The BiosphereChapter 3

The study of interactions between organisms and their environment.

What is Ecology?

Individual Population Community Ecosystem Biome Biosphere

Levels of Organization

Section 3-1

Figure 3-2 Ecological Levels of Organization

Observing Experimenting Modeling

Ecological Methods

To sustain an ecosystem there must be a constant input of energy and a cycling of materials.

Ecosystems

Energy Producers Consumers

Energy Flow

photoautotrophsherbivores

chemoautotrophs

carnivores

omnivores

decomposers

Energy flows in one direction through an ecosystem.

A food chain shows the transfer of energy from producers to consumers.

A freshwater stream food chain:

algaeaquatic insectscrayfishtrout

Note: all food chains start with a producer!

Feeding Relationships

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

Each step in a food chain or web is called a trophic level.◦ Producers always make up the first trophic level.◦ Consumers make up the second and higher

trophic levels.◦ Each trophic level depends upon the level below it

for energy.

Feeding Relationships

Section 3-2

Figure 3-8 A Food WebFood Web

Ecological pyramids show relative amounts of energy or biomass contained within each trophic level.

Only 10% of energy is transferred to the next trophic level.◦ Most of it is used for life processes and is lost as

heat.

Ecological Pyramids

Pyramid of NumbersThe relative number of individual organisms at each trophic level decreases.

Biomass PyramidThe greatest biomass is at the base of the pyramid.

Energy PyramidOnly 10% of the energy available at a trophic level is transferred to the next level. Much of the energy is lost as heat.

Section 3-2

Ecological PyramidsEcological Pyramids

Unlike the one-way flow of energy, matter is recycled within and between ecosystems.◦ Water, carbon, nitrogen and phosphorus are some

nutrients that are cycled.

Cycles of Matter

Evaporation, transpiration, condensation, and precipitation cycle water between the earth and the atmosphere.

Water Cycle

Condensation

Seepage

Runoff

Precipitation

TranspirationEvaporation

RootUptake

Section 3-3

The Water CycleWater Cycle

Carbon is cycled through carbon dioxide in the air, carbonates and fossil fuels in the ground, and organic molecules in living things.◦ Respiration, decomposition, and burning release

CO2 into the atmosphere.◦ Photosynthesis removes it and converts it to

organic molecules.

Note: only photosynthesis can remove a significant amount of CO2 from the atmosphere.

Carbon Cycle

Carbon Cycle

All organisms need nitrogen to build proteins. 80% of air is nitrogen. Nitrogen–fixing bacteria living in certain plant

roots use atmospheric nitrogen to make nitrates.

Producers absorb nitrates and make proteins. Consumers eat producers and get protein. Everybody dies. Decomposers return nitrogen to the soil and air.

Nitrogen Cycle

Organisms need phosphorus for molecules such as DNA, RNA and ATP.

Phosphorous is found mostly in rock, soil and ocean sediments as phosphate.

Plants take in phosphates to make needed compounds.

Consumers eat producers and obtain phosphates.

Everyone dies and decomposers return phosphates to the soil.

Phosphorus Cycle

Phosphorous Cycle

The availability of certain nutrients limits the primary productivity of an ecosystem.◦ Primary productivity is the rate at which organic

matter is made by producers.◦ Farmers apply fertilizers to boost productivity.

Fertilizers usually contain nitrogen, phosphorus and potassium.

Limiting Nutrients

Fertilizer Application

Limiting nutrients will limit the growth of producers.◦ Phosphorus limits plant growth in freshwater.◦ Nitrogen limits plant growth in saltwater.

A large input of either of these results in an “algal bloom”.

What causes a large input of these nutrients?

Limiting Nutrients

Algae Bloom