**(2A) Surveying Methods 1,
Surveying using quadrats**

**
**A
**quadrat** is defined as a frame, traditionally square, used
in ecology and geography to isolate a standard unit of area for study of
the distribution of an item over a large area.

You can measure how common an organism is in two
or more sampled areas of a habitat using a small **quadrat** and
comparing the distribution numbers of species of plants or animals in
each location in a much larger area.

For a plant in the same habitat (e.g. same field)
you might choose dry/damp areas or bright light/shaded areas or any
permutation of conditions (here 4 possibilities, yes?).

Suppose you are surveying a field, you can place
the 1 m^{2} quadrat in specific locations or choose some places
at random over a wide area.

The** frame **of the quadrat can be made of wood or
metal. Illustrated is 1 m x 1 m quadrat and wire strung across at 10 cm
intervals. In this case there 100 10x10 cm square possibilities for
sampling, each has x,y coordinates of 1-10,1-10. You do NOT count all 100
mini-squares, instead you can use a random number function on your
calculator to select e.g. 10 of them. The square with x,y co-ordinates
of 7,4 is shown on the quadrat diagram. This 'mesh' size is ok for very
small organisms e.g. tiny flowers.

I wrote myself a quick computer programme in BBC
basic (above left) to generate 10 random x,y coordinates (above
right).
Link to the above programme
(**it might work** on Microsoft platforms after querying it, probably won't
work on other platforms?)

After placing the quadrat at selected locations
you e.g. count the flowers in each 10 x 10 cm^{2} square or the
total in the whole1 m^{2} of the quadrat - the whole quadrat is
1 m x 1m.

Here the yellow flowers are quite large and best
counted per 1 m^{2}, giving you quantitative data e.g. **
species of flower/m**^{2}.

To count the population using 10 x 10 cm squares
it needs to be a very small flower or insect.

Photos from the Cornfield wild flower project
Hutton-le-Hole - Ryedale Folk
Museum

Again, I've superimposed a **1 m**^{2}
quadrat, sub-divided into 20 cm x 20 cm smaller quadrats.

Here you could count each species of flower per m^{2}
or choose a smaller are of 20 x 20 cm^{2} (**0.04 m**^{2}
quadrat) or 40 x 40 cm^{2} (**0.16 m**^{2} quadrat)
areas - you just have to make a sensible decision.

**
(2B) Examples
of quadrat calculations based on
sampling data**

**
Example
1. Calculating a population
density**

Suppose you did a count of some **very small
species of flower** in 10 of 10 cm^{2} mini-quadrats (10 cm x
10 cm) of a 1 m^{2}
quadrat placed in a **sunny** location. The mini-quadrats can be
selected using the random number generator.

Data counts 1-10: **7, 8, 12, 9, 9, 10, 11,
10, 9, **and** 8** flowers

Total count = 93 flowers

**Average** per 10 cm^{2} = 93/10 =**
9.3** flowers/mini-quadrat

Now there are 100 10 cm^{2} squares in
the full 1 m^{2} quadrat.

Therefore total in 1 m^{2} quadrat =
9.3 x 100 = **930** flowers.

The 'flower density' = **
930 per m**^{2}

If you repeated the measurements in a more **shaded** spot, you might find a much lower population density of
the same flower.

**Estimating a
population size from the population density**

Using the above data from small sampling areas (see also
example 2).

If you know the total area, call it
**A in m**^{2},
you just multiply the **930
x A = total population** in that area (see next example).

This is just a scaling up exercise from several small sample areas
chose at random.

**Example 2.
Calculating a population
size (abundance)**

Suppose you counted the abundance of a
relatively rare flower using a **1 m**^{2} quadrat placed
**8
times** at random across a piece of land (its habitat) measuring 80 m
x 120 m.

Flower data counts 1-8: **2, 5, 0, 1, 2, 0, 1**
and **4**

(a) Calculate the **average density** of
the rare flower per metre^{2}

Total flower count = 15

Flower density = 15/8 = **
1.875/m**^{2}
(no need to round up at this stage)

(b) Calculate the whole **population size**
of the flower in this particular habitat

Total area of habitat = 80 x 120 = 9600 m^{2}

Total population = density x total area

Population size = 1.875 x 9600 = **
18,000 flowers**

(maybe its not that rare in this made-up
calculation!)

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