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Ecological Investigations 1Ecological Investigations 1

Counting PlantsCounting Plants

IntroductionIntroduction

Ecology is the study of the relationships organism have with each other and the non living environment. To study these relationships ecologists often ask questions which at first seem straight forward.

How many different species live in this habitat?

What is the population size of this species?

It is when you look more closely that the meaning of words like species and population, that measurement of these things becomes much more complex.

SpeciesSpecies

Species: a group of organisms that can interbreed and produce fertile offspring.

One of the major practical difficulties in ecology is the identification of species. For example some groups of flowering plants such as grasses are difficult to identify without the presence of the flowers and superficially may look very similar. Yet their may be many species of grass present in a habitat and often they are the dominant plant group. If species are not correctly identified it is likely that any data collected is worthless.

The QuadratThe Quadrat

A quadrat normally consists of a square metal frame 0.5 x 0.5 metres in size. The inside of the square is divided up by wires into smaller squares. The quadrat is placed on the sample area and the population within is assessed.

A quadrat can actually be of almost any size depending on the area one wishes to sample. Quadrats may be etched onto slides, or for long term ecological investigation a permanent quadrat can be marked out on the ground. For example to record the changes in the herb layer of a woodland over time.

Quadrats and CountingQuadrats and Counting

Inevitably some of the plants will run over the boundary of the quadrat. The method for accurately assessing the population is to count how many cross the boundary and divide this number by two. Add this to how many fall within the quadrat.

How to count the number of individual plants in a Quadrat::

Quadrats and CountingQuadrats and Counting

Question 1Question 1: How many daisy plants are in the diagram of the quadrat illustrated opposite?

PopulationPopulation

Population:Population: The number of individuals of a particular speciesliving in a defined area.

How would you use a quadrat to measure the population size of a plant species in a field?

Population SizePopulation Size

1. Place two tape measures at right angles bordering the area to be sampled. One tape measure will represent the X axis and the other the Y axis.

Tape measuring alongthe x axis of field

Tap

e m

easu

ring

alo

ngth

e y

axis

of f

ield2. Use random number tables to find two

coordinates one for the X axis and one for the Y axis.

3. Place the quadrat in this position and count the number of daisies

4. Repeat.

5. Find the mean number of daisies per quadrat. (e.g per meter)

6. Multiply by the area of the field for an estimate of the number of daisies in the field.

How to find the number of daisy plants in a field

PopulationPopulation SizeSize

Tape measuring alongx axis of field

Tap

e m

easu

ring

alo

ngy

axis

of f

ield

Quadratnumber

Number of Daisiesin 1m2 Quadrat

1 5

2 0

3 9

4 6

5 12

6 2

7 5

8 1

9 7

10 3

Total =

Mean =

Question 2Question 2: If the x axis is 90 metres and the Y axis 80 metresEstimate the number of daisies in the field.

Random SamplingRandom Sampling

Question 3Question 3: a) Why place the quadrats randomly in the field?

b) Why are many areas of the field sampled with the quadrat?

Sample size and Measuring PopulationsSample size and Measuring Populations

Question 4Question 4: Use the graph to determine minimum number of quadrats needed.

The number of quadrats needed to accurately assess population size in an area can be calculated by plotting the graph illustrated below. As the number of quadrats increases (i.e. the area surveyed) the cumulative mean becomes more reliable.

Species richnessSpecies richness

Species richness:Species richness: The number of different species found in given area.

How to find the number of species of plant in a field

1. Place two tape measures at right angles bordering the area to be sampled. One tape measure will represent the X axis and the other the Y axis.

Tape measuring alongthe x axis of field

Tap

e m

easu

ring

alo

ngth

e y

axis

of f

ield

2. Use random number tables to find two coordinates one for the X axis and one for the Y axis.

3. Place the quadrat in this position and count the number species in each quadrat.

4. Repeat.

Sample Size and Species RichnessSample Size and Species Richness

The number of quadrats needed to accurately assess the species richness in an area can be calculated by plotting the graph illustrated below. As the number of quadrats increases (i.e. the area surveyed) the number of new species found becomes less. Once the graph has levelled out further sampling is probably unnecessary.

