Arboreal animals and the architecture of tropical forests

Seen from above, the tropical forests of Asia, Africa, and the Americas may appear similar. But for arboreal animals, each is a distinct world.

The study by Emmons & Gentry (1983) revealed that tropical forests are not all the same. Their structural differences help explain the variety of forms and movements among arboreal animals.

The distance between trees, the density of lianas, the fragility of branches, the diversity of layers, and the abundance of palms, among other factors, define the three-dimensional space of each forest. This complex architecture imposes selective pressures and shapes life in the canopy.

Some animals leap between trees, others glide, hang by their tails, or swing from their arms. Each movement is a response to the architecture of the canopy — branches, leaves, trunks, and lianas that guide locomotion above the forest.

In Asian forests, where trees are farther apart and lianas are scarce, squirrels, frogs, lizards, and even snakes have developed bodily adaptations that allow them to glide. These improvised wings are passports to cross the wide gaps of the forest.

Life high in the trees demands absolute balance. In different Neotropical groups — such as monkeys, anteaters, marsupials, and porcupines — the prehensile tail evolved as a “fifth limb,” providing extra safety and expanding access to food in the canopy.

African forests are interwoven with a natural web of lianas. This connectivity makes it easier for primates and other animals to move, reducing the pressure for radical anatomical adaptations. Here, the forest offers its own suspension bridges.

Monkeys, anteaters, marsupials, and snakes developed prehensile tails in the Americas. Gliding reptiles, amphibians, and mammals evolved in Asia. Distinct histories, similar solutions: evolutionary convergence in response to common ecological challenges.