Hunting is a major threat to wildlife in tropical regions. A previous study led by Ana Benítez-López at Radboud University, showed that bird populations declined on average by 58 percent and mammal populations by 83 percent in hunted forests. The same group of scientists has now been able to map the expected decline for each mammal species across all tropical forests.
4000 mammal species mapped
The scientists base their conclusions on data collected over the span of 40 years on the numbers of mammals in hunted and unhunted areas. Based on these numbers, they estimated the impact of hunting on approximately 4000 mammal species in the tropics. The populations of medium sized mammals, such as monkeys, showed an average decline of 27 percent. The average decline in large mammals, like jaguars, leopards, elephants and rhinos is even bigger: more than 40 percent. "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", Ana Benítez-López explains.
Where are species more threatened by hunting?
According to the study, more than half of tropical forests are under hunting pressure. 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." The scientists identified hotspots where hunting pressure is highest. "We mapped the tropical areas and for each location estimated how severe the impact of hunting on mammals is. We found the biggest declines in Western Africa, with more than 70 percent of population reduction. 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."
Take into consideration in retaining biodiversity
Hunting is not the only driver of animal decline in tropical landscapes. Other drivers are habitat destruction and fragmentation by deforestation and logging. The abundance decline of mammals may have profound implications for ecosystem functioning. Benítez-López: "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". In addition, some rural communities are dependent on wild meat for their food supply, but their main sources of protein may be slowly disappearing. "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. Further, now we have identified hotspots of hunting that require monitoring and conservation", Benítez-López concludes.
Ana Benítez-López, Luca Santini, Aafke M. Schipper, Michela Busana, Mark A. J. Huijbregts. Intact but empty forests? Patterns of hunting-induced mammal defaunation in the tropics. PLOS Biology. DOI: 10.1371/journal.pbio.3000247