How did rodents get so diverse? Costa Rica may have answers

David Villalobos Chaves
David Villalobos Chaves
January 30, 2020 | David Villalobos Chaves

If I asked you to think of a mammal, images of lions, elephants, gorillas, and other large, charismatic species might pop into your head. But statistically, you should be thinking about rodents. Rodents make up over 40 percent of all mammal species and represent one of the most diverse mammalian groups, ranging from the burrowing naked mole rat to the ecosystem shaping American beaver.

The diversification of rodents is one of the most striking events in mammal evolution, due to their large number of species and diverse ecological roles. In the past, scientists investigated how various evolutionary processes, like new physical features and behaviors that allow rodents to use the environment in novel ways and coexist with other species, may have led to the rapid radiation of rodent species. But there is still a lack of detailed information on the ecological preferences, behavior and anatomy of most wild rodent species, which prevents us from fully understanding why rodents became so diverse in the first place.

This past summer, I conducted fieldwork in Costa Rica where we collected data on the diverse community of rodents in Tapanti-Macizo de la Muerte National Park. We are trying to understand the anatomical and behavioral characteristics that allow rodent species to utilize different resources, co-exist in their environment, and diversify from common ancestors. 

Working in the rain forest of Central America is not easy. It involves carrying and setting hundreds of heavy traps on very steep hills, often in the rain with annoying insects buzzing around your head and deadly creatures such as venomous snakes. Despite these challenges, we were able to capture hundreds of rodents from several species, some of which are endemic to the Costa Rica-Panama mountain range, meaning they are found nowhere else. We measured physical characteristics like body size and bite force as a proxy for feeding performance, collected fecal samples for diet analysis, and conducted behavioral observations.

These data will help fill in the gaps for a better understanding of how Neotropical rodent communities are structured and which adaptations allow species to thrive in their ecosystem. This ongoing research will also be highly valuable to inform conservation decisions that affect these small yet highly diverse and ecologically important mammals.

David Villalobos Chaves is a University of Washington Ph. D. student in the Lab of Curator of Mammals Sharlene Santana and a mammalogy volunteer at the Burke Museum of Natural History and Culture. He is a Costa Rican biologist interested in the natural history, ecology and evolution of mammals, with a special focus on highly diverse groups such as rodents and bats. 

Read more Mammalogy research stories.