Ecologists learn lessons from the 'ghosts of megafauna'

Scientists have been assessing the ecological consequences of a megafauna-depleted world and what, if anything, should be done about it.

Researchers discussed whether the loss of big beasts contributed to regional and global system changes, such as Arctic warming and more wildfires.

Megafauna (animals with a mass of 44kg or more) once dominated but disappeared in an ecological "blink of an eye".

The global scientific gathering was held at the University of Oxford, UK.

Co-organiser Yadvinder Malhi, professor of ecosystem science at the university's Environmental Change Institute, said the conference was "unique" as it brought together many disciplines that would not normally meet during their day-to-day work.

Assessing the event's discussions, he observed: "There was such a strong consensus emerging that megafaunal extinctions did have a huge impact on the structure of ecosystems, which still ramifies through to the ecosystems today.

"What we think as natural now are still carrying many disequilibria - or ghosts - resulting from the loss of the megafauna in terms of their structure, functioning and nutrient recycling."

Prof Malhi added that a greater understanding of the impacts of megafaunal extinctions helped researchers model the consequences of losing big beasts from today's landscapes in sub-Saharan Africa and Asia.

"Somehow, it seems as if megafauna have been linked to dinosaurs in people's popular imagination," he told BBC News.

"But, ecologically speaking, it was only a blink of an eye ago that there were megafauna everywhere."

A recent study highlighted the long-lasting impact of losing big animals in the Amazon region 12,000 years ago, cutting off a key way that nutrients were distributed across the landscape.

Writing in the Nature Geoscience journal, the researchers said the animals would have distributed vital nutrients for plants via their dung and bodies.

The effects were still visible today and raised questions about the impact of losing large modern species, such as elephants, from the landscape.

One area that has proved to be somewhat divisive within the scientific community is whether the demise of many large species was the result of changes to the global climate system or human activity.

Two presentations at the Megafauna and Ecosystem Function from the Pleistocene to the Anthropocene conference presented data from around the globe that looked at when species extinctions were recorded, and whether this coincided with the arrival of humans or a significant event in the climate record.

Both presentations - one by Lewis Bartlett from the University of Exeter (audio link), the other by Chris Sandom from the universities of Oxford and Aarhus (audio link) - concluded that, on a global scale, human arrival was a "decisive factor". In other words, the creatures were hunted and displaced until they became extinct.

"When you look at the global picture with a consistent set of data, it is very hard to argue against a strong human role," said Prof Malhi.

But he added: "It has been an area that has been hugely contentious for a long time, so I am sure there will be people who will say that the issue is still unsettled."

Other speakers included researchers sharing their experiences of re-wilding projects that included the reintroduction or preservation of megafauna.