Design an investigation

Bird species on reservoir islands

Units 1, 2 and 9
10 points
About 23 minutes

You can use a calculator on this question, just like on exam day.

You read about a real-world environmental situation with a described figure or model, then pick out the parts of a scientific investigation (hypothesis, variables, controls), explain the science behind it, and propose solutions to the problems it raises. On the exam: Question 1 of 3 in the 70-minute free-response section (Section II is 40% of the exam score).

The question and its sources

When a river valley was dammed to create a reservoir, the tops of several forested hills became islands. Ecologists surveyed the breeding bird species on five of these islands ten years after the reservoir filled.

Figure 1: Map of the reservoir

The map shows the reservoir as a long body of water running north to south. A continuous mainland forest lines the west shore. Five forested islands, labeled A through E, sit in the reservoir at different distances east of the west shore.

Islands A and C are each 0.5 km from the mainland forest. Islands B and D are each about 4 km from it. Island E is 2.0 km from it. Islands A and B are large, Islands C and D are small, and Island E is medium-sized. No boats or roads connect the islands to the mainland.

Source: Hypothetical map

Table 1: Breeding bird survey results

Island	Area (hectares)	Distance from mainland forest (km)	Number of breeding bird species
A	120	0.5	38
B	115	4.0	24
C	10	0.5	17
D	12	4.2	9
E	60	2.0	25

Source: Hypothetical data

Suggested time: 23 minutes

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Part (a)

1 point

Using Figure 1 and Table 1, describe how distance from the mainland affects the number of bird species on islands of similar size.

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Part (b)

1 point

Explain why larger islands generally support more species than smaller islands.

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Part (c)

1 point

The ecologists plan a follow-up study to test the hypothesis that island area affects the number of breeding bird species. Identify the independent variable in this study.

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Part (d)

1 point

Identify the dependent variable in the follow-up study.

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Part (e)

1 point

Identify one variable the ecologists should keep the same for every island in the follow-up study.

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Part (f)

1 point

The ecologists can survey each island for only one morning. Explain how surveying each island on several different days would improve the study.

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Part (g)

1 point

Identify one regulating ecosystem service provided by the island forests.

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Part (h)

1 point

Visitors' boats could accidentally bring rats to the islands. Explain why island bird populations are especially vulnerable to an invasive predator such as the rat.

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Part (i)

1 point

Many of the birds on the islands eat caterpillars that feed on tree leaves. Explain how a decline in these birds could affect the producers on the islands.

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Part (j)

1 point

Propose one realistic action the reservoir managers could take to help maintain bird diversity on the small islands.

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