Arboreal- Definition, Biomechanics of Trees, Adaptions

Arboreal is anything that pertains to trees. Since trees are everywhere, anything that relates to the tree, be it the animals that live it or any structure that resembles the branching shape of a tree, such as the architectural design or the chandelier piece in any room. The arboreal word comes from the Latin word arboreus, meaning ‘pertaining or relating to trees’.

Arboreal
Arboreal

Trees are ubiquitous. Hence it provides shelter and food and is an important means of transportation for various species whose livelihood depends on trees. Since the beginning of flora and fauna, trees have been an important source of life, directly or indirectly. They glue together the whole ecosystem of its surrounding. They manage not only the biotic factors of the ecosystem but also the abiotic factors such as water resources. They also bless the living organism with their medicinal properties, besides everything else. The benefits and properties of trees are numerous, and the concept of ‘Mother Nature’ is embodied by a woman depicting the beauty of a healthy relationship shared by plants and animals, constituting a balanced ecosystem.

The locomotion of animals in trees is referred to as Arboreal Locomotion. Transportation in trees is generally referred to as ‘Climbing.’ This mode of locomotion is specially adapted by animals surviving in a habitat surrounded by trees. Some animals are exclusively arboreal, like sloths, flying lemurs, brushtail possums, monkeys, etc., while others might occasionally scale or climb up for various purposes. The movement through trees poses numerous biomechanical challenges and thus shapes the ecological, anatomical, and behavioral factors in animals moving through them. In this article, we’ll try to understand arboreal animals’ challenges in locomotion via trees and their adaptation.

Biomechanics of Trees

Trees are shaped by their surrounding and the growing environment. Every region has a bunch of endemic and native tree species. Every native tree has a particular tree form and different wood physical and biomechanical properties. Arboreal habitats pose diverse mechanical challenges for animal locomotion through trees, such as branch incline, dealing with obstructions, balancing, etc. Animals residing in these trees adapt to these changes and overcome the challenges.

Balancing

Moving in a tree requires many balancing techniques to save oneself from tipping over and falling. 

  • The arboreal animals face the issue of a narrow base of support in a horizontal branch and tipping to the side due to imbalance. 
  • The vertical and steep branches do not pose the threat of tipping over but slipping downwards or pitching backward creates a difficult obstruction to the movement of limbed animals. 
  • Branches with wider diameters require much more balance than thinner branches as the animal cannot place their forelimbs closer to the center of the branch, which might lead to a slipping downward scenario. 

Branch Diameter

Many terrestrial animals deal with the center of mass swinging from side to side during movement on the land surface. 

  • But in arboreal locomotion, the center of mass tends to edge over the branch diameter, increasing the risk of toppling over and falling. 
  • Not only do animals deal with varying branch diameters while moving, but they also rely on food consumption on the branches, depending on their ability to adapt various grasping techniques to clamp themselves for balance. 

Branch Inclination

Animals have to deal with the branches placed at an angle to gravity. 

  • Being vertically oriented poses a special problem in the arboreal habitat, making it more difficult to deal with gravity moving up and down the branch while avoiding the chance of falling. 
  • As the branch inclination goes up, animals have to fight the force of gravity with the ability to raise their body. To overcome this challenge, arboreal species engage all their limbs, emphasizing upper body strength and increasing the frequency of their movement pattern sequence. 
  • Another issue of vertically inclined branches is the descendant movement. They must fight the change in gravity to control their gait while moving down and declining the risk of falling. 
  • To achieve this, arboreal animals increase their limb contact with the branch, increasing frictional force and braking power.

Dealing with Obstructions

Obstructions lead to impeding locomotion for limbed animals. These obstructions can be the branches of the tree the animal is in or branches from neighboring trees. This poses a challenge for limbed animals as it decreases the frequency of movements. But these obstructive branches are the additional contact point for better directional locomotion for crawling animals like snakes.

Anatomical Adaptions

Trees serve as shelter to many diverse living organisms. Adaptations of arboreal animals present a perfect example of the core hypothesis used in biology – ‘Form Fits Function.’ The specialized anatomical adaptations of tree-dwellers are perfectly engineered for the function it executes. Arboreal animals form an interesting group from different taxa, including mammals, birds, reptiles, insects, and arachnids. All these organisms are very different from each other. Yet, they are represented in a category of arboreal animals since they perform common tasks, present similar behavioral patterns, and show evolutionary anatomical adaptations to survive in a tree or forest. It is observed that arboreal animals are mostly concentrated geographically in tropical forests but are also found throughout the world in all forest ecosystems. Surviving in the trees poses fascinating challenges for arboreal animals, like raising offspring, locomotion through the trees, opting for shelter in extreme weather, and food gathering and storage. All these challenges are conquered by anatomical adaptations.

