How do an increase in the organic matter in soil and an increase in soil depth affect the population of plants in an area?

• Larger plants become the dominant organisms
• Mosses replace flowering plants
• Nitrogen-fixing bacteria kill young trees
• Grasses become diseased

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Which result of ecological succession leads to an increase in animal species diversity?

• Soil develops more slowly
• Food choices increase
• Precipitation rates stabilize
• Temperatures drop steadily

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As ecosystems move through the stages of succession, the populations of organisms in them change. Which of the following describes the stage of succession likely to have the most species diversity?

• A newly formed volcanic island
• An agricultural field that has not been plowed for one year
• A temperate forest that has never been cleared by logging
• A field that is regularly mowed

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Bats eat insects that damage crops and mosquitoes that are vectors for disease. One million bats can eat several tons of insects per night, saving billions of dollars in pesticides yearly. 
Agricultural and public health scientists are concerned about the spread of white-nose syndrome (WNS). WNS is a result of a fungus that can infect cave dwelling bats. While bats hibernate during winter months, the fungus covers the bats' face and wings.
WNS has a near 100% mortality rate, and 5.7 million bats have died since the discovery of the fungus in 2006. Many scientists are searching for ways to protect these bats. The relationship between the fungus and the bats can best be defined as______________.

• Commensal, because the bats provide a surface for the fungus to grow
• Parasitic, because the fungus obtains nutrients and shelter from the bats
• Competitive, because both organisms use caves as shelter during the winter
• Mutualistic, because the relationship involves two distinct species living together

Three-spined sticklebacks that harbor a tapeworm are less likely to perform courtship behavior correctly and are less successful reproducing. Which one of the following terms classifies the tapeworm's relationship to sticklebacks?

• Competition
• Mutualism
• Commensalism
• Parasitism

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The food web shows the flow of energy through a sagebrush-steppe ecosystem.
Which of these organisms are in a trophic level that receives a larger percentage of the energy captures by the producers than the percentage received at the bats' trophic level?

• Mountain lions
• Snakes
• Hawks
• Ground squirrels

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Which of the following observations is consistent with the argument that bacteria found in human intestines are in a mutualistic relationship wit humans?

• The bacteria do not use the same nutrients as humans
• The bacteria provide vitamins to humans
• The bacteria increase the risk of cancer in humans
• The bacteria are also found in other organisms

Below is a food web diagram. Based on the diagram, it is reasonable to conclude that energy could follow which of the following paths as it cycles through this ecosystem?

• Sun ---> plant seeds ---> deer
• Plant seeds ---> field mouse ---> robin
• Eagle ---> deer ---> plant seeds
• Grass ---> deer ---> mountain lion

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How would the deaths of many individual organisms due to a random event such as a flood or fire most likely affect a population of plants?

• Adaptations would appear more quickly
• Biodiversity in the population would increase.
• Population size would decrease.
• New methods of reproduction would evolve.

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Bank swallows are birds that make their nests on the edges of rivers. Bank swallows can’t swim or breathe underwater. They feed on flying insects and in the spring, lay four or five eggs.
Which of the following observations would provide evidence that the population of bank swallows has been affected by a change in the environment?

• The largest swallows catch and eat more insects than the smallest ones.
• Swallows that lay four eggs one year may lay five eggs the following year.
• Fewer swallows build nests along the river when the water level rises.
• Swallows share a food source with other animals that also eat insects.

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