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MCAS Ecology

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Feb 2016 MCAS: In the past, coyotes lived throughout the western prairies and central Rocky Mountains in North America. Over time, the coyotes’ range has expanded. Humans have tried trapping and hunting coyotes to decrease their numbers. However, biologists currently estimate the number of coyotes to be at an all-time high.  Which of the following statements best explains why the number of coyotes continues to increase despite increases in death rates due to hunting and trapping?

A. Coyote lifespan is increasing, so only the oldest coyotes encounter hunters or trappers.
B. Coyote birth rates remain high, so more coyotes are added to the population than are removed.
C. Coyotes are migrating more often, so male coyotes have more fights over territories.
D. Coyotes have to compete with more species, so the coyote emigration rate has increased.


Feb 2016 MCAS.

Here are the ecological roles of several organisms in a rainforest ecosystem.

fig tree           – producer
jaguar            – secondary consumer
mango tree –  producer
monkey        – primary consumer
toucan bird – primary consumer

a. In your Student Answer Booklet, draw a food web that includes all the organisms listed here. . Make sure the arrows represent the correct direction of energy flow.

Decomposers, such as bacteria, are not listed here:

b. Describe the role of decomposers in the rainforest ecosystem.

c. Describe what would most likely happen to producer populations and consumer populations if all decomposers in an ecosystem were removed. Explain your answer for each type of population.


Spring 2017

The graph below shows the changes in the population size of a mammal
species introduced onto an isolated island in 1957.

Graph changes in population

Which of the following conclusions is best supported by the data?

A. Every year, more individuals were born than died.
B. A predator of this mammal was removed from the island in 1990.
C. The population decreases were the result of low immigration rates.
D. In the 1980s, the mammal’s population size stayed around its carrying capacity.


The graph below shows changes that occurred in the size of a population of animals over a year.

Graph population size year

Which of the following is best supported by the graph?
A. Between month 1 and month 5, the immigration rate was zero.
B. Between month 4 and month 6, a predator was introduced into the ecosystem and increased the death rate.
C. Between month 5 and month 7, the birth and emigration rates decreased and the death and immigration rates increased.
D. Between month 8 and month 12, the birth and immigration rates equaled the death and emigration rates.


A female Hymenoepimecis wasp will temporarily paralyze a spider and then lay an egg on the spider’s abdomen. After the paralysis wears off, the spider resumes its normal activity. When the egg hatches, the larva grows by sucking its required nutrients from the spider. What type of relationship exists between the spider and the Hymenoepimecis wasp?

A. commensalism
B. mutualism
C. parasitism
D. predator-prey


Spring 2017

A food web is shown below:

Food web

An organism in the food web is labeled X.

a. Identify and describe the ecological role of organism X in the food web.

b. Identify the organism in the food web whose population size would likely increase the
most if the bat became extinct. Explain your answer.

There are many types of relationships between organisms, including competitive and

predator-prey relationships.

c. Identify two organisms in the food web that have a competitive relationship. Explain your answer.

d. Identify two organisms in the food web that have a predator-prey relationship. Explain your answer.


Which of the following statements best explains why introduced species often threaten native species in an ecosystem?

A. Introduced species often have less genetic diversity than native species.
B. Introduced species often lack natural predators in their new environment.
C. Introduced species often form mutualistic relationships with native species.
D. Introduced species often cause short-term droughts in their new environment.


Spring 2017

Red lionfish have been introduced into the Caribbean Sea and the Gulf of Mexico. The red lionfish are predators that compete with native fish for space and food, causing coral reef fish population sizes to decrease. Government and environmental groups are encouraging coastal communities to catch red lionfish and serve them at restaurants.

Which of the following best explains how catching and eating red lionfish could help preserve coral reefs?

A. Reef fish will learn that red lionfish are no longer dangerous.
B. Red lionfish will return to their native habitats to avoid being caught.
C. Humans will fill the role of predator and control the red lionfish population.
D. Restaurants that serve red lionfish will attract more tourists to visit coral reefs.


Approximately 250 million years ago, over 90% of species living in the oceans became extinct. Which of the following conditions most likely contributed to this mass extinction?

A. changes in global climate
B. evolution of new parasite species
C. mutation of species’ DNA sequences
D. increases in the rates of photosynthesis


Biologists studied a population of lizards. They found that small lizards had trouble defending their territories and that large lizards were more likely than small or medium lizards to be preyed upon by owls. Which of the following graphs represents the most likely distribution for body size in this lizard population?

Lizard population vs body size Ecology MCAS


MCAS 2014 Open Response

The Elk Mortality graph shows changes in elk mortality with wolves present and without
wolves present.

a. Summarize what the Elk Mortality graph shows about elk mortality from November to April with wolves present and without wolves present.

Based on these data, scientists can estimate the size of scavenger populations through the winter. The graph below shows the size of a scavenger population with wolves present and without wolves present.

Elk scavenger

b. Explain the cause of these data patterns for the scavenger population.

c. Describe one way that the wolves’ effect on the elk population could benefit organisms other than scavengers in the ecosystem.


In a certain population, the death rate is greater than the birth rate from year 1 to year 2, and the immigration rate equals the emigration rate. Which of the following graphs represents this information?

population vs year graph


Many individuals in wild animal populations die at a young age. Which of the following factors most directly limits lifespan and therefore has a large effect on a species’ population size?

A. low birth rate
B. low immigration rate
C. high prey numbers
D. high predator numbers



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