An example of the needs of an ecosystem being at odds with those of humans is

farmers choosing pastures over range lands
designating small plots of land for crops
the extermination of the prairie dog pest
limiting livestock to prevent overgrazing

The extermination of the prairie dog pest.

Explanation:

This is the best example of the needs of an ecosystem being at odds with the needs of humans. In this example, the prairie dog is eliminated because it is considered a "pest." I causes problems for farmers and is therefore bad for agriculture. However, the extermination of the prairie dog poses a risk to the environment, as it eliminates a species from the ecosystem and therefore threatens its balance.

i'm sure the answer you are looking for would be

a. an ice age

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