Pro-Rewilding Science
One of the main reasons scientists support the idea of rewilding is that it is believed to be able to increase the biodiversity of a system. Biodiversity has recently become a measure for the health of a system, the higher the biodiversity the healthier the system. Having more layers of predators is thought to allow different specialization to occur, which in turn allows for a greater variety of species to compete within the system. Experiments on the effect of predators and meso-predators have been done in order to determine their roles in a system. Another reason conservationist tend to support rewilding is due to its ability to prevent extinction. By introducing these species into North America conservationists are expanding the species realized niche and giving the species a greater chance a survival. Another reason some people support rewilding is because it will in some ways return the environment to its past conditions. Many scientists hope that by restoring similar environmental hierarchies the land will be restored to its previous health.
Anti-Rewilding Science
In general ecologists and conservationist support the idea of rewilding, yet this does not mean that all scientists agree on this topic. Some scientists believe that since rewilding is still a new concept, it is impossible to truly know or understand the effects rewilding will have on an environment. Some scientists are worried that our lack of knowledge on specific species abundance and composition from the original time of the creatures existence is enough to avoid rewilding. Other scientists do not agree with rewilding since the actual species that existed is now extinct it means that proxy species will be used in their place. Many people believe that this defeats the purpose of rewilding the system, since you can't use the original species. Another large concern of those against rewilding is focused on the effects an escapee would have on vegetation/habitat outside of the reserve. Since these animals are so large they can do much more damage than a smaller animal escaping from a zoo.