Assisted Migration as a Tool to Combat Climate Change

Linnea Johnson(Environmental Science), Paul Kieras (Natural Resources Conservation), Rebecca Tiernan (Natural Resources Conservation)

Every year, human encroachment threatens natural habitats and the communities of species who inhabit them (Fordham et al., 2012). However, habitats are even more threatened now due to the inevitable threat of climate change (Williams, Kutzbach, & Jackson, 2007). While it is not often on the forefront of our minds, species are losing habitat, their geographic ranges are shifting, and their ability to migrate to a better home is becoming less and less (Miller et al., 2012).

In Malaysia, models predict that within the next eighty years suitable habitat will suffer a loss of 63% due to climate change alone (Struebig et al., 2015, p. 2897-98). The orangutan (Pongo pygmaeus) is especially threatened because it cannot successfully disperse to areas of suitable habitat due to habitat fragmentation (Struebig et al., 2015). Struebig et al. (2015) concluded worsening climates would not only affect the amount of suitable habitat, but would increase the vulnerability of breeding female orangutans. They state because of large scale fragmentation, orangutans will not persist because of the inability to reach climate and habitat refuge.

The sad truth of the matter is, at the current rate of climate change, by the end of the 21st century, some of Earth’s current climates may no longer exist (Williams et al., 2007). In particular, coastal species and other species adapted to cold temperatures will be highly threatened (Miller at al., 2012). Warming will yield more intense storms, higher wave heights, and more surge events, all of which will drive coastal species to extinction through eliminating habitat and heightening the effects of predation, competition, and disease (Lopez, 2015).   Climates in high latitudes will likely disappear from the globe entirely, along with the communities they support (Williams et al., 2007). Some species have successfully compensated to climate change by shifting their ranges, however “the extent to which other species can adapt to changing climate[s]…[is] difficult to assess” (“Early warning signs”, n.d., para. 4).

But why should we care? What does the loss of species biodiversity really cost us? There is of course the loss of aesthetic value (“Cost the Earth Sources”, 2015). Even more importantly, there is also the trillions of dollars worth of ecosystem services provided to us thanks to biodiversity (“Cost the Earth Sources”, 2015). Trees alone supply us with nearly $16.2 trillion worth of services while freshwater values in at $73.48 trillion (“Cost the Earth Sources”, 2015, Freshwater-Trees). Burgess (2001) discusses biodiversity as a difficult concept for many to understand because we are unable to immediately perceive the consequences of extinctions. However, biodiversity is essential to maintain because every species plays a vital function in the ecosystem, and while some are more valuable than others, there is no way of knowing the impact the loss of one species could have (Burgess, 2001).

It will not be an easy task to save the Earth’s species, and no perfect solutions have yet been found. However, in the case of the orangutan and the case of many other species, one of their only hopes may be the use of assisted migrations (Struebig et al., 2015). Assisted migration is the “translocation of species to a favorable habitat…to protect them from human induced threats such as climate change” (Chauvenet et al., 2013a, p.162). In the near future, climate change will render many habitats unsuitable for plants and animals, thus assisted migrations will be an essential species-specific method of combatting the inevitable loss of biodiversity.

Increasing temperatures have caused many animals to relocate towards the poles or to higher elevations in search for hospitable climates (Ross-Flanigan, 2012). Species are moving away from the equator towards higher latitudes three times faster than researchers thought they would (Bryn, B. 2011). Areas that were once part of a species historic range are no longer suitable because of increased warming. The National Audubon Society released in 2009 that “more than half of the 305 most common North American songbirds are wintering farther north than they did in 1966” (Ross-Flanigan, 2012, Prospecting for Pattern). For example, the American Robin now winters an average of 200 miles farther north than it did in 1960 (Bryson, 2009). Species relocating themselves to more suitable habitats is a common theme for a variety of taxa. For example, the mountain ringlet butterfly moved 490 feet higher in altitude where it found climate refuge, but became extinct in the lower part of its range (Gray, L. 2011). As another example, the American pika (Ochotona princeps), are small mountain dwelling rodents who inhabit North American mountain ranges (Tolme, 2005). Pikas are seeking refuge at higher elevations due to their inability to tolerate increasingly warm temperatures (Tolme, 2005). However, the pika is closer and closer to reaching the peaks of its ranges and will soon run out of places to go, already having disappeared from 40% of the mountain ranges it inhabited just decades ago in the 1900s (Ross-Flanigan, 2012, para. 3).

