One of the characteristics of living things is response to a stimulus in the environment. Based on the stimulus, an organism will "make changes" in its actions. We have seen how living things have special cells to detect those environmental stimuli, whether internal or external.

Behaviors are the actions or reactions of an organism to stimuli based on input from their senses. The way an organism "behaves" determines its place in the ecosystem.

• Behaviors determine whether an organism or species will survive.
   
• Behaviors determine the reproductive success of an organism or species.
   
• Changes in behavior allow organisms to adapt to changing conditions.

Innate behaviors are those that an organism has at birth - often called instincts. Nest-building is a good example of an innate behavior. All birds of the same species build nests that are almost identical.

Salmon have an innate behavior of returning to the same river in which they were hatched to lay their own eggs.

 
Many animals exhibit social behaviors. Everyone knows about "social" insects, like bees, that have a society with division of labor - queen, drone, workers. Some animals have a complex set of behaviors that are actually used for communication.

Cooperation behaviors allow a group of smaller animals to attack a larger one.

Territorial Behaviros

• During breeding season, males defend an area against other males.
  

  

• Males attempt to attract females with courtship displays.

• Birds, and some animals, migrate to escape poor weather and food supply.
• Geese fly 70% faster when they are in formation.
   
• It is believed that birds use migration cues such as the sun & stars, mountains, and changes in the earth's magnetic field.
   
• Monarch butterflies migrate over 1000 miles to winter in Mexico.

• Instead of migrating, some animals will hibernate to escape extremely cold weather.
   
• Bears can loose up to 30% of their body weight during hibernation.
   
• The metabolism of hibernating animals drops to extremely low levels. Ground squirrels (warm-blooded mammals) are known to maintain a body temperature just above freezing during hibernation.
   
• Some species actually produce glycerol, a type of "antifreeze", in their cells to resist ice crystal formation.

Aestivation

• Some animals are adapted to escape extremes in hot, dry weather.
   
• Most amphibians, and even some fish (like the lungfish), can burrow into the mud as a body of water dries up and wait until the water returns.
   
• Some even secrete a lipid, fatty substance, and coat their body to prevent water loss during this period of inactivity.

Predator-prey relationships:

Optimal foraging brings a predator the maximum net food energy gain. Predators do not normally spend great effort pursuing rare, energy-poor, or hard to handle prey.

Prey availability is a key factor in the foraging behavior of predators. Increasing numbers of prey elicit two types of responses from predators:

• Functional response - There is a relationship between prey density and the number of prey consumed per predator per unit of time. The predator seems to focus its attention on the shape and general appearance of the abundant prey, filtering out other potentially distracting stimuli. The abundant prey makes up an increasing percentage of the predator's diet.
   
• Numerical response - There is a relationship between prey density and predator density. Predator numbers increase as a prey population increases.

Reproductive Strategies

Living things have a wide range of strategies to insure reproductive success.

The Class Insecta, of the Phylum Arthropoda, is one of the most successful groups of living things on Earth today.

All insects go through one of two types of metamorphosis.

Most insects go through complete metamorphosis, which enhances their chance of survival. Since the larval and adult stages usually live in different habitats and eat different foods, they do not compete for space and food.

CONCEPTS (continued)  

Complete metamorphosis:

• Egg
   
• Larva - Looks nothing like the adult.
   
• Pupa - A stage in which the larva changes into the adult form.

  The pupa of butterflies is enclosed in a protective case called a chrysalis.

  The pupa of moths is enclosed in a protective case called a cocoon.

  Most butterflies and moths spend the winter in the pupa stage, often buried in the ground.
  

• Adult

• Egg
   
• Nymph - The nymph looks similar to the adult but does not have wings or sexual parts.
   
• Adult

No amphibians live in the ocean. Since the skin of amphibians is very thin, the high mineral content in sea water will dehydrate them to the point of death. Some will tolerate the brackish water of estuaries.

Amphibian lungs are poorly efficient. For this reason, amphibians also use their moist skin for respiration (cutaneous respiration).

Amphibians must reproduce in the water or very wet soil. Their eggs are covered with only a thin membrane that is permeable to water. For this reason, amphibian eggs cannot survive out of the water.

The tadpole stage has gills and feeds only on plants. During the metamorphosis, lungs form and the digestive system changes to that of a carnivore. The tadpole and the adult do NOT compete for food.

Neoteny is a process by which larva-like salamanders reproduce.

• Facultative neotenic organisms may or may not turn into the mature form at a later data.
   
• Obligate neotenic organisms will never turn into the mature form.

By remaining in the fully aquatic form, the animal exploits its aquatic environment as long as food and other favorable conditions last. Research indicates that neoteny occurs because the hypothalamus of the brain fails to produce the hormone that causes the pituitary to stimulate the thyroid gland to produce growth hormones that trigger metamorphosis.

Some scientists think that neoteny may be an evolutionary response to the hazards of life on land.

The amniote egg decreased the dependency of life on aquatic environments, allowing them to reproduce on land.

• Amnion - encloses embryonic fluid.
   
• Yolk sac - encloses the yolk.
   
• Allantois - stores embryo wastes.
   
• Chorion - lines the shell and regulates movement of gases in and out of the shell.

2 Reproductive Strategies In Birds:

Altricial birds

• Lay few eggs and incubate them for a short period.
   
• The young hatch blind, naked, and helpless.
   
• They depend on both parents for several weeks.
   
• The survival rate of the young is high.

• Lay many eggs and incubate them for a long period.
   
• The young birds are active as soon as they hatch.
   
• They can walk, swim, and feed themselves.
   
• Many of the young are caught by predators. But the larger number of offspring make up for this.
   
• Some just don't pay attention to Mom!

Egg-laying mammals, Monotremes

• Oviparous, egg-laying mammals.
   
• The female curls around the eggs to protect and incubate them.
   
• Although females have mammary glands, they do not have nipples. Milk is "sweated" onto the fur and licked by the young.
   
• Duck-billed platypus and spiny anteater, neither are native to North America.

Marsupials

• Viviparous mammals, giving birth to live young, but the young are born very prematurely. They make their way into the pouch where they attach to a nipple and continue to develop.
   
• The Opossum is the only marsupial in North America.
   
• Nearly 250 other species in New Guinea, Tasmania, and Australia - areas with no large mammalian predators.

Eutherians

• Viviparous mammals, giving birth to well developed young that have been nourished by a placenta in the uterus of the female.
   
• The most successful group, making up 95% of all mammal species.
   
• Every mammal native to the United States is a placental mammal, except the Opossum.

    EOI Practice Test