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Bio­di­ver­sity


A Col­lec­tion of News by Moos


201620Mar14:33

New track­ing tech­nol­ogy high­lights vul­ner­a­bil­ity of Wilde­beest migration

Infor­ma­tion
pub­lished 20 March 2016 | mod­i­fied 20 March 2016
Archived

Recent efforts to com­bat habi­tat frag­men­ta­tion and poach­ing have tem­porar­ily sta­bi­lized wilde­beest pop­u­la­tions in north­ern Tan­za­nia, but this iconic migrat­ing species of the African savan­nah remains vul­ner­a­ble, a Dart­mouth College-​led team has found using an unusual wildlife photo-​identification track­ing tech­nol­ogy devel­oped at Dartmouth.

Wildebeest during Great MigrationNumer­ous wilde­beest pho­tographed after hav­ing crossed the river Mara from Serengeti to the Mara.
Author: Bjørn Chris­t­ian Tør­ris­sen. Licensed under the Cre­ative Com­mons Attribution-​Share Alike 3.0 Unported license.

Wilde­beest migra­tion
The annual wilde­beest or gnu migra­tion in East Africa is one of the largest and longest-​distance mam­mal migra­tions on Earth. An esti­mated 1.3 mil­lion wilde­beest travel round-​trip between pro­tected areas in Tan­za­nia and Kenya to coin­cide with the sea­sonal pat­terns of rain­fall and grass growth. Wildlife migra­tion requires large con­nected land­scapes and access to sea­son­ally avail­able resources, but human devel­op­ment – such as roads, live­stock fences, farms, sub­ur­ban set­tle­ments and energy infra­struc­ture – has frag­mented migra­tion cor­ri­dors in many ter­res­trial ecosys­tems around the world.

In east­ern and south­ern Africa, habi­tat frag­men­ta­tion has coin­cided with wide­spread declines in the abun­dance and geo­graphic range of ungu­late pop­u­la­tions. As the num­ber and per­me­abil­ity of migra­tion routes decrease, migra­tory ani­mals have fewer for­ag­ing options. In north­ern Tan­za­nia, migra­tory wilde­beest in the Tarangire-​Manyara Ecosys­tem, a savannah-​woodland ecosys­tem that sup­ports one of the most diverse com­mu­ni­ties of migra­tory ungu­lates in the world, have expe­ri­enced a grad­ual loss of con­nec­tiv­ity between sea­sonal ranges and under­gone fluc­tu­a­tions in abun­dance over time. Sim­i­lar pat­terns have played out else­where in Africa.

The Wilde­beest migra­tion: an ani­ma­tion:


(Source: Go2Africa Safaris YouTube chan­nel)

Count­ing wilde­beest
Typ­i­cally, wildlife biol­o­gists mon­i­tor large mam­mal pop­u­la­tions by count­ing them from the air or attach­ing expen­sive GPS col­lars. Wilde­beest cen­suses are com­monly con­ducted using sample-​based aer­ial sur­veys, although the dense clump­ing of herds leads to low pre­ci­sion. So, the Dartmouth-​led team used an unusual computer-​assisted pho­to­graphic capture-​mark-​recapture method to exam­ine the link between wilde­beest abun­dance and their abil­ity to freely move within the Tarangire-​Manyara Ecosystem.

Wildlife photo-​recognition soft­ware has been used for years to iden­tify and track species with unique spot­ted or striped mark­ings such as chee­tahs and zebras, but sim­i­lar soft­ware was inef­fec­tive for species whose coat or skin pat­terns are irreg­u­lar in size, shape and edges, such as giraffes and wilde­beest. Then, in 2011, Dart­mouth sci­en­tists devel­oped “Wild-​ID,” an irreg­u­lar pattern-​matching algo­rithm that has proven highly accu­rate – its error rate is vir­tu­ally zero for giraffes and about 8 per­cent for wilde­beest. In stud­ies since then by Dart­mouth and other sci­en­tists on a grow­ing vari­ety of wildlife, Wild-​ID has proven to be more accu­rate, less inva­sive, less expen­sive, less time con­sum­ing and cover more ter­ri­tory than tra­di­tional mark-​recapture and aer­ial sur­vey meth­ods. And Wild-​ID is so accu­rate on giraffes that Dart­mouth researchers no longer need to phys­i­cally cap­ture and tag them as they con­duct the largest ever study of giraffes and one of the largest ever individually-​based demog­ra­phy stud­ies of a large mammal.