In addition to increasing temperatures, human-caused habitat fragmentation will seriously impact the ability of species to migrate to suitable habitats. The Quino checkerspot butterfly must shift its range further north to seek refuge from increasing temperatures in southern California (Zimmer, 2009). However, the butterfly is unable to migrate due to its inability to pass through the human-dominated landscapes ranging from San Diego to Los Angeles to San Francisco (Zimmer, 2009). The blue-tongued pygmy lizard (Tiliqua adelaidensis), native to Australia, faces a similar debacle (Fordham et al., 2012). Climate change will render its preferred grassland habitats unsuitable, however the lizard’s risk of extinction is significantly higher due to human-caused habitat fragmentation (Fordham et al., 2012). Besides butterflies and lizards, our favorite mammals face serious risk as well. As we mentioned, the Malaysian orangutan will soon have to seek refuge from changing climate change (Struebig et al., 2015). However, Struebig et al. (2015) found that connectivity amongst habitat is lacking due to human-caused deforestation, and so the primates will have a very difficult, if not impossible, time migrating on their own.

Zimmer (2009) states “conventional strateg[ies] for moving species…may not work against global warming” (para. 13). As an example, Zimmer (2009) explains protecting the mountaintops for American pikas migrating to higher elevations will not matter if the entire mountain becomes too warm. Combined with fragmentation, assisted relocations will likely be necessary to preserve biodiversity that will inevitably be lost if animals are unable to disperse amongst habitat patches (Hogan, 2015). However, managed relocations have thus far been purely an “abstract” idea with no solidified data on the success of the practice (Zimmer, 2009). What we do have access to is modeling, which will be an essential tool in assessing a species’ short and long term risk of habitat loss due to climate change (Chauvenet, Ewen, Armstrong, Blackburn, and Pettorelli, 2013a). Chauvenet, Ewen, Armstrong, and Pettorelli (2013b) and Fordham et al. (2012) both performed model studies on the New Zealand hihi bird and Australian blue-tongued pygmy lizard respectively, finding in both cases that long-term climate projections will make current habitats unsuitable. However, we can only rely on theoretical modeling for so long before finally taking the plunge to relocate species to suitable habitat. Thus, we propose assisted migrations be carried out based on an evaluative criteria we have collected through reviewing literature on invasive species, climate change, reintroductions, and population dynamics. Our criteria suggests species will be suitable for assisted migration if they fit the following guidelines: (1) the suggested relocation is to an intracontinental location, (2) the species is not a fish or a crustacean, (3) the suggested relocation is located in an area in the species’ historic range, and (4) the global population is large enough so that in the case of a failed relocation, the entire species will not become extinct.

