Investigating diversity - topic 4

paper 1

species richness

number of species in a community

index of diversity

the relationship between the number of species and the number of individuals in each species

How has our knowledge of biodiversity increased?

DNA sequencing now used

rather than just recording observable characteristics

Aseptic techniques 

wash hands with soap 

flame neck of bottle

use sterile spreader 

Standard deviations do overlap

the difference between the two means may not be statistically significant

there is a lot of variation within each group.

You cannot confidently say the independent variable caused a real difference.

Standard deviations do not overlap

The difference between means is likely to be statistically significant.

There is less variation within groups.

More confidence that the independent variable caused a real difference.

Two ways genetic diversity between species is measured

Comparing amount of antibody bound to antigen, comparing amino acid sequence

When to use student’s t-test?

comparing mean of data sets

How to obtain DNA source from organisms no longer alive

Preserved remains, bone, skin etc

When to use correlation coefficient?

to test for a correlation between two continuous variables

When to use chi-squared?

difference between observed and expected frequencies is due to chance.

calculated test statistic

the value you get when you do the maths for a statistical test. e.g. t value for Student’s t-test

If calculated value ≥ critical value

result is significant

calculated value < critical value 

result is not significant 

If significant (calculated ≥ critical)

result is significant at P ≤ 0.05.

probability results are due to chance is less than 5%

reject the null hypothesis

if not significant (calculated < critical)

result is not significant P > 0.05

the probability the results are due to chance is greater than 5%

do not reject the null hypothesis

how to measure species richness

random sampling

systematic sampling

using identification tools

problems measuring species richness

some species missed

Species richness alone does not reflect how many individuals of each species exist

Misidentification affects accuracy.

higher species richness =

more stable ecosystems

indicates greater biodiversity