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201521Dec13:31

Extinc­tion of large ani­mals could make cli­mate change worse

Infor­ma­tion
pub­lished 21 Decem­ber 2015 | mod­i­fied 21 Decem­ber 2015
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Brazilian or lowland tapirNew research reveals that a decline in fruit-​eating ani­mals such as large pri­mates, tapirs and tou­cans could have a knock-​on effect for tree species and sub­se­quently for forests’ car­bon stor­age capabilities.

This is because large ani­mals dis­perse large seeded plant species often asso­ci­ated with large trees and high wood den­sity — which are more effec­tive at cap­tur­ing and stor­ing car­bon diox­ide from the atmos­phere than smaller trees. Seed dis­per­sal by large-​bodied ver­te­brates is via the inges­tion of viable seeds that pass through the diges­tive tract intact. Remov­ing large ani­mals from the ecosys­tem upsets the nat­ural bal­ance and leads to a loss of heavy-​wooded large trees, which means that less CO2 can be locked away.

The study was led by researchers from São Paulo State Uni­ver­sity in Brazil, in col­lab­o­ra­tion with Uni­ver­sity of East Anglia (UEA), the Span­ish National Research Coun­cil (CSIC) and the Uni­ver­sity of Helsinki, Fin­land. The find­ings are pub­lished on 18 Decem­ber in the jour­nal Sci­ence Advances.

We show that the decline and extinc­tion of large ani­mals will over time induce a decline in large hard­wood trees. This in turn neg­a­tively affects the capac­ity of trop­i­cal forests to store car­bon and there­fore their poten­tial to counter cli­mate change
Prof Car­los Peres, School of Envi­ron­men­tal Sci­ences, UEA, UK »

Prof Peres said: “Large birds and mam­mals pro­vide almost all the seed dis­per­sal ser­vices for large-​seeded plants. Sev­eral large ver­te­brates are threat­ened by hunt­ing, ille­gal trade and habi­tat loss. But the steep decline of the megafauna in over­hunted trop­i­cal for­est ecosys­tems can bring about large unfore­seen impacts.”

The study
The research team stud­ied data from more than 2,000 tree species in Brazil’s Atlantic For­est, and more than 800 ani­mal species. They found that fru­gi­vores which are not tar­geted by hunters — such as small birds, bats and mar­su­pi­als — are only able to dis­perse small seeds, which are asso­ci­ated with small trees.
Mean­while large heavy-​wooded trees, which can cap­ture and store greater amounts of car­bon, are asso­ci­ated with larger seeds. And these are only dis­persed by large animals.

Prof Mauro Galetti from São Paulo State Uni­ver­sity said: “The big fru­gi­vores, such as large pri­mates, the tapir, the tou­cans, among other large ani­mals, are the only ones able to effec­tively dis­perse plants that have large seeds. Usu­ally, the trees that have large seeds are also big trees with dense wood that store more carbon.”

Defaunation frugivoresSim­u­la­tion path­way of fru­gi­vore defau­na­tion on car­bon stor­age.
They gen­er­ated down­graded com­mu­ni­ties with altered species com­po­si­tion. Each sim­u­la­tion had two main steps. First, they sim­u­lated directed extinc­tions induced by defau­na­tion (loss of tree species with seed size ≥12.0 mm) or ran­dom extinc­tion (that is, tree species removal inde­pen­dent of seed size). Sec­ond, they sim­u­lated a com­pen­satory replace­ment of the indi­vid­u­als by the remain­ing species pool after defau­na­tion by adding the same num­ber of indi­vid­u­als and basal area removed. Dark blue indi­cates tree indi­vid­u­als of hard-​wood species with large seeds (≥12.0 mm) and dif­fer­ent trunk diam­e­ters, light blue rep­re­sents other tree species.
Car­olina Bello et al. Sci­ence Advances 18 Dec 2015: Vol. 1, no. 11, e1501105 DOI: 10.1126/sciadv.1501105

Car­olina Bello, a PhD stu­dent from the São Paulo State Uni­ver­sity, added: “When we lose large fru­gi­vores we are los­ing dis­per­sal and recruit­ment func­tions of large seeded trees and there­fore, the com­po­si­tion of trop­i­cal forests changes. The result is a for­est dom­i­nated by smaller trees with milder woods which stock less carbon.”

non defaunated forest

defaunated forest

Pedro Jor­dano, of the Span­ish National Research Coun­cil (CSIC) said: “Not only are we fac­ing the loss of charis­matic ani­mals, but we are fac­ing the loss of inter­ac­tions that main­tain the proper func­tion­ing and key ecosys­tem ser­vices such as car­bon storage.”

One of those charis­matic ani­mals is the Low­land or Brazil­ian tapir (Tapirus ter­restris) which is clas­si­fied as Vul­ner­a­ble by the IUCN Red List of Threat­ened Species. Its ongo­ing pop­u­la­tions reduc­tion is esti­mated to be slightly greater than a 30% in the past 3 gen­er­a­tions (33 years) due to habi­tat loss, ille­gal hunt­ing and com­pe­ti­tion with live­stock, and esti­mated on cur­rent rates of decline this rate of decline is inferred to con­tinue for the next 3 gen­er­a­tions (33 years). The Low­land tapir has been extir­pated over large por­tions of its range and severely reduced in other large portions.

Cam­era trap footage of a low­land tapir at night:


(Source: Yasuni Wilder­ness YouTube channel)

Prof Peres added: “Inter­gov­ern­men­tal poli­cies to reduce car­bon emis­sions from trop­i­cal coun­tries have pri­mar­ily focused on defor­esta­tion, and to a lesser extent on for­est degra­da­tion result­ing from tim­ber extrac­tion and wild­fires. But our research shows that a decline in large ver­te­brate pop­u­la­tions and the loss of key eco­log­i­cal inter­ac­tions also poses a seri­ous risk for the main­te­nance of trop­i­cal for­est car­bon storage.

We hope that our find­ings will encour­age UN pro­grammes on Reduc­ing Emis­sions from Defor­esta­tion and For­est Degra­da­tion (REDD+) to con­sider fau­nally intact forests and their full func­tion­al­ity as a crit­i­cal pre­con­di­tion of main­tain­ing for­est car­bon stocks.”

Car­olina Bello said: “The effec­tive­ness of these pro­grammes will be improved if the preser­va­tion of eco­log­i­cal processes that sus­tain the ecosys­tem ser­vice of car­bon stor­age over time is guaranteed.”


(Source: Uni­ver­sity of East Anglia press release, 18.12.2015; IUCN Red List of Threat­ened Species)


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