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S295/G

Module Examination 2018

THE BIOLOGY OF SURVIVAL

PART A

Short answer questions Answer all SIX questions in this first part of the exam. Write your answers in the answer book provided, limiting your answer for each part of a question to a few sentences or more. You are advised to spend no more than 1 hour 15 minutes on this Part A of the paper, which carries 30 of the total marks for the examination. Each question is worth 5 marks.

Question 1

In many plant species, height is a trait which is subject to natural selection. Individual plants which are unusually short or unusually tall are selected against, and most plants that survive to flower and produce seeds are within a narrow height range. This was found to be the case for one particular species of tobacco, Nicotiana rustica, which originates from the rainforest area of southern Mexico. Researchers planted several hundred individual Nicotiana rustica plants in an experimental plot, and measured the ‘height at flowering time’ of each. They found that the vast majority of individual plants were between 0.85m and 1.05m in height at the time when they first came into flower.

(a) Why might individual plants be at a selective disadvantage if they are

(i) unusually short and (ii) unusually tall?

Ans: These traits are extreme traits, hence, they are selected against in a stabilizing selection.

(b) What sort of selection is operating in this example? Draw a sketch graph, appropriately labelled, illustrating this selection. Indicate on the graph which heights of plant are selected for and which are selected against.

Ans: Stabilizing natural selection

(c) Why might the researchers have chosen to measure height at flowering time rather than height on a particular date?

Ans: The researchers chose to measure height at flowering time rather than height on a particular date to ensure equity among the studied population

(d) A closely related variant strain of Nicotiana rustica is native to an isolated, windy, exposed part of Mexico, where it has been reproductively isolated for many generations. The researchers grew this variant strain in an adjacent experimental plot. In what way might you predict the mean height at flowering time might differ in this variant strain from that of the rainforest plants, and why?

Ans: The mean height of this plant strain would differ. It would either be extremely short, or extremely tall. This is owing to the fact that it has been reproductively isolated for over a long period, and has not been able to cross pollinate with other individuals, hence, variation is largely limited.

Question 2

Look at the phylogeny shown in Figure 1, which shows a suggested phylogeny for a selection of orders of birds, and answer the questions that follow.

(a) Give an example of two orders which appear to be sister groups, according to the phylogeny shown in Figure 1.

(b) According to the phylogeny shown in Figure 1, which orders form the sister group to Falconiformes?

(c) Which of the lineages shown in Figure 1 is the most ancestral? Explain your answer.

(d) The term ‘birds of prey’ is often used to describe predatory birds which feed on rodents and other small mammals. These birds are characterised by exceptionally good vision, which allows them to detect their prey during flight, and also by having powerful talons and beaks. Such birds include hawks, eagles and vultures, and also falcons and kestrels. According to the phylogeny shown in Figure 1, are ‘birds of prey’ monophyletic or paraphyletic? Explain your answer.

(e) Explain how birds of prey might provide an example of convergent evolution.

Question 3

(a) What is mimicry?

(b) Provide an animal example of a mimic. Describe both the costs and the benefits to the mimic.

(c) Provide a plant example of a mimic. Describe both the costs and the benefits to the mimic.

Question 4

(a) Why is ATP important to autotrophs and heterotrophs?

(b) Explain the role of ‘coupling’ in ATP synthesis.

(c) Explain the relationship between the process of uncoupling and heat generation in BAT in mammals, stating one enzyme that is involved.

Question 5

a) Explain the difference between a pollinator and a flower visitor.

b) The majority of flowering plants are bisexual. How do flowering plants avoid inbreeding?

Question 6

There are many mineral nutrients needed for plant growth and growth rate can be limited by any one of them being in short supply.

(a) Nutrient limitation was studied in a dry arctic heath using a nutrient addition experiment. Figure 2 shows the response of above ground plant biomass to four treatments. Identify which nutrient is limiting plant growth in this ecosystem and state what evidence there is to support your conclusion.

Figure 2 Results of a nutrient addition experiment in a dry arctic heath, error bars represent the standard error of the mean. (Data are means ± 1 standard error, n= 15.)

