Media Releases

Invading species can extinguish native plants despite recent reports

January 9, 2013

TORONTO, ON – Ecol­o­gists at the Uni­ver­si­ty of Toron­to and the Swiss Fed­er­al Insti­tute of Tech­nol­o­gy Zurich (ETH Zurich) have found that, giv­en time, invad­ing exot­ic plants will like­ly elim­i­nate native plants grow­ing in the wild despite recent reports to the con­trary.

A study pub­lished in Pro­ceed­ings of the Nation­al Acad­e­my of Sci­ences (PNAS) reports that recent state­ments that inva­sive plants are not prob­lem­at­ic are often based on incom­plete infor­ma­tion, with insuf­fi­cient time hav­ing passed to observe the full effect of inva­sions on native bio­di­ver­si­ty.

“The impacts of exot­ic plant inva­sions often take much longer to become evi­dent than pre­vi­ous­ly thought,” says Ben­jamin Gilbert of U of T’s Depart­ment of Ecol­o­gy & Evo­lu­tion­ary Biol­o­gy (EEB) and lead author of the study. “This delay can cre­ate an ‘extinc­tion debt’ in native plant species, mean­ing that these species are slow­ly going extinct but the actu­al extinc­tion event occurs hun­dreds of years after the ini­tial inva­sion.”

Much of the debate sur­round­ing the threat posed to bio­di­ver­si­ty by the inva­sions of non-native species is fueled by recent find­ings that com­pe­ti­tion from intro­duced plants has dri­ven remark­ably few plant species to extinc­tion. Instead, native plant species in invad­ed ecosys­tems are often rel­e­gat­ed to patchy, mar­gin­al habi­tats unsuit­able to their non-native com­peti­tors.

How­ev­er, Gilbert and co-author Jonathan Levine of ETH Zurich say that it is uncer­tain whether the col­o­niza­tion and extinc­tion dynam­ics of the plants in mar­gin­al habi­tats will allow long-term native per­sis­tence.

“Of par­tic­u­lar con­cern is the pos­si­bil­i­ty that short term per­sis­tence of native flo­ra in invad­ed habi­tats masks even­tu­al extinc­tion,” says Levine.

The researchers con­duct­ed their research in a Cal­i­for­nia reserve where much of the remain­ing native plant diver­si­ty exists in mar­gin­al areas sur­round­ed by inva­sive grass­es. They per­formed exper­i­ments in the reserve and cou­pled their results with quan­ti­ta­tive mod­els to deter­mine the long term impacts of inva­sive grass­es on native plants.

“Inva­sion has cre­at­ed iso­lat­ed ‘islands of native plants’ in a sea of exotics,” says Gilbert. “This has decreased the size of native habi­tats, which reduces seed pro­duc­tion and increas­es local extinc­tion. It also makes it much hard­er for native plants to recol­o­nize fol­low­ing a local extinc­tion.”

“Our research also allows us to iden­ti­fy how new habi­tats for native flo­ra could be cre­at­ed that would pre­vent extinc­tion from hap­pen­ing. These habi­tats would still be too mar­gin­al for invaders, but placed in such a way as to cre­ate ‘bridges’ to oth­er habi­tat patch­es,” says Gilbert.

The find­ings are report­ed in the paper “Plant inva­sions and extinc­tion debts” in PNAS’ Ear­ly Edi­tion this week. The research is sup­port­ed by fund­ing from the Nat­ur­al Sci­ences and Engi­neer­ing Research Coun­cil of Cana­da and the Packard Foun­da­tion.

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Note to media: Vis­it for images relat­ed to the research study described here.



Ben­jamin Gilbert
Depart­ment of Ecol­o­gy and Evo­lu­tion­ary Biol­o­gy
Uni­ver­si­ty of Toron­to
416–978-4065 (office)
647–778-0900 (cell)

Sean Bet­tam
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to