Investigating the Effects of An Abiotic Factor on the Frequency and Distribution of a Freshwater Invertebrate

Investigating the Effects of An Abiotic Factor on the Frequency and Distribution of a Freshwater Invertebrate

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Investigating the Effects of An Abiotic Factor on the Frequency and Distribution of a Freshwater Invertebrate



(i) Planning
------------



Introduction
============

Before a complex biological study can be planned and formulated, the
terminology in the title above must be clarified. The investigation
requires a sound knowledge of ecology, which essentially is the study
of organisms, whether they be animals or insects, and their
relationship with the environment in which they live.

The title of the investigation states that it is the effect of an
abiotic factor that is being investigated, as opposed to a biotic
factor. There is a very subtle difference between these two factors.
Biotic and abiotic factors can both affect how an organism lives and
interacts with the immediate environment.

1. Biotic factors are the effects of all the other living organisms
that inhabit the studied ecosystem. Organisms can influence each other
in many ways of which predation is only one. Many organisms must
compete with one another for food, and there are organisms, which feed
directly from others as parasites.

2. Abiotic factors are different from biotic factors in that they
don’t involve other organisms. This means that anything, which affects
an organism in its ecosystem that is not living, is classed as an
abiotic factor. Popular examples of abiotic factors include the
climate and water currents. It has to be accepted that different
organisms will respond in different ways to the same abiotic factor.
It will be important to remember this throughout the course of the
investigation.

Now that these key terms have been clarified the title can be fully
understood and a scientific investigation can be planned.

A good starting point is to decide upon the abiotic factor and
freshwater organism that will be investigated. Hence it is important
to construct a list of possible biotic factors, this essentially will
be a list of any organisms that may be found in the studied ecosystem.
In a similar fashion a list of abiotic factors must also be

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determined.

The data for the investigation will be collected some along the course
of Upper Gordale Beck, a tributary of the river Aire close to Malham.
Having studied similar mountainous streams on previous occasions it is
possible to work out what Upper Gordale Beck will be like.

Possible organisms which may inhabit the Upper Gordale Beck ecosystem:

1

Trueworm

14

Cranefly lava

2

River limpet

15

Non-biting midge

3

Freshwater shrimp

16

Biting midge

4

Freshwater mite

17

Diving beetle

5

Swimming mayfly nymph

18

Riffle beetle

6

Flat mayfly nymph

19

Black water beetle

7

Burrowing mayfly nymph

20

Dragonfly nymph

8

Stonefly nymph

21

Alderfly nymph

9

Lesser water boatman

22

Damselfly nymph

10

Cased caddis (stones)

23

Whirligig beetle

11

Cased caddis (vegetation)

24

Snail

12

Caseless caddis

25

Leech

13

Blackfly lava

26

Water fly

Although 26 aquatic organisms have been identified above, it is highly
possible that throughout the data collection other organisms will be
encountered. These must not be ignored and can be easily added to the
bottom of the list above if need be.

A similar list can be drawn up of abiotic data.

Abiotic factors that could affect the organisms of Upper Gordale Beck

1

Flow rate

9

Turbidity of water

2

Air temperature

10

Vegetation - percentage cover

3

Water temperature

11

Bed rock - percentage cover

4

pH of water

12

Stones - percentage cover

5

Percentage oxygen

13

Mud - percentage cover

6

Amount of nitrate

14

Shade - percentage cover

7

Amount of phosphate

15

Stream depth

8

Amount of ammonium

16

Stream width

17

Cross-sectional area of stream

To construct a list like the one above requires a great deal of
scientific knowledge. The inclusion of each of the abiotic factors can
be justified.

Flow rate. This may not affect large organisms that can withstand
stream currents; likewise it may not affect organisms which hide
themselves under rocks. However organisms which are more fragile may
not be able to inhabit sections of the stream where the rate of flow
is high.

Air and water temperature. Different organisms enjoy different amounts
of warmth at different times of the day and at different times of the
year. The local temperature at a particular site of a stream could
easily decide which organisms thrive there.

pH of the water. Surprisingly this could change quite considerably
along just a small length of stream. Differing pHs can be caused by
the chemicals farmers put on their land getting into the water. Hence
anywhere downstream of a farm may have an unsuitable pH for the normal
organisms to live.

Percentage of oxygen. This will of course only affect those organisms
that breathe using oxygen from the water. However some of the listed
organisms do breathe in this way, and it would be a fair assumption to
say that these organisms should be more frequent where the oxygen
content of the water is higher.

Amount of phosphate/nitrate/ammonium. Like pH the amounts of these
compounds can change considerably along just a short length of stream.

Now that these lists have been drawn up, an abiotic factor can be
chosen as the one whose effect should be investigated. Also one
particular organism must be selected.

Choices

Abiotic factor = Flow rate

Freshwater organism = Swimming mayfly nymph

If upon investigation either of these two do not provide suitable
results for experimental writeup, it will be very simple to change the
investigation to involve a different abiotic factor or organism.
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