• It does no good to reintroduce a species into a hostile environment. Many reintroductions don't succeed because the condition or pressures that caused the original population to decline or die out--human exploitation, habitat loss, or an exotic predator, for example--are still present. Another hazard is disease; translocated organisms might not be immune to local diseases, or they might bring a new pathogen (a disease-causing agent) with them that could infect members of the remnant wild population.
  - In Australia, 673 quokkas, small wallabies, were turned loose in a fenced enclosure over a period of twelve years. Even though predators were poisoned and shot, enough survived and evaded the fences to prevent the quokkas from establishing a breeding population.