Animals and Plants Are Relocating Because of Climate Change. Should They Be Considered Invasive?

Jenny Morber August 8, 2020

American pika may move to even higher elevations in the mountains in response to human-caused climate change.

Edi­tor’s Note: This arti­cle was orig­i­nal­ly pub­lished by Ensia and is repub­lished here under a Cre­ative Com­mons license.

Caribbean corals sprout off Texas. Pacif­ic salmon tour the Cana­di­an Arc­tic. Peru­vian low­land birds nest at high­er elevations.

In the past 100 years, the plan­et has warmed in the range of 10 times faster than it did on aver­age over the past 5,000. In response, thou­sands of species are trav­el­ing pole­ward, climb­ing to high­er ele­va­tions, and div­ing deep­er into the seas, seek­ing their pre­ferred envi­ron­men­tal con­di­tions. This great migra­tion is chal­leng­ing tra­di­tion­al ideas about native species, the role of con­ser­va­tion biol­o­gy and what kind of envi­ron­ment is desir­able for the future.

In a 2017 review for Sci­ence, Uni­ver­si­ty of Tas­ma­nia marine ecol­o­gy pro­fes­sor Gret­ta Pecl and col­leagues wrote, “[C]limate change is impelling a uni­ver­sal redis­tri­b­u­tion of life on Earth. For marine, fresh­wa­ter, and ter­res­tri­al species alike, the first response to chang­ing cli­mate is often a shift in loca­tion.” In fact, Pecl says, data sug­gest that at least 25% and per­haps as much as 85% of Earth’s esti­mat­ed 8.7 mil­lion species are already shift­ing ranges in response to cli­mate change.

But when they arrive, will they be wel­come? Tra­di­tion­al def­i­n­i­tions clas­si­fy species accord­ing to place. Native” species arrived with­out human help and usu­al­ly before wide­spread human col­o­niza­tion, so are like­ly to have nat­ur­al preda­tors and are unlike­ly to go rogue. Non-natives are new­com­ers and sus­pect. Though 90% cause no last­ing dam­age, 10% become inva­sive — mean­ing that they harm the envi­ron­ment, the econ­o­my or human health. Last year a multi­na­tion­al report flagged inva­sive species as a key dri­ver of Earth’s bio­di­ver­si­ty crisis.

How we define species is crit­i­cal, because these def­i­n­i­tions influ­ence per­cep­tions, pol­i­cy and man­age­ment. The U.S. Nation­al Inva­sive Species Coun­cil (NISC) defines a bio­log­i­cal inva­sion as the process by which non-native species breach bio­geo­graph­i­cal bar­ri­ers and extend their range” and states that pre­vent­ing the intro­duc­tion of poten­tial­ly harm­ful organ­isms is … the first line of defense.” But some say exclud­ing new­com­ers is myopic.

If you were try­ing to main­tain the sta­tus quo, so every time a new species comes in, you chuck it out,” says Camille Parme­san, direc­tor of the French Nation­al Cen­tre for Sci­en­tif­ic Research, you could grad­u­al­ly lose so many that that ecosys­tem will lose its coher­ence.” If cli­mate change is dri­ving native species extinct, she says, you need to allow new ones com­ing in to take over those same functions.”

As Uni­ver­si­ty of Flori­da con­ser­va­tion ecol­o­gist Brett Schef­fers and Pecl warned in a 2019 paper in Nature Cli­mate Change, past man­age­ment of redis­trib­uted species … has yield­ed mixed actions and results.” They con­clud­ed that we can­not leave the fate of bio­di­ver­si­ty crit­i­cal to human sur­vival to be ran­dom­ly per­se­cut­ed, pro­tect­ed or ignored.”