Question 5Question 5: What factors might stop this method from being an accurate measure of the number of plant species in the area?

Species Richness and Species DiversitySpecies Richness and Species Diversity

Species richness is the number of species in a given area. Species richness takes no account of the size of the population of these species. In the table above both area 1 and 2 have the same species richness (five), but the population size of these species is quite different.

Species diversity is a measure of the number of species in a defined area but also includes some measure of the population size of each species.

Species Area 1 Area 2

Daisy 2 30

Dandelion 1 22

Plantain 1 15

Common bent grass 100 52

Tussock grass 40 48

Species DiversitySpecies Diversity

D = diversity index

N = total number of individual plants

n = number of individuals per species

= sum

)1(

)1(

nn

NND

The index allows you to quantify and compare the diversity of areas.

To Quantify The Diversity Of Species:

It is useful to quantify the diversity of communities. This can be done by using the Simpson diversity index illustrated below.

Species diversitySpecies diversitySpecies Area 1 Area 2

Daisy 2 30

Dandelion 1 22

Plantain 1 15

Common bent grass

100 52

Tussock grass 40 48

)1(

)1(

nn

NND

D = diversity indexN = total number of individual plantsn = number of individuals per species = sum

)140(40)1100(100)11(1)11(1)12(2

)1144(144

Area 1=

Area 2=

Question 6Question 6: Calculate the species diversity for area 2 ?

Species FrequencySpecies Frequency

Species frequency: is the probability of finding a species in a quadrat (given area).

Example: Daisies occur in 4 out of 10 random quadrats (the number in each quadrat is irrelevant). The species frequency is therefore 0.4 ( or 40%).

Species Richness, Diversity and FrequencySpecies Richness, Diversity and Frequency

Question 7Question 7: a) Calculate species, frequency and diversity for area 1 and 2.b) Suggest an explanation for the differences between the two areas.c) Suggest why the results collected may not be an accurate.

  Untrampled Area 1, quadrats Trampled Area 2 , quadrats

Species, 1m2 quadrats 1 2 3 4 5 1 2 3 4 5

Achillea millefolium 4 1 3 - 2 1 3 8 - -

Bellis perennis 4 4 3 2 2 4 5 5 7 3

Carlina vulgaris 3 - 2 1 1 - 1 2 3 6

Festuca ovina 21 35 71 51 44 35 17 32 21 12

Festuca rubra 4 21 17 23 14 22 4 16 20 14

Senecio jacobea 2 3 4 3 2 1 - 6 - -

Taxus baccata 1 - 3 1 - - 1 - - -

Two areas of a downland nature reserve were studied. One of area had a greater number of visitors and was more trampled than the other. Five quadrats were

randomly thrown in the two areas and the specie present identified and counted

Species CoverSpecies Cover

Unfortunately simply counting individual plants can give misleading results particularly when plants vary considerably in size. Imagine a quadrat in which there is a clump of mosses, flowers, bushes and an Oak tree. Counting the small moss plants would be difficult but might reveal 1000 individuals and only 1 oak. Yet it is obvious that the large Oak is the dominant individual in the quadrat.

Quadrats and Percentage CoverQuadrats and Percentage Cover

A tussock of grass could be counted as one plant or (which takes more time) one could count every stem within the tussock as a plant. The grass stems may or may not be joined and in the field it is very difficult to find out.

It is also important to distinguish between counting the plant as being present if its roots are within a quadrat or if its leaves are present. Which ever of these two methods are used will give different types of information.

The overhanging branch of an oak is obviously affecting plants within a quadrat but if you wish to know the species density of the oak it might be better to look for the presence of the roots.

