Title: Experimental methods using quadrats and transects - Organisation of an ecosystem - Edexcel - GCSE Biology (Single Science) Revision - Edexcel - BBC Bitesize
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GCSE Edexcel
# Org nis tion of n ecosystem
# - Edexcel
# Experiment l methods using qu dr ts
# nd tr nsects
The feeding rel tionships between org nisms in n
ecosystem c n be seen in food ch ins. S mpling
llows us to me sure the bund nce nd distribution
of these species.
Prt of Biology (Single Science) Ecosystems nd m teri l
cycles
Sve to My Bitesize
# Pges
Levels of org nis tion
Experiment l methods using qu dr ts nd tr nsects
Required pr ctic l
Science c lcul tions
Trophic levels
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settings Pyr mids of biom ss
Tr nsfer of biom ss
Clcul ting e ffi ciency of biom ss tr nsfers
# Experiment l methods using qu dr ts nd
# tr nsects
It is import nt to estim te the number of org nisms in popul tion to better
underst nd the rel tionships in community. This inform tion is useful for
monitoring the imp ct of conserv tion projects th t im to conserve
endangered species or habitats . It is lmost lw ys impossible to count
ll of the org nisms in popul tion. So we look t sm ll section of
popul tion to dr w conclusions bout the rest. This process is c lled
sampling nd the re or p rt of popul tion looked t is c lled smple.
# Smpling
When s mpling popul tion, the numbers of org nisms re counted within
smple site, nd then the results multiplied to estim te the tot l number in
the entire h bit t. L rge nim ls nd pl nts c n o en simply be counted.
However, m ny sm ller nim ls like insects nd sm ller m mm ls need to be
tr pped fi rst so they c n be counted nd then rele sed erw rds. Pitf ll
tr ps re sm ll tr ps dug into the ground, which o en h s food inside to
ttr ct sm ll m mm ls. The sides of these tr ps re smooth to stop the
mmm ls esc ping.
Another method is to use l rge nets to sweep through gr sses or le ves of
trees in process c lled sweep netting. To c tch qu tic org nism nets re
oen held downstre m of n re of river bed which is then gently disturbed
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settings by the person doing the s mpling. The sm ll nim ls fl ot into the net. This is
clled kick-s mpling.
Pooters re sm ll devices used when s mpling to suck up sm ll insects s fely
without them going into your mouth.
# Using qu dr ts
Quadrats re squ re fr mes of wire usu lly 0.25 m 2. These re pl ced on
the ground to look t the pl nts or slow-moving nim ls within them. When
looking t pl nts in qu dr t the following s mpling c n be used:
1. Number of n individu l species: the tot l number of individu ls of one
species (eg d isies) is recorded.
2. Species richness: the number of di ff erent pl nt or nim l species is recorded
but not the number of individu ls within species.
3. Percent ge cover: the percent ge of the qu dr t re th t is covered by one
species (eg gr ss). This is e sier to estim te if qu dr t h s wires m king
sm ller sections. Percent ge cover r ther th n number of individu ls is used
when estim ting pl nt frequencies if it is di ffi cult to identify individu l pl nts,
such s gr sses or moss.
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settings Rndom or system tic
Rndom s mpling using qu dr t involves the pl cing of qu dr ts t r ndom
coordin tes. Reg rdless of whether you re investig ting the number of
individu l species, the species diversity or the percent ge cover in di ff erent
re s you would use r ndom s mpling.
Most s mpling is random , but system tic s mpling c n be used if there is
trend or p ttern cross the h bit t, such s dist nce up be ch, or ltitude
on hillside. If you re using the wrong kind of s mpling method for your
experiment, this c n le d to biased results.
# Wh t re we s mpling for?
Sometimes we w nt to see if the number of species or percent ge cover
ch nges within n re . This is o en s result of ch nge in n abiotic
fctor.
An ex mple of this is n investig tion into whether the growth of se weed
depends upon the dist nce it is found on the se shore from the tide. As we re
looking to link line r ch nge (in this c se the number of hours the se weed
is covered by the tide) we would use system tic s mpling.
A qu dr t could be pl ced t regul r dist nces, for ex mple every fi ve metres,
long n im gin ry line c lled transect , which would run down the shore.
System tic s mpling would be used long the tr nsect to link ch nges in
species to biotic f ctors, such s immersion by w ter, temper ture
fl uctu tions, light intensity, ll of which re in fl uenced by the tide.
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settings The results from tr nsects c n be dr wn into kite di gr ms. The width of the
br from the middle t ny dist nce shows how m ny individu ls were
observed t th t point.
# Zon tion
In the ex mple bove, the distribution of d ndelion pl nts gr du lly ch nges
from 5 m to 20 m long the tr nsect. A ch nge in the distribution of species
cross hbit t is c lled zonation . It c n h ppen bec use of ch nge in n
biotic f ctor.
# Question
At wh t dist nces were the most gr sses nd d ndelions seen?
Show nswer
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