Exist­ing Tools

One approach to man­ag­ing these cli­mate-dri­ven habi­tat shifts, sug­gest­ed by Uni­ver­si­ty of Cal­i­for­nia, Irvine marine ecol­o­gist Piper Walling­ford and col­leagues in a recent issue of Nature Cli­mate Change, is for sci­en­tists to adapt exist­ing tools like the Envi­ron­men­tal Impact Clas­si­fi­ca­tion of Alien Taxa (EICAT) to assess poten­tial risks asso­ci­at­ed with mov­ing species. Because range-shift­ing species pose impacts to com­mu­ni­ties sim­i­lar to those of species intro­duced by humans, the authors argue, new man­age­ment strate­gies are unnec­es­sary, and each new arrival can be eval­u­at­ed on a case-by-case basis.

Karen Lips, a pro­fes­sor of biol­o­gy at Uni­ver­si­ty of Mary­land who was not asso­ci­at­ed with the study, echoes the idea that each case is so var­ied and nuanced that try­ing to fit cli­mate shift­ing species into a sin­gle cat­e­go­ry with broad man­age­ment goals may be imprac­ti­cal. Things may be fine today, but add a new mos­qui­to vec­tor or add a new tick or a new dis­ease, and all of a sud­den things spi­ral out of con­trol,” she says. The nuance means that the answer to any par­tic­u­lar prob­lem might be pret­ty different.”

Lau­ra Mey­er­son, a pro­fes­sor in the Depart­ment of Nat­ur­al Resources Sci­ence at the Uni­ver­si­ty of Rhode Island says sci­en­tists should use exist­ing tools to iden­ti­fy and address inva­sive species to deal with cli­mate-shift­ing species. I would like to oper­ate under the pre­cau­tion­ary prin­ci­ple and then reeval­u­ate as things shift. You’re sort of shift­ing one piece in this machin­ery; as you insert a new species into a sys­tem, every­thing is going to respond,” she says. Will some of the species that are expand­ing their ranges because of cli­mate change become prob­lem­at­ic? Per­haps they might.”

The real­i­ty is that some cli­mate-shift­ing species may be harm­ful to some con­ser­va­tion or eco­nom­ic goals while being help­ful to oth­ers. While sport fish­er­man are excit­ed about red snap­per mov­ing down the East Coast of Aus­tralia, for exam­ple, if they eat juve­nile lob­sters in Tas­ma­nia they could harm this envi­ron­men­tal­ly and eco­nom­i­cal­ly impor­tant crus­tacean. At the end of the day … you’re going to have to look at whether that range expan­sion has some sort of impact and pre­sum­ably be more con­cerned about the neg­a­tive impacts,” says NISC exec­u­tive direc­tor Stas Burgiel. Many of the [risk assess­ment] tools we have are set up to look at neg­a­tive impact.” As a result, pos­i­tive effects may be deem­pha­sized or over­looked. So that notion of cost ver­sus ben­e­fit … I don’t think it has played out in this par­tic­u­lar context.”

Loca­tion, Loca­tion, Location

In a com­pan­ion paper to Wallingford’s, Uni­ver­si­ty of Con­necti­cut ecol­o­gy and evo­lu­tion­ary biol­o­gy asso­ciate pro­fes­sor Mark Urban stressed key dif­fer­ences between inva­sive species, which are both non-native and harm­ful, and what he calls cli­mate track­ing species.” Where­as inva­sive species orig­i­nate from places very unlike the com­mu­ni­ties they over­take, he says, cli­mate track­ing species expand from large­ly sim­i­lar envi­ron­ments, seek­ing to fol­low pre­ferred con­di­tions as these envi­ron­ments move. For exam­ple, an Amer­i­can pika may relo­cate to a high­er moun­tain ele­va­tion, or a mar­bled sala­man­der might expand its New Eng­land range north­ward to seek cool­er tem­per­a­tures, but these new loca­tions are not dras­ti­cal­ly dif­fer­ent than the places they had called home before.

