Biodiversity (CIE A Level Biology)

Compare species diversity with species richness.

Fertilisers are commonly used today by most farmers as they help to increase crop yield and profit. If it rains shortly after fertilisers are applied to a field then some of the fertiliser can enter nearby water sources as runoff. A conservationist investigated the effect that fertiliser runoff from a nearby farm had on the distribution of organisms living in a stream. At the point where fertiliser had entered the stream, she found a high density of specific organisms but a low index of diversity. Suggest how fertiliser contaminating the stream could result in these findings and provide an explanation for your answer.

Predict how the index of diversity will change as the conservationist moves further away from the farm to take her sample.

Justify your answer.

The conservationist wanted to use their findings to take action against the local farm. However, the farmer’s lawyer argued that the scientific methods of the conservationist were not rigorous enough to conclude that fertilizer runoff was affecting species richness in the nearby stream. The lawyer demanded that more samples at random locations are to be taken.Explain the importance of taking a large number of samples at random sites.

Distinguish between the biological terms niche and ecosystem.

A Biology teacher investigated the different species of insects found in a grassy meadow and in a nearby farmed field. The insects were collected using traps at randomly chosen sites both in the grassy meadow and in the farmed field. Table 2.1 below shows the data collected.

Table 1

Use the formula below to calculate Simpson's index of diversity (D) for the insects collected in the farmed field.

Show your working.

Without doing any further calculations and using the data in Table 2.1, predict whether the index of diversity for insects from the grassy meadow will be higher or lower than the index of diversity for insects from the farmed field.

Explain your answer.

A student stated that the results of this investigation suggested that farming caused a reduction in species diversity.

Evaluate this by providing arguments in support of and against this statement.

The Frégate Island giant tenebrionid beetle or Frégate beetle (Polposipus herculeanus), is a flightless species of beetle of the family Tenebrionidae. It is endemic to Frégate Island in the Seychelles. A PhD student wanted to estimate the number of Frégate beetles on the island.

Explain how they could use the mark-release-recapture method to do this.

The PhD student in part (a) used the mark-release-recapture technique to estimate the size of the population of Frégate beetles on the island. They collected 176 beetles and marked them before releasing them back into the same area. Later, they collected 198 beetles, 22 of which were marked.

Calculate an estimate of the number of beetles on the island. Use the formula below and show your working.

The PhD student made sure that their study met the conditions required for the results from the mark-release-recapture method to be valid.

State three of these conditions.

Explain the difference between the biological terms population and community.

A farmer was interested in improving the stability of their agricultural ecosystem.

State the meaning of the term ecosystem.

The farmer investigated the effect of different types of animal grazing on beetles in their fields. They measured the number of different beetle species and the total number of beetles in cow grazed (1), donkey grazed (2) and sheep grazed (3) fields.

Their results are shown in Fig. 1 below. Note that the error bars represent standard deviation.

Fig. 1

Calculate the percentage difference in number of species of beetle between a cow-grazed field and a donkey-grazed field. Give your answer to one decimal place.

The farmer considered the results in Fig. 1 and concluded that the type of grazing had little effect on beetles, and therefore on the stability of the agricultural ecosystem.

Discuss the farmer's conclusion.

Suggest three considerations that the farmer should have taken into account when planning the investigation to ensure valid results.

A piece of UK grassland that was traditionally grazed by sheep has been left ungrazed for the past ten years.

Outline the steps to be followed in an investigation to estimate the population density of thistle plants that have colonised the area since grazing has been discontinued. 

A biologist wanted to investigate the biodiversity of insects living in farmed fields in Somerset. The biologist used sweep-netting along transects through the middle of fields on four different farms and counted the number of different insect species present in the sweep-net samples from each farm. Table 1 below shows the results of this study.

Table 1

The biologist used the data in Table 1 to report that the difference between the mean number of insect species present on Farm B and the number present on the other three farms differed significantly (p < 0.05).

Explain what the biologist meant by the term “differed significantly (p < 0.05)”. Use the words probability and chance in your answer.

The biologist in part (b) wanted to know many fields they should sample at each farm. They carried out a preliminary investigation and recorded the total number of different insect species present in an increasing number of fields. Fig. 1 shows the results.

Fig. 1

Use the results in Fig.1 to explain why sampling 5 fields would not be an appropriate number and why 25 would also not be an appropriate number of fields to sample.

An ecologist had heard people say that stinging nettles (Urtica dioica) and the dock leaf plant (Rumex obtusifolius) often grow together. The ecologist decided to assess the abundance of these two species in a field. To do this, they recorded the percentage cover of each species in 11 randomly placed quadrats. Their results are shown in Table 1 below.

Table 1

To determine the relationship between the percentage cover of these two species, the ecologist decided to calculate Spearman's rank correlation coefficient. They created a new table, which is represented in Table 2 below.

Table 2

Complete Table 2.

Using the formula provided below, calculate Spearman's rank correlation coefficient (r_s) for the data from part (a).

Show your working.

Before they started collecting data for the investigation described in part (a), the ecologist made a null hypothesis.

Table 3

Give a full conclusion that the ecologist can make from this investigation.

The diversity of dung beetle species was investigated at two grassland sites in North America.

Dung beetles feed on animal faeces (dung).

The first grassland site was grazed by cattle and the second grassland site was not grazed by cattle. The areas of the two grassland sites were the same.

At each grassland site, dung beetles were collected, identified and counted.

The results are shown in Table 1.

Table 1

Simpson’s index of diversity (D) for the dung beetles on the grassland site grazed by cattle was calculated as 0.522, using the formula:

Key to symbols:
n = number of individuals of each species present in the sample
N = the total number of all individuals of all species present in the sample

Calculate Simpson’s index of diversity (D) for the dung beetles on the grassland site that was not grazed by cattle.

Complete Table 2 to show your working.

Write your final answer to three decimal places.

Table 2

dung beetle species	number of dung beetles on grassland not grazed by cattle
A	6641
B	774
C	108
D	85
total	7608

[3]

Describe what the results in Table 1 and both figures for Simpson’s index of diversity show about the effect of grazing by cattle on the diversity of dung beetles.

Other species of beetle that do not feed on animal dung are found on the grassland sites.

Name and describe one method for estimating the population size of a species of beetle that does not feed on dung in each of the two areas of grassland.