Removing or relocating an animal from its territory results in undue stress and conflict with other animals and affects the animal's chance for survival. Further, relocating an animal outside of its natural habitat has detrimental effects upon ecosystems.
There are several reasons for removing an animal from its native territory. These include collection for scientific study, temporary removal of sick or injured animals for rehabilitation and the removal and relocation of nuisance wildlife. When collecting animals for study or rehabilitation, the researcher should always take care to place the animal back in its original location. Animals occupy specific territories and become accustomed to the landscape of that territory. Placing an animal in unfamiliar territory disadvantages it in terms of finding food and shelter. It also causes a great deal of stress, affecting the animal's overall health.
While relocation of nuisance wildlife seems like a humane option, it is often a death sentence for the animal and a risk to other animals. In most cases nuisance wildlife are common species and another animal of the same species may already inhabit the new territory, resulting in territorial disputes. Relocation also risks the spread of disease.
An even greater threat than relocation within a native ecosystem is the introduction of non-native species to an ecosystem. This can occur if study species escape. It can also occur from the release of exotic pets into the wild. A non-native animal may have less competition and fewer predators in the new ecosystem, resulting in an invasive species that is detrimental to the ecosystem as a whole. Invasive species out-compete native species for resources and spread disease within the new ecosystem.