Disruptions and Change (U8 C)

Researchers were studying species diversity in a savanna rangeland community in southwest Queensland, Australia. Researchers counted the numbers of plants species in four different categories at two nearby sites within the savanna rangeland; one lightly grazed by herbivores and one heavily grazed by herbivores (Figure 1). Which of the following best predicts the results of a drought in the savanna research area with regards to community resilience to this environmental change?

• The heavily grazed area is more likely to recover more quickly from the drought due to reduced competition between species.

• The lightly grazed area is likely to recover more quickly from the drought due to greater biodiversity.

• The lightly and heavily grazed areas are likely to recover at equal rates due to the overlapping categories of plant species.

• The lightly and heavily grazed areas are likely to recover at equal rates due to the similar climates and locations.

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In the Florida Everglades, Burmese pythons are an invasive species. They were introduced into southern Florida in 1992. These pythons feed on many of the native Florida species, establishing the pythons as the top predator in the environment. By the year 2000, their population had increased dramatically.

Figures 1 and 2 display data collected by ecologists studying the results of the Burmese python invasion. Figure 1 shows counts of animals collected from nighttime road surveys in southern Florida, which are used to estimate population size. Figure 2 shows data collected from mosquitoes captured from the wild.  DNA  sequencing was used to identify the species of blood that the mosquitoes had in their stomachs, identifying various hosts used by the mosquitoes. In 1996, the native Culex cedecei mosquitoes in southern Florida preferentially took blood meals from white-tailed deer and raccoons. It was predicted that changes in host population size would alter these host preferences. Additionally, it is known that cotton rats are often infected by the Everglades virus, which normally exists in animals, but is capable of infecting humans. Ecologists predict that increased feeding on cotton rats by C. cedecei may significantly increase the tendency of this virus to infect humans.

Which of the following most accurately explains an impact of Burmese pythons on the Everglades community in southern Florida using the data provided?

• Python parasitism has reduced the population of white-tailed deer and raccoons.

• Python predation has caused a trophic cascade that changed the mosquitoes’ niche.

• Pythons have a mutual symbiosis with cotton rats, allowing their population to increase.

• Intraspecific competition for food between white-tailed deer and raccoons has increased due to pythons.

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 In the Florida Everglades, Burmese pythons are an invasive species. They were introduced into southern Florida in 1992. These pythons feed on many of the native Florida species, establishing the pythons as the top predator in the environment. By the year 2000, their population had increased dramatically.

Figures 1 and 2 display data collected by ecologists studying the results of the Burmese python invasion. Figure 1 shows counts of animals collected from nighttime road surveys in southern Florida, which are used to estimate population size. Figure 2 shows data collected from mosquitoes captured from the wild.  DNA  sequencing was used to identify the species of blood that the mosquitoes had in their stomachs, identifying various hosts used by the mosquitoes. In 1996, the native Culex cedecei mosquitoes in southern Florida preferentially took blood meals from white-tailed deer and raccoons. It was predicted that changes in host population size would alter these host preferences. Additionally, it is known that cotton rats are often infected by the Everglades virus, which normally exists in animals, but is capable of infecting humans. Ecologists predict that increased feeding on cotton rats by C. cedecei may significantly increase the tendency of this virus to infect humans.

Based on the data, which of the following most accurately matches a potential change with its predicted effects on the southern Florida ecosystem?

• Introduction of a new top predator species that preys solely on Burmese pythons would cause an increase in the raccoon population.

• If the population of Burmese pythons were to decrease, then the cotton rat population would increase.

• If more Burmese pythons are introduced in the Everglades, then mosquitoes will begin feeding on white-tailed deer frequently again.

• Introduction of a new snake species that competes with the Burmese python for food would lead to an increase in the white-tailed deer population.

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Phytoplankton (dashed line) are important because they occupy the bottom of the food web absorbing  CO2 , functioning as a carbon sink. A scientist suggests that an El Niño event in early 1998 caused a significant decrease in the abundance of phytoplankton that year in the equatorial Pacific Ocean. Which of the following observations would best support this alternative hypothesis?

• Previous dips in plankton abundance coincided with other El Niño events.

• Primary consumers also experienced a dip in abundance in early 1998.

• After mid-1998, there is no correlation between phytoplankton and zooplankton abundance.

• CO2 levels in surface waters increased significantly in this region during 1998.

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Fur color is a genetically controlled trait in mice. A population of a species of mouse that typically lives in habitats with light-colored soil was studied for several generations. The background color of the habitat of this population became darker after the second generation due to human activity. A researcher sampled approximately 120 mice in each generation and recorded the fur color phenotypes as shown in Figure 1. The researcher claims that there is no selective advantage to fur color, so light and dark fur color phenotypes are present in similar frequencies in the fourth generation of this mouse population. Based on the data in Figure 1, which of the following best evaluates this null hypothesis?

