AP®BiologyCollege BoardExam QuestionsUnit 8: EcologyBiodiversity & Disruptions to Ecosystems

Biodiversity & Disruptions to Ecosystems (College Board AP® Biology)

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1
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Pisaster ochraceus, or the purple sea star, is a species of starfish commonly found in the Pacific ocean. A long-term study was carried out, between 1963 and 1973, into the impact of the presence of P. ochraceus on the local ecosystem. P. ochraceus was removed from several experimental sites, and the resulting effects on some local species was compared with areas where P. ochraceus was still present. Figure 1 below shows some of the results.

Two bar charts compare the abundance of mussels, small invertebrates, and algae in 1963 and 1973, showing significant increases in mussels by 1973.
Figure 1. Abundance of mussels, small invertebrates and algae in the presence of P. Ochraceus (A) and in the absence of P. Ochraceus (B).

Which of the following provides the best explanation for the data shown in Figure 1?

  • P. ochraceus feeds on mussels, which increase in number in the absence of predation.

  • In the absence of P. ochraceus the mussel population increases and the populations of small invertebrates and algae decrease.

  • P. ochraceus is a keystone species.

  • P. ochraceus feeds on algae, so there is more food for mussels in the absence of P. ochraceus.

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2
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Interdependence between living organisms means that the stability of an ecosystem can be affected by small changes in a single species. Some small changes may result in adaptation. Which of the following correctly describes an example of adaptation in living organisms?

  • Coat colour phenotype in mice is influenced by the mother's diet during pregnancy.

  • Favourable genetic variation arises in a toad population in response to environmental factors.

  • A random mutation in one individuals within a fish population gives rise to a new allele that has a neutral effect.

  • A mutation provides a bacterial cell with the ability to produce a chemical that deters competition.

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3
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A group of scientists carried out a study looking at biodiversity in a series of rivers in the UK. The table below contains information about the occurrence of two species of crayfish at different river sites in the UK between the 1970s and the early 2000s.

River

Crayfish species

Frequency of occurrence of crayfish

1970s

1980s

1990s

2000s

1

Austropotamobius pallipes

100

100

100

6.2

Pacifastacus leniusculus

0

0

0

31.6

2

Austropotamobius pallipes

100

100

58.6

0

Pacifastacus leniusculus

0

0

38.1

100

3

Austropotamobius pallipes

100

71.2

0

0

Pacifastacus leniusculus

0

22.8

58.1

100

Which of the following statements correctly describe the data in the table?

  • The mean frequency of Austropotamobius pallipes across the three rivers in 1990 is 90.4.

  • The population of Pacifastacus leniusculus in river 3 increases by 155 % between 1980 and 1990.

  • Pacifastacus leniusculus is an invasive species and is causing the decrease in population size for Austropotamobius pallipes.

  • The ratio of Pacifastacus leniusculus to Austropotamobius pallipes in river 1 during the 2000s is 4:1.

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Dutch elm disease is fungal disease of elm trees that causes vascular blockages and resulting leaf loss in elm trees native to Europe and North America. It is thought that human factors, such as the import and export of plants, and climate change, are contributing to the spread of the fungus. A group of scientists researched whether some transgenic varieties of elm tree, known as FS5 and AN1, had increased resistance to the fungus. They inoculated three groups of trees (control, FS5 and AN1) with the fungus and observed their symptoms. Some of the results are shown in Figure 1 below. The error bars represent standard error.

Bar chart showing percentage of leaves attached to trees. Control group has the least; FS5 and AN1 groups have progressively more, with AN1 the highest.
Figure 1. Percentage of leaves retained by trees in a control group, and in transgenic groups FS5 and AN1.

Which of the following hypotheses can be accepted?

  • AN1 modification prevents infection with Dutch elm disease.

  • FS5 and AN1 modifications have no impact on the symptoms of Dutch elm disease.

  • FS5 and AN1 modifications both reduce symptoms of Dutch elm disease.

  • AN1 modification reduces symptoms of Dutch elm disease.

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Throughout geological time the diversity of Earth's ecosystems has changed due to geological factors, the most famous of which is the meteor impact linked to the extinction of the dinosaurs at the end of the Cretaceous period. Figure 1 shows changes in diversity of each of the limbed vertebrate classes over 400 million years.

Graph showing biodiversity over 400 million years, with increasing families of amphibians, reptiles, birds, and mammals during various geological periods.
Graph showing biodiversity over 400 million years, depicting increases in amphibian, reptile, bird, and mammal families across geological periods.

Which of the following claims is supported by the data in Figure 1?

  • The end-Cretaceous extinction had a greater impact on limbed vertebrate diversity than the end-Permian extinction.

  • The meteor impact that is linked to the extinction of the dinosaurs wiped out most of the earth's reptile species.

  • There have been more speciation events in mammals than in any other class over the last 50 million years.

  • Limbed vertebrate diversity has increased at a mean rate of around 0.9 families per million years over the last 400 million years.

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