I. Nutritional Requirements:
• The diet supplies three needs:
• 1.Fuel (ATP)
• 2.The organic raw materials for biosynthesis
• 3.Essential nutrients--substances that the animals cannot make for itself from any
• For example, ascorbic acid (vitamin C) is an essential nutrient for humans
and other primates, guinea pigs, and some birds and snakes, but not for
most other animals.
B. Homeostasis is always the goal.
• 1.Overnourishment results from excessive food intake.
• While fat hoarding can be a liability today, it probably provided a fitness advantage
for our hunting/gathering ancestors, enabling individuals with genes promoting
the storage of high-energy molecules during feasts to survive the eventual
• 2. If the diet is missing one+ essential nutrients the animal is malnourished.
• For example, many herbivores living where soils and plants are deficient in
phosphorus eat bones to obtain this essential nutrient.
• 3.Animals require 20 amino acids to make proteins.
• Most animals can synthesize half of these if their diet includes organic nitrogen.
• 4.Essential amino acids must be obtained from food.
• Eight amino acids are essential in the adult human with a ninth, histidine, essential
• 5.Vitamins are organic molecules required in small quantities.
• 6.Minerals are simple inorganic nutrients, usually required in small amounts.(Fe, Ca, P, I)
• Humans and other vertebrates require relatively large quantities of calcium and
phosphorus for bones among other uses.
II.Food Types and Feeding Methods
• A. Most animals fit into one of three dietary categories.
• 1.Herbivores, eat mainly autotrophs (plants, algae).
• 2.Carnivores, eat other animals.
• 3.Omnivores, consume animals and plants.
B. Diverse feeding adaptations have evolved among animals
Suspension-feeders sift small food particles from the water.
• Baleen whales, the largest animals ever to live, swim with their mouths
open, straining millions of small animals from the water forced through
baleen attached to their jaws.
• 2.Deposit-feeders (earthworms) eat their way through dirt and extract organic material.
• 3.Substrate-feeders live in or on their food source, eating their way through the food.
• For example, maggots
burrow into animal
carcasses and leaf miners
V. Structural adaptations of digestive systems are often associated with diet
• A.Dentition (teeth) reflects diet.
• Particularly in mammals,
of teeth for processing
different kinds of food is
one of the major reasons
that mammals have been
• B.Large, expandable stomachs are common in carnivores.
• For example, a 200-kg African lion can consume 40 kg of meat in one meal.
• C.The length of the vertebrate digestive system is also correlated with diet.
• In general, herbivores and omnivores have longer alimentary canals relative
to their body sizes than do
more time for digestion
and more surface area
for absorption of nutrients.
• The most elaborate adaptations for a herbivorous diet have evolved in the
ruminants, which include deer, cattle, and sheep.