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

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Sea otters and beavers are examples of keystone species in their respective ecosystems.

Which of the following correctly describes a keystone species?

  • A species that has a disproportionate effect on ecosystem structure relative to its abundance.

  • A species that is the most abundant organism in an ecosystem.

  • A well-known species that helps conservationists to educate the public about the effects of human activities on ecosystems.

  • A species that can survive independently of other organisms.

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Which of the following correctly explains how invasive species can affect ecosystems?

  • They introduce new beneficial traits that increase genetic diversity in native species.

  • They always increase biodiversity by adding more species to an ecosystem.

  • They can outcompete native species for resources, leading to population declines or extinctions.

  • They introduce a new selective pressure, increasing rates of mutation in native species.

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The diversity of an ecosystem can be measured in terms of species diversity, and in terms of the genetic diversity of its populations.

Which of the following correctly describes the relationship between the diversity of an ecosystem and its resilience to change?

  • Essential abiotic factors must be correctly regulated in order to maintain ecosystem diversity.

  • Ecosystems with greater biodiversity are more resilient to environmental change.

  • Resilience to environmental change is greater in ecosystems with low levels of biodiversity.

  • The diversity of species within an ecosystem may influence ecosystem structure.

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Which of the following best explains how geological and meteorological events affect ecosystems?

  • Ecosystems remain stable over time because geological and meteorological changes only affect non-living components of the environment.

  • Geological activity prevents environmental disruptions by maintaining landforms and climate conditions.

  • Changes in Earth's surface and atmospheric conditions can alter resource availability, disrupt food webs, and lead to population change.

  • Meteorological events maintain ecosystem balance by ensuring that all species have access to resources.

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Geological events can create significant abiotic and biotic changes in ecosystems.

Which of the following correctly describes a geological event that can result in ecosystem change?

  • El Niño is a climate pattern that can change ocean currents and result in changes to local nutrient availability.

  • Large-scale wildfires can destroy producers and cause habitat loss.

  • Continental drift involves movement of tectonic plates that can redistribute heat from the earth's interior, changing the abiotic conditions.

  • Drought can reduce water availability for all living organisms in an area.

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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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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 individual 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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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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Figure 1 below shows the relative biomass and ecological impact of three species, identified as X, Y and Z.

Graph showing the relationship between relative biomass of species and impact on ecosystem with points marked X, Y, and Z on a diagonal line.
Figure 1. The relative biomass and ecosystem impact of species X, Y and Z.

Which of the following statements about the data in Figure 1 is most likely to be correct?

  • Species X and species Z may both be keystone species.

  • Species with the highest biomass in an ecosystem always have the greatest ecological impact.

  • A comparison of relative biomass and ecological impact is the only way of designating keystone species status.

  • Species Y is dominant in its ecosystem, while species X may be a keystone species.

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Potato blight, caused by the fungal pathogen Phytophthora infestans, is a highly destructive disease affecting potato and tomato crops worldwide. The disease spreads rapidly under warm, humid conditions and is transmitted through airborne spores or contaminated material. Symptoms of potato blight include lesions on leaves, followed by the spread of infection to the tubers, making them inedible. A group of researchers investigated the effect of fluctuating daily temperatures on the progress of potato blight infection. They measured the growth rate of blight lesions over a range of average temperatures and at different levels of temperature fluctuation. Some of their results are shown in Figure 1. Error bars represent standard deviation.

Graph showing lesion growth rate against average temperature with lines for temperature fluctuations of 0°C, 5°C, and 10°C, peaking around 20°C.
Figure 1. The effect of average temperature and temperature fluctuation on growth rate of potato blight lesions.

Which of the following statements about the study described above is correct?

  • The results indicate that the null hypothesis for this study can be accepted.

  • Average temperature is the only independent variable in this study.

  • The results indicate that climate change is likely to affect the progress of potato blight infections.

  • Increasing the size of temperature fluctuations increases the rate at which a blight infection progresses.

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A study looked at the impact of agricultural system on the diversity of root-colonizing fungi, known as arbuscular mycorrhizal fungi (AMF), in summer squash crops. The agricultural systems studied were:

  • monoculture: A single crop is cultivated

  • polyculture: Several crops species are grown in the same place at the same time

The study measured several factors to assess the impact of agricultural systems on AMF diversity; factors measured included:

  • the observed number of different fungal species

  • the overall species diversity, taking into account the number of species and the number of individuals of each species; assessed using an index of diversity known as the Shannon diversity index (this is an alternative to the Simpson's index of diversity)

  • the percentage of roots that were colonized by AMF

Some of the results obtained are shown in Table 1 below

Table 1. The impact of agricultural system on AMF diversity

Observed number of species

Shannon index of diversity

% Colonization

χ2

p value at which difference is significant

χ2

p value at which difference is significant

χ2

p value at which difference is significant

5.6

0.02

8.9

0.003

0.2

0.68

Which of the following conclusions is supported by the data in Table 1?

  • Agricultural system has a significant impact on AMF diversity using all three measures of diversity.

  • There is a 0.3 % probability that the difference in Shannon index of diversity is due to the agricultural system used.

  • There is a 98 % probability that the difference in observed number of fungal species is due to the agricultural system used.

  • There is a higher probability that the difference in Shannon index value is due to chance than that the difference in observed number of AMF species is due to chance.

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