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6.5 Ecosystems - Coggle Diagram
6.5 Ecosystems
Ecology definitions:
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Ecosystem: a community of organisms and the habitat in which it lives (i.e. both the biotic and abiotic factors)
Producer: an organism which converts light energy into organic molecules. It is the first organism in a food chain.
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Trophic level: the stage in a food chain made up of a particular group of organisms. Producers, primary consumers, and secondary consumers are examples of different trophic levels.
Decomposers: organisms which feed on, and break down, dead organisms and waste materials. They play an important role in nutrient recycling.
Biotic factors: the living features of an ecosystem. The number of predators, food availability and infectious disease are examples of biotic factors.
Abiotic factors: the non-living features of an ecosystem. Light availability, rainfall and soil pH are examples of abiotic factors.
The Carbon Cycle
Carbon dioxide is released into the atmosphere through respiration and the combustion of fossil fuels.
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When plants are eaten by animals, the carbon stored in organic molecules is used to synthesise organic molecules within the animal. When plants and animals die, decomposers break down and respire the organic molecules, adding carbon dioxide to the atmosphere again.
In the absence of decomposers (i.e. in bogs or deep oceans), the carbon compounds can be converted into fossil fuels such as coal by high temperature and pressure and a time frame of millions of years.
In addition to coal, limestone and chalk can form from substances deposited on the seabed. Calcium carbonate, the main component of limestone and chalk, is formed from the shells of dead marine organisms. The movement of tectonic plates causes calcium carbonate rocks to be drawn deep into the Earth’s crust. They then undergo chemical reactions which release carbon dioxide, returned to the atmosphere through volcanic activity.
When sea levels change, these rocks can become land, which may return to the ocean by physical or chemical weathering. Physical weathering occurs by hikers and plant roots. Chemical weathering occurs when rainwater reacts with calcium carbonate, releasing bicarbonate ions into the groundwater. There, the bicarbonate ions further react to reform calcium carbonate.
The Nitrogen Cycle
Plants can only absorb nitrogen in the form of nitrate so they depend on nitrogen-fixing bacteria to convert nitrogen in the air into nitrate in the soil. These bacteria either live freely in the soil or inside root nodules of leguminous plants (e.g. peas, beans). This is another example of a symbiotic relationship – the plant gets nitrates while the nitrogen-fixing bacteria get organic compounds like glucose.
The Haber process is used to convert nitrogen into ammonia which is used in fertilisers. Nitrifying bacteria convert the ammonium ions into nitrites which are then converted into nitrates, in a process called nitrification. Plants absorb the nitrates and incorporate the nitrogen into amino acids which are used to build proteins. The breakdown of proteins in our bodies produces urea which is removed from our body in our urine.
Another source of ammonia is the decomposition of dead matter by saprobionts in a process called ammonification. The ammonia is converted into ammonium ions in the soil.
In some conditions, denitrifying bacteria convert nitrates in the soil into nitrogen in the air. This usually happens in soil which is lacking oxygen (anaerobic conditions), such as waterlogged soil. Therefore, improving drainage can make soil more fertile by retaining more nitrates.
Food chains
We can use food chains to show which organisms feed on other organisms within an ecosystem and therefore the flow of energy from one organism to another. Energy always starts from the Sun and is converted into glucose by photosynthesis in green plants. Glucose is used in respiration to generate energy which is used to help the organism to grow (increase in biomass).
Organisms which produce biomass by capturing the energy from sunlight are called producers and are at the beginning of every food chain. An organism which feeds on a producer are called primary consumers and will also be herbivores, since producers tend to be mostly green plants.
The next organism in the food chain is the secondary consumer which will be eaten by the tertiary consumer.
Food Webs
Food webs show the interaction of multiple interconnected food chains within an ecosystem. For example, in the marine ecosystem pictured below there are a number of food chains which are all connected together.
You can see that if the population size of any of these organisms changes, it will affect all the other organisms in the food web. This is known as interdependence. For instance, if the number of squid in the ocean decreased, this would boost mackerel populations (as there are fewer squid to eat them) and reduce the amount of seaweed and red algae, since there are more mackerel consuming these plants.
Decomposers are also part of food webs. They break down dead material and allow nutrients to be recycled.
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Net Productivity
Biomass is the amount of energy that is available to the next trophic level - it can also be referred to as net productivity. You can think of this as the amount of weight an organism has been able to pack on - the fatter the organism, the more food (and energy) will be available for the organism that is going to eat it.
Net productivity is calculated by taking the gross productivity (all the energy consumed by the organism) and subtracting the amount lost in respiration.
We can also calculate how efficient energy transfer is by dividing the net productivity by the total amount of energy taken in by the organism. This number is then multiplied by 100 to convert it into a percentage.
Using Transects
To see how the distribution of different species changes along a habitat, we use something called a transect, which is essentially a line placed from one part of the habitat to another.
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Succession
Succession describes the change in an ecological community over time, from a relatively sparse landscape to a stable community of several different plants and animals. There are two types of succession:
Primary succession is when an ecological community develops in the absence of soil (i.e. from bare rock). This may happen after a volcanic eruption which results in the formation of new rock or if the sea level lowers and exposes new land.
Secondary succession is when an ecological community develops from a barren landscape in which soil is present. Secondary succession may happen after a forest fire, for example. Succession occurs in the following stages:
The first organisms to colonise an ecosystem are pioneer species, which includes things like moss, lichen and marram grass. There is no soil to begin with, therefore there’s nothing to absorb water. This means that the pioneer species are specially adapted live in dry, hostile conditions.
When the pioneer organisms die and decompose, they form a basic soil called humus. This makes the environment less hostile and changes the abiotic conditions. As soil forms and more water becomes available, other plant life will be able to survive here.
As those plants die and decompose, the soil becomes deeper and thicker. Larger plants, such as shrubs can now survive and biodiversity increases. The organisms which are best adapted to the changing ecosystem will out-compete and replace those which are less adapted.
Eventually, a stable community of plant and animal life is formed - this is called the climax community. The ecosystem is now supporting the largest and most complex community possible and the ecosystem stops changing significantly.