The world must act immediately to stop the rapid loss of animal and plant species and the habitats they live in, the United Nations warned on Monday at the start of a major summit on biodiversity.

The 193 members of the U.N.'s Convention on Biological Diversity (CBD) began gathering in the central city of Nagoya in Japan to try to work out strategies to head off a manmade mass extinction.

“The time to act is now and the place to act is here,” CBD executive secretary Ahmed Djoghlaf said as the meeting opened, describing the event as a “defining moment” in the history of mankind.

“The savings from a coordinated ecosystems approach to climate change, biodiversity loss, avoiding deforestation and land degradation are incalculable”.

The 12-day conference aims to throw a spotlight on a global environmental issue that has drawn less attention in recent years than the related problem of manmade climate change, blamed on a surge of greenhouse gas emissions.

Scientists say worldwide human population pressures are wiping out ecosystems such as tropical forests and coral reefs, killing off animal and plant species that form the web of life which humanity depends on. “Our prosperity and indeed our survival depend on healthy ecosystems,” said Jim Leape, the chief of the Worldwide Fund for Nature (WWF). “The Earth's forests, oceans and rivers are the very foundation of our society and economy”.

“Even in purely economic terms, it is far, far more cost effective to conserve or restore healthy ecosystems than to artificially provide natural services that we currently take for granted”.

Delegates in Nagoya plan to set a new target for 2020 for curbing species loss, and will discuss boosting medium-term financial help for poor countries to help them protect their wildlife and habitats. But similar pledges to stem biodiversity loss, first made when the U.N. biodiversity convention was adopted in 1992, have not been fulfilled. At the start of the decade, U.N. members pledged under the Millennium Development Goals to achieve “a significant reduction” in the rate of wildlife loss by 2010, the International Year of Biodiversity. Instead, habitat destruction has continued unabated, and some experts now warn that the planet faces its sixth mass extinction phase — the latest since dinosaurs vanished 65 million years ago.

Nearly a quarter of mammals, one-third of amphibians, more than one in eight birds, and more than a fifth of plant species now face the threat of extinction, said the International Union for Conservation of Nature (IUCN).

In May, a U.N. report warned of looming “tipping points” that could irreversibly damage ecosystems such as the Amazon rainforest, through logging and land clearance, and coral reefs through global warming and overfishing. The Earth's 6.8 billion humans are effectively living 50 per cent beyond the planet's bio-capacity in 2007, according to a new assessment by WWF, adding that by 2030, humans will effectively need the capacity of two Earths.