Illegal hunting is causing catastrophic declines in mammal populations living in the world’s remaining tropical forests, a new study has warned.

Jaguars, leopards, elephants and rhinos have seen population declines of 40 per cent in just 40 years and the study warned that hunting – half of which is done illegally – has left many tropical forests "empty" of wildlife.

Even the world’s most pristine jungles are having their ecosystems damaged as key species are wiped out by hunters looking to collect valuable horns and bones, an international team of researchers lead by the Radboud University in Holland, found.

Within the tropics, only 20 per cent of remaining habitats are considered intact.

“Without adequate measures wildlife hunting will increase in the future,” lead researcher Dr Benítez-López told The Independent.

According to the study, more than half of tropical forests are under hunting pressure (Benítez-López/PLOS)

“Our calculations show that even in protected areas mammal populations could be under hunting pressure, particularly in Western and Central Africa, and South East Asia. If projections of human population growth for Africa are true, the demand will continue to increase. Plus there are many roads planned that will traverse tropical forests."

Until now there were vast understudied areas in the tropics where hunting impacts on mammal communities were unknown, according to the study which is published in the Plos Biology journal.

The biggest declines were seen in Western Africa, with more than 70 per cent population reductions. Researchers found primates and pangolins were most at risk.

Declines have largely been caused by increased human accessibility to remote areas.

$5,000,000,000,000: The cost each year of vanishing rainforest Show all 2 1 /2 $5,000,000,000,000: The cost each year of vanishing rainforest $5,000,000,000,000: The cost each year of vanishing rainforest 80 per cent of the world's remaining terrestrial biodiversity live in forests Getty Images $5,000,000,000,000: The cost each year of vanishing rainforest 75 per cent of global fish stocks are fully or over-exploited AFP/Getty Images

Dr Benítez-López said: “Hunters target primarily large-bodied species because they provide relatively large meat yields and commercially valuable by-products such as horns and bones. In addition, large mammals reproduce at slow rates, which means that it takes longer for their populations to recover when exploited.”

The study estimated the impact of hunting on 4,000 mammal species in the tropics. More than half of tropical forests are under pressure from hunting.

Dr Benítez-López said: “Hunting of carnivores may lead to an increase in herbivores with negative consequences for the vegetation whereas the hunting on species that feed on fruits and disperse their seeds can have negative consequences on forest regeneration”

The decline of mammals may have profound implications for ecosystem functioning.

“In the tropics habitat loss due to land use change (deforestation and conversion to croplands or rangelands) is still the leading cause of defaunation, yet hunting has comparable effects and, more importantly, it is responsible for massive declines in animal populations in seemingly undisturbed forests,” said Dr Benítez-López.

“Even forests that are considered intact according to satellite images – in which there is no visible deforestation or logging – could be partially defaunated.”

Rural communities who rely on wild meat for their food may find their main source of protein disappearing.

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“Hunting effects were to this point not considered in large-scale biodiversity assessments and our results may help to fill this gap and to eventually produce more representative estimates of human-induced biodiversity loss,” she said.

The study looked at more than 3,200 data estimates from the last 40 years. It included more than 160 studies and hundreds of authors studying around 300 mammals across the tropics.