Ecosystem Dynamics

Food Chains and Food Webs

Maroochydore SHS

Energy in Ecosystems

Energy that sustains majority of living systems is solar energy

Solar energy is converted to chemical energy in photosynthesis and is held briefly in the biosphere before it is radiated into space as heat

Getting Energy

Autrotrophs (Producers) produce their own food using the suns energy (Photosynthesis)

Autrotrophs are eaten by other organisms, which in turn are eaten

This is how food passes through ecosystem

Food chain = the path that food takes from organism to organism

Based on the way they obtain food, the organisms can be classified in three groups:

1.Producers2.Consumers3.Decomposers

Producers (Autotrophs)

Convert simple inorganic chemicals to complex organic molecules (food)

Most use solar radiation (sun) as a source

Productivity = measured by the amount of energy that is fixed in chemical compounds or by increase in biomass in a particular length of time

Example of a Producer…Plants…

Utilize energy from the sun and nutrients from the abiotic environment (carbon dioxide from the air or water, other nutrients from the soil or water) Result = photosynthesis

ConsumersUsed food by other organisms as their energy sourceThree levels of consumers:1. First-order (Primary) are herbivores2. Second-order (Secondary) eat first-

order consumers (carnivores which eat herbivores)

3. Third (Tertiary) and higher order eat second-order consumers (carnivores which eat other carnivores)

Decomposers

Most are simple forms of life (bacteria, fungi and some protozoans) These break down the dead bodies and waste products of other living thingsConvert complex organic molecules into simple inorganic chemical which are then released into the environment and can be reused

Food Chain

Simple linear series that shows the series of organisms existing in any ecosystem

Can be described as a transfer of energyEach organism in the series feeds on and obtains energy from the preceding organism and provides energy to the next organism

Trophic (feeding) levels describe the relative positions of producers and consumers in a food chain

Food ChainsA food chain shows what a set of organisms in an ecosystem eats with each organism acting as a link in the chain. Each link is called a trophic level.

Arrows connect each level and point in the

direction in which the food is going.Energy flows through an ecosystem from plants (producers) to herbivores (primary consumers to carnivores (secondary consumers)

The ant is eaten by the bird.

There are rarely more than 6 links in any food chain

This is because energy is lost to the environment in the form of heat at each level of a food chain

The closer a consumer is to the producer, the more efficient is the energy transfer

Food chains always start with the sun and then a plant.

The lettuce is eaten by the slug, the slug is eaten by the bird.

The top of the food chain.

Some animals are said to be at the top of the food chain. This is because they are not

hunted by other animals.

No other animal hunts the lion. The lion is at the top of

the food chain. Can you think why?

Food Webs

Displays the interactions between organisms in a community

In a food web there is greater stability since a variety of food sources compensates for seasonal fluctuations

All waste and dead materials are acted upon by decomposers

Law of Conservation of Matter and Energy

Ecosystems conform to this law which states that:

“matter and energy cannot be created or destroyed but can be changed to

other forms”

Ecological Pyramids

May be:Pyramid of numbers

Showing the #s of individual organisms at each level

Pyramid of biomassBased on the total dry mass of the organisms at each level

Pyramid of energyShowing the productivity of the different levels

Large amounts of energy and biomass are dissipated at every trophic level

Pyramid of Numbers

This pyramid illustrates that when the primary producers (leaves) are small, a large quantity of them

is required to support the primary consumers (herbivores)

Pyramid of Energy availability

The relationship of the flow of Energy in the ecosystem - represented here by an inverted pyramid. Generally only 10% of

the energy of each trophic level is passed on as energy to the next, higher level