste and there are more cattle giving off methane as waste gas

Also released from natural stores e.g. frozen ground which is released as temperature rises and ice thaws. 

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Affect of global warming on organisms

Crop yield:

CO2 concentration is a limiting factor for photosynthesis, increasing in global CO2 concentration could mean crops grow faster, increasing crop yield

Insect pests:

Affects life cycle so insects go through larvae stage to adults quicker

Mosquitos become more abundant with warmer and wetter summers

Tropical insects less abundant as they thrive in specific temperature ranges so if its too hot, fewer insects will be able to reproduce successfully

Wild animals and plants:

Some species become more widely distributed and abundant as they thrive in warmer temperatures

Some species become less widely distributed and abundant as they need cooler temperatures

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Succession is the process by which an ecosystem changes over time. 2 types:

1. Primary succession- this happens on land that's been newly formed or exposed.

2. Secondary succession- this happens on land that's been cleared of all plants but where soil remains

 Features that emerge during succession:

-non-living environment becomes less hostile e.g. soil form and nutrients plentiful

-a greater number and variety of habitats that in turn produce:

-increased biodiversity as different species occupy these habitats, reaching a peak in mid-succession but decreasing as climax community is reached

- more complex food webs, leading to increased biomass, especially mid-time

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Succesion stages called Seral stages

Primary succession starts when species colonise a new land surface. First species to colonise the area are called pioneer species- first seral stage

Abiotic conditions are hostile e.g. no soil to retain water. Only pioneer species grow as they're specialised to cope e.g. marran grass can grow on sand dunes near the sea as they have deep roots to get water and can tolerate the salty environment.

Pioneer species change the abiotic conditions- they die and microorganisms decompose humus (organic material). This forms  basic soil

Conditions less hostile and soil retains water, so new organisms move in and grow. They die and are decomposed, adding more organic material so soil is deeper and richer in minerals.Larger plants start to grow. 

Secondary succession happens in the same way, but there's already a soil layer so the pioneer species in secondary succession are larger plants e.g. shrubs

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Succession diagram

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At each stage, different plants and animals that are better adapted for the improved conditions move in, out-compete that plants and animals that are already there and become the dominant species in the ecosystem. 

As succesion goes on, ecosystem becomes more complex. New species move alongside existing species. So species diversity increases.

Amount of biomass also increases as plants at later stages are larger + denser

Final stage called climax community - the ecosystem is supporting the largest and most complex community of plants and animals it can. This stage won't change much and is in a steady state

Different ecosystems have different climax communities.

Human activities prevent succession and climax community developing. When succession is stopped artificially, climax community is called a plagioclimax.

Deflected succession is when succession is prevented by humans and the plagioclimax is different from the one that would've developed. 

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Often involves managing succession in order to preserve an ecosystem in its current seral stage

e.g. moorland in Scotland that provides habitats for many plant and animal species. 

If it was left to natural processes, succession would lead to a climax community of spruce forest, and habitat would be lost.

Ways to manage succession:

1. Animals left to graze on land, so larger plants can't establish themselves and vegetation kept low

2. Managed fires are lit, after fires secondary succession will occur on the moorland, so the pioneer species growing back will be the species tht is being conserves e.g. heather

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