The conifer tree Torreya taxifolia once grew in abundance in ravines along the Apalachicola River on the Florida panhandle (Godfrey 1988). After decades of decline, the species is now considered critically endangered according to the IUCN (Schwartz et al. 1995). In a last-ditch effort to save the species from extinction, a group known as the Torreya Guardians translocated saplings far northward to an area in North Carolina where it had never previously existed (Gray et al. 2016). Though some argue that this may have been the critical step in preserving the Florida Torreya, the actions of the Torreya Guardians raise the question of whether or not human assisted introductions of species for conservation purposes are necessary and well justified despite potential risks of collateral damage. More broadly, the intentional movement of organisms from current areas of occupancy to locations where the probability of future persistence is predicted to be higher, known as assisted migration (Richardson et al. 2009), has come under fierce debate.

A Torreya taxifolia sapling, post-migration. Photo: courtesy of Torreya Guardians.

Assisted migration (also known as assisted colonization or managed relocation) is a relatively new concept, born of the perceived need to prevent the extinction of species that are unable to move or adapt fast enough in response to climate change. In a case study, a team of researchers transplanted the marbled white butterfly, Melanargia galathea (pictured above), to an area north of its native range in England. The butterfly was able to successfully establish a reproducing population without having a negative impact on the native biological community. The researchers cite similarities between the inhabitants of the recipient ecosystem and the inhabitants of the butterfly’s native range as the reason for successful integration (Willis et al. 2009). In this example, the butterfly was preserved and did not appear to harm the recipient community.

Many in the scientific community, however, argue that there is considerable uncertainty and risk involved in transplanting a novel species to an unfamiliar and new location. It can be challenging to predict how an introduced species will interact with a new community, or what unforeseeable parasites and pathogens it may carry. For example, the watercress darter is an endangered fish species that was translocated to a spring outside of its native range, where it successfully established a reproducing population. Unfortunately, unexpected and devastating competition by the watercress darter led to the extinction of the native rush darter just a few years later (Olden et al. 2011). Ricciardi and Simberloff (2008) argue that there is no possible way to anticipate all potential outcomes of a species introduction, as was the case with the watercress darter. Further, lagged responses are also possible, where an introduced species does not cause damage until several decades later, when it is too late to reconsider translocation.

Thus, an impasse is born. Human actions have been responsible for the loss and destruction of many habitats and their inhabitants. Therefore, is it not the responsibility of humans to preserve all species even though it may cause unforeseen damage to other ecosystems? For all intents and purposes, the scientific community is still unclear on whether to support or abandon the concept of assisted migration. It is a novel conservation strategy, for which there are few documented examples of success, but many examples of the dangers of species introduction (Ricciardi and Simberloff 2008). There are other – perhaps safer – options to reducing a species’ risk of extinction, including increasing habitat connectivity to allow species to gradually migrate themselves instead of transplanting them far outside of their native range (Lawler and Olden 2011). Considering assisted migration parallels the notion of putting a critically endangered animal in the zoo. Humans take action to prevent extinction by moving an animal into captivity just as they would move an animal into a new habitat, in an attempt to be forward-thinking. Considering the risk and uncertainty involved in managed relocation, this may be the time for us to think much further into the future and reduce habitat loss and extinction rates before either assisted migration or zoos are necessary.

Molly Payne, Undergraduate/FEC Lab

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