U1 S2 L3 & L4Energy Flow in Ecosystems

What Affects the amount of Energy Reaching Ecosystems?

• Albedo• Other Environmental Factors

The flow of energy from the sun

The Albedo Effect

Albedo is a measure of the amount of light reflected from an object.

Albedo is normally expressed as a decimal value representing the percentage of light reflected.

For example, clouds have an average albedo about 0.27 so about 27% of the suns energy is normally reflected by clouds back to space.

On a clear day, more light would be able to penetrate to the Earths surface.

What has a greater albedo effect, snow covered glaciers or the canopy of the rainforest?

To stay warm in the winter what color would you wear? Why?

Albedo affects the amount of energy from the sun available for an ecosystem.

The Higher the albedo the less the energy available to an ecosystem!

Sample Albedo Values

Energy Budget

• Defined as the total Energy available to organisms in an ecosystem.

• What determines the energy budget?An ecosystem's energy budget depends on primary productivity

Primary Productivity– The total amount of food created by primary producers as a result of

Photosynthesis.

Photosynthesis

6CO2(g) + 6H2O(l) C6H12O6(s) + 6 O2(g)Glucose or Food

–Only an estimated 1% of the light that does reach the primary producers is actually converted into chemical energy by photosynthesis.

Examining Primary Productivity

• Gross Primary Productivity (GPP)– Defined as the total amount of food created by plants in an area at any one

time.• Net Primary Productivity (NPP)

– Defined as the amount of food left to be passed on to the next trophic level after plants use some for their own purposes.

NOTE: NPP is ALWAYS less than GPP!!!

Factors Affecting Primary Productivity

• The factors that affect productivity in the various terrestrial and aquatic ecosystems include:

– light intensity, – temperature, – carbon dioxide availability, – availability of nitrogen and phosphorus, – latitude/altitude (terrestrial ecosystems) or – depth (aquatic ecosystems)

Food Chains

One possible path for the flow of energy in an ecosystem.

• If the community has a great deal of biodiversity, there will be several organisms that can feed on more than one type of food resource, and as a result there would be several possible food chains.

• Each step in the food chain is called a trophic level.

Corn Mouse Snake Hawk

Food Webs

• All the possible Food Chains in an Ecosystem.

Food Chains and Energy Flow

• What happens to energy as it flows along a food chain?– Energy is lost!!!– How? – Cellular Respiration is used to convert sugar in foods into energy for

organisms to use, but at the same time some energy is lost as heat!!

– Because energy is lost along the food chain, Pyramids of Energy, Biomass and Numbers are created.

Pyramid of Energy

• The idea that each higher trophic level has less energy available to it.• 10% rule – only 10% of the energy of one trophic level gets transferred to the next

trophic level (90% is lost as heat)!!

Pyramid of Biomass

• A pyramid that represents the total biomass of organisms at each trophic level.• Biomass -- The total dry weight of organisms in a trophic level.

• Why dry weight?– Because amount of water varies in each ecosystem, so dry weight is used as a

better measuring tool.• Pyramid is similar in structure to a pyramid of Energy. 10% rule. • There can be exceptions!!!!

10000 Kg

1000 Kg

100 Kg

10 Kg

Pyramid of Numbers

• Pyramid that represents the total number of organisms that can be supported at each trophic level.

• There can be exceptions!!!Normal

Exception

Conditions Necessary for a Stable, Self-sustaining or Sustainable Ecosystem

• Stability means that there is an ecological balance between the various organisms that make up the food web, and because of this balance the ecosystem is self-sustaining over long periods of time.

• To be stable there must be a balance between food production, food consumption, and decomposition of dead organisms and/or their wastes.

Keystone Species

• A keystone species is one considered so important to the stability of the ecosystem, that if there was a decline in that species, the community would not be able to maintain its stability and may even collapse.

• For example:– sea otters in kelp forests keep sea urchins in check. Kelp roots are merely anchors, and

not the vast nutrient gathering networks of land plants. Thus the urchins only need to eat the roots of the kelp, a tiny fraction of the plant's biomass, to remove it from the ecosystem.

Example: The Sea Otter (Coast of California)

Another Example of a Keystone Species

• The beaver is another example of a keystone species.

• It transforms its territory from a stream to a pond or swamp

Niche vs habitat

Habitat

• the place were an organism lives. • The habitat of an organism is part of its niche. • The organism's habitat is its address - where it lives.

• Every organism has its own habitat. – The habitat of slime molds is the damp floor of the forest.

• The organism's habitat is were the organism is best adapted to survive. – a fish is adapted to life in water because it has gills to get oxygen.

• A single area may satisfy the needs of many kinds of plants and animals. These organisms that associate together in a common habitat form communities.

• For Example:

– The Pine Marten prefers to live in undisturbed mature coniferous or mixed forest, with large evergreens and scattered birch and other hardwood trees.

– For denning and nesting sites, the martens uses hollow trees, stumps and logs.

Niche

• The role that a species plays within its ecosystem. • In balanced ecosystems, each species occupies its

own niche.• The niche is like the organism's profession - what it

does to survive.• The function or position of an organism or population

within an ecological community.• The particular area within a habitat occupied by an

organism.

Competition

• Organisms are forced to compete against their own species and also different species in order to survive.

• The stronger and more fit organisms have an advantage over those who are weaker, and they have a better chance of surviving.

• Competition arises when organisms have requirements in common and they must compete to meet their own needs.

• The more needs organisms have in common, the more intense the competition.

• When the resources that are being competed for become scarce the competition becomes more intense, and eventually one of the species becomes eliminated.

– Habitats have finite amounts of the resources needed by living organisms, such as food, water and space, and all organisms strive to reproduce themselves and increase their numbers.

– Sooner or later the demand for these resources is going to exceed supply, and organisms have to compete with each other to get them.

• Plants typically compete with each other for:– light (for photosynthesis) – water, and – nutrients (minerals)

• Animals typically compete with each other for:– food – water – mates (so they can reproduce), and – living space

Intra-specific competition

• Competition between the same species

– Many birds of the same species compete for the best nesting grounds.

– In cases when food or water is scarce, members of the same species will compete for food in order to survive.

– Bull moose competing for a mate

Inter-specific competition

• Competition between different species

– Different species often compete for space, food, or water. – Fox and coyote compete for the rabbit