18.2 Biodiversity

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.

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.