Reasoning And Interpretation

REASONING AND INTERPRETATION – Practice questions
1. Understanding the ecological mechanism that causes extinction is fundamental to conservation as not all organisms are threatened by the same factors. A total of 1012 threatened bird species in 95 families were studied to see how they were threatened by different factors:
· habitat loss
· persecution by humans and introduced predators
· other factors (introduced competitors, hybridization and disease) and unknown risk factors. Scientists investigated the relationship between body size and the risk of extinction, both due to habitat loss and to persecution/predation. Birds were classified as small (mean body mass 1 to 1000 g) and large (mass greater than 1000 g). The results are shown in the pie chart and bar charts below.

[Source: Modified from B Owens et al., Proceedings of the National Academy of Sciences, (2000), 97, pages 12144–12148. Copyright 2000 National Academy of Science, USA] (a) (i) State the percentage of species affected in some way by habitat loss.
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(ii) Calculate the approximate number of bird species threatened by predation / persecution only.
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........................................................................................................................... (b) State two factors that could have caused habitat loss.
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2 ..................................................................................................................................

(c) By referring to the bar charts, outline the effect of body size on the risk of extinction.
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2. The discovery of well preserved fossil hominids has been particularly valuable as body size can be estimated. These new data show that different parts of the hominid body evolved at different times and at various rates. Eight species of hominid, five of Australopithecus and three of Homo were analysed. The table below shows the geological dates and the estimated body and brain sizes of these species and of three modern African apes.
(Note: Myr = millions of years ago)

Primates
Species
Dates / Myr
Body mass / kg
Brain

Male
Female
volume / cm3

A. afarens is
4.0–2.8
45
29
384

A. africanus
3.0–2.3
41
30
420
Australopithecus
A. aethiopicus
2.7–2.3
–
–
399

A. boisei
2.1–1.3
49
34
488

A. robustus
1.8–1.0
40
32
502

H. habilis
2.4–1.6
52
32
597
Homo
H. erectus (early)
1.8–1.5
58
52
804

H. erectus (late)
0.5–0.3
60
55
980

H. sapiens
0.4–0
58
49
1350

Pan paniscus
0
38
32
343
Modern African apes
Pan troglodytes
0
49
41
395

Gorilla gorilla
0
140
70
505
[Source: H McHenry, Proceedings of the National Academy of Science, USA, (1994), 91, pages 6780–6786] (a) Identify, giving a reason, which hominid species is the least related to H. sapiens.
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(b) Compare the body mass of the three different primate groups.
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3. In starfish larvae (Dendraster excentricus) there is a correlation between food availability, the diameter of the tentacle and early development to the adult stage. Larvae were placed in tanks with high food availability (shown by o) and low food availability (shown by -). The “clearance rate” (shown in Graph 1) is a direct indication of how quickly food can be digested and used for growth. In Graph 2, the juvenile tentacle diameter is an indication of the larval development. This graph shows a sample of larvae of the same age. The greater the tentacle diameter the further advanced the larva is in its development to an adult. When larvae were placed in a high food availability tank, 68% changed into the adult stage. When larvae were placed in a low food availability tank, only 42% changed into the adult stage after 10 days. Graph 1 Graph 2

[Source: adapted from Hart and Strathmann, Biological Bulletin, (1994), 186, pages 291.299] (a) State the relationship between low food availability and tentacle diameter of larvae.
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(b) (i) Compare low and high food availability larvae with respect to larval age up to 10 days.
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(ii) Suggest a reason for the increased percentage of larvae changing into adults in a high food availability tank.
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(c) Discuss the selective advantages of larvae having a large tentacle diameter.
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ANSWERS
1. (a) (i) 70 (%)
(ii) 101 (±1) (b) fire; flood; logging / deforestation; hurricanes / strong winds; drought; land clearance; climatic changes; pollution; Accept other appropriate answers.

(c) small size more likely to suffer from habitat loss; large size from persecution / predation;

2. (a) (i) A. afarensis because smallest brain / less similar / smallest female;
A. robustus because smallest male body mass;
(ii) fossil of body not found / incomplete / only skull found / fossil not in good condition; (b) the largest primate in the table (Gorilla gorilla) is found amongst modern
African apes;
Australopithecus smaller than Homo; modern African apes have a greater range of body mass (than the other groups); all male primates larger than females / Australopithecus have generally a bigger difference between male and female body mass than Homo; Do not accept comparisons within the same group of primate.

3. (a) low food availability limits tentacle diameter (b) (i) highest clearance rate in high food availability; up to five days of age no difference in clearance rate
(between low and high food availability larvae); (ii) more food / nutrients leads to faster developments

(c) larger tentacle diameter leads to higher food uptake; as tentacle diameter increases this leads to higher clearance rate; increased food uptake leads to faster development; faster development to adult stage leads to earlier reproductive stage; reference to competition / natural selection;