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Energy pyramids and population growth

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Harvey Buckle

on 24 October 2017

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Transcript of Energy pyramids and population growth

30th January 2017
Energy and pyramids and population growth
To know how energy is passed from one trophic level to the next
To know how and why populations change
What would happen if the population of slugs decreased?
Slugs, rabbits and insects all eat grass. If there were fewer slugs there would be more grass for the rabbits and insects. With more food the populations of rabbits and insects would increase. However, the thrushes would have to eat more insects to maintain their population, so it is also possible that the population of insects could decrease. This is turn may reduce the populations of voles and frogs.
If we draw a pyramid of biomass, it looks like pyramid 2. Note the large biomass of the one oak tree, compared with the small biomass of lots of caterpillars, indicated by the shape of the pyramid.
The wider the bar, the more biomass there is. Pyramids of biomass always have this shape (but pyramids of numbers can be any shape).
Populations changes
Notice that the frogs, voles and insects have more than one predator, but the rabbits and slugs have just one predator.This leads to some interesting effects if the population of a particular organism in the food web decreases. Some animals can just eat more of another organism if food is in short supply, while others may starve and die. This in turn can affect the populations of other organisms in the food web.

If we look at the
Oak trees are very large, but caterpillars are very small. One oak tree can feed many caterpillars, but many caterpillars are needed to feed a blue tit, and many blue tits are needed to feed a sparrow hawk. If we draw a pyramid of numbers for this food chain, it looks like pyramid 1. Note there's only one oak tree, but lots of caterpillars indicated by the shape of the pyramid.
The wider the bar, the more organisms there are. Remember that energy is lost at each step in a food chain.
What would happen if the population of insects decreased?
What about energy transfer?
When e___ is transferred from tr___ level to trophc level to another energy is l___.

This because of: 1. R_______
2. Pes______
3. Wa___
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