In Pennsylvania, wolves have been extinct for many years. They used to feed on white-tailed deer, but not that the wolves are gone, the population of white-tailed deer has exploded. This means that this community: a. Was under top down control
b. Was under bottom up control
c. Lacks a fundamental niche for wolves
d. Lacks a fundamental niche for deer

The correct answer is a: The community was under top-down control

Explanation:

Top-down control refers to scenarios where superior predators control the structure and dynamic of an ecosystem. These systems are affected by the presence/absence of the superior predator influences all the lower links in the trophic chain.  

In the exposed example wolves, that are considered to be the top predators, affected the white-tailed deer populations being the cause of its decrease.  As wolves used to feed on white-tailed deer, they kept these populations under control, but once the wolves got extinct, the deer population increased again. Probably, this explosion in the deer´s population also affected its lower link in the trophic chain.

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primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs