Unit 3 Ecosystems

Topic 1: Energy flow and matter cycling

Ecosystem

A location determined by the interactions between organisms, their physical environments, and other organisms

Abiotic factors determine which organisms can live in a place

Energy and matter

Energy flows through ecosystems

Matter cycles within and between ecosystems

ENERGY LAWS:

The first law of thermodynamics: – Energy cannot be created or destroyed by

organisms.– Organisms can change energy from one form to

another. The second law of thermodynamics:

– When energy changes from one form to another, it is always degraded to a more dispersed form.

– In other words, energy quality decreases as it changes forms (eg chemical energy heat)

Energy in ecosystems Almost all energy in ecosystems

originated in the sun as a result of nuclear fusion reactions.

This comes to earth as photons; ultraviolet radiation is used by autotrophs to convert carbon dioxide and water into carbohydrates.

The conversion of carbon from an inorganic to an organic form is called carbon fixation.

This process through which this occurs is called photosynthesis.

Do you remember the overall equation?

Primary productivity The RATE of biomass production in autotrophs of an

ecosystem. Measured in either kilocalories per area per year OR

kilojoules per area per year Depends on a number of abiotic factors:

– Light intensity, nutrient & mineral availability, temperature, precipitation

NPP of world ecosystems:

Primary production Gross primary production

(GPP)= the total organic matter produced by plants with energy captured during photosynthesis

Net primary production (NPP)= the amount of biomass available to consumers at the next trophic level (after respiration, metabolic processes, and losses to detritus)

Ecological efficiency The percentage of energy (as biomass) transferred

from one trophic level to the next.– Varies between 5 and 40%.– An average of 10% is assumed for calculation purposes. – This is called the 10% Rule.

What is the Ecological efficiency of this example?

Food chains

Food chains show individual energy pathways in an ecosystem.

Energy and biomass pyramids The availability of energy at

each trophic level can be depicted as energy or as biomass.

Due to metabolic processes and respiration, the amount of energy decreases at each trophic level (remember the 10% rule!).

Because there is less energy available to the next level, fewer organisms can be supported.

Thus, biomass decreases with each trophic level.

ENERGY BIOMASS

Food webs Food webs show all possible

trophic interactions between organisms in an ecosystem.

This is a more realistic portrayal of ecological communities.

There should be even more connections in this figure. Can you name them? Can you think of organisms that are missing from this picture?

Make a food web on page 6.

Biogeochemical cycles

Descriptions of how matter cycles through ecosystems– Organisms– Geological and atmospheric states– Changes in chemical form

Hydrologic cycle

Carbon cycle

Nitrogen cycle

Sulfur cycle

Phosphorus cycle