sampling and chi square Flashcards
what is ecology why is it important to study it
how is it different to other fields of biology
-study of relationships between species
-studying ecology provides a better sense of how organisms fit together in their relationships n natural environment
-not done in lab = impossible to control some factors
what are the techniques for sampling biodiversity of a habitat?
-quadrats
-sweepnets
-pitfall traps
-pooters
what is random sampling
advantages and disadvantages?
-sample sites inside the habitat are randomly selected eg inside a meadow using randomly generated numbers as coordinates
-used to study large fairly uniform area in limited time
advantages:
-not biased
-time efficient
disadvantages:
-rare species may be missed
-inaccurate if species aren’t uniformly distributed
what are examples of non-random sampling?
-opportunistic
-stratified
-systematic
explain opportunistic sampling?
advantages and disadvantages
-making sampling decisions based on prior knowledge e.g choosing a specific location
e.g sampling orchids
advantages:
simpler and quicker
disadvantages:
-might be biased
explain stratified sampling
advantages and disadvantages
-dividing a habitat into area which appear different, sampling each area speperately
advantages:
-ensures all different areas of a habitat are sampled
disadvantages:
-possibility of over representation of some areas in the sample
explain systematic sampling
advantages and disadvantages
-when samples are taken at fixed intervals across the habitat e.g using line/belt transect
advantages:
-useful to consider how a gradient of an abiotic factor might change
disadvantages?
-small amount of sampling at each interval means some species might be missed
explain quadrats
what data can be generated from using quadrats?
-divide up sampling area, focus attention onto one small area at a time
-large nummber of quadrats at random to eliminate bias, effect of chance and minimise error
1)population density
2)frequency - record presence or absence
3)percentage cover
explain the method for investigating the abundance of grassland plants on 2 sites
-lay out 2 tape measures to form a grid axis
-use a random number generated to obtain random coordinates
-place quadrat at coordinates
-count number of daisies and plantain , estimate % cover of clover
explain the chi-squared equation
x^2 = chi squared
o= observed, data collected
e= expected, number expected if there was no difference
how do you calculate expected value for chi-squared
add up the total number of measurements and divide by the number of groups of data
work out the chi squared calculation for this example
you are investigating the feeding habits of a group of st brendans students
-37 students went to mcdonalds
-33 used cafe max
null hypotheses- no significcant difference in number going to McD and cafe max
-expected = 37+33 = 70/2 = 35
(37-35)^2 divided by 35 = 0.11
(33-35)^2 divided by 35 = 0.11
0.11+0.11 = 0.22
how do u find the degree of freedon?
(r-1)(c-1)
r is number of rows
c is number of columns
or 2 groups = 2-1 = 1 degree of freedom
which number do we usually use for the probability
0.05 column
5%
explain what it means when the chi squared value is less than or more than the critical value at p= 0.05
less than= accept null hypothesis = no significant difference between observed and expected results, probability that results are due to chance are greater than p=0.05 5%
more than= there is a significant difference between the observed and expected results and the probability that the results are due to chance is less than 5%
