AboutZoos, Since 2008


Island bio­geog­ra­phy the­ory chal­lenged — rethink ‘nat­ural’ habi­tat for wildlife

pub­lished 27 April 2014 | mod­i­fied 27 April 2014

Pro­tect­ing wildlife while feed­ing a world pop­u­la­tion pre­dicted to reach 9 bil­lion by 2050 will require a holis­tic approach to con­ser­va­tion that con­sid­ers human-​altered land­scapes such as farm­land, accord­ing to researchers from Stan­ford University.

Agriculture-in-2080Wildlife and the nat­ural habi­tat that sup­ports it might be an increas­ingly scarce com­mod­ity in a world where at least three-​quarters of the land sur­face is directly affected by humans and the rest is vul­ner­a­ble to human-​caused impacts such as cli­mate change. But what if altered agri­cul­tural land­scapes could play vital roles in nur­tur­ing wildlife pop­u­la­tions while also feed­ing an ever-​growing human population?

A new study, pub­lished on 16 April in the jour­nal Nature and co-​authored by three Stan­ford sci­en­tists, finds that a long-​accepted the­ory used to esti­mate extinc­tion rates, pre­dict eco­log­i­cal risk and make con­ser­va­tion pol­icy rec­om­men­da­tions is overly pes­simistic. The researchers point to an alter­na­tive frame­work that promises a more effec­tive way of account­ing for human-​altered land­scapes and assess­ing eco­log­i­cal risks.

Cur­rent pro­jec­tions fore­cast that about half of Earth’s plants and ani­mals will go extinct over the next cen­tury because of human activ­i­ties, mostly due to our agri­cul­tural meth­ods. “The extinc­tion under way threat­ens to weaken and even destroy key parts of Earth’s life-​support sys­tems, upon which eco­nomic pros­per­ity and all other aspects of human well-​being depend,” said co-​author Gretchen Daily, the Bing Pro­fes­sor in Envi­ron­men­tal Sci­ence at Stan­ford and senior fel­low at the Stan­ford Woods Insti­tute for the Environment

But that grim future isn’t a fore­gone con­clu­sion. “Until the next aster­oid slams into Earth, the future of all known life hinges on peo­ple, more than on any other force,” Daily said.

Nature is not an island
Con­ser­va­tion­ists have long assumed that once nat­ural land­scapes are frac­tured by human devel­op­ment or agri­cul­ture, migra­tion cor­ri­dors for wildlife are bro­ken, block­ing access to food, shel­ter and breed­ing grounds. A schol­arly the­ory was devel­oped to esti­mate the num­ber of species in such frac­tured land­scapes, where patches of for­est sur­rounded by farms resem­ble islands of nat­ural habitat.

If we’re valu­ing cof­fee fields and other human-​made habi­tats at zero, we’re doing a dis­ser­vice to our­selves and wildlife
Chase Menden­hall, lead author, doc­toral stu­dent biol­ogy, Stan­ford University »

The “equi­lib­rium the­ory of island bio­geog­ra­phy” is a pil­lar of bio­log­i­cal research – its ele­gant equa­tion to esti­mate the num­ber of species in a habi­tat has almost reached the sta­tus of a sci­en­tific law, accord­ing to Menden­hall. The the­ory dri­ves the default strat­egy of con­serv­ing bio­di­ver­sity by des­ig­nat­ing nature reserves. This strat­egy sees reserves as “islands in an inhos­pitable sea of human-​modified habi­tats” and doesn’t ade­quately account for bio­di­ver­sity pat­terns in many human-​dominated land­scapes, accord­ing to the Stan­ford study.

“This paper shows that farm­land and for­est rem­nants can be more valu­able for bio­di­ver­sity than pre­vi­ously assumed,” said Daniel Karp, who earned his PhD in biol­ogy at Stan­ford in 2013 and is cur­rently a NatureNet post­doc­toral fel­low at the Uni­ver­sity of Cal­i­for­nia, Berkeley.

Island biogeography theoryTo test the island the­ory against a more holis­tic the­ory of agri­cul­tural or coun­try­side bio­geog­ra­phy, the researchers turned to bats – a species acutely sen­si­tive to defor­esta­tion. The study focused on bat pop­u­la­tions within a mosaic of for­est frag­ments and farm­land in Costa Rica and on islands in a large lake in Panama. The researchers also did a meta-​analysis of 29 stud­ies of more than 700 bat species to bol­ster and gen­er­alise their find­ings globally.

Island bio­geo­graphic the­ory accu­rately pre­dicted bats’ responses to for­est loss on the Pana­man­ian islands sys­tem, but didn’t come close to accu­rately fore­cast­ing sim­i­lar responses in the Costa Rican coun­try­side land­scape. For exam­ple, the island the­ory pre­dicted that the Costa Rican cof­fee plan­ta­tions would have inad­e­quate habi­tat to sus­tain a sin­gle species of bat. In real­ity, plan­ta­tions in the coun­try­side typ­i­cally sup­ported 18 bat species, com­pared to the 23 to 28 sup­ported by trop­i­cal for­est frag­ments and nature reserves.

“Con­ser­va­tion oppor­tu­ni­ties for trop­i­cal wildlife are tightly linked to ade­quate man­age­ment of these human-​modified habi­tats,” said co-​author Christoph Meyer, a researcher at the Uni­ver­sity of Lisbon’s Cen­ter for Envi­ron­men­tal Biology.

Over­all, as for­est cover dis­ap­peared, the rate of species loss was “sub­stan­tially and sig­nif­i­cantly higher” in the island ecosys­tem, and species abun­dances were “increas­ingly uneven” com­pared to the coun­try­side ecosys­tem, the study found.

The rea­son for the dis­crep­an­cies, accord­ing to the study’s authors, is that island bio­geo­graphic the­ory was orig­i­nally based on actual islands sur­rounded by water, and does not account for fac­tors such as a coun­try­side landscape’s abil­ity to sup­port more species and slow extinc­tion rates com­pared to true island ecosys­tems. Espe­cially in the trop­ics, island bio­geo­graphic theory’s appli­ca­tion is “dis­tort­ing our under­stand­ing and con­ser­va­tion strate­gies in agri­cul­ture, the enter­prise on which the future of bio­di­ver­sity most crit­i­cally hinges,” the study’s authors wrote.

“Not only do more species per­sist across the ‘sea of farm­land’ than expected by island bio­geo­graphic the­ory, novel yet native species actu­ally thrive there,” said co-​author Eliz­a­beth Hadly, Pro­fes­sor in Envi­ron­men­tal Biol­ogy at Stan­ford and senior fel­low at the Stan­ford Woods Insti­tute for the Envi­ron­ment. “This indi­cates that human-​altered land­scapes can fos­ter more bio­log­i­cal diver­sity than we anticipated.”

A new approach
The fate of much of the world’s wildlife is play­ing out in human-​altered land­scapes that are increas­ingly threat­ened by chem­i­cal inputs such as her­bi­cides and pes­ti­cides. Bio­di­ver­sity is not the only loser. Peo­ple are los­ing many of nature’s ben­e­fits, called ecosys­tem ser­vices, such as water purifi­ca­tion pro­vided by forests and wet­lands and pest con­trol pro­vided by birds and bats.

The study’s find­ings point to the need for new approaches that inte­grate con­ser­va­tion and food pro­duc­tion, to make agri­cul­tural lands more hos­pitable to wildlife by reduc­ing chem­i­cal inputs, pre­serv­ing frag­ments of for­est and other nat­ural habi­tats and reward­ing farm­ers and ranch­ers for the ben­e­fits that result.

“A the­ory of coun­try­side bio­geog­ra­phy is piv­otal to con­ser­va­tion strat­egy in the agri­cul­tural ecosys­tems that com­prise roughly half of the global land sur­face and are likely to increase even fur­ther in the future,” the researchers wrote. A new approach that could inspire con­ser­va­tion­ists, researchers and pol­i­cy­mak­ers to adopt new think­ing to ensure a long-​term sus­tain­able agri­cul­tural food pro­duc­tion. Which is nec­es­sary, because the pro­jec­tions made in 2009, by UNEP/​GRID-​Arendal, of expected changes in agri­cul­tural out­puts in 2080 due to cli­mate change were not very pos­i­tive. While recently, sci­en­tists have reported (UN-​IPCC) that crop yields are expected to decline faster due to cli­mate change than thought before (MIT news, 31.03.2014).

(Source: Stan­ford Uni­ver­sity news release, 16.04.2014)

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