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    Euro­pean wild­cat (Felis sil­vestris)
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    Jaguar (Pan­thera onca)
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Loss of preda­tors affect­ing ecosys­tem health

pub­lished 10 April 2012 | mod­i­fied 05 Decem­ber 2012

The research by sci­en­tists from Ore­gon State Uni­ver­sity was pub­lished online 4 April 2012 in the Euro­pean Jour­nal of Wildlife Research, and exam­ined 42 stud­ies done over the past 50 years.

It found that the loss of major preda­tors in for­est ecosys­tems has allowed game ani­mal pop­u­la­tions to greatly increase, crip­pling the growth of young trees and reduc­ing bio­di­ver­sity. This also con­tributes to defor­esta­tion and results in less car­bon seques­tra­tion, a poten­tial con­cern with cli­mate change.

These issues do not just affect the United States and a few national parks. The data from Canada, Alaska, the Yukon, North­ern Europe and Asia are all show­ing sim­i­lar results. There’s con­sis­tent evi­dence that large preda­tors help keep pop­u­la­tions of large her­bi­vores in check, with pos­i­tive effects on ecosys­tem health.

(William Rip­ple, an OSU pro­fes­sor of forestry and lead author of the study)

Den­si­ties of large mam­malian her­bi­vores were six times greater in areas with­out wolves, com­pared to those in which wolves were present, the researchers con­cluded. They also found that com­bi­na­tions of preda­tors, such as wolves and bears, can cre­ate an impor­tant syn­ergy for mod­er­at­ing the size of large her­bi­vore populations.

Wolves can pro­vide food that bears scav­enge, help­ing to main­tain a healthy bear pop­u­la­tion,” said Robert Beschta, co-​author of the study. “The bears then often prey on young moose, deer or elk — in Yel­low­stone more young elk calves are killed by bears than by wolves, coy­otes and cougars combined.”

black beargrey wolf moose

In Europe, the coex­is­tence of wolves with lynx also resulted in lower deer den­si­ties than when wolves existed alone.

In recent years, OSU researchers have helped lead efforts to under­stand how major preda­tors help to reduce her­bi­vore pop­u­la­tion lev­els, improve ecosys­tem func­tion and even change how her­bi­vores behave when they feel threat­ened by pre­da­tion — an impor­tant aspect they call the “ecol­ogy of fear.”

In sys­tems where large preda­tors remain, they appear to have a major role in sus­tain­ing the diver­sity and pro­duc­tiv­ity of native plant com­mu­ni­ties, thus main­tain­ing healthy ecosys­tems,” said Beschta.

When the role of major preda­tors is more fully appre­ci­ated, it may allow man­agers to recon­sider some of their assump­tions about the man­age­ment of wildlife.

In Idaho and Mon­tana, hun­dreds of wolves are now being killed in an attempt to reduce ranch­ing con­flicts and increase game herd levels.

The new analy­sis makes clear that the poten­tial ben­e­fi­cial ecosys­tem effects of large preda­tors is far more per­va­sive, over much larger areas, than has often been appre­ci­ated. It points out how large preda­tors can help main­tain native plant com­mu­ni­ties by keep­ing large her­bi­vore den­si­ties in check, allow small trees to sur­vive and grow, reduce stream bank ero­sion, and con­tribute to the health of forests, streams, fish­eries and other wildlife.

It also con­cludes that human hunt­ing, due to its lim­ited dura­tion and impact, is not effec­tive in pre­vent­ing hyper-​abundant den­si­ties of large her­bi­vores. This is partly “because hunt­ing by humans is often not func­tion­ally equiv­a­lent to pre­da­tion by large, wide-​ranging car­ni­vores such as wolves,” the researchers wrote in their report.

More stud­ies are nec­es­sary to under­stand how many wolves are needed in man­aged ecosys­tems,” Rip­ple said. “It is likely that wolves need to be main­tained at suf­fi­cient den­si­ties before we see their result­ing effects on ecosystems.”

The preser­va­tion or recov­ery of large preda­tors may rep­re­sent an impor­tant con­ser­va­tion need for help­ing to main­tain the resiliency of north­ern for­est ecosys­tems, espe­cially in the face of a rapidly chang­ing climate.

The above news item is reprinted from mate­ri­als avail­able at Ore­gon State Uni­ver­sity via Sci­enceDaily. Orig­i­nal text may be edited for con­tent and length.

(Source: Ore­gon State Uni­ver­sity, 09.04.2012)

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