We determined these guidelines through reviewing an extent of literature. For our first criteria, we turned to Mueller and Hellmann (2008) who analyzed the effects of 468 invasive species in North America. They determined species introduced intercontinentally through assisted migrations would likely be less harmful to the environment than a species relocated intercontinentally. The percentage of intracontinental species that became invasive in North America was found to be just 14.7% (Mueller and Hellmann, 2008, p.564). Mueller and Hellmann (2008) also helped us to establish our second criteria through their finding that the taxonomic groups of fish and crustaceans were significantly more likely (p<0.001) to become invasive even when relocated intercontinentally (p.565). Crustaceans and fish consisted of more than 30% of invasive species in the study, thus leading us to conclude both of those taxon should be avoided (Mueller and Hellmann, 2008, p. 565). We established our third criteria by reviewing Fordham et al. (2012) who state organisms that have undergone recent constrictions of their geographical range would be more likely to successfully colonize areas within their historical range. They suggest the movement of the blue-tongued pygmy lizard, a species whose range has been so severely constricted it was thought to have been extinct until being rediscovered twenty years ago. Fordham et al. (2012) believe the lizard’s long-term persistence will be improved if translocated to areas of its historical range. And finally, for our fourth and final criteria, we turned to Griffith, Scott, Carpenter, and Reed (1989) who evaluated the success of translocating species for reestablishment. Griffith et al. (1989) claim large numbers of animals released at once were unlikely to be successful, thus considerations for species to be translocated must occur before a population’s number is so small there would be no stable, remaining source in case of an unsuccessful attempt.

Some members of the scientific community are concerned that assisted migration will not be a viable option because of the potential risk of translocated species becoming invasive. Mueller & Hellman (2008) state it is extremely difficult to predict the probability of a species becoming invasive, and if they do become invasive, there could be potentially disastrous ecological effects (p. 563). For example, when the watercress darter was translocated to a nonnative stream, it displaced native fish and caused devastating ecological impacts on the ecosystem (Olden et al., 2009). Though introduced non-native species can have detrimental effects on native ecosystems, this is not often the case. Ecologist Dan Simberloff states, “… of the 7,000 estimated non-native species in North America, approximately only 1,000 are considered invasive” (Arnold, 2011). Among the 6,000 noninvasive species, honeybees arrived at least eight separate times in the past four centuries from Europe, Africa and the Middle East and did not have any disastrous effects on North American ecosystems (Zimmer, 2011). Conservation biologist Dov Sax predicts “[that] the proportion of non-native species that are viewed as benign or even desirable will slowly increase overtime” (Zimmer, 2011, para. 6). Introduced species can benefit native ecosystems by preventing native species from overexploitation of resources. For example, scientists introduced Carcinus maenas, a predatory crab native to the North Atlantic, in Cape Cod, Massachusetts in attempt to prevent the native Seasarma reticulatum crab from depleting the marsh grasses. Researchers found that the marshes are regrowing and that the presence of the introduced crab was enough to deter the native crab from overexploiting marsh grass (Orenstein, 2013).

Since there is a risk of a translocated species becoming invasive, opponents of assisted migration suggest that species should be left in their original range to adapt to environmental conditions on their own. Many scientists argue that moving species may be counterproductive because they may adapt to their new environment quickly enough to persist without assistance (Grasberg, 2012). Grasberg (2012) recognizes that some scientists think species would be better off adapting to climate change in their current home range. Unfortunately, evolution is far too slow to keep up with climate change. An ecologist from the University of Arizona led a study that found species would have to evolve 10,000 times faster than they have in the past to adapt novel habitats due to climate change in the next 100 years (Stolte, 2008). Since wildlife species do not evolve fast enough to adapt to dramatically warmer climate conditions, it is essential that we use assisted migration to move qualifying species to more favorable conditions (Stolte, 2008).

Global climate change will contribute to the extinction of many beloved wildlife species. Do we go forward and actively conserve species through assisted migration? Or is the alternative to sit back and do nothing? Though it is risky, assisted migration is currently our best bet to save species whose ranges are being constrained. If scientists follow our evaluative criteria, assisted migration will be very useful tool to use for ensuring certain species are able to combat climate change.


