AboutZoos, Since 2008


Species rich­ness could be false indi­ca­tor for health of ecosystems

pub­lished 17 August 2017 | mod­i­fied 17 August 2017

Alpine meadow SteiermarkSci­en­tists pro­pose a new method for improv­ing the assess­ment of changes in biodiversity.

Assess­ing the state of an ecosys­tem solely on the basis of short-​term changes in the num­ber of dif­fer­ent species it con­tains can lead to false con­clu­sions. This is the con­clu­sion reached by an inter­na­tional team includ­ing researchers of the Helmholtz Insti­tute for Func­tional Marine Bio­di­ver­sity (HIFMB) at the Uni­ver­sity of Old­en­burg and the Ger­man Cen­tre for Inte­gra­tive Bio­di­ver­sity Research (iDiv). In order to assess ecosys­tems in a way that is mean­ing­ful for nature con­ser­va­tion, experts should instead focus on analysing the turnover of species within a sys­tem. The researchers reached this con­clu­sion using a math­e­mat­i­cal model and envi­ron­men­tal data analy­sis. The new method can be applied effec­tively using data already avail­able from envi­ron­men­tal mon­i­tor­ing pro­grammes. The study is pub­lished on 1 August in the Jour­nal of Applied Ecol­ogy.

A grow­ing num­ber of species are under threat of extinc­tion – in par­tic­u­lar due to global envi­ron­men­tal changes. Polit­i­cal instru­ments such as the Inter­na­tional Con­ven­tion on Bio­log­i­cal Diver­sity (CBD) or the Euro­pean Union’s Marine Strat­egy Frame­work Direc­tive aim to mit­i­gate this bio­di­ver­sity cri­sis. In prac­tice, tak­ing the num­ber of species (species rich­ness) as a sim­ple met­ric for deter­min­ing the state of an ecosys­tem seems an obvi­ous approach. “But this met­ric has its pit­falls because it doesn’t fully reflect the changes in the sys­tem,” says the Old­en­burg bio­di­ver­sity expert Hille­brand, who is also the lead author of the study. On the con­trary, accord­ing to the sci­en­tists’ model cal­cu­la­tions, neg­a­tive influ­ences on an ecosys­tem do not auto­mat­i­cally result in a reduc­tion in species rich­ness. Con­versely, the num­ber of species in a sys­tem does not auto­mat­i­cally increase as soon as an ecosys­tem recov­ers from human impact.

The rea­son for this is: “Species rich­ness is a result of the bal­ance between the immi­gra­tion and the extinc­tion of species. How­ever, these two processes do not occur at the same speed,” Hille­brand explains. “A few indi­vid­u­als of a species can quickly migrate into a local habi­tat and colonise it, but it may take sev­eral gen­er­a­tions for a species to be replaced by a new, more com­pet­i­tive species, or to die out as a result of changed conditions.”

This means you can’t reli­ably say, on the basis of short-​term trends, whether more or fewer species will be left in an ecosys­tem over a long period of time,” Hille­brand stresses, adding: “So species rich­ness can be a false friend.”

In their pub­li­ca­tion the sci­en­tists there­fore rec­om­mend closer mon­i­tor­ing of how many species are migrat­ing into a sys­tem, how many are leav­ing it, and how many species are becom­ing more or less abun­dant within the sys­tem. As an exam­ple the sci­en­tists used this method to analyse long-​term mea­sure­ments from var­i­ous ecosys­tems — such as data on drift­ing microal­gae (phy­to­plank­ton) from the mud flats of the Dutch Wad­den Sea and the lakes of North Amer­ica, as well as data from grass­land ecosys­tems on six dif­fer­ent continents.

In extreme cases, the major­ity of species in an ecosys­tem could be replaced by new species. But if you only look at the num­ber of species, the so-​called species rich­ness, that num­ber doesn’t change at all.

Prof. Dr. Jonathan Chase, co-​author, Ger­man Cen­tre for Inte­gra­tive Bio­di­ver­sity Research (iDiv) and the Mar­tin Luther Uni­ver­sity Halle-​Wittenberg

There­fore, species rich­ness alone can be a mis­lead­ing met­ric and can obscure what is really going on in an ecosys­tem,” added Chase.

For their analy­ses the researchers explic­itly used data gath­ered by con­ser­va­tion­ists in envi­ron­men­tal mon­i­tor­ing pro­grammes. In this way the sci­en­tists want to ensure that their tool can be used with the avail­able resources, which in prac­tice are often lim­ited. “We hope that in this way we can build a bridge between the basic research and nature con­ser­va­tion in prac­tice,” Hille­brand says.

(Source: iDiv media release, 02.08.2017)

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