How do you work out the modal value of species richness from a graph?
It’s the one with the most dots on the row of species richness
68% of all the fish caught in this investigation came from sample A.
A student thought this showed that sample A had a greater index of diversity than any of the other samples.
It is not possible to draw this conclusion from the given data.
Give reason why
3 marks
- Number of individuals of each species not known;
- Almost all (of sample A / the 68%) could be of the same species;
- Two / other samples have a higher number of species / higher species richness but a lower number of individuals / fish;
- Other samples may have more individuals of each species;
The student wanted to use the data from plot 1 to estimate the total number of the beetle species in the meadow.
Suggest how the student should use the data from plot 1 and other information provided to estimate the total number of the beetle species in the meadow.
4 marks
- Determine the area of plot 1.
- Calculate (total) area of meadow;
- Divide area of meadow by area of plot;
- Multiply by number of beetles (per plot)/41;
Accept multiply by incorrect figure taken from figure (eg 43)
Explain why it is more useful to calculate an index of diversity than to
record species richness.
2 marks
1.
(Index of diversity also) measures abundance / number / population (size) of each species;
Ignore “total number of species” unqualified
Accept: every species for each species.
2.
(So useful because) may be many of some species
OR
(So useful because) may be few of other species;
The scientists decided to collect animals from the soil samples for 40 minutes.
Suggest how the scientists decided that 40 minutes was an appropriate
time.
2 marks
1.
Repeat soil sorting for different times and record number of species collected;
2
Find optimum time / time beyond which further sorting does not lead to increase in animal species found
Suggest an explanation for the effect size when non-native species were introduced to communities
2 marks
- Non-native species out-competes / kills / eats / is a disease of native
- Some (populations of) native species become extinct (in the
community);
Describe how you would investigate the effect of an invasion by a non-native species of plant (a biotic environmental factor) over many years on the abundance of a native species of plant in a community.
3 marks
- Set up grid system with coordinates;
- Place large number of quadrats (at coordinates) selected at random;
- Count number of / estimate percentage cover of native plant in quadrats;
- Repeat at same time each year (for many years);
Same answer if you were asked this question:
Outline a method the ecologists could have used to determine the plant species richness at one site.
Suggest how this student would obtain data to give a more precise value for the index of diversity of this habitat.
2 marks
- Take more samples and find mean
- Method for randomised samples described
All larger area = 1 mark
