Chapter 3The Biosphere

3-1 What is Ecology?• Ecology is the scientific study of interactions

among organisms and between organisms and their environment, or surroundings.

Levels of Organization

Collection of all the living

organisms and the nonliving,

physical environment in a place

Parts of Earth in which life exists

3-2 Energy Flow

Where does the energy for life processes come from?

• The Sun! Sunlight is the main energy source for life on Earth.

• Only plants, some algae, and certain bacteria can capture energy from sunlight or chemicals and use that energy to produce food.

• The organisms that make their own food are called autotrophs (also known as producers).

• Photosynthesis is responsible for adding oxygen to (and removing carbon dioxide from) Earth's atmosphere.

Examples of Photosynthetic Autotrophs

Plants are the main autotrophs

on land.

Algae are the main autotrophs

in freshwater ecosystems and

in the upper layers of the

ocean.

Photosynthetic bacteria are

important in certain wet ecosystems, such as tidal flats and salt marshes.

Life Without Light• Some autotrophs can

produce food in the absence of light.

• When organisms use chemical energy to produce carbohydrates, the process is called chemosynthesis.

• Example: Bacteria that live in volcanic vents or tidal marshes

Consumers• Organisms that rely on other organisms for their

energy and food supply are called heterotrophs (also known as consumers because they consume/eat their food).

There are many different types of heterotrophs.

• Herbivores eat plants. (ex. cows, caterpillars, deer) • Carnivores eat animals. (ex. snakes, dogs, owls)• Omnivores eat both plants and animals. (ex.

humans, bears, crows)• Detritivores or Scavengers feed on plant and animal

remains and other dead matter. (ex. ants, vultures, crabs, earthworms)

• Decomposers break down organic matter. (ex. bacteria and fungi)

• Energy flows through an ecosystem in one direction, from the sun (or inorganic compounds) to autotrophs (producers) and then to various heterotrophs (consumers).

Feeding Relationships

Food Chains• A food chain is a series of steps in which

organisms transfer energy by eating and being eaten. It shows the energy transfer flowing in one direction only.

Food Webs• Ecologists describe

a feeding relationship in an ecosystem that forms a network of complex interactions as a food web.

• A food web links all the food chains in an ecosystem together.

• This food web shows some of the feeding relationships in a salt-marsh community.

• The more complex the food web the more stable the ecosystem. Why?

• The most complex food webs are in the Tropical Rainforest and the Coral Reefs where there is high biodiversity.

Trophic Levels• Each step in a food chain or

food web is called a trophic level.

o Producers make up the first trophic level.

o Consumers make up the second, third, or higher trophic levels.

• Each consumer depends on the trophic level below it for energy.

How efficient is the transfer of energy among organisms in an ecosystem?

• Ecological pyramid: a diagram that shows the relative amounts of energy or matter contained within each trophic level in a food chain or food web.

• Ecologists recognize three different types of ecological pyramids:

o energy pyramidso biomass pyramidso pyramids of numbers

Energy Pyramids

• Shows the relative amount of energy available at each trophic level.

• Only 10% of the energy that is stored in one trophic level is passed on to the next level.

• The more levels that exist between a producer and a top-level consumer in an ecosystem, the less energy that remains from the original amount. Maximum number of trophic levels is 5!!!!

• 90% of the energy at each level is lost as heat to the environment and used up in life processes

Biomass Pyramids• Represents

the amount of living organic matter at each trophic level.

• Typically, the greatest biomass is at the base of the pyramid.

Pyramid of Numbers• Shows the relative number of individual

organisms at each trophic level.