KEGS Biology Blog


Monday 17th September 2012 Section 2
September 16, 2012, 5:33 pm
Filed under: Uncategorized

Limitations of sampling techniques, Simpsons diversity index calculation

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Limitation of Sampling Techniques- Using Quadrats
 LIMITATION: Specimen such as plant leaf overlapping into 2 squares of the quadrat.
 CONSEQUENCE: Not be representative as the % of species accounted for is inaccurate.
 SOLUTION: Only count the square where the root of the specimen is located.

 LIMITATION: pH/season/weather/temperature/water levels/human activity.
 CONSEQUENCE: Only representative of the weather, time etc. when we took the sample.
 SOLUTION: Take different samples at different time of the year, different seasons, time etc.

 LIMITATION: Missing species due to coverage of long grass for example.
 CONSEQUENCE: The data won’t be representative of the area as species are omitted.
 SOLUTION: Be thorough with every single square of the quadrat, for every placement.

Simpson’s Index of Biodiversity
D = (n / N)2
n= number of individual species (Species Richness)
N= total number of individuals of all species (Species Evenness)

Species No. of Species (n) n/N (n / N)2
Daisies 40 40/100 (40/100) 2
Grass 20 20/100 (20/100) 2
Dandelions 40 40/100 (40/100) 2

N= 100 0.16 + 0.04 + 0.16

Therefore, Simpson’s Index of Biodiversity would be
= 1- (0.16+0.04+0.16)
= 1- 0.36
= 0.64

Comment by mehleen

What does that number mean ? And what about it it’s higher or lower ? Does it mean something different ?

Comment by halima95

A good Website explaining biodiversity and the simpsons index, although may be slightly higher than A-level
http://www.countrysideinfo.co.uk/simpsons.htm

Comment by jaimieclifford

Please view :-

http://www.thestudentroom.co.uk/showthread.php?t=1890265

and click on the link mentioned on the first user comment tited -” F212.pdf ”

It is all relevant to our course however the section on biodiversity commences on Page 17 and continues to the end… for example Page 18 has a good level of detail about Quadrats and their limitations and general reliablilty… It might be useful for the field trip.

Comment by deelanvadher

http://www.habitats.freeserve.co.uk/howto.htm

gives a few good suggestions on how to go about sampling

Comment by bensubhani

http://www.ehow.co.uk/info_8713298_advantages-disadvantages-quadrat-use.html

This website has simple but easy to understand disadvantages and advantages of using quadrats in experiments. May help for the assessment if struggling.

Comment by danialnaqvi

The last part on that website titled “study errors” is the most useful bit so if you go on it just scroll down to that part.

Comment by halima95

Limitation: co-ordinates may not cover all area and therefore you are not sampling from the whole area.
Improvement: increase number of intervals between each co-ordinate points

Limitation: one species might be counted in more than one square within a gridded quadrat, therefore being counted twice.
Improvement: count species from the root.

Limitation: not being able to identify species might mean counting different species as one or the same species as different.
Improvement: use a key to identify species also look at leaves.

Limitation: sample is not representative of the whole area (might miss some species)
Improvement: take several quadrats to cover more area.

Limitation: co-ordinates do not cover area completely, quadrat is too small.
Improvement: use a large quadrat.

Limitation: some species that are hidden underneath other species might be missed.
Improvement: be careful to look underneath other species.

Limitation: time of year, only visiting once means data only valid for that time.
Improvement: visit more than once throughout the year at different times to collect data.

Comment by helenquah




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