Bio 205

Feeding

Transport

• ingestion
• oral transport
• deglutition (swallowing)

Differences in these components of transport depend on fluid medium

• water
  • dense - gravity is low but inertia is high
  • viscous - friction and pressure drag are large
• air
  • light - gravity is large but inertia is low
  • less viscous - friction and pressure drag are small

modes of ingestion

• aquatic
  • filter feeding
    • Primitively, filter feeding was a mechanism of acquiring food particles. This is retained in amphioxus and larval lampreys. Gnathostome filter feeders ingest food particles via some other mechanism (suction or ram feeding - see below) and simply use gill rakers, baleen (in whales), or modified beaks (in flamingos) to sieve the food particles from the water as it exits the buccal cavity (into the opercular cavity in fishes or out of the mouth in tetrapods).
  • suction feeding. The fundamental ingestion method in aquatic vertebrates. Sucking water into the mouth creates a flow past the food particle. This flow creates drag (remember a force in the direction of the flow) on the particle due to skin friction and any separation of the flow downstream. This drag cause the particle to flow with the water. In air, this mechanism cannot work because of low drag. That is the suction force would need to be really large to create a large enough drag on the food particle. Suction also works better in water because many particles (passively floating prey or actively swimming prey) tend to be suspended in the water column and are not affected by gravity while in air, gravity is more influential and the suction force would need to balance gravity as well.

   

• ram feeding - moving the body over the food item. May be used for filter feeding suspended prey or feeding on active, elusive prey. Some suction may be used to compensate the tendency to push the food item out of the way with the pressure wave in front of the moving predator.
• biting, scraping, etc. - Biting and scraping are less common in aquatic predators because there is the tendency for a biting mouth to push out the prey, unless it is firmly attached to something, such as a fish or a coral. For example, Pirahna may bite from a larger fish because the force pushing the prey is very small relative to the mass of the prey (and its resistance to being pushed out of the way). Or, parrotfish may bite corals because the coral is attached to the bottom and will not move in response to the closing mouth.
• terrestrial
  • Projection
    • whole body -
    • craniocervical - e.g. snake strikes, heron or egret feeding (even chickens feeding on cornseed in a barnyard).
    • hyolingual - e.g. frog, salamander, and chameleon tongue strikes.
      • why hyolingual ingestion is rare in water. In tongue projection, muscle contractions are used to accelerate the tongue toward the front of the buccal cavity. The tongue's own momentum (its mass times velocity) carries the tongue out of the buccal cavity toward the prey item. This requires large accelerations of the tongue and little resistance to tongue motion once it is flying through the air. In water, much larger muscles would be needed to accelerate a tongue since the added mass would be much greater (remember, in an accelerating body, both the mass of the body and the mass of the displaced fluid are accelerated. The mass of displaced air is much less than the mass of an equal amount (in volume) of water. Also, the increased viscosity of the water would make the drag much greater on the tongue moving in water and hence the projecting tongue would slow down much more rapidly in water than in air. Hence, tongue projectile mechanisms are extremely rare in aquatic vertebrates (but not in George Lucas star wars films).
  • forelimb or hindlimb transport

Oral transport

• aquatic
  • suction
• terrestrial
  • inertial - the head accelerates forward over the prey item. Similar to a car accelerating forward making any passengers or loose items move back to the back of the car.
  • lingual
    • why lingual transport is rare in water - lingual transport works because of adhesion (friction) between the tongue and the food particle. Friction is a force moves the item with the tongue. This is only possible in air where the drag on a food particle is low. In water, where the drag is high, the drag tending to keep the particle from moving with the tongue would tend to be higher than the friction keeping the particle moving with the tongue. E.g. put a ping pong ball on your flat palm and move your hand toward your mouth. The ball comes along for the ride. Now do this in water. The drag on the ball will be much higher than the friction and your hand will slide out from underneath the ball.