Animal Nutrition and Digestion

Section 1: Diet and Nutrition in Animals

  • Evolution and ecology determine an animal's diet.
  • Example: The lesser long-nosed bat (Leptonycteris yerbabuena) feeds on organ pipe cactus in Sonora, Mexico.
  • Different animals consume different foods:
    • Blue whales: Primarily krill.
    • Antelopes: Grass.
    • Lions: Antelope.

Four Stages of Food Processing in Animals

  1. Ingestion

    • Taking food into the digestive cavity.
    • Involves cutting, tearing, chewing, predigestion with salivary juices, and swallowing.

  2. Digestion

    • Breaking down food into microscopic and molecular fragments.

  3. Absorption

    • Nutrients are taken up from digestive organs and distributed to the body's tissues.
    • Ingestion and digestion occur "outside" the body, within the digestive tract.
    • The alimentary canal is like a tube open at both ends, surrounded by the body.
    • The digestive tract connects to the outside via the mouth and anus, and to the interior via absorptive tissues.

  4. ## Excretion

    • Elimination of waste from the digestive tract.
    • Waste products are indigestible materials (e.g., cellulose) that were never absorbed.
    • Metabolic wastes are expelled through other routes (e.g., kidneys filtering toxins, salts, and nitrogen wastes into urine).
  • All animals process food similarly, but details vary.
  • Animals seek foods their bodies can digest, showing strong preferences.
  • Food preference influences ecosystem stability.

Types of Diets

  • Herbivores: Eat plants and algae.
  • Carnivores: Eat meat.
  • Omnivores: Eat plants and animals (e.g., humans).
  • Diet and ingestion mechanisms co-evolve.
    • Herbivores (e.g., horses) have flat teeth for grinding tough plant material.
    • Spiders inject prey with digestive enzymes, liquefying them before ingestion.
    • Tigers use sharp teeth and powerful jaws to tear prey.

Four Main Ways Animals Acquire Food

  1. Suspension Feeders

    • Strain food particles from water using specialized structures.
    • Examples:
      • Clams and sponges (use cilia and flagella).
      • Flamingos (use bills to filter feed).
      • Blue whales (use baleen plates).

  2. Substrate Feeders

    • Live in or on their food source.
    • Examples:
      • Earthworms.
      • Termites (consume leaves, wood, microorganisms, and even dead animal flesh).

  3. Fluid Feeders

    • Drink liquid from living plants or animals.
    • Examples:
      • Mosquitoes (blood).
      • Vampire bats (blood).
      • Hummingbirds (nectar).
      • Ants (tree sap).

  4. ### Bulk Feeders

    • Eat large pieces of food.
    • Some chew carefully; others swallow prey whole.
    • Examples:
      • Humans.
      • Greater roadrunners (eat lizards, rattlesnakes, scorpions, and tarantulas).

Digestive Organ Adaptations

  • Digestive organs evolve to match diet.
    • Herbivores have longer digestive tracts to process plant matter.
    • Cellulose in plants is hard to digest.
    • Meat is nutrient-rich and easier to break down.
  • Carnivores may eat infrequently and have expandable stomachs.
  • Some sharks can evert their stomachs to expel indigestible items.
  • Some animals regurgitate, re-chew, and re-swallow food (e.g., cows, birds).
  • Rabbits eat partially digested droppings to further process nutrients.
  • Simpler digestive systems in some animals help us understand evolutionary constraints on digestion.
  • Humans can consume a wide variety of foods compared to most animals.