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Mammal diversity in rainforests linked to plant productivity

A new study of tropical rainforests has revealed a previously unknown link between mammal diversity and forest production. Researchers at Rice University analyzed camera-trap data from 15 wildlife preserves located within tropical rainforests. 

“In general, rainforest ecosystems are extremely diverse, and our study shows that mammal communities in rainforests can be predictably different, and these differences may be controlled, in part, by differences in plant productivity in forests,” said study co-author Daniel Gorczynski.

Even in protected areas, it is difficult to keep track of the health of wildlife and ecosystems. The Rice team turned to camera-trap photos from the Tropical Ecology Assessment and Monitoring Network (TEAM), which uses motion-activated cameras to monitor species trends in tropical forests in Asia, Africa, and South America.

According to study co-author Professor Lydia Beaudrot, the study’s scientific contributions demonstrate the importance of having the same data collection replicated on the ground in forests all around the world.

“The TEAM data are an incredible resource for basic and applied ecology and conservation,” said Professor Beaudrot. “Given the pace of tropical forest loss, it is more important now than ever to use standardized camera-trap data to understand environmental and anthropogenic effects on wildlife.”

For each site, the researchers collected data on all species of terrestrial mammals with an average body mass greater than one kilogram. All mammals at the same site were treated as a single community, and data was compiled for communities with as many as 31 species and as few as five. 

By compiling the functional traits for the species in each community – like diet and reproductive habits – the experts calculated the community’s “functional diversity.” 

“We found that species with unique characteristics – for example, species that are very large or eat unique foods – are relatively more common in forests with high productivity,” said Gorczynski. The research also showed that species with unique characteristics were less common at sites with low productivity.

“Higher productivity is thought to make rare resources, like certain food types that unique species often eat, more readily available, which unique species can capitalize on. And because they are unique, they don’t have to compete as much with other species for rare resources, and they can persist at higher abundances.”

Gorczynski explained that the species that are considered unique varied by site. These included elephants, tapirs, and ground-dwelling monkeys. He noted that this relationship between mammal diversity and productivity had not been previously recognized.

“Most studies of rainforest mammals rely on range maps, which don’t give you an idea of how common different species are,” said Gorczynski. “We were able to find this relationship because we used camera trap observations. The observational data gives us an idea of how common different species are, which allows us to compare the relative abundances of species with different traits.”

According to study co-author Jorge Ahumada, the research also shows that destructive human activities, like deforestation, decrease the diversity of species’ traits in protected areas. He said that simply counting the number of species in a tropical forest does not provide a full picture of mammal diversity or ecosystem health. 

“We found that in areas where local species extinctions have been documented due to significant deforestation or poaching, such as in Korup National Park in Cameroon, large carnivores like leopards and golden cats are the first to go,” said Ahumada. 

“Without these apex predators, entire food chains can be thrown out of balance. Eventually, populations of smaller herbivores will skyrocket, forcing more competition for the same limited resources.”

The study is published in the journal Proceedings of the Royal Society B.

By Chrissy Sexton, Staff Writer

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