(b) Nutrient limitation is a major challenge to plants. Explain how plants have adapted to low nutrient availability in the environment.

PART B

Data handling and interpretation question

Answer ALL parts of the question in Part B of the examination. You are advised to spend about 1 hour on this question. This part carries 25 of the marks for this examination.

Show all your working for calculations.

 

Question 7

Male peacocks form a lek and display their large brightly-coloured tails to females during the mating season. Their tails vary in length and also in the number of iridescent eyespots on the tail. Although females mate only once in the season, males can mate with several females and there is large variation in mating success among males. A researcher decided to test whether male mating success (the number of females that males mated with) was determined by differences in tail morphology, specifically, the number of eyespots on the train of the tail. The researcher observed the mating behaviour of the 10 male peacocks over the breeding season and noted how many females each male mated with. The researcher observed a total of 41 matings and the most successful male mated with 10 females, while some males failed to mate at all. Male mating success and the number of eyespots on each male’s tail are presented in Table 1.

Table 1 The number of eyespots on each of the 10 male’s tails and male mating success (the number of females that each male mated with).

Male Peacock number	Number of eyespots	Mating success
1	141	0
2	161	8
3	153	2
4	142	1
5	147	1
6	155	4
7	158	7
8	152	3
9	148	5
10	165	10

 

(a) Plot the data in the most appropriate way (e.g. bar chart, pie chart, scatter plot, histogram etc.) and explain why you chose this type of presentation.

(b) Why did the researcher use a Spearman rank test on this data?

(c) State a null hypothesis for this study.

(d) On the separate Answer sheet, complete Table 2.

The formula for the Spearman rank correlation coefficient is:

                          

(e) Calculate the value of r_s

(f) Using the appropriate critical value from Table 3, is there a significant correlation between the two variables?

(g) Based on your statistical result can you accept or reject the null hypothesis?

(h) What does the result mean with respect to mating success in peacocks?

(i) If male mating success in peacocks is a result of female choice based on eyespot number, are females likely to be choosing among males on the basis of direct or indirect benefits they get from their choice of mate? Explain your answer.

PART C

Question 8

Journal extract questions

Answer ALL parts of the question in Part C of the examination. You are advised to spend 45 minutes on this part of the paper. Your answers should be written concisely, but in sentences. You should include diagrams and calculations in your answer where appropriate. This part carries 20 marks.

This question relates to your reading of an extract from a published scientific journal paper that describes a study of the relationship between bird song frequency and offspring predation in and around nests. In the paper, the authors describe both observational and experimental investigations of how bird song in pairs of nesting birds affects predation of both eggs and chicks from nests. It is expected that you have already read the entire extract of the journal paper, which is provided here again as a separate document.

Now read the exam questions relating to the journal extract and refer to it throughout when answering all of the question parts.

(a) According to the authors’ Introduction:

(i) In what way is singing a variable behaviour?

(ii) How do superb fairy-wrens within a mating pair differ in their pattern of parental care?

(iii) From their cited papers, which southern hemisphere bird species, other than the fairy-wren, also sings solo year-round to defend their territory?

Your answer should include this bird’s common and Latin name

(b) According to the authors’ Methods:

(i) How was the study using artificial nests performed?

(ii) How do incubation calls produced by females differ from chatter songs?

(c) According to the authors’ Results:

(i) How does male song vary with the three nesting phases?

(ii) Describe the relationship between egg predation and both male and female song rate. How, and where, are these data presented in the paper, and what are the outcomes of the statistical analysis performed on these data?

(iii) How did song rate affect egg predation at artificial nests?

(iv) What are the authors’ findings regarding the distance males and females sang from the nest and what statistical test was used to determine if their finding was due to chance or not?

(d) According to the authors’ Discussion:

(i) What two possible explanations do the authors suggest for the observed variability amongst females in song rate?

(ii) What is the nature of the trade-off between producing incubation calls at a high rate and not doing so?

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Last updated: Sep 02, 2021 10:07 AM

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