<P> Animals locomote for a variety of reasons, such as to find food, a mate, a suitable microhabitat, or to escape predators . </P> <P> Animals use locomotion in a wide variety of ways to procure food . Terrestrial methods include ambush predation, social predation, grazing . Aquatic methods include filterfeeding, grazing, ram feeding, suction feeding, protrusion and pivot feeding . Other methods include parasitism and parasitoidism . </P> <P> A variety of methods and equipment are used to study animal locomotion: </P> <Ul> <Li> Treadmills are used to allow animals to walk or run while remaining stationary with respect to external observers . This technique facilitates filming or recordings of physiological information from the animal (e.g., during studies of energetics). Motorized treadmills are also used to measure the endurance capacity (stamina) of animals . </Li> <Li> Racetracks lined with photocells or filmed while animals run along them are used to measure acceleration and maximal sprint speed . </Li> <Li> Kinematics is the study of the motion of an entire animal or parts of its body . It is typically accomplished by placing visual markers at particular anatomical locations on the animal and then recording video of its movement . The video is often captured from multiple angles, with frame rates exceeding 2000 frames per second when capturing high speed movement . The location of each marker is determined for each video frame, and data from multiple views is integrated to give positions of each point through time . Computers are sometimes used to track the markers, although this task must often be performed manually . The kinematic data can be used to determine fundamental motion attributes such as velocity, acceleration, joint angles, and the sequencing and timing of kinematic events . These fundamental attributes can be used to quantify various higher level attributes, such as the physical abilities of the animal (e.g., its maximum running speed, how steep a slope it can climb), neural control of locomotion, gait, and responses to environmental variation . These, in turn, can aid in formulation of hypotheses about the animal or locomotion in general . </Li> <Li> Force plates are platforms, usually part of a trackway, that can be used to measure the magnitude and direction of forces of an animal's step . When used with kinematics and a sufficiently detailed model of anatomy, inverse dynamics solutions can determine the forces not just at the contact with the ground, but at each joint in the limb . </Li> <Li> Electromyography (EMG) is a method of detecting the electrical activity that occurs when muscles are activated, thus determining which muscles an animal uses for a given movement . This can be accomplished either by surface electrodes (usually in large animals) or implanted electrodes (often wires thinner than a human hair). Furthermore, the intensity of electrical activity can correlate to the level of muscle activity, with greater activity implying (though not definitively showing) greater force . </Li> <Li> Sonomicrometry employs a pair of piezoelectric crystals implanted in a muscle or tendon to continuously measure the length of a muscle or tendon . This is useful because surface kinematics may be inaccurate due to skin movement . Similarly, if an elastic tendon is in series with the muscle, the muscle length may not be accurately reflected by the joint angle . </Li> <Li> Tendon force buckles measure the force produced by a single muscle by measuring the strain of a tendon . After the experiment, the tendon's elastic modulus is determined and used to compute the exact force produced by the muscle . However, this can only be used on muscles with long tendons . </Li> <Li> Particle image velocimetry is used in aquatic and aerial systems to measure the flow of fluid around and past a moving aquatic organism, allowing fluid dynamics calculations to determine pressure gradients, speeds, etc . </Li> <Li> Fluoroscopy allows real - time X-ray video, for precise kinematics of moving bones . Markers opaque to X-rays can allow simultaneous tracking of muscle length . </Li> </Ul>

What type of land animals are able to exchange