A lot of peo­ple didn’t think track­ing hun­dreds, let alone thou­sands, of indi­vid­ual wilde­beest was pos­si­ble, but we man­aged with Wild-​ID
Tom Mor­ri­son, lead author, Wyoming Coop­er­a­tive Fish and Wildlife Research Unit, Depart­ment of Zool­ogy and Phys­i­ol­ogy, Uni­ver­sity of Wyoming, USA »

Mor­ri­son – who con­ducted the wilde­beest study as part of his PhD in Dartmouth’s Ecol­ogy and Evo­lu­tion­ary Biol­ogy pro­gram and who is cur­rently study­ing Tanzania’s other well-​known wilde­beest migra­tion, in Serengeti National Park – added, “The Wild-​ID tech­nique not only pro­vided an under­stand­ing of pop­u­la­tion size, but impor­tantly, it also allowed us to know the move­ment and migra­tion pat­terns of indi­vid­ual ani­mals over time. Together, this infor­ma­tion pro­vides a basis for pre­dict­ing the future prospects of this wilde­beest population.”

Wilde­beest Migra­tion on National Geo­graphic:

Results
In their study, Mor­ri­son and his col­leagues found that as the num­ber of migra­tion routes declined in this Tan­zan­ian ecosys­tem, so too has the pop­u­la­tion size of wilde­beest, although the cur­rent pop­u­la­tion appears rel­a­tively sta­ble in size despite rapid declines in the past. More specif­i­cally, the researchers found dimin­ished con­nec­tiv­ity within and between sea­sonal areas as a result of human activ­i­ties; a reduc­tion in the over­all pop­u­la­tion size com­pared to his­tor­i­cal num­bers, with high vari­abil­ity over time; the con­tin­ued use of highly con­strained move­ment cor­ri­dors between the three main sea­sonal ranges; higher recruit­ment in the non-​migratory sub­pop­u­la­tion (Lake Man­yara National Park) than in other areas of the ecosys­tem; and an increase in the rel­a­tive abun­dance of res­i­dent to migrant wilde­beest. The find­ings are pub­lished online on 11 March in the jour­nal Bio­log­i­cal Con­ser­va­tion.

The results don’t defin­i­tively link trends in wilde­beest abun­dance with changes in land-​use and wildlife har­vest­ing, but the cur­rent geo­graphic extent and pop­u­la­tion size of wilde­beest in the Tarangire-​Manyara Ecosys­tem are vastly smaller than in stud­ies from recent decades.

What was prob­a­bly once a pop­u­la­tion of tens of thou­sands of ani­mals now num­bers roughly 10,000 despite a land­scape that rivals the Serengeti-​Mara Ecosys­tem in total area,” Mor­ri­son says. “Recent con­ser­va­tion efforts to pro­tect sea­sonal habi­tat and to enforce anti-​poaching poli­cies out­side pro­tected areas have likely helped sta­bi­lize the pop­u­la­tion, at least tem­porar­ily, since the early 2000’s rel­a­tive to the severe declines observed in the 1990’s, but we cau­tion that sev­eral key vul­ner­a­bil­i­ties remain.

Photo iden­ti­fi­ca­tion of large num­ber of ani­mals using the Wild-​ID soft­ware can assist sci­en­tists who mon­i­tor threat­ened pop­u­la­tions,” Mor­ri­son adds. “Migra­tory species require large areas to sus­tain their pop­u­la­tions, and this require­ment is a sig­nif­i­cant chal­lenge in set­tings that are expe­ri­enc­ing rapid human pop­u­la­tion growth and devel­op­ment such as north­ern Tan­za­nia. Sim­ply mon­i­tor­ing pop­u­la­tions is dif­fi­cult and expen­sive in many species, and we offer a new tool for esti­mat­ing a fun­da­men­tal met­ric of pop­u­la­tion health (pop­u­la­tion size) and link­ing this to move­ments of indi­vid­ual animals.”

(Source: Dart­mouth press release, 17.03.2016)


UN Biodiversity decade

Goal: 7000 tigers in the wild

Tiger range countries map

Tiger map” (CC BY 2.5) by Sander­son et al., 2006.

about zoos and their mis­sion regard­ing breed­ing endan­gered species, nature con­ser­va­tion, bio­di­ver­sity and edu­ca­tion, which of course relates to the evo­lu­tion of species.
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