• The null hypothesis is rejected, because the change to a darker background color led to an increase in the dark-colored fur phenotype.

• The null hypothesis is rejected, because there is no significant difference between the frequencies of the two phenotypes right after the human-caused change to the habitat in the third generation.

• The null hypothesis cannot be rejected, because there is no significant difference between the frequencies of the two phenotypes right after the human-caused change to the habitat in the third generation.

• The null hypothesis cannot be rejected, because the darker background color caused by the human-caused change to the habitat led to a decrease in the light fur color phenotype.

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Zebra mussels are an invasive species that has become widely established throughout the United States. Figure 1 shows the percent change in the population sizes of selected groups of organisms in the Hudson River since the introduction of zebra mussels. In this study chlorophyll-containing bacteria are considered phytoplankton and all other bacteria are considered bacterioplankton. Which of the following hypotheses about the effect of zebra mussels on the Hudson River community is best supported by the data in Figure 1 ?

• Shoreline fish have replaced open water fish as top predators in a stable community.

• Zebra mussels have integrated into the existing community with little effect on the community stability.

• The reduction in primary productivity has resulted in an unstable community that will eventually collapse.

• Bacterioplankton have replaced phytoplankton as the energy harvesters in the community.

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Potatoes as a food crop originated in South America. There are over 4,000 variations of potato grown there. Potatoes were brought to Europe by Spanish colonists in the late 1500s. One variety became the chief crop grown in much of Ireland by the early 1800s. Table 1 summarizes the spread of potatoes as a food crop. The Irish Lumper variety of potato was introduced into Ireland in the early 1800s. The Lumper soon became the only variety of potato grown in much of Ireland. The potato blight destroyed most of the Lumper crop between 1845 and 1852 resulting in the death of about 1 million Irish from starvation.

A researcher suggests that the Irish monoculture (growing a single crop) of the Lumper potato did not significantly change the overall resistance of the potato crop in Ireland to diseases. Which of the following observations best refutes this null hypothesis?

• Before the arrival of the potato blight, there were already two other potato plant diseases in Ireland.

• The number of fatalities from the Irish potato famine was greater than the rest of the European countries combined.

• During the early nineteenth century, the vast majority of people in Ireland depended on the Lumper potato for food.

• Growing more varieties of potatoes increases competition for available resources, which may yield fewer potatoes.

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In the Florida Everglades, Burmese pythons are an invasive species. They were introduced into southern Florida in 1992. These pythons feed on many of the native Florida species, establishing the pythons as the top predator in the environment. By the year 2000, their population had increased dramatically.

Figures 1 and 2 display data collected by ecologists studying the results of the Burmese python invasion. Figure 1 shows counts of animals collected from nighttime road surveys in southern Florida, which are used to estimate population size. Figure 2 shows data collected from mosquitoes captured from the wild.  DNA  sequencing was used to identify the species of blood that the mosquitoes had in their stomachs, identifying various hosts used by the mosquitoes. In 1996, the native Culex cedecei mosquitoes in southern Florida preferentially took blood meals from white-tailed deer and raccoons. It was predicted that changes in host population size would alter these host preferences. Additionally, it is known that cotton rats are often infected by the Everglades virus, which normally exists in animals, but is capable of infecting humans. Ecologists predict that increased feeding on cotton rats by C. cedecei may significantly increase the tendency of this virus to infect humans.

Scientists hypothesize that the invasive Burmese pythons are responsible for recent increases in human Everglades virus infections. Evaluate this alternate hypothesis using the data provided.

• The alternate hypothesis is supported because invasive Burmese pythons caused an increase in the mosquito population. This enabled them to transmit the Everglades virus at a higher frequency if they were infected.

• The alternate hypothesis is supported because the invasive Burmese pythons caused mosquitoes to switch to feeding on cotton rats. This means that mosquitoes are more likely to carry the Everglades virus when they bite humans.

• The alternate hypothesis is refuted because humans are used as hosts for only a small percentage of mosquito feedings. Humans therefore will not have an increase in Everglades virus infection.

• The alternate hypothesis is refuted by the data because the population of cotton rats increased. Since there are more cotton rats, they will contain the Everglades virus and prevent it from infecting humans.

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Figure 1 shows the changing pattern of human population sizes in rural and urban areas from 1960 to 2016 with regard to the global population. A scientist interested in investigating how human population trends might affect local animal species’ richness stipulates a null hypothesis that animal biodiversity in rural areas will be unaffected in the future by the human population trends shown in Figure 1. Which of the following would best refute this null hypothesis?

• More rural areas will become available for animal habitats over time.

• Urbanization causes habitat fragmentation.

• Urbanization decreases the per person fossil fuel use in urban areas.

• Water in urban areas is treated before it is released into the rivers that flow into rural areas.

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