Over a hundred years ago, the prairies of South Dakota were home to dozens of kinds of grasses and hundreds of kinds of insects. This supported many populations of small mammals and birds. Today the prairies are dominated by domesticated wheat crops that humans can harvest and use for food. Pesticides used in growing the crops have killed off many kinds of insects that once lived there. In addition, the pesticides have poisoned populations of native mammals, such as prairie dogs. Which of these is most likely an additional change that has occurred in this ecosystem?
A.
There has been an increase in the amount of space available to mammal populations.
B.
There has been an increase in the variety of food sources available to bird populations.
C.
Native grasses have adapted to become more edible to humans.
D.
Pesticides have been washed into local sources of drinking water.
D. Pesticides have been washed into local sources of drinking water.
D. Pesticides have been washed into local sources of drinking water.
To determine the most likely additional change that has occurred in this ecosystem, we need to analyze the information given. The prairies of South Dakota were once home to diverse grasses, insects, mammals, and birds. However, over time, domesticated wheat crops have dominated the prairies, and pesticides used in growing the crops have negatively impacted the insect and mammal populations.
A. There is no mention of an increase in the amount of space available to mammal populations in the given information. Therefore, option A is unlikely to be the correct answer.
B. The information states that the prairies are now dominated by wheat crops, which suggests a decrease in the variety of food sources available. Therefore, option B is unlikely to be the correct answer.
C. The information does not mention any adaptations of native grasses to become more edible to humans. Therefore, option C is unlikely to be the correct answer.
D. The information explicitly mentions that pesticides used in growing the crops have killed off many kinds of insects and poisoned populations of native mammals. This suggests that the pesticides have the potential to contaminate local sources of drinking water. Therefore, option D is the most likely additional change that has occurred in this ecosystem.
So, the correct answer is D. Pesticides have been washed into local sources of drinking water.