Cli­mate track­ing species may move faster than their com­peti­tors at first, Urban says, but com­pet­ing species will like­ly catch up. Apply­ing per­spec­tives from inva­sion biol­o­gy to cli­mate-track­ing species … arbi­trar­i­ly choos­es local win­ners over col­o­niz­ing losers,” he writes.

Urban stress­es that if peo­ple pre­vent range shifts, some cli­mate-track­ing species may have nowhere to go. He sug­gests that humans should even facil­i­tate move­ment as the plan­et warms. The goal in this crazy warm­ing world is to keep every­thing alive. But it may not be in the same place,” Urban says.

Parme­san echoes Urban, empha­siz­ing it’s the dis­tance that makes the dif­fer­ence. “[Inva­sives] come from a dif­fer­ent con­ti­nent or a dif­fer­ent ocean. You’re hav­ing these enor­mous trans-glob­al move­ments and that’s what ends up caus­ing the species that’s exot­ic to be inva­sive,” she says. Things mov­ing around with cli­mate change is a few hun­dred miles. Inva­sive species are mov­ing a few thou­sand miles.”

In 2019 Uni­ver­si­ty of Vien­na con­ser­va­tion biol­o­gy asso­ciate pro­fes­sor Franz Essl pub­lished a sim­i­lar argu­ment for species clas­si­fi­ca­tion beyond the native/non-native dichoto­my. Essl uses neona­tives” to refer to species that have expand­ed out­side their native areas and estab­lished pop­u­la­tions because of cli­mate change but not direct human agency. He argues that these species should be con­sid­ered as native in their new range.

They Nev­er Come Alone

Mey­er­son calls for cau­tion. I don’t think we should be intro­duc­ing species” into ecosys­tems, she says. I mean, they nev­er come alone. They bring all their friends, their microflo­ra, and maybe par­a­sites and things cling­ing to their roots or their leaves. … It’s like bring­ing some mat­tress off the street into your house.”

Burgiel warns that label­ing can have unin­tend­ed con­se­quences. We in the inva­sive species field … focus on non-native species that cause harm,” he says. Some peo­ple think that any­thing that’s not native is inva­sive, which isn’t nec­es­sar­i­ly the case.” Because resources are lim­it­ed and land man­age­ment and con­ser­va­tion are pub­licly fund­ed, Burgiel says, it is crit­i­cal that the pub­lic under­stands how the deci­sions are being made.

Piero Gen­ovesi, chair of the Inter­na­tion­al Union for the Con­ser­va­tion of Nature’s Inva­sive Species Spe­cial­ist Group, sees the debate about clas­si­fi­ca­tion — and there­fore about man­age­ment — as a poten­tial dis­trac­tion from more press­ing con­ser­va­tion issues.

The real bulk of con­ser­va­tion is that we want to focus on the nar­row pro­por­tion of alien species that are real­ly harm­ful,” he says. In Hawaii we don’t dis­cuss species that are there [but aren’t] caus­ing any prob­lem because we don’t even have the ener­gy for deal­ing with them all. And I can tell you, no one wants to remove [non-native] cypress­es from Tus­cany. So, I think that some of the dis­cus­sions are prob­a­bly not so real in the work that we do in conservation.”

Indige­nous frame­works offer anoth­er way to look at species search­ing for a new home in the face of cli­mate change. Accord­ing to a study pub­lished in Sus­tain­abil­i­ty Sci­ence in 2018 by Dart­mouth Native Amer­i­can stud­ies and envi­ron­men­tal stud­ies asso­ciate pro­fes­sor Nicholas Reo, a cit­i­zen of the Sault Ste. Marie Tribe of Chippe­wa Indi­ans, and Dart­mouth anthro­pol­o­gy asso­ciate pro­fes­sor Lau­ra Ogden, some Anish­naabe peo­ple view plants as per­sons and the arrival of new plants as a nat­ur­al form of migra­tion, which is not inher­ent­ly good or bad. They may seek to dis­cov­er the pur­pose of new species, at times with ani­mals as their teach­ers. In their paper Reo and Ogden quote Anish­naabe trib­al chair­man Aaron Pay­ment as say­ing, We are an exten­sion of our nat­ur­al envi­ron­ment; we’re not sep­a­rate from it.”

