Investigation into whether light intensity affects the diversity of animal species in a stream.

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Peter Tran

Biology A2 Coursework

Investigation into whether light intensity affects the diversity of animal species in a stream

Introduction

Fouldon Common, situated in West Norfolk, is a large Common which had been used as grazing land for many hundred years. As this use faded, much of the Common has developed plant life and many different habitats in which many organisms. This investigation is to be performed on Fouldon Common, the stream to be more precise.

The stream runs along the edge of the common and it's spring-fed. It is a pleasant habitat and large variety of stream life can be found including some fish, sticklebacks and stone loaches, etc and a range of insects, especially mayfly larvae, stonefly larvae, flatworms, leeches and Great diving beetles.

Organisms survive in many different microhabitats and organism diversity varies accordingly. Stream life can vary greatly between different habitats and there are many factors, which affect this range in abundance and diversity of organisms. Factors such as water depth, temperature, availability of Oxygen, and light intensity all affect the organisms which may be found in a particular habitat. I have chosen to measure the effect of light intensity on the species diversity in streams of Fouldon Common. In the investigation, streams of varying light intensity must be chosen and representative samples of the species within each site taken in order to determine this factor's effect on species diversity.

Prediction

I believe that the varying light intensity will affect the species diversity of organisms in the different sites of the stream. The greater the light intensity, the greater the species diversity.

A number of variables that cannot be controlled will inevitably affect the final results, such as the

This experiment will be conducted in November, so the no. of different species expected won't be very large, as the stream will be

Strong currents will erode the banks but a muddy bottom will be eroded quicker than a rocky bottom. The plants will be able to colonise a slow flowing stream with a muddy

Photosynthesis must take place in order for any species to survive. Photosynthesis is the process by which plants convert light energy into chemical energy using carbon dioxide gas and water. The reaction takes place in the chloroplasts of cells, found most commonly in the palisade cells. A simple equation for this reaction is given below:

6CO2 + 6H2O light + Chlorophyll in Chloroplasts C6H12O6 + 6O2

Once light energy is converted into energy in the form of a six carbon sugar (glucose), this can be stored in the plant as starch or can be to promote growth in the plant. Primary consumers consume producers (plants) and are able to utilise energy from the plant. In this way, energy in transferred along the food chain. However, the process is very inefficient and a lot of energy is lost between the trophic levels (see diagram below)

Due to this inefficiency, light intensity for an environment has a large effect on the trophic level and the species present. If the light intensity is high, it gives rise to a possibility of more primary consumers which means that there is more chance of survival for secondary consumers and so forth. This also decreases the effect of both Biotic and Abiotic factors, which limit species diversity
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Varying oxygen levels also affect the species found in each habitat. As a product of photosynthesis, it is credible to say that higher light intensities mean higher oxygen levels. More oxygen means organisms who respire aerobically may survive and one could conclude that higher oxygen levels gives greater species diversity. However, other factors affect this. Some organisms survive primarily by anaerobic respiration meaning oxygen levels have less of an effect on their survival. Another factor may also limit the organisms found, such as the soil composition which may not be preferable to the plant-life found in the stream.
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