Subscribe to our free daily newsletters
. Earth Science News .




Subscribe to our free daily newsletters



WOOD PILE
Browsing antelope turned ancient African forests into grassy savanna ecosystems
by Staff Writers
Johannesburg, South Africa (SPX) Sep 07, 2016


The arrival of medium and large antelope in Africa coincides directly with the evolution of thorn trees in the African savanna. Image courtesy Gareth Hempson. For a larger version of this image please go here.

Millions of years ago, Africa's savannas were covered with thick, ancient forests, which disappeared and turned into the grassy ecosystems that they are today. Almost a fifth of the world's land surface is covered by savannas. Yet, for years it has been a mystery how these grassy ecosystems came to replace the ancient forests.

One answer, it was thought, might be climate change, yet most savannas occur in climates that also support forests. The other possibility was fire. Savanna trees and shrubs are often adapted to frequent fires, while forest trees are not.

But a study that includes a group of South African scientists has found that the arrival of browsing medium sized antelopes was probably what turned Africa's ancient forests into the open savannas.

By comparing the timing of the evolution of thorns on about 2000 woody tree species in southern Africa and the time that antelopes arrived in Africa, a group of scientists, including Dr Gareth Hempson from the School of Animal Plants and Environmental Studies at the University of Witwatersrand, found that trees like African acacias evolved thorns as a defence mechanism at exactly the same time that antelope arrived in Africa.

"It all makes perfect sense," says Hempson. "Spines (thorns) really appear to be most effective against medium- and large-sized browsers like impala and kudu, and spiny trees are most common in the places where these animals are most abundant," says Hempson.

Hempson developed a herbivore biomass map of Africa while he was a post-doctoral fellow at Wits and the University of Cape Town.

"After presenting my herbivore biomass data at a conference, Dr Tristan Charles-Dominique [the lead author on the paper, from the University of Cape Town] said he had to show me something - we placed our laptops next to each other and compared his spiny tree abundance maps with my animal density maps - the match with medium and large browsing species was remarkable!"

The study that was published in the journal, Proceedings of the National Academy of Sciences (PNAS) on Monday (5 September 2016) analysed the distribution of nearly 2000 woody species from southern Africa and found that spiny plants are most common in arid savannas with high densities of mammal browsers. They are rare in humid savannas on infertile soils and absent in forests.

The study used DNA data for African trees collected by Professor Michelle van der Bank and her team at the University of Johannesburg, to reconstruct the history of spiny plant evolution. In collaboration with Prof Jonathan Davies, an expert in phylogenetic analysis from McGill University, the team was then able to date the evolutionary origins of spines.

"We were shocked," said Professor van der Bank "to discover that spiny plants only appeared about 15 million years ago, 40 million years after mammals replaced dinosaurs". For most of this time, Africa was an island continent dominated by now-extinct ancestors of browsing elephants and hyrax. "Apparently, spines just didn't work as a plant defense against these ancient mammal groups" commented Prof van der Bank.

But in a remarkable example of apparent coevolution, the diversification of spiny plants (thorn trees) coincides with the appearance of antelope.

Antelope were latecomers to Africa appearing only after the continent collided with Eurasia. They browsed in novel ways and were highly efficient herbivores. This injection of new types of browsers, argue the authors, demolished young forest trees, opening up forests to the grass invaders.

"We know something of the history of fire from fossil charcoal, but we do not have good fossil evidence for browser/plant interactions" said Professor William Bond, (SAEON and UCT) an author on the study, "Could we use the evolutionary history of spiny plants to examine whether mammal browsing opened up the ancient forests to savannas?"

The evidence is striking: "It was astonishing to see that there was this wide radiation of thorns across tree species just after the arrival of antelope on the continent," says Hempson.

The parallel radiation of spiny plants and the antelope that feed on them initiated the rise of savannas in the drier more fertile regions of Africa. Fire only began to roll back the forests to create wetter savannas several million years later.

One implication of the study is that the loss of Africa's native browsing antelope may threaten the future of drier savannas, and lead to their replacement by dense, woody scrub of little ecological or economic value.


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

.


Related Links
University of the Witwatersrand
Forestry News - Global and Local News, Science and Application






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
WOOD PILE
Honduras, Guatemala most dangerous for environmentalists: AI
Guatemala City (AFP) Sept 1, 2016
Honduras and Guatemala are the most dangerous countries in the world for environmentalists due to the persecution and even murder of activists, Amnesty International said in a report Thursday. The London-based global rights group pointed to "an insidious wave of threats, bogus charges, smear campaigns, attacks and killings of environmental and land activists in recent months" in the Central ... read more


WOOD PILE
Chinese glass bridge, world's longest, closes

Europe 'close to limits' on refugee influx: Tusk

Merkel vows to 'win back trust' after poll loss blamed on migrant crisis

Germany's anti-migrant populists beat Merkel's party in local vote

WOOD PILE
Berlin's IFA fair dons virtual reality headsets

Shrinking the inside of an explosion

New optical material offers unprecedented control of light and thermal radiation

'Materials that compute' advances as Pitt engineers demonstrate pattern recognition

WOOD PILE
Warming oceans are 'sick,' global scientists warn

Obama highlights environment on Pacific atoll

Pacific tuna meet fails to agree on cutbacks

Flood threat as plastic bags clog Bangkok's bowels

WOOD PILE
Technique could assess historic changes to Antarctic sea ice and glaciers

A mammoth undertaking

By mid-century, more Antarctic snowfall may help offset sea-level rise

Giant cruise ship heads to Arctic on pioneering journey

WOOD PILE
Iran's pistachio farms are dying of thirst

Early-onset spring models may indicate 'nightmare' for ag

Crop domestication is a balancing act

ChemChina rolls over $43 bn Syngenta offer

WOOD PILE
17 unaccounted for in typhoon-hit northern Japan

Floods kill 60, displace 44,000 in N.Korea: UN

Hurricane Newton barrels toward Mexico resort

Romeo the miracle dog survives Italy quake

WOOD PILE
COP22 host Morocco's mosques are going green

Mali defence minister fired after jihadists seize town: officials

Corruption 'epidemic' in Tunisia: anti-graft chief

S.Sudan court martials 60 soldiers

WOOD PILE
Study: Math-capable parents yield math-capable kids

Smarter brains are blood-thirsty brains

UT study cracks coldest case: How the most famous human ancestor died

Scientists think human ancestor Lucy fell from a tree




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement