Translocation is the human action of moving an organism from one area and releasing it in another. In terms of wildlife conservation, its objective is to improve the conservation status of the translocated organism or to restore the function and processes of the ecosystem the organism is entering. Two overarching goals of translocation are population restoration and conservation introduction. Population restoration includes reinforcing existing populations and reintroducing populations to areas where they have disappeared. Conservation introduction involves assisted colonization of organisms in entirely new areas, and ecological replacement of organisms to new areas to fulfill a vacant role in the ecosystem. The International Union for the Conservation of Nature (IUCN) catalogs translocation projects and creates extensive guidelines for their design and execution around the globe.

Overview

Translocation can be an effective management strategy and important topic in conservation biology, but despite their popularity, translocations are a high‐cost endeavor with a history of failures. It may decrease the risk of extinction by increasing the range of a species, augmenting the numbers in a critical population, or establishing new populations. Translocation may also improve the level of biodiversity in the ecosystem. Translocation may be expensive and is often subject to public scrutiny, particularly when the species involved is charismatic or perceived as dangerous (for example wolf reintroduction). Translocation as a tool is used to reduce the risk of a catastrophe to a species with a single population, to improve genetic heterogeneity of separated populations of a species, to aid the natural recovery of a species or re-establish a species where barriers might prevent it from doing so naturally. It is also used to move ecological features out of the way of development. Several critically endangered plant species in the southwestern Western Australia have either been considered for translocation or trialled. Grevillea scapigera is one such case, threatened by rabbits, dieback and degraded habitat. The rarest marsupial in the world, Gilbert's potoroo, has been successfully translocated to remote islands in Western Australia as "insurance populations". Translocation is a traditional, if rarely used, conservation tool. However, in this century of rapid climate change it has recently been reframed as assisted migration of narrowly endemic, critically endangered species that are already experiencing (or soon expected to experience) climate change beyond their levels of tolerance. Two examples of critically endangered relict species for which assisted migration projects are already underway are the western swamp tortoise of Australia and a subcanopy conifer tree in the United States called Florida torreya.

Types

Population restoration

Reinforcement

Reinforcement is the deliberate introduction and integration of an organism into an area where its species is already established. This mode of translocation is implemented in populations whose numbers have dropped below critical levels, become dangerously inbred, or who need artificial immigration to maintain genetic diversity. Before enacting reinforcement of a population, the root cause of the population decline should be addressed, allowing for the effort to not go to waste. Further notable considerations include assessing the capacity of the environment to sustain the desired population, and assuring translocated individuals have a diverse genetic makeup and are from a similar climatic or ecological area. Benefits of reinforcement include an increase in genetic diversity, increased populations sizes, and the reduction of Allee effect. Unfortunately, reinforcement also comes with a range of detrimental effects, which have been found through research in recent years. Some concerns specifically involve behavior and morphology changes in the population. Behavioral changes include reduced anti-predator responses, high aggression in resource competition, reduced breeding success, and difficulty finding successful habitat during dispersal. Morphological changes include altered dental health plus digestion struggle due to non-captive diets, and decreased defenses against predators. Along with these changes, the spread of disease poses additional problems. As captive individuals start breeding with wild individuals, genes which are unable to resist wild diseases might spread through the population, leading to large mortality when diseases arise.

Reintroduction

Reintroduction is the intentional process of reinstating an organism into an ecosystem previously occupied by that species. Individuals who are reintroduced can be caught from the wild and translocated to the new area or can come from captive breeding programs in zoos, wildlife sanctuaries, and similar organizations. The purpose of reintroduction is to create a free-ranging, viable, and reproductively sustainable population which will help restore its environment. Multiple challenges have arisen with reintroductions, mainly concerning genetics and life history traits. Research assessing these concerns of reintroduction tend to primarily focus on genetics. The concern involving genetics revolves around reintroduced individuals not having locally selected traits, which the extinct population most likely had. In regards to life history traits, most reintroduced species are endangered, and knowledge about the life history traits of endangered species tends to be limited. Knowing when the species is sexually mature, how many offspring they will have, their average lifespan, and more, are vital to the success of these programs. Oftentimes the effectiveness of reintroductions are also questioned due to the lack of these considerations and neglected post release monitoring.

