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Research sheds new light on wolves’ impact on ecosys­tems in Yellowstone

pub­lished 12 Feb­ru­ary 2013 | mod­i­fied 12 Feb­ru­ary 2013

YellowstoneNew research by Col­orado State Uni­ver­sity (CSU) finds that the removal of wolves from Yel­low­stone National Park caused com­plex changes in eco­log­i­cal processes that can­not be sim­ply reversed by wolf rein­tro­duc­tion alone. The research find­ings are pre­sented in a new paper, “Stream hydrol­ogy lim­its recov­ery of ripar­ian ecosys­tems after wolf rein­tro­duc­tion,” which is pub­lished online Feb­ru­ary 6 in Pro­ceed­ings of the Royal Soci­ety B: Bio­log­i­cal Sci­ences and con­cludes that the effects of apex preda­tor removal are unpre­dictable and are not sym­met­ri­cal with the effects of preda­tor rein­tro­duc­tion.

The rein­tro­duc­tion of the wolf in Yel­low­stone has con­tributed to pos­i­tive improve­ments in the Park’s ecosys­tems, but it isn’t a sim­ple on and off light-​switch effect
Kristin Mar­shall, lead author, recent Col­orado State Uni­ver­sity alumna »

“Our research shows that the com­plex­ity of the eco­log­i­cal dam­age caused by the erad­i­ca­tion of a key preda­tor species requires care­ful con­sid­er­a­tion of dynamic vari­ables for restora­tion, and so addi­tional cau­tion must be empha­sised to avoid preda­tor removal in the first place.”

Obser­va­tional stud­ies by other researchers have sug­gested that the rein­tro­duc­tion of wolves to Yel­low­stone ini­ti­ated dra­matic restora­tion of ripar­ian ecosys­tems. How­ever, Marshall’s research shows that changes in the hydrol­ogy of streams caused by the loss of beaver from the ecosys­tem pre­vents rapid restora­tion of wil­lows even when they are totally pro­tected from brows­ing by elk. The plants required both remov­ing brows­ing and restor­ing the beaver-​modified stream con­di­tions that occurred prior to wolf removal in order to thrive.

Mar­shall con­ducted her research while she was a doc­toral stu­dent at CSU’s Warner Col­lege of Nat­ural Resources in the Grad­u­ate Degree Pro­gram in Ecol­ogy. Her research was part of a larger, 10-​year exper­i­ment con­ducted by a team of researchers from CSU’s Warner Col­lege of Nat­ural Resources that exam­ined the effects of beaver dams and removal of brows­ing on restora­tion of wil­lows in Yel­low­stone. The paper is co-​authored by Marshall’s research co-​advisors at CSU: David Cooper, senior research sci­en­tist in the Depart­ment of Forestry and Range­land Stew­ard­ship, and Thomp­son Hobbs, senior research sci­en­tist with the Nat­ural Resource Ecol­ogy Lab and pro­fes­sor in the Depart­ment of Ecosys­tem Sci­ence and Sus­tain­abil­ity.

Hobbs and Cooper have worked together on the research project for the past decade and empha­sise the impor­tance of beavers to the process. “The loss of wolves caused the loss of beaver and wil­lows from small streams,” said Hobbs. “Our exper­i­ment shows that you can’t get beavers back with­out wil­lows and you can’t get wil­lows back with­out beavers.”

The study was funded by the National Sci­ence Foun­da­tion and will pro­vide new insights to help solve the ongo­ing debate on the role of wolf-​driven trophic cas­cades in the greater Yel­low­stone ecosys­tem.

The research illus­trates the value of long-​term eco­log­i­cal exper­i­ments to under­stand­ing how species inter­ac­tions cas­cade through food webs to deter­mine ecosys­tem resilience,” says Alan Tessier, pro­gram direc­tor in the National Sci­ence Foundation’s Divi­sion of Envi­ron­men­tal Biol­ogy, which funded the research. “The results have imme­di­ate prac­ti­cal appli­ca­tions in restor­ing and pro­tect­ing ecosys­tems such as that of Yel­low­stone.”

(Source: Col­orado State Uni­ver­sity press release, 06.02.2013)

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