A stream runs through a mountain forest. Willow trees grow on each side of the stream. A small deer population feeds on the willows. Mountain trout rely on the willow shade for shelter. The apex predator in the forest is the mountain lion. The mountain lions primarily eat deer, but also eat rodents, fish, and other prey species. Analyze the components of the ecosystem. What would likely be an early outcome if the mountain lion population vanishes?

In the described ecosystem, the mountain lion is an apex predator that helps regulate the population of deer. Its presence keeps the deer population in check, which in turn influences the health of the willow trees and the overall balance of the ecosystem.

If the mountain lion population were to vanish, the deer population would likely experience significant growth due to the lack of predation. This increase in deer numbers would lead to increased herbivory pressure on the willow trees, which may result in overbrowsing. The overbrowsing could limit the ability of willow trees to regenerate and thrive, potentially impacting the stream's ecosystem as well since willows provide shade and habitat for mountain trout.

Based on these dynamics, the most plausible early outcome of the mountain lion's disappearance would be:

The willow tree population will increase the next summer.

is incorrect because, instead, they will likely decline due to increased grazing by a growing deer population. The most valid early outcome would be:

The rodent population will increase within a few months.

An increase in deer (who feed on willows) can lead to more food available for rodents, as fewer willows would result in lower competition for food sources, allowing rodents to thrive. The initial answer options provided do not include this definitive outcome, but given the options, if looking for the most immediate ecological change, increased rodent populations are a likely outcome of reduced predation.