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quadrat investigation

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quadrat investigation

Postby Lizzy23 » Sun Apr 03, 2005 11:51 am

Heyy!!

I was wondering if anyone could give me some advice!
For some biology coursework i have to plan the following investigation:

"You are required to plan an investigaion to find out the distribution and abundance of 2 named species of plant in a specific habitat nad to determine if this is affected by the water content of the soil"

It also says quadrats should be used.

I have no idea how to begin, so would be very grateful for some help!

Thank you
Lizzy xXx
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Postby Jesskat14 » Sun Apr 03, 2005 2:49 pm

You could use the quadrats in a belt transect. The abundance of the 2 species would be noted as a percentage cover of the quadrat. Cover the area in a straight line from one side to the other and make a note of the water content of the soil.
The data can then be compared using a t-test.
You would find a t-value for the soil with low water content and soil with high water content, and compare the 2 values under a certain level of significance. If the value is above the degrees of freedom and the other is below then there is a significant difference and the abundance of the plants is affected by the amount of water in the soil. You would have to do 2 t-tests for each specie of plant.
Hope this helps, and that you know what a t-test is!
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Postby Lizzy23 » Mon Apr 04, 2005 12:29 pm

thank you!

Just a few more questions though

How many quadrats should be done along the line?? How many would give significant results?

Also can you only use square quadrats with belt transects or can you use point quadrats as well?? Because i thought point quadrats give a better estimate of percentage cover...

Thank you again

Lizzy xXx
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Postby Jesskat14 » Mon Apr 04, 2005 12:42 pm

I would say to use square quadrats and then use a percentage cover of each quadrat.
Point quadrats would take other species of plant into account.
For the number it depends on the length of the transect, and for the size of the quadrat 1 metre square would probably be ok.
When I did an ecology case-study I was in a group of about 20, split into groups of 2/3, we did 4 quadrats for each group in the transect for 4 species of seaweed (oh it was SO exciting! :lol:) . That worked out at about 30 quadrats give or take, so probably about that many should be ok.
Hope that helps :)
Jess
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Postby Lizzy23 » Thu Apr 07, 2005 12:16 pm

Thank you for your help!

Could you explain to me what a T-test is?? Sorry but i have no idea :cry: and i have to explain how i would analyse my data, so any brief explaination, would be fantastic!!!!

Thank you agin!!!

xXx xXx
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Postby Jesskat14 » Thu Apr 07, 2005 1:09 pm

I'm going to have to write it out in words because I can't put the symbols in!

T = The modulus of x1 - x2, where x1 and x2 are the means of the 2 populations. all divided by the square root of: ( the variance (sd squared) of population 1 divided by the number of measurements in population 1) + (the variance of population2 divided by the number of measurements in population 2).

The degrees of freedom is the sum of the measurements used in both populations minus 2.

Hope that all helps! It should be in an ecology textbook. I'm using Collins Biology A2 level.
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Postby Chris4 » Thu Apr 07, 2005 1:16 pm

T-tests... Brings back memories. :D
Comparing two sets of data.
Have a look here: http://www.usip.edu/biology/bs130/stati ... 0test.html

Found a website with a program which does a t-test for you. You just put the two sets of data in. Could use this to check your result.
http://www.bio.miami.edu/rob/Students_t.html

The example on this website may help
http://www.tiem.utk.edu/~gross/bioed/st ... append.htm

If i had my statistics in biology textbook i could give you more info, but its been a few years since i did t-tests so i cant remember anything thats not already on the websites above.
Good luck. :P
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dry soil mass calculations?

Postby new member » Wed Apr 13, 2005 10:47 am

how do examine the soil to find out 'dry soil mass calculations' for the bio coursework.
apparently there is some method where you heat it to make the water evaporate but im not too sure on the validity.

please help :shock:
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Postby Palaestra » Tue Apr 19, 2005 5:25 pm

Hi!

to work out dry mass i believe you are right- you can heat them, weigh them, let them dry for 24hrs and then weigh again, keep repeating until you get the same masses....

would i be right in saying that the higher the dry mass, the less water present in that soil sample?
(i'm doing the sam planning exercise as the person who started the topic)
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Postby whateva_u_want » Wed Apr 20, 2005 9:15 pm

i think thats right, but im not sure. i am also doing the same planning exercise and was wondering how can u show that it is just the water content of the soil that affects the population, because surely pH and the positioning of plants (e.g if they are under a big tree or something so don't get much light) and other factors will have an effect, and in a field or wherever, its not like you can control the other variables. Any ideas?
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Postby whateva_u_want » Thu Apr 21, 2005 2:05 pm

sorry i have another question aswell. apparently, there are different types of water in the soil, there is water that is available to the plants and water that is not because it is too tightly bonded to the soil, surely we want to find the water that is available to the plants to be able to compare the water content of the soil, however the dry mass test will evapourate all the water from the soil, including that which is not available to the plants, so i'm slightly confused on what we should do here. HELP!
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Postby szehang » Wed May 11, 2005 3:11 pm

how can i analyse those abiotic factors? are they the variables which needed to be controlled?
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