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201310Dec22:12

Qual­ity of bio­di­ver­sity, not just quan­tity, is key

Infor­ma­tion
pub­lished 10 Decem­ber 2013 | mod­i­fied 03 Novem­ber 2014
Archived

For years, sci­en­tists have believed that pre­serv­ing more species, no mat­ter which ones, is a key com­po­nent to enhanc­ing how well an ecosys­tem performs.

Sapelo salt marshNot so fast, say sci­en­tists at Duke Uni­ver­sity and the Uni­ver­sity of Mass­a­chu­setts at Boston. In a new study of bio­di­ver­sity loss in a salt marsh, pub­lished online on 2 Decem­ber in the Pro­ceed­ings of the National Acad­emy of Sci­ences, they find that it’s not just the total num­ber of species pre­served that mat­ters, it’s the num­ber of key species.

Hav­ing a group of dis­tantly related species, rep­re­sent­ing markedly dif­fer­ent ecolo­gies and biol­ogy, is as impor­tant, or more impor­tant, than just hav­ing more species in general
« Brian R. Sil­li­man, Rachel Car­son asso­ciate pro­fes­sor of marine con­ser­va­tion biol­ogy at Duke’s Nicholas School of the Environment

If humans want to reap the ben­e­fits of the full range of func­tions that salt marshes and other coastal ecosys­tems pro­vide, we need to pre­serve the right mix of species, they said. “It’s qual­ity, not just quan­tity,” said lead author Marc J. S. Hensel, a Ph.D. stu­dent at the Uni­ver­sity of Mass­a­chu­setts at Boston. “We need to pre­serve a wide vari­ety of species.”

Salt marshes per­form a long list of eco­log­i­cal ser­vices: they buffer coastal ero­sion, fil­ter runoff, reduce the risk of flood­ing, pro­vide habi­tat for juve­nile fish, crabs and shrimp, and store excess car­bon, keep­ing it from re-​entering Earth’s atmosphere.

To bet­ter under­stand how the loss of key species affects these func­tions, Sil­li­man and Hensel con­ducted a tightly con­trolled eight-​month field exper­i­ment in a salt marsh on Sapelo Island, Geor­gia. They set up eight dif­fer­ent exper­i­men­tal treat­ments, each with a dif­fer­ent mix of three of the marsh’s most abun­dant “con­sumer” species: pur­ple marsh crabs, marsh peri­win­kle snails and fun­gus. At first, all three species were present, to mir­ror the nat­ural “intact” con­di­tions of the marsh. Sil­li­man and Hensel then began sequen­tially remov­ing species — first one, then two, then all three — to sim­u­late extinctions.

Through­out the exper­i­ment, they mea­sured the effects of each species mix on three impor­tant salt marsh func­tions: over­all grass growth (pro­duc­tiv­ity), the rate of dead plant removal (decom­po­si­tion), and how fast tidal or storm surge water per­co­lated through the marsh (filtration).

The effect of the species removals on indi­vid­ual func­tions var­ied con­sid­er­ably, because in salt marshes, each species is very good at per­form­ing one or two func­tions. How­ever, when all three key species were present, the aver­age rate of all func­tions — a mea­sure of over­all ecosys­tem health — rose simultaneously.

“Our study pro­vides a rare, real-​world exam­ple that the loss of key species can have pro­found impacts on the over­all per­for­mance of an ecosys­tem,” Sil­li­man said. “It sug­gests that the abil­ity of nature to per­form well at mul­ti­ple lev­els may depend not just on the over­all num­ber of species present, but on hav­ing many dis­tantly related species, each of which per­forms a par­tic­u­lar task that keeps an ecosys­tem healthy and allows it to pro­vide the mul­ti­ple ben­e­fits humans value. If we had only been look­ing at three dif­fer­ent species of sim­i­larly func­tion­ing crabs, or only one marsh func­tion, we would have missed that, and erro­neously pre­dicted that only one con­sumer species is needed to main­tain high sys­tem per­for­mance,” he added.



(Source: Duke Envi­ron­ment news release, 09.12.2013)


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