3.4.6 Biodiversity within a community

Question 1

Give two differences in the variation in body length of male and female thorny lizards.

Answer 1

Females are (generally) longer / larger / bigger / up to 115(mm) / males are (generally) shorter / smaller / up to 100(mm)

Females show a greater range / variation / males show a narrower range / variation.

Question 2

The ecologists also determined the index of diversity of lizards in an oil palm plantation next to the woodland area. They found fewer species of plant in the oil palm plantation. Lizards feed on plants and insects.
Explain why fewer species of plant would lead to fewer species of lizard in the oil palm plantation.

Answer 2

(Fewer plant species) − no mark
1. (So) few(er) habitats / niches;
Ignore habitat size
2. (So) lower diversity of insects / fewer insect species / fewer insect types;
3. (So) fewer food sources / less variety of food.

Question 3

Suggest how this student would obtain data to give a more precise value for the index of diversity of this habitat.

Answer 3

Take more samples and find mean; Method for randomised samples described.

Question 4

What is the difference between these two measures of biodiversity?

Answer 4

Take more samples and find mean; Method for randomised samples described.

Question 5

The scientists carried out a statistical test to see if the difference in the distribution of each species between the canopy and understorey was due to chance. The P values obtained are shown in the table.
(3)
Explain what the results of these statistical tests show.

Answer 5

For Zaretis itys, difference in distribution is probably due to chance / probability of being due to chance is more than 5%;
For all species other than Zaretis itys, difference in distribution is (highly) unlikely to be due to chance;
Because P < 0.001 which is highly significant / is much lower than 5%.

Question 6

The ecologists captured insects from a number of sites on the island. Suggest how they decided where to take their samples.

Answer 6

Draw grid over (map of) area;

Select squares / coordinates at random.

Question 7

Give two assumptions made when using the mark-release-recapture method.

Answer 7

No emigration / immigration;
No losses to predation;
Marking does not affect survival;
Birth rate and death rate equal;
(In this case) all belong to one population.

Question 8

Suggest the advantage of using the fluorescent powder in this experiment.

Answer 8

Only glows brightly with UV, so doesn’t make insects more visible; So doesn’t affect / increase predation;
OR
Glows brightly with UV marking visible;
So makes it easy to pick out labelled insects.

Question 9

Use the information provided to suggest one way in which the method used by the ecologists might have caused the increase in their estimates of the size of the insect population.

Answer 9

Scientists removed large numbers of insects (which were not returned) from same area / same population;
Affecting ratio of marked to unmarked.

Question 10

What two measurements are needed to calculate an index of diversity?

Answer 10

Number of (individuals of) each species;
Total number of individuals / number of species;

Question 11

Some fields acted as controls. They were sprayed with a solution that did not contain the herbicide. Explain the purpose of these control fields.

Answer 11

(Shows) results are due to the herbicide / are not due to another factor / (to) compare the effect of using and not using the herbicide / shows the effect of adding the herbicide;

Question 12

Suggest an explanation for the relationship between the concentration of herbicide and the mean crop yield.

Answer 12

(More) weeds killed so more crops / plants survive / higher yield / less competition;
High concentrations (of herbicide) harm / damage / kill / are toxic to crops / plants

Question 13

Explain the relationship between the concentration of herbicide and the mean index of diversity of insects.

Answer 13

Reduced plant diversity / fewer plant species / fewer varieties of plant;
Fewer habitats / niches;
Fewer food sources / varieties of food;

Question 14

Speciation is far less frequent in the reformed Amazonian forest. Suggest one reason for this.

Answer 14

Similar / same environmental / abiotic / biotic factors / similar / same selection pressures / no isolation / gene flow can occur (within a species);

Question 15

The Amazonian forest today contains a very high diversity of bird species.
• Over the last 2 000 000 years, long periods of dry climate caused this forest to
separate into a number of smaller forests.
• Different plant communities developed in each of these smaller forests.
• Each time the climate became wetter again, the smaller forests grew in size and merged to reform the Amazonian forest.
(a) Use the information provided to explain how a very high diversity of bird species has developed in the Amazonian forest.

Answer 15

1.No interbreeding / gene pools are separate / geographic(al) isolation;
2. Mutation;
3. Different selection pressures / different foods / niches / habitats;
3 Accept: different environment / biotic / abiotic conditions or named condition
3 Neutral: different climates
4. Adapted organisms survive and breed / differential reproductive success;
5. Change / increase in allele frequency / frequencies;