Conservation introduction

Assisted colonization

Assisted colonization is the process of deliberately releasing endangered organism beyond its native habitat in order to prevent the extinction of its species. This process of creating “insurance populations” is primarily used when the species faces current or future threats and prevention of them or protection from them is not deemed feasible. One of the primary goals of such populations is to hold onto aspects of the populations that would be lost if captured for captive breeding. One of the main aspects lost within those populations is genetic diversity as selective pressures are no longer present. This form of translocation can move organisms to areas close to their native range or move them far distances to areas separated by non-habitats. There are many examples of assisted colonization proving to be successful, but there are voices challenging the effectiveness of this process, highlighting potential unintended consequences. The introduction of these species can alter ecosystem process, ecological interactions between organisms, decrease biodiversity, cause hybridization, and in some cases even cause other species to go extinct.

Ecological replacement

Ecological Replacement is the process of deliberately releasing organisms beyond their native habitat, to fulfil an ecological function which has been vacated in an environment. If a species integral to an ecosystem has been lost due to extinction, a related species will be placed to fulfil the same role and re-establish the ecosystem function. These typically range from a related sub-species to another species within the same genus. An example of such is the ecological services herbivores provide. Besides consuming plants, herbivores also spread seeds and provide disturbances for new plants to grow as seen with the Galápagos Tortoises on Pinta Island. If a primary herbivore is lost, the ecosystem would greatly suffer as the consumed plants would take over due to being unregulated. The process of ecological replacement is used as a form of conservation to maintain healthy ecosystems, but unintended ecological replacement can also occur through invasive species. If an invasive organism is introduced to an area which contains a closely related species, the invasive organism can ecologically take over the role of the native species.

Non-conservation oriented

Nuisance removal

Nuisance Removals involve the translocation of individuals deemed as nuisance after coming into conflict with humans in a particular area. As the human population continues to grow and development expands into previous wild areas, human-animal conflicts will continue to increase. These conflicts range from herbivores consuming plants in urban landscapes and agriculture, to carnivores hunting pets, livestock, or attacking humans. Previous methods of controlling such conflicts was through lethal control of the nuisance animals, but practices have been shifting to translocations. Many problems have arrived with such translocations as there is a lack of scientific security as these translocations do not occur for conservation goals, but for human needs instead.

Introductions

Introductions involve the purposeful or accidental translocation of species beyond their native range. After an introduction occurs, the animal is considered a non-native species in that area. If this new species does not harm its new environment, it will remain a non-native species, but once the introduced species begins to enact damage on the natural functions of the ecosystem, it becomes classified as an invasive species. When species are purposely introduced into an area, there can be a multitude of motivations behind them. A common purpose is for pest control in human areas and as a way to protect crops. Another common introduction of species is through the pet trade. As anything from reptiles, mammals, birds, and amphibians are owned as pets, many species have been introduced after escaping or being released by owners. Other reasons include economic gain from having a natural resource grown or cultivated in a new area, or for decorative displays. Unintentional introductions can also occur though a variety of different means, but many result from global shipping routes. Aquatic species are a common example as they are commonly transported with ship ballast water and from recreational boat hull fouling communities.

Trends

Between 1973 and 1989 an estimated 515 translocations occurred per year in the United States, Canada, New Zealand and Australia. The majority were conducted in the United States. Birds were the most frequently translocated, followed by threatened and endangered species, then non-game species. Of the 261 translocations in the United States reported wild species were most frequently translocated, and the greatest number occurred in the Southeast.

Success and failure

Species translocation can vary greatly across taxa. For instance, bird and mammal translocations have a high success rate, while amphibian and reptile translocations have a low success rate. Successful translocations are characterized by moving a large number of individuals, using a wild population as the source of the translocated individuals, and removing the problems which caused their decline within the area they are being translocated. The translocation of 254 black bears to the Ozark Mountains in Arkansas resulted in more than 2,500 individuals 11 years later and has been seen as one of the most successful translocations in order Carnivora. Another example of successful translocation is the gray wolf translocation in Yellowstone National Park. Often, when conducting translocation programs, differences in specific habitat types between the source and release sites are not evaluated as long as the release site contains suitable habitat for the species. Translocations could be especially damaging to endangered species citing the failed attempt of Bufo hemiophys baxteri in Wyoming and B. boreas in the Southern Rocky Mountains. For species that have declined over large areas and long periods of time translocations are of little use. Maintaining a large and widely dispersed population of amphibians and other species is the most important aspect of maintaining regional diversity and translocation should only be attempted when a suitable unoccupied habitat exists. Among plants, the translocation of Narcissus cavanillesii during the construction of the largest European dam (Alqueva dam) is considered one of the best known examples of a successful translocation in plants.

Examples

North America

South America

Europe

Africa

Asia

Australia