Relationships in Ecosystems Review

Drought is a weather condition that may limit the amount of water resources available to an ecosystem. Which of the following may be one result of drought?

• Fish populations may decline due to lower river levels.

• Birds may not build nests due to temperature change.

• Flowering plants may produce more seeds due to lack of water.

• Predator populations may increase due to increased prey populations

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Biologists believe that the tick-deer relationship is parasitic because the tick feeds off the deer and the deer is harmed by the tick bite. During springs with sufficient rain, forest vegetation increases, providing abundant food resources for deer to produce young. Which of these patterns supports the idea that the tick-deer relationship is parasitic? 

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A student is studying interactions between organisms in a food web. She wonders what could happen in a prairie ecosystem if foxes suddenly disappeared. Which of these is the best answer to her question?

• If foxes disappear, all other populations will grow.

  
  

• If foxes disappear, all other populations will shrink.

• If foxes disappear, the population of an organism that feeds on foxes will likely grow.

• If foxes disappear, the population of an organism on which foxes feed will likely grow.

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Every five years, certain kind of oak trees experience “masting,” in which they produce and drop hundreds of acorns. How can masting affect organisms such as black bear, deer, and squirrels that feed on them?

• The oak population and the populations of organisms that eat acorns will both decline.

  
  

• The number of acorns available will not affect the black bear, deer, or squirrel populations.

• The population of oak trees, black bear, deer, and squirrels will all show a slight increase.

• The oak population will decline, while the population of black bear, deer, and squirrels will increase.

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A collection of organisms that belong to different populations but all live in the same area and interact with one another.

• Population
• Ecosystem
• Community
• Ecosphere

A group of interbreeding organisms (species) living in the same area

• ecosystem

• community

• population

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The graph shows the population of a group of rabbits in a restricted area studied over a period of five years. Which statement might explain why the population leveled off as shown in the graph?

• The resources in the area ran out.

  
  

• The rabbits encountered a new disease.

• Predators were introduced into the area.

• Competition for resources limited the rabbit population.

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Which of these is the most likely reason that a population in an ecosystem could have a sharp decline?

• The number of prey suddenly increases.
  

• he number of predators suddenly decreases.

• The competition for the same resource suddenly drops.

• The abiotic resources in the environment suddenly drops.

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Owls are a predator species that hunts field mice. The graph shows the number of western screech owls spotted at night on the British Columbia coast per hour over the course of several years. Screech owls prey on field mice. What does the change in owl sightings suggest about the population of field mice? Explain your answer.

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Scientists are studying how the average temperature affects how roots of grasses in grassland ecosystems grow. The amount of plant roots found in the soil is called root matter. The graph shows the amount of root matter that can be found in soil depending on the average annual temperature. Based on the graph, what prediction could scientists make about the populations of grass in this grassland ecosystem?

• In years with high temperatures, grass populations will increase.

  
  

• As the average annual temperatures increase, grass populations increase.

• During years with high average temperatures, all grasses in the ecosystem die.

• If average annual temperatures increase, over time grass populations will probably decrease.

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