B12E

The overgrowth of algae poses a major problem for coral reefs. Intensive fishing is one factor that contributes to algae overgrowth because it does which of the following?

• allows more sunlight to be available to algae

• inhibits the spread of pathogens in algae colonies

• reduces the number of organisms that feed on algae

• increases the competition between different algae species

The Nile River flows into the Mediterranean Sea. The Aswan High Dam contains the flow of water from the river and reduces the annual fall flooding. The floodwater is trapped behind the huge dam, allowing irrigation for agriculture. Sediments that would be washed away by the annual floods are also trapped behind the dam. The graph shows the water flow from the Nile that enters the Mediterranean Sea. How has this dam most likely affected the Mediterranean Sea ecosystem?

• reduced nutrients from the land support fewer producers in the sea

• water trapped behind the dam causes the marine ecosystem to move inland

• the flooding in August through November causes marine life to be destroyed

• the water temperature of the sea has increased

Dead zones are low oxygen areas that develop on the sea floor. Scientists hypothesize that phytoplankton blooms cause these dead zones. Phytoplankton blooms occur when excess nutrients are introduced by pollution from fertilizers, sewage plants, and the burning of fossil fuels. Which of the following would most likely cause an increase in these contributors to dead zones?

• rainfall patterns that increase freshwater runoff from terrestrial ecosystems

• replacing coal fired power plants with windmills

• farming practices that reduce nitrate and phosphate applications

• constructing efficient water recovery and treatment plants

Amphibians are dying in large numbers after being infected by an aquatic fungus called Batrachochytrium dendrobatidis. The origin of this fungus is unknown, but scientists suspect that humans are helping spread it. More than 350 amphibian species have been affected, and at least 200 species of frogs have suffered serious reductions in population or become extinct. The map below shows teh worldwide distribution of B. dendrobatidis. What will be the most likely impact of the decline in frog populations resulting from the fungal infection?

• new species of frogs that feed on both the fungus and the infected species of frogs will evolve

• plants will no longer grow in the waters of affected ecosystems, and fish species will increase

• the fungus will move on land and destroy reptile and mammal populations in tropical ecosystems

• populations of algae and mosquitoes will increase, leading to fish die offs and potential increases in human malaria cases

On March 24, 1989, an oil tanker ran aground on Bligh Reef in Prince William Sound, Alaska, and spilled millions of liters of crude oil. The graph shows pink salmon populations in Prince Willliam Sound from 1970 to 1999. What do these data suggest about the effect the oil spill had on pink salmon?

• pink salmon were nearly eliminated after the oil spill

• pink salmon populations steadily declined in the 10 years following the spill

• pink salmon populations declined and never fully recovered

• pink salmon populations seemed to be minimally affected

In dry desert areas poor drainage can lead to a buildup of salt in water supplies. A student performed an investigation to study the effects of salinity on the germination rates of seeds. The student places seeds in several solutions containing 0% to 3% salt. The length of the radicle, which is a root of the germinating seed, ranged from 49 mm in the 0% salt solution to 0 mm in the 3% salt solution. The data from this investigation suggest that increased salinity in more areas may lead to a decrease in which of the following?

• air pollution

• food production

• oceanic evaporation

• nonrenewable resources

Food webs such as the one shown were first used in 1927 by the animal ecologist Charles Elton. The food web above represents the feeding relationships among organisms in an Alaskan ecosystem. An environmental change that removed which of these organisms from the ecosystem would cause the most instability in the ecosystem?

• auklets

• foxes

• salmon

• zooplankton

Which of the following is most likely to cause the greatest disruption to an ecosystem?

• empying an aquarium containing non native species into a local waterway

• cutting down a small cedar tree to make holiday decorations

• cleaning the windshield of a car with alcohol based grass cleaner

• mowing the lawn in a city park

The picture shows a pika, a small mammal found in grassland ecosystems. The vast grasslands of the Tibetan plateau are home to the plateau pika. The numerous pikas are prey for many predators of thh grasslands, which serve as a major watershed for much of the area. The watershed drains large quantities of groundwater during the rainy season, or the monsoon season. Pikas have extensive burrows that help drain groundwater rapidly and are used as nesting sites by many bird species. However, many people advocate the eradication of the plateau pikas because they compete with livestock for grass. Which of these will most likely happen if the plateau pikas are completely removed from the Tibetan plateau grasslands?

• the ecosystem will become unstable because predators will have fewer prey, the birds will have fewer nesting sites, and the area downriver will become vulnerable to flooding without the burrows to aerate the soil and provide drainage for monsoon rains

• the ecosystem will become more stable because the pika will be replaced by other species of small mammals that can fill the niche, bird species will adapt to nesting aboveground, and the soils will become compacted without the burrows

• the ecosystem will be come unstable because the predators will migrate to nearby ecosystems, the birds will nest in nearby trees, and the soils will be aerated by other small mammals

• the ecosystem will become more stable because the pika will no longer be there to eat the grasses, the birds will migrate to other ecosystems during nesting season, and the soils will be able to absorb more of the monsoon rains without the pika burrows

Roads are often built through forests for industrial purposes or as land is developed for residential and commercial needs. How would road construction through a forest most likely affect the ecosystem?

• non native species would replace native species

• the number of primary consumers would increase

• the natural succession of the vegetation would change

• all producers would be eliminated from the community