Issues Magazine

Relocating Species to Ensure Survival in a Changing Climate

By Tara G. Martin and Eve McDonald-Madden

In the face of climate change, conservation measures to protect species may not be enough. Managed relocation is the radical last resort.

Human-induced climate change is altering ecosystems worldwide. Because of these ecosystem changes, the geographic range of species is shifting towards the poles or to higher elevations. The speed of these changes may exceed species’ ability to adapt or disperse, leaving many species without suitable places to live and thus at an increased risk of extinction.

Indeed, some of our most species-rich areas of the globe and most valued ecosystems, such as coral reefs and mountain rainforests, may cease to exist in their current form as a result of climate change. In these cases, standard conservation actions such as creating conservation reserves may offer insufficient protection. Instead, species persistence may require the radical action of managed relocation.

What Is Managed Relocation?
Managed relocation is also known as assisted translocation, assisted colonisation or assisted migration. It involves physical movement of plants or animals from an area that has or will become unsuitable because of climate change to locations where the climate is predicted to be suitable but where the plants or animals have never occurred before. If the relocation is successful, persistence of the population, species or ecosystem may be ensured.

For example, relocation of low-latitude staghorn coral species, which have a higher temperature range tolerance, to higher latitudes may be one way of preserving forms of this species as the climate changes. Relocating a sub-population of the high elevation wet tropics golden bowerbird to lower latitude high elevation rainforest may prolong the persistence of this species.

Managed relocation flies in the face of traditional conservation strategies. In fact, there is an entire discipline, invasion ecology, devoted to managing the negative consequences of moving species into new regions around the globe.

Currently there is much debate over the merits of managed relocation as a tool to combat the impact of climate change. For some, managed relocation forms an essential part of the conservation toolbox available to conservation managers while for others the risks of moving species far outweigh the potential benefits.

Moving Species Is Not New
Moving species is nothing new in conservation science. In Australia alone, more than 200 translocations or reintroductions of 42 vertebrate species have been undertaken for conservation purposes. Mammals and birds have made up the overwhelming majority of animal relocations, and there have been many successes.

For example, in 2003, in response to the collapse of northern quoll (Dasyurus hallucatus) populations in the mainland Top End of the Northern Territory, two populations were established on Pobassoo Island and Astell Island using a total of 64 founder individuals. Five years later, results from monitoring suggest that the quoll populations on these islands have increased dramatically, with more than 800 adult female quolls on Pobassoo Island and more than 4800 on Astell Island. This is a remarkable success story.

Another successful island translocation concerns Australia’s most endangered mammal, Gilbert’s potoroo (Potorous gilbertii). While still highly threatened on the mainland, monitoring data of a population established from 19 individuals on Bald Island off the coast of Western Australia suggests that the population is thriving in its new location.

Risks of Managed Relocation
While there are many examples of success, these must be tempered with the other side of the relocation story. Not all relocations are successful. Australia has a higher rate of relocation failure than many other parts of the world. The most frequent reason for failure is predation by cats and foxes. Other factors include chronic overgrazing by livestock and other introduced herbivores and poor fire management across most mainland habitats. For example, the relocation of over 600 quokkas (Setonix brachyurus) from Rottnest Island to Jandakot in Western Australia between 1972 and 1988 failed as a result of predation by foxes, cats and overgrazing by rabbits.

At the other end of the spectrum, some species relocations can be overly successful, with relocated populations expanding to such high numbers that they have a major impact on other valued species and ecosystems, creating new and unforeseen conservation problems.

For example, in some parts of southern Australia relocated populations of koalas are eating themselves out of house and home. In 1923, fearing that the fur trade would annihilate koalas unless some were protected, six adults were relocated to Flinders Chase National Park on Kangaroo Island. Two years later an additional 12 adults were relocated. These were the first koalas to inhabit the island. Estimates now suggest there are more than 10,000 koalas on the island, contributing to major tree mortality through over-browsing and leading to the complete collapse of Kangaroo Island’s woodland ecosystems.

The most widely raised concern by ecologists over managed relocation is the potential for the translocated species to become a pest and disrupt ecosystem functions at the newly colonised site. Moving species between continents is considered the most risky, in terms of both relocation failure and the risk of the relocated species becoming invasive.

Experts agree that the most suitable scenario to undertake managed relocation will be when the risk of extinction of a target species is high but the risk to the existing ecosystem at the receiving site is low. Examples of such cases might include attitudinally restricted plants and frogs, which have a low capacity for dispersal but could be moved to higher altitudes close to their native range. What is clear from Australia’s translocation history is that there is both the potential to save species on the brink of extinction and the risk of creating new conservation problems.

Decisions about implementing managed relocation will rely on good predictions about the impact of climatic shifts on a species or ecosystem as well as the suitability of new areas in which to move. There is always a risk we might move a species that, if left, may have adapted to climate change.

Often climate change will be just one of several threats facing a species. Therefore, alleviating the threat of climate change by moving a species to a more suitable climate may not alleviate the other threats. Where we do have confidence that climate change is the key factor causing the decline in our population there is still the challenge of predicting optimal future habitats, particularly for rare species where detailed climate–habitat data and potentially important biotic interactions are often lacking.

Implications for Managers and Decision-Makers
There is general consensus that managed relocation should be considered as a last resort. Undertaking managed relocation will be costly. In many cases it may be more cost-effective to direct funds toward measures that help species adapt and survive in situ, such as improving habitat quality and ecosystem resilience, providing refuges from extreme climatic conditions and allowing for genetic translocation to boost evolutionary potential.

If managed relocation is to be implemented we first need ways to ensure that the species of concern are actually declining due to climate change. To achieve this we need adaptive monitoring programs that enable us to observe early signs of range contraction and identify what is causing this change. We will need robust protocols to help determine which species to move, when and where to move them, and to decide whether relocation of species outside their historic range is economically efficient, ecologically safe and socially acceptable. Successful managed relocation requires an experimental and timely approach – an adaptive management approach.

Assuming we have this capacity to shift species around provides some comfort, at least on a theoretical basis, but at the end of the day we need viable ecosystems into which we can move species. Managed relocation is not a quick fix: it will be used in some specific circumstances for species that we really care about, but it will not be a saviour for all biodiversity in the face of climate change.