E6 Respiratory and Circulatory Biomechanics

Topic

Perception and prediction provide the information that allows a predatory mammal to successfully plan and execute an attack, or enables prey to escape that very attack. Several sensory systems are involved in gathering this information: vision, which detects the prey's position and speed; hearing, which locates the prey by comparing the timing of sound arrival at each ear; olfaction, which detects wind direction; and mechanoreceptors, which detect ground vibrations caused by another animal's movement.

Predicting the prey's heading—based on information from these sensory systems—allows the predator to choose an interception route rather than directly chasing the prey along the path it has already traveled. By intercepting the prey's future trajectory instead of following its past path, the predator minimizes both the distance it must cover and the energy required to catch the prey.

In its simplest form, this interception route follows a precise rule: the predator continuously adjusts its own direction of movement so that the angle at which it views the prey remains constant throughout the chase. By maintaining this constant viewing angle, the predator and prey eventually meet at the same point, without the predator needing to explicitly calculate the prey's future position.

During the chase, the predator also needs to know the time remaining until it catches the prey. This "time-to-contact" is determined by dividing the distance separating the two animals by the rate at which that gap is closing—a calculation the visual system can perform directly based on how rapidly the prey's image expands within the visual field, without needing to separately determine distance and speed. That same visual system that estimates time-to-contact has a limit on its ability to detect changes: the smallest change in a stimulus that an animal can perceive is not a fixed amount but is proportional to the magnitude of the background stimulus against which the change occurs; thus, detecting the same absolute change is easier against a weak background than against an intense one.

Once the sensory system detects the need to correct the trajectory, that correction does not happen immediately: there is a motor response latency between the moment the need for correction is detected and the moment the body actually corrects its course, and this latency determines how much time the animal truly has available to adjust its trajectory before contact.

At the end of this chain of perception and prediction—with which this description began—what determines whether it is worth it for the predator to attempt an attack is the attack's efficiency: the ratio between the energy the predator gains from the prey (if successful in capturing it) and the energetic cost of the entire effort involved in perceiving, predicting, pursuing, and correcting the trajectory during the attack. When this ratio is favorable, the hunting strategy is metabolically profitable; when it is not, pursuing that particular prey ceases to make energetic sense for the predator.

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