Yes, rats do live in the rainforest, but the term encompasses a vast and diverse group of native rodents integral to the ecosystem, rather than solely the common pest species. Rainforests worldwide, from the Neotropics to the Paleotropics, host hundreds of unique rodent species. These animals have successfully adapted to the complex environment of the tropical forest. They occupy the ecological niche typically associated with “rats,” playing a significant role in the health and function of this unique biome.
Taxonomy and Species Diversity
The popular image of a “rat” usually refers to members of the genus Rattus, which include the invasive Black Rat (Rattus rattus) and Brown Rat (Rattus norvegicus). While these introduced species can sometimes be found in disturbed rainforest edges, the vast majority of rodents inhabiting pristine rainforests are native species belonging to entirely different families. These native forest species are often highly specialized and rarely venture into human settlements.
In the Neotropical rainforests of Central and South America, the most prominent native rodent families are the Cricetidae and the Echimyidae. Cricetidae, or New World rats and mice, is one of the largest mammal families, with many genera adapted to life in the forest understory and canopy. The Echimyidae family, commonly known as spiny rats, is particularly diverse in this region and includes terrestrial and arboreal species like the Central American spiny rat (Proechimys semispinosus) and various tree rats.
Similarly, in the Paleotropics, native Murid rodents have diversified into forest specialists distinct from invasive pests. Genera like Maxomys and Niviventer in Asia, and native Australian species like the Fawn-footed Melomys, are examples of forest-dwelling species. Rainforests are biodiversity hotspots for rodents, and these native species typically avoid the fragmented or degraded habitats where invasive Rattus species thrive.
Ecological Function and Habitat Role
These native rodents are functionally intertwined with the forest’s reproductive and trophic cycles, performing roles that are fundamental to maintaining tree diversity. Their most significant impact is on seed ecology, acting as both seed predators and, paradoxically, seed dispersers. They consume a large number of seeds from tropical trees, which prevents the immediate establishment of seedlings near the parent plant.
Many species engage in scatter-hoarding, where they bury or cache seeds for later consumption. If the rodent forgets where a seed is stored, or dies before retrieving the cache, the buried seed is effectively dispersed away from the parent tree, increasing its chance of germination and survival. Studies in tropical forests have tracked seeds moved by rodents up to 19 meters from their origin, resulting in successful seedling recruitment.
Beyond their role in plant regeneration, rodents serve as a primary prey base, linking the plant community to the higher levels of the food web. Their high reproductive output provides a reliable food source for a wide array of predators, including snakes, raptors, and small carnivores like ocelots. This predator pressure influences the rodents’ foraging decisions, affecting their seed-caching and dispersal behaviors.
Adaptations to Vertical Rainforest Layers
Rainforest rodents have evolved specific physical traits that allow them to exploit the different vertical layers of the forest, from the floor to the canopy. Arboreal species, which live mostly in the trees, show traits for enhanced climbing and balance. These adaptations often include long, prehensile or semi-prehensile tails that function as a fifth limb for grasping branches and providing stability. Many climbing species, such as the New World climbing rats of the genus Tylomys, also possess specialized pads and flexible ankles for a secure grip on smooth bark or slender vines.
These arboreal specialists inhabit the mid-story and upper canopy, feeding on fruits, flowers, and insects. Terrestrial species, in contrast, are adapted for life on the forest floor, possessing robust bodies and shorter limbs suited for running and burrowing. Spiny rats, like those in the genus Proechimys, are ground-dwellers that create complex burrow systems beneath the leaf litter and root systems. This vertical stratification reduces competition among the numerous rodent species coexisting in the same forest.