Chapter 9-The Cycling of Matter and Flow of Energy in Communities

Food Chains

The autotrophs (producers) in a food chain are the organisms that are able to convert solar energy into chemical bond energy in glucose through photosynthesis. This is because they have chloroplasts in their cells. All the heterotrophs (consumers) in the food chain pass along this energy.

Remember all organisms release the energy from the bonds of glucose by putting that energy into the bonds of ATP through cellular respiration.

The arrows show the direction that energy moves in a food chain.

Food Webs

In any ecosystem, food chains are connected to other food chains because the same organisms are used as food sources by many different organisms. These interconnected food chains are called a food web.

The phytoplankton (tiny plant-like protists) that live in the water are the autotrophs in the food web below. Notice that the dragon fly is actually part of 3 different food chains and provides energy for the trout, salamander and frog. In this case, the human is a secondary consumers because is eats a primary consumer (trout). In a different food web humans could be primary consumers when they eat vegetables. That’s because we are omnivores.

How many different food chains can you find in the food web below?

Energy Pyramids

Energy pyramids are designed to show that less energy is available as you move farther along a food chain.

In any food chain, the greatest amount of energy will be in the autotrophs. These are shown at the bottom of the pyramid. For example, all the primary consumers (1st level consumers) in this food web contain more energy than all the tertiary consumers (3rd level consumers).

Only about 10% of the energy moves from one step of a food chain (trophic level) to the next. The other 90% of the energy is used by the organisms in that trophic level to carry out their life processes.

Think about it for a minute-you eat lots of food (energy) every day but you don’t keep getting bigger! Most of the food (energy) is used for your daily activities and to keep your body functioning.

Below is an example of how much energy moves from producers to Tertiary (3rd level) consumers. Look at the energy units. Notice that only 10% of the energy from each trophic level moves on to the next trophic level.

Ecological Succession

Ecological succession is the change that occurs in the types of organisms living in an ecosystem over many years. Primary Succession occurs in areas that begin as bare rock with no soil present (a new volcanic island). Secondary Succession happens after something happens to an area (forest fire) but there would still be some soil and even small plants and animals.

Primary Succession (Land)

Pond Succession-here is an example of how a pond could gradually fill in and become a terrestrial (land) ecosystem

Symbiosis-organisms in an ecosystem interact with each other. Here are three types of interactions.

Mutalism-both benefit

The alligator gets its mouth cleaned and the bird gets a meal.

The bee gets nectar and the flower gets pollinated.

Commensalism-one benefits and the other is not affected

The bird eats the insects stirred up by the moving oxen but the oxen are not affected.

The clown fish is protected by from attack by the poisonous tentacles of the sea anemone (the clown fish is immune). The anemone is not affected.

Parasitism-one organism benefits and one is harmed (but not killed, usually).

Tick

The tick feeds on the blood of the mammal. The tick uses the blood as a food source. The mammal can suffer from loss of blood if many ticks are feeding on it.

Fungus

The fungus grows on and feeds from the strawberries on the plant. The fungus gets nutrients but the strawberry plant may not have as many offspring if too many of the seeds are destroyed by the fungus