Prehensile Tail

  • Arboreal limbed animals such as spider monkeys, opossums, tree pangolins, anteaters, etc., have a prehensile tail. 
  • They are primarily used as an anchor to balance the animal’s body while climbing, hanging, or swinging from the trees.
  •  These especially adapted tails serve a variety of additional tasks such as food gathering, manipulating, and holding an object.

Gliding Membranes

Several arboreal animals have developed a unique anatomical adaptation to descend from the trees. 

  • This adaptation of flexible membranes between the forelimb and hindlimb helps increase the surface area of an animal without adding weight, allowing them to glide from trees. 
  • The gliding and parachuting actions also bridge the gap between the trees. 
  • Examples of animals that use gliding as a locomotory descendent movement include flying squirrels, geckos, flying frogs, and more.

Limb Length and Strong Grip

This specialized anatomical feature is exclusively observed in primates. 

  • This feature includes long, strong arms for gripping branches, crossing gaps between trees, and other resources such as fruits. 
  • Scientists refer to this special ability of primates to swing with long arms from one branch to another as ‘Brachiation’. 
  • Besides long arms in brachiating primates, they also possess some other beneficial features like shorter spines, flexible wrists allowing free movement, small fingernails instead of long claws, smaller thumbs, and long curved fingers for better gripping of branches. 

Center of Gravity

Arboreal animals have a characteristically lower center of gravity to maintain balance and minimize the chances of falling from the tree while climbing and swinging. Other ways to maintain the center of gravity are accomplished by changes in posture, altered body positions, diagonal sequence gait, and smaller body size.

Adhesion and Gripping Feet

Adhesion is an anatomical adaptation alternative to claws. Wet adhesion via suction or capillary action can be commonly observed in arboreal salamanders and tree frogs. Dry adhesion that functions via van der waal forces to adhere to substrates is seen in geckos.

Animals dwelling in trees must have a strong grip to hold on tightly to the branches. Arboreal primates and limbed animals possess hairless fingertips allowing the animal to squeeze the branch between the fingertips to generate friction. Other useful adaptations opted for by these animals include adhesive pads, claws, and flexible ankle joints that can turn forwards and backward to stay in one place.

Conclusion

Anything that relates to trees is referred to as arboreal. The animals that opt to live in the tree for survival have to deal with many challenges, such as branch inclination, gravity, locomotion, and many more. And to overcome this, arboreal animals have unique specialization and adaptation, perfectly suited for living in the trees. Anatomical adaptations include longer forelimbs, gripping feet, low center of gravity, gliding membranes, and more. These features provide interesting research for scientists to study their evolutionary patterns and behavioral interaction with the environment.

References

  1. Dixit, Saurav, Anna Stefańska, and Adam Musiuk. “Architectural form finding in arboreal supporting structure optimisation.” Ain Shams Engineering Journal 12.2 (2021): 2321-2329.
  2. Arboreal – https://www.vocabulary.com/dictionary/arboreal
  3. Arboreal locomotion – https://en.wikipedia.org/wiki/Arboreal_locomotion#cite_note-Cartmill-1
  4. Tree biomechanics and environment – https://www.forestresearch.gov.uk/research/tree-and-wood-properties/tree-biomechanics-and-environment/
  5. ANIMALS THAT LIVE IN TREES (AND HOW THEY’VE ADAPTED TO SURVIVE) – https://www.plt.org/educator-tips/animals-live-trees

About Author

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Nidhi Dewangan

Nidhi Dewangan has a bachelor’s and Master’s degree in Biochemistry from Pandit Ravishankar Shukla University, Raipur (C.G.), India. She is the author of the Chapter “Commonly found Bacteria and Drug-Resistant Gene in Wastewater” in the book “Antimicrobial Resistance in Wastewater and Human Health” published by Elsevier, under the guidance of Dr. Awanish Kumar, Assistant Professor at the Department of Biotechnology, NIT Raipur. She’s also a University and a National player in Squash. She has represented her University and won team events in the All India University Squash Championships. Her research interest is genetics and computational biology.

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