It is important to define what is meant by an individual; it is not as easy as you might think!

Quadrats and Percentage coverQuadrats and Percentage cover

A more accurate, qualitative method, is to estimate the percentage cover of the plant species in each quadrat this can be more accurately estimated by using the small squares.

In the diagram opposite the percentage

cover of plant species A =

Fully covered squares = 5

Part squares = 11

11÷2 = 5.5

5.5 + 5 = 10.5 out of 25 possible squares

Multiplying by 4 will give a percentage cover of 42% for species A.

Quadrats and Percentage CoverQuadrats and Percentage Cover

Question 7Question 7: What is the percentage cover of plant species B in the quadrat opposite?

In practice a quicker, though less accurate method, is simply to estimate by eye the degree of cover giving each plant species a value between 1 and 10.

Species Distribution and ZonationSpecies Distribution and Zonation

Zonation: A gradual change in plant and animal communities up (or down) an environmental gradient. Examples can be found from low to high water on a Rocky shores, from valley floor to mountain top in the Scottish mountains or from the edge of a lake onto drier land.

Species Distribution and Line TransectsSpecies Distribution and Line Transects

Line Transects: Run a tape measure across the area to be studied and record the species touching the tape. This method can be simplified by using a pin frame recording only the plants touched by a pin.

To Measure The Distribution Of Species Along An Environmental Gradient:

Species Distribution and Belt TransectsSpecies Distribution and Belt Transects

Belt Transects: A tape measure is run across the area to be studied. If the transect is a small one quadrats are placed continuously along the tape measure and the species present and their percentage cover recorded. If the transect is longer the quadrats are placed periodically, the interval between the quadrats depends upon the size of the area being studied and how rapidly the distribution changes. A 10 metre belt transect across a woodland edge might require 10 quadrats to record the change in distribution. The more samples taken the more accurate results will be.

Species Distribution and Kite DiagramsSpecies Distribution and Kite Diagrams 

Percentage Species Cover In Each Quadrat

Species 1 2 3 4 5 6

A 90 80 20 10   

B 

20 40 20 

C   

20 40 70

D   

20  30 

E       

10 70

Kite Diagrams: The results from such a belt transect are shown in the table opposite. To graphically display the data and make it easier to interpret, a kite diagram can be drawn.

The quadrat number (distance along the transect) is plotted along the X axis. The percentage cover for each species is plotted Along the Y axis.

Other graphs can be plotted below the kite diagram e.g. slope profile, pH and water content of soil etc. This will enable you to establish relationships between changes in the living organisms (biotic) and the physical (abiotic) environment.

Species Distribution and Kite DiagramsSpecies Distribution and Kite DiagramsPercentage Cover of Flora in each Quadrat

Flora 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Sundew 10 20 10

Bracken 40 60 50 40 30 20 10

Rush 10 10 20 30 60 40

Bog Moss 20 10 20 30 40 90 70 80

Stonecrop 10 30 10 20 10

Abiotic Factors

Profile (Metres) 3 2.8 2.4 2 1.8 1.75 1.65 1.6 1.3 1.0 0.8 0.5 0.2 0.2 0.2

Moisture Content (%)

15 15 15 15 30 35 35 30 35 38 50 60 80 80 80

Light (arbitrary units) 80 100 80 80 80 100 120 120 120 140 160 200 240 240 240

pH 5.6 5.6 5.7 5.7 5.7 5.6 5.8 6.0 6.0 6.0 6.0 5.9 5.8 5.9 5.7The distribution of plants along a section of heathland was investigated using a belt transect. At the same time, measurements of some abiotic factors were taken. The results are shown in the table above.

Question 9Question 9: Plot a kite diagram for all five species. Using the same X axis (quadrats) plot the four types of abiotic data.

The EndThe Endnextnext::

Ecological Investigations 2Ecological Investigations 2

Counting AnimalsCounting Animals