Arnold, C. (2011, August 31). Are all invasive species bad? Retrieved from:

Burgess, B.B. (2011). Fate of the wild University of Georgia Press. Retrieved from

Bryson, G. (2009). Warming brings more birds north in winter. Retrieved November 16, 2015, from:

Bryn, B. (2011). Science: species ranges are shifting faster than expected in warmer temperature. Retrieved November 23, 2015, from :

Chauvenet, A. L. M., Ewen, J. G., Armstrong, D. P., Blackburn, T. M., & Pettorelli, N. (2013a). Maximizing the success of assisted colonizations. Animal Conservation 16(2), 161-169. doi:10.1111/j.1469-1795.2012.00589.x

Chauvenet, A., Ewen, J., Armstrong, D., & Pettorelli, N. (2013b). Saving the hihi under climate change: a case for assisted colonization. Journal of Applied Ecology 50, 1330-1340. doi: 10.1111/1365-2664.12150

Cost the Earth sources. (2015, October 8). BBC. Retrieved November 9, 2015, from

Early Warning Signs of Global Warming: Plant and Animal Range Shifts. (n.d.). Union of Concerned Scientists. Retrieved November 10, 2015. Retrieved November 9, 2015, from

Fordham, D. A., Watts, M. J., Delean, S., Brook, B. W., Heard, L. M. B., & Bull, C. M. (2012). Managed relocation as an adaptation strategy for mitigating climate change threats to the persistence of an endangered lizard. Global Change Biology 18(9), 2743-2755. doi:10.1111/j.1365-2486.2012.02742.x

Grasberg, M. (2012). Assisted migration and urban ecosystems. Baruch College. Retrieved from:

Gray, L. (2011). Climate change pushing animals further north. Retrieved on November 23, 2015 from:

Griffith, B., Scott, M., Carpenter, J.W., & Reed, C. (1989). Translocation as a species conservation tool: Status and strategy. Science 245, 477-480. Retrieved from

Hogan, C. (2015, July 4). Habitat fragmentation. The Encyclopedia of Earth. Retrieved from

Lopez, J. (2015). Biodiversity on the brink: The role of “assisted migration” in managing endangered species threatened with rising seas. Harvard Environmental Law Review, 39 (1), 157-190.

Miller, K., Miller, H., Moore, J., Mitchell, N., Cree, A., Allendorf, F., Sarre, S,…., & Nelson, N. (2012). Securing the demographic and genetic future of the tuatara through assisted colonization. Conservation Biology 26(5), 790-798. doi: 10.1111/j.1523-1739.2012.01902.x

Mueller, J. & Hellmann, J. (2008). An assessment of invasion risk from assisted migration. Conservation Biology 22(3), 562-567. doi: 10.1111/j.1523-1739.2008.00952.

Olden, J. D., Kennard, M. J., Lawler, J. J., & Poff, N. L. (2011). Challenges and opportunities in implementing managed relocation for conservation of freshwater species. Conservation Biology, 25(1), 40-47. doi:10.1111/j.1469-1795.2012.00589.x

Orenstein, D. (2013, April 3) Invasive crabs help cape cod marshes. Retrieved from:

Ross-Flanigan, Nancy. (2012, June 30). Animals on the move: a warming climate means shifting ranges and mixed-up relationships for a lot of species. Science News, 181(13), 16+. Retrieved from

Stolte, D. (2013). Evolution too slow to keep up with climate change. University of Arizona. Retrieved from:

Struebig, M. J., Fischer, M., Gaveau, D. L. A., Meijaard, E., Wich, S. A., Gonner, C., Sykes, R.,…&Kramer-Schadt, S. (2015). Anticipated climate and land-cover changes reveal refuge areas for borneo’s orang-utans. Global Change Biology, 21(8), 2891-2904. doi: 10.1111/gcb.12814

Tolme, P. (2005, December 1) Global Warming and the American Pika. Retrieved from:

Williams, J. W., Kutzbach, J. E., & Jackson, S. T. (2007). Projected distributions of novel and disappearing climates by 2100 AD. Proceedings of the National Academy of Sciences of the United States of America, 104(14), 5738-5742.

Zimmer, C. (2009, April 20). As climate warms, species may need to migrate or perish. Yale Environment 360. Retrieved from

Zimmer, C. (2011, February 24). Alien species reconsidered: finding a value in non-natives. Yale Environment 360. Retrieved from:



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