The Need for Collaboration

The suc­cess­ful con­ser­va­tion of Earth’s species in a way that keeps bio­di­ver­si­ty func­tion­al and healthy will like­ly depend on col­lab­o­ra­tion. With­out glob­al agree­ments, one can envi­sion sce­nar­ios in which coun­tries try to impede high-val­ue species from mov­ing beyond their bor­ders, or new­ly arriv­ing species are quick­ly overharvested.

In Nature Cli­mate Change, Shef­fers and Pecl call for a Cli­mate Change Redis­tri­b­u­tion Treaty that would rec­og­nize species redis­tri­b­u­tion beyond polit­i­cal bound­aries and estab­lish gov­er­nance to deal with it. Treaties already in place, such as the Con­ven­tion on Inter­na­tion­al Trade in Endan­gered Species of Wild Fau­na and Flo­ra, which reg­u­lates trade in wild plants and ani­mals; the Migra­to­ry Bird Treaty Act; and the Agreed Mea­sures for the Con­ser­va­tion of Antarc­tic Fau­na and Flo­ra, can help guide these new agreements.

We are liv­ing through the great­est redis­tri­b­u­tion of life on Earth for … poten­tial­ly hun­dreds of thou­sands of years, so we def­i­nite­ly need to think about how we want to man­age that,” Pecl says.

At the heart of these ques­tions are val­ues. Gen­ovesi agrees that con­ser­va­tion­ists need a vision for the future. What we do is more to be reac­tive [to known threats]. … It’s so sim­ple to say that destroy­ing the Ama­zon is prob­a­bly not a good idea that you don’t need to think of a step ahead of that.” But, he adds, I don’t think we have a real answer in terms of okay, this is a thresh­old of species, or this is the tem­po­ral line where we should aim to.” Defin­ing a vision for what suc­cess would look like, Gen­ovesi says, is a ques­tion that hasn’t been addressed enough by sci­ence and by deci­sion makers.”

At the heart of these ques­tions are val­ues. All of these per­cep­tions around what’s good and what’s bad, all [are based on] some kind of val­ue sys­tem,” Pecl says. As a whole soci­ety, we haven’t talked about what we val­ue and who gets to say what’s of val­ue and what isn’t.”

This is espe­cial­ly impor­tant when it comes to mar­gin­al­ized voic­es, and Pecl says she is con­cerned because she doesn’t think we have enough con­sid­er­a­tion or rep­re­sen­ta­tion of Indige­nous world­views.” Reo and col­leagues wrote in Amer­i­can Indi­an Quar­ter­ly in 2017 that cli­mate change lit­er­a­ture and media cov­er­age tend to por­tray native peo­ple as vul­ner­a­ble and with­out agency. Yet, says Pecl, The regions of the world where [bio­di­ver­si­ty and ecosys­tems] are either not declin­ing or are declin­ing at a much slow­er rate are Indige­nous con­trolled” — sug­gest­ing that Indige­nous peo­ple have poten­tial­ly man­aged species more effec­tive­ly in the past, and may be able to man­age chang­ing species dis­tri­b­u­tions in a way that could be infor­ma­tive to oth­ers work­ing on these issues.

Mean­while, researchers such as Lips see species clas­si­fi­ca­tion as native or oth­er as stem­ming from a per­spec­tive that there is a bet­ter envi­ron­men­tal time and place to return to. There is no pris­tine, there’s no way to go back,” says Lips. The entire world is always very dynam­ic and chang­ing. And I think it’s a bet­ter idea to con­sid­er just sim­ply what is it that we do want, and let’s work on that.”

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