CHAPTER 3 How Ecosystems Work

The Sun

• The sun is the main source of Energy for all life on earth.

• The sun is the start of most food chains.• Less than 1% of the sun’s energy that

reaches earth is used by living things.

CHAP. 3-1 Energy Flow

• Feeding Relationships:• Autotrophs – get energy from sun or

chemicals to produce food (photosynthetic or chemosynthetic); also called producers

• Heterotrophs – depend on autotrophs or other heterotrophs for food; also called consumers

Types of Heterotrophs• Herbivores – feed only on

plants; ex – rabbits, deer• Carnivores – feed only on animals

ex. – tigers and lionsOmnivores – feed on plants & animals ; ex. –

bears, humans

Types of Heterotrophs

• Detritivore- feeds on detritus (dead matter)– Scavengers – feed on dead organisms; ex. –

vultures, crayfish– Decomposers – feed on dead or decaying plant &

animals; ex. – bacteria, protozoa, fungi

Feeding Relationships• Food Chain - Model to show how

matter & energy flow through an ecosystem

• Energy must 1st pass from producers to consumers

• Food chains only show 1 possible • route

Feeding Relationships• Food webs – show all possible routes• Each organism

represents a feeding step or trophic level

Trophic LevelsEach step in a food web or food pyramid

is called a trophic level (energy level)

10% RuleOnly 10% of the energy from one

trophic level is passed on to the next.100% grass 10% cow 1% humans

Levels of Consumers

• Primary consumers– Eat producers

• Secondary consumers– Eat herbivore

• Tertiary consumers– Eat carnivore

• Quaternary consumers– Eats carnivore that ate the carnivore

Ecological Pyramids

• Diagram that shows the amounts of matter or energy contained at each trophic level

• 3 pyramids:• Pyramid of Energy• Pyramid of Numbers• Pyramid of Biomass

Pyramid of Energy• Shows the amount of energy which is

moving from one level to the next.• Shows that only

about 10% of theenergy available within a trophiclevel is transferredto the next trophic level

Pyramid of Numbers• Shows the

decreasingnumber oforganismsat each successivefeeding level

Pyramid of Biomass• Biomass- total amount of living tissue in a given trophic level.• Shows the amt. of potential

food at each feeding level; decreases at each successive level

Biomagnification

• The tendency for the concentration of pollutants to increase in animals higher up on the food chain.

• Ex: mercury in Tuna, or DDT in Eagles

3-3 Succession• Succession: Changes in an ecosystem over time; include organisms dying out & new ones taking their place

• Pioneer species – the 1st species to populate the area

• Climax Community- the community that eventually forms if the land is left undisturbed.

Primary Succession• Primary succession – occurs on surfaces

where no soil existed; ex. – after a volcano erupts

Secondary Succession• Secondary succession – follows a disturbance

that destroyed an ecosystem but did not destroy the soil; ex. – after a forest fire