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Top con­sumers’ extinc­tion increase extinc­tion risks through­out the food web

pub­lished 24 June 2012 | mod­i­fied 05 Decem­ber 2012

Global warm­ing may cause more extinc­tions than pre­dicted if sci­en­tists fail to account for inter­ac­tions among species in their mod­els, Yale and Uni­ver­sity of Con­necti­cut researchers argue in Sci­ence.

Cur­rently, most mod­els pre­dict­ing the effects of cli­mate change treat species sep­a­rately and focus only on cli­matic and envi­ron­men­tal dri­vers, but we know that species don’t exist in a vac­uum. They inter­act with each other in ways that deeply affect their viability
pri­mary author, Phoebe Zar­netske, Yale School of Forestry & Envi­ron­men­tal Studies »

Zar­netske said the com­plex­ity of “species inter­ac­tion net­works” dis­cour­ages their inclu­sion in mod­els pre­dict­ing the effects of cli­mate change. Using the single-​species, or “cli­mate enve­lope,” approach, researchers have pre­dicted that 15 per­cent to 37 per­cent of species will be faced with extinc­tion by 2050. But research has shown that top con­sumers — preda­tors and her­bi­vores — have an espe­cially strong effect on many other species. In a warm­ing world, these species are “biotic mul­ti­pli­ers,” increas­ing the extinc­tion risk and alter­ing the ranges of many other species in the food web.

wolves hunting yellowstoneThe paper argues that focus­ing on these biotic mul­ti­pli­ers and their inter­ac­tions with other species is a promis­ing way to improve pre­dic­tions of the effects of cli­mate change, and recent stud­ies sup­port this idea. On Isle Royale, an island in Lake Supe­rior, ris­ing win­ter tem­per­a­tures and a dis­ease out­break caused wolf pop­u­la­tions to decline and the num­ber of moose to surge, lead­ing to a decline in bal­sam fir trees. Stud­ies in the rocky inter­tidal of the North Amer­i­can Pacific Coast show that higher tem­per­a­tures altered the ranges of mus­sel species and their inter­ac­tion with sea stars, their top preda­tors, result­ing in lower species diver­sity. And in Arc­tic Green­land, stud­ies show that with­out cari­bou and muskoxen as top her­bi­vores, higher tem­per­a­tures can lead to decreased diver­sity in tun­dra plants and, in turn, affect many other species depen­dent on them.

Cli­mate change is likely to have strong effects on top con­sumers. As a result, these effects can rip­ple through an entire food web, mul­ti­ply­ing extinc­tion risks along the way
co-​author Dave Skelly, Yale Uni­ver­sity »

“Species inter­ac­tions are nec­es­sary for life on Earth. We rely on fish­eries, tim­ber, agri­cul­ture, med­i­cine and a vari­ety of other ecosys­tem ser­vices that result from intact species inter­ac­tions,” said Zar­netske. “Humans have already altered these impor­tant species inter­ac­tions, and cli­mate change is pre­dicted to alter them fur­ther. Incor­po­rat­ing these inter­ac­tions into mod­els is cru­cial to informed man­age­ment deci­sions that pro­tect bio­di­ver­sity and the ser­vices it provides.”

Mul­ti­species mod­els with species inter­ac­tions, accord­ing to the paper, would enable track­ing of the biotic mul­ti­pli­ers by fol­low­ing how changes in the abun­dance of tar­get species, such as top con­sumers, alter the com­po­si­tion of com­mu­ni­ties of species. But there needs to be more data.

Col­lect­ing this type of high-​resolution bio­di­ver­sity data will not be easy. How­ever, insights from such data could pro­vide us with the abil­ity to pre­dict and thus avoid some of the neg­a­tive effects of cli­mate change on biodiversity
(co-​author Mark Urban, Uni­ver­sity of Connecticut)

In their study the researchers inter alia refer to last year’s pub­li­ca­tion in Sci­ence from James Estes and col­leagues. This study looked into the effect on nature of the loss of large top con­sumers, such as wolf, cougar, red deer and rhi­noc­eros. It sup­ports long-​standing the­ory about the role of top-​down forc­ing in ecosys­tems but also high­lights the unan­tic­i­pated impacts of trophic cas­cades on processes as diverse as the dynam­ics of dis­ease, wild­fire, car­bon seques­tra­tion, inva­sive species, and bio­geo­chem­i­cal cycles. So it is con­cluded that the loss of these ani­mals may be humankind’s most per­va­sive influ­ence on nature.

The above news item is reprinted from mate­ri­als avail­able at Yale School of Forestry & Envi­ron­men­tal Stud­ies and Sci­ence Mag­a­zine. Orig­i­nal text may be edited for con­tent and length.

(Source: Yale Uni­ver­sity, 21.06.2012; Sci­ence, 15.07.2011)

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