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Arboreal locomotion is the locomotion of in . In in which trees are present, animals have evolution to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The habitats pose numerous mechanical challenges to animals moving through them and lead to a variety of anatomical, behavioral and ecological consequences as well as variations throughout different species.Matt Cartmill (1985). "Climbing". pp. 73–88 In: Hildebrand, Milton; Bramble, Dennis M.; ; Wake, David B. (editors) (1985). Functional Vertebrate Morphology. Cambridge, Massachusetts: Belknap Press. 544 pp. . Furthermore, many of these same principles may be applied to climbing without trees, such as on rock piles or mountains.
Some animals are exclusively arboreal in habitat, such as .
Arboreal animals frequently have elongated limbs that help them cross gaps, reach fruit or other resources, test the firmness of support ahead, and in some cases, to brachiation. However, some species of lizard have reduced limb size that helps them avoid limb movement being obstructed by impinging branches.
Many arboreal species, such as , green tree pythons, emerald tree boas, , , , and Phalangeriformes, use to grasp branches. In the spider monkey and crested gecko, the tip of the tail has either a bare patch or adhesive pad, which provides increased friction.
Various organisms use Claws to negotiate rough surfaces such as or corky substrates and re-orient the direction of the force the animal applies. This allows lizards such as Agamas and Cordylidae to inhabit cliffs, and to climb tree trunks that are so large as to be essentially flat. However, claws can interfere with an animal's ability to grasp very small branches, as they may wrap too far around and prick the animal's own paw.
Adhesion is an alternative to claws, which works best on smooth surfaces. Wet adhesion is common in and arboreal salamanders, and functions either by suction or by capillary adhesion. Dry adhesion is best typified by the specialized toes of , which use van der Waals forces to adhere to many substrates, even glass. In some species of geckoes, such as in the genus Lygodactylus, the reliance on van der Waals forces is supplemented by a patch of specialised scales under the tip of the tail; a tail regenerated after defensive autotomy however, lacks that adhesive tip. have evolved highly mobile ankle joints that permit rotating the foot into a 'reversed' posture. This allows the claws to hook into the rough surface of the bark, opposing the force of gravity.
Many arboreal species lower their center of mass to reduce pitching and toppling movement when climbing. This may be accomplished by postural changes, altered body proportions, or smaller size.
Small size provides many advantages to arboreal species: such as increasing the relative size of branches to the animal, lower center of mass, increased stability, lower mass (allowing movement on smaller branches), and the ability to move through more cluttered habitat. Size relating to weight affects gliding animals such as the reduced weight per snout-vent length for Flying frog.
Some species of primate, bat, and all species of sloth achieve passive stability by hanging beneath the branch. Both pitching and tipping become irrelevant, as the only method of failure would be losing their grip.
Behavioral specializations
Arboreal species have behaviors specialized for moving in their habitats, most prominently in terms of posture and gait. Specifically, arboreal mammals take longer steps, extend their limbs further forwards and backwards during a step, adopt a more 'crouched' posture to lower their center of mass, and use a diagonal sequence gait.
Brachiation
Brachiation is a specialized form of arboreal locomotion, used by primates to move very rapidly while hanging beneath branches. Arguably the epitome of arboreal locomotion, it involves swinging with the arms from one handhold to another. Only a few species are , and all of these are primates; it is a major means of locomotion among and , and is occasionally used by female . Gibbons are the experts of this mode of locomotion, swinging from branch to branch distances of up to 15 m (50 ft), and traveling at speeds of as much as .
Gliding and parachuting
To bridge gaps between trees, Gliding animals such as the flying squirrel have adapted membranes, such as Patagium for gliding flight. Some animals can slow their descent in the air using a method known as parachuting, such as Rhacophorus (a "flying frog" species) that has adapted toe membranes allowing it to fall more slowly after leaping from trees.
Limbless climbing
Many species of snake are highly arboreal, and some have evolved specialized musculature for this habitat. While moving in arboreal habitats, snakes move slowly along bare branches using a specialized form of concertina locomotion, Astley, H. C. and Jayne, B. C. (2007). Effects of perch diameter and incline on the kinematics, performance, and modes of arboreal locomotion of corn snakes ( Elaphe guttata)" J. Exp. Biol. 210, 3862–3872. but when secondary branches emerge from the branch being moved on, snakes use lateral undulation, a much faster mode. As a result, snakes perform best on small perches in cluttered environments, while limbed organisms seem to do best on large perches in uncluttered environments.
Evolutionary history
The earliest known climbing tetrapod is the varanopid amniote Eoscansor from the Late Carboniferous (Pennsylvanian) of North America which is clearly specialised with adaptations for grasping, likely onto tree trunks. Suminia, a anomodont synapsid from Russia dating to the Lopingian, about 260 million years ago, was also likely a specialised climber.
See also
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