World biodiversity has declined by almost one third in the past 35 years due mainly to habitat loss and the wildlife trade, the World Wide Fund for Nature (WWF) said.
It warned that climate change would add increasingly to the wildlife woes over the next three decades.
"Biodiversity underpins the health of the planet and has a direct impact on all our lives so it is alarming that despite of an increased awareness of environmental issues we continue to see a downtrend trend," said WWF campaign head Colin Butfield.
"However, there are small signs for hope and if government grasps what is left of this rapidly closing window of opportunity, we can begin to reverse this trend."
WWF's Living Planet Index tracks some 4,000 species of birds, fish, mammals, reptiles and amphibians globally. It shows that between 1970 and 2007 land-based species fell by 25 per cent, marine by 28 per cent and freshwater by 29 per cent.
Marine bird species have fallen 30 per cent since the mid-1990s.
The report comes ahead of a meeting in Bonn next week of member states of the UN Convention on Biological Diversity to try to find out how to save the world's flora and fauna under threat from human activities.
Some scientists see the loss of plants, animals and insects as the start of the sixth great species wipe out in the Earth's history, the last being in the age of the dinosaurs which disappeared 130 million years ago.
Scientists point out that most of the world's food and medicines come initially from nature, and note that dwindling species put human survival at risk.
"Reduced biodiversity means millions of people face a future where food supplies are more vulnerable to pests and disease and where water is in irregular or short supply," said WWF director general James Leape.
"No one can escape the impact of biodiversity loss because reduced global diversity translates quite clearly into fewer new medicines, greater vulnerability to natural disasters and greater effects from global warming. The head of Britain's world-renowned Kew Gardens in an interview last month likened biodiversity - the broad array of plants and animals spread across the planet - to a planetary health monitor.
"First-aiders always check the ABC - Airway, Breathing and Circulation - of a patient to see if anything needs immediate attention," Stephen Hopper said.
"Biodiversity is the ABC of life on the planet - and it is showing it is in deep trouble," he added.
Kew is doing its part through the Millennium Seed Bank project, which is well on the way to collecting and storing safely 10 per cent of the world's wild plants.
The next goal - as yet a wish without any financial backing - is to raise that total to 25 per cent by 2020.