Biomechanical Studies of Food and Diet Selection


The ways animals acquire food are largely determined by the medium in which they feed. As water is dense and viscous, resistive forces are important and affect the way prey can be captured resulting in the independent evolution of suction feeding in many vertebrate groups. Alternatively, on land, gravitational forces play an important role and will affect prey capture and transport by imposing limits on the use of adhesive forces and thus tongue‐based capture and transport. Biomechanical approaches involving the analysis of movements and forces can, combined with theoretical models, help explain the selective pressures operating on the feeding system. As such, these approaches may help explain the divergence of the feeding system in animals occupying different ecological niches and may help us understand the proximate factors driving adaptive radiations.

Key Concepts:

  • The density of the medium animals live in determines their prey capture strategy.

  • Prey capture using suction has evolved independently in many vertebrate groups.

  • Tongues work only on land.

  • Trade‐offs are inherent to mechanical systems.

  • Biomechanical models are limited by the quality of the input data used.

  • Tooth morphology and wear are powerful indicators of feeding ecology.

  • Functional approaches can help explain ecomorphological patterns.

  • The feeding system and prey mechanical defences co‐evolve.

Keywords: feeding; biomechanics; modelling; functional morphology; ecomorphology; suspension feeding; suction feeding; bite force; trade‐offs

Figure 1.

Suspension‐feeding mechanisms have been classified into seven major groups: sieving, direct interception, inertial impaction, gravitational deposition, motile particle deposition, electrostatic attraction, and crossflow filtration. Sieving (a) is the simplest method and consists of retaining only those particles larger than the pores of the sieve. Direct interception and inertial impaction (b) are rather similar and rely on the retention of food particles on the mesh of the filter itself. In gravitational deposition (c), the particles are deposited on the filter through gravitational processes. Motile particle deposition (d), on the other hand, relies on the active movements of the particles independent of the water current to intersect with the filter. Electrostatic attraction is a filtering method that has been proposed for invertebrates and possibly also in anuran larvae. Here small particles are thought to adhere to the mucous layer covering filters due to electrostatic attraction forces. In crossflow filtration (e), the incoming flow is parallel with the filtering surface. This only allows passing of clear filtrate, whereas a gradually more condense particle‐laden flow continues towards the oesophagus. (Modified after Rubenstein and Koehl, ; Lauder, ).

Figure 2.

Biomechanical trade‐offs between speed and force generation. (a) In simple lever systems the force exerted is determined by the input force (Fi) and the distance between the point of exertion of the input (I=inlever) and output forces (O=outlever, Fo=output force) and the fulcrum. The shorter O becomes, the larger the output force of the system (bottom panel). However, for a given force Fi the displacement (d1, d2) within a given time increment will also be set by the length of the lever arms. If the length of the outlever O increases, the displacement d2 in the same time period will be larger and thus the velocity of movement will be higher as well. (b) In a third order lever system, as is observed in the jaw closing system of mammals, the same rules apply. In a real jaw system, long jaws will result in a rapid closing and opening action and short jaws will be associated with a powerful bite.

Figure 3.

Biomechanical analysis of mammalian skulls. Depicted are schematic representations of the skull of a carnivore (cat) and an omnivore (pig). Note how the fulcrum is positioned much higher up the jaw in the case of the pig. This allows omnivores and herbivores to exert grinding movements (entire tooth row in contact upon closure). In carnivores, on the other hand, the jaws exert a cutting motion. Also indicated are the force vectors exerted by the jaw muscles. The temporalis (blue), and the masseter (red) muscle vectors are shown. The size of the arrow indicates the importance of the muscle. Whereas in carnivores the temporalis is the largest jaw‐closer muscle, in omnivores and herbivores the masseter is the largest jaw‐closer muscle. Note also how the position of the biggest muscle groups is such that in carnivores maximal force is generated with open jaws, and in omnivores and herbivores with closed jaws (i.e. the line of action of the muscle is optimal). rB, moment arm bite force; rT, moment arm temporalis muscle; rM, moment arm masseter muscle; FB, bite force.

Figure 4.

Tooth shape and function. (a) Where two flat surfaces are moved towards each other crushing is achieved. By adding a translation component to the movement, a grinding action is added to the system. Note that the addition of irregularities on the surface of the teeth will greatly improve the efficiency of the movement. The tooth of a blue‐tongued skink (Tiliqua scincoides) is shown to illustrate a typical crushing tooth. This animal uses its teeth to crush hard objects such as snails. (b) If pointed teeth are brought together in a dorsoventral plane a piercing movement is the result. By adding a translational component, a lacerating action is created. As illustration, the teeth of a tokay gecko (Gekko gecko) are shown. These simple, pointed teeth are used to pierce the exoskeleton of small arthropods. (c) When the teeth become sharp ridges, splitting will be the result of movements in the dorsoventral plane. By adding movements parallel to the long axis of the ridge, a cutting action can be achieved. The teeth of a large herbivorous scincid lizard (Corucia zebrata) are shown as illustration of this tooth type. These teeth are used to crop small pieces from larger leaves. Modified after Sibbing .

Figure 5.

The effect of body size on bite forces in vertebrates. Depicted are the sizes of skulls and corresponding bite forces for different taxa. In black the theoretical scaling of length to force is indicated (slope=2), and the dashed line represents the scaling line for lizard and turtle bite forces. Note how in lizards and turtles bite force increases much faster with skull length than in mammals or archosaurs. This implies that if one scaled a lizard up to the size of a Tyrannosaurus rex, it would be biting at least ten times as hard. Data from in vivo studies are indicated with circles, from modelling studies with diamonds and from indentation studies with hexagons. (Based on data gathered by the authors for bats and turtles and lizards; Thomason, ; Dean et al., ; Lindner et al., ; Erickson et al., ; Binder and Van Valkenburg, ; Rayfield et al., ; McBrayer and White, ).



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Herrel, Anthony, Van Wassenbergh, Sam, and Aerts, Peter(Jun 2012) Biomechanical Studies of Food and Diet Selection. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0003213.pub2]