Deer Population Effects
The eastern cougar was an apex predator throughout its range. Once the cougar was driven to extinction, the population of its chief prey, the white-tailed deer, boomed. Across most of the cougar's previous range, population control measures have been implemented to try to deal with the dangerous increase in deer. Increased deer populations have placed more stress on the herbaceous plants that form their diets. The overconsumption of these plant has not only put a stress on those species, but has deprived other animal populations, such as butterflies and rabbits, of food.
Increase in Other Apex Predators
It is thought that the extinction of the eastern cougar will increase the populations of other apex predators by increasing the availability of prey. Predators such as the black bear feed on white-tail deer and other prey that the eastern cougar previously hunted. In New Jersey, one state where the eastern cougar lived, black bear encounters with humans have become increasingly common in recent years. This is thought to be caused by an increase in their population due to an abundance of food.
Ultimate Effect on Prey Species
When the balance of the predator/prey relationship is upset, it is difficult to predict the long-term effects. There is a theory that the extinction of one apex predator leads to a boom in the population of its prey species. This can lead to a population number that exceeds the carrying capacity for a region, leading to famine and disease for that species. Although the extinction of the eastern cougar might seem like good news for its prey species in the short term, over a longer time line it could hurt their numbers.
Reduction in Biodiversity
The tangible effects of the eastern cougar going extinct are a boom in the populations of its prey. The intangible effect is the loss of biodiversity for its region. Once a species is extinct it is gone forever, barring extreme reintroduction measures. Even if this situation is corrected, there are intangible effects that we cannot be certain of, and ripples sent down the food chain might cause additional adverse ecological outcomes in the future. Some types of shrubs and trees have already been influenced by the eastern cougar's extinction. When deer populations are not kept in check, they graze seedlings and saplings to the ground, preventing a new generation of forest from growing.