Energy in Ecosystems

All organisms require energy to live Recall Photosynthesis: Energy from the sun is “captured”. The energy becomes chemical energy stored in organic compounds (PE). Producers: use energy from the sun to make their own food (organic compounds) Usually plants Can also be bacteria, plankton, and algae Consumers: obtain energy by consuming organic compounds (eating other living things). Can be herbivores or carnivores.

Trophic Level Pyramid Trophic level pyramid: a way to organize organisms based on the level at which they feed. Producers form the base of the pyramid. All energy for an ecosystem originates in the organic compounds made by the producers.

Energy flow: the trophic level pyramid Producers form the base of the pyramid. Primary consumers are the next level, followed by secondary consumers, then tertiary consumers. Energy flows through an ecosystem as consumers feed on other organisms (i.e.: as they consume the organic molecules contained within them).

Energy Flow: Food chains All energy in an ecosystem begins with the producers that make their own food. Energy is stored within these compounds, so an organism acquires energy if it consumes these compounds. A food chain shows that energy flows from a producer to a primary consumer and beyond.

An arrow is drawn indicating the movement of food molecules and, therefore, energy.

Energy Flow: The Food Web Food chains in an ecosystem often overlap as a result of an organism being eaten by more than one type of consumer Food Web: A diagram that shows how energy flows between all of the organisms in an ecosystem (a series of interconnected food chains)

A Food Web

All organisms require energy continued… Many organisms get their energy from other organisms Consumers Herbivores– get their energy from eating plants or other producers (1o consumer) Carnivores– get their energy from eating other animals (2o or 3o consumer) Omnivores– eat plants and animals Detritivores– eat only “dead” organisms Decomposers– bacteria and fungi that break down large molecules found in waste into smaller molecules

Why is the bottom of the pyramid so much bigger than the top? The size of each level represents the amount of energy that is available at that level Only about 10% of the available energy makes its from one level to the next level (not all of an organism is eaten, some energy is lost as heat during metabolism, etc.) Since producers create their own food/energy from the sun or molecules, they have 100% energy Using the 10% assumption, the primary producers would only have 10% of the producers’ original energy Secondary consumers would have 1%, tertiary consumers 0.10%, etc.

Energy at the 2nd trophic level Amount of energy contained within plant material eaten by the caterpillar Amount of energy that is stored in the body of the caterpillar that can potentially be passed on to the third level.

Pyramid shape continued… The result is that many producers are required at the bottom of a pyramid to support only a few higher-level consumers at the very top This low level of energy transfer keeps food chains fairly short

Pyramid Shape, cont’d The pyramid shape of a trophic level diagram also shows that producers are more numerous than herbivores, herbivores are more numerous than secondary consumers, etc.

Why aren’t detritivores part of the trophic level pyramid? Detritivores rarely pass energy onto the next level in the pyramid. Rather, they obtain some of the energy that is “lost” in each energy transfer by consuming the energy in the “leftovers” that might not otherwise be eaten. Since they don’t pass energy on to higher levels of the pyramid, they are not shown in the pyramid (nor in food chains or food webs)

Why do some ecosystems have more extensive food webs and species richness than others? Species Richness (Biodiversity) = # of different species in an area. The species richness in an ecosystem is entirely dependent upon the producers If conditions (temperature, sunlight, water, etc.) are good there will be many producers and high primary productivity (large mass of producers) More producers = more energy available for consumers = more consumers=high species richness Tropical rainforests and estuaries have high productivity and species richness, while deserts and temperate grasslands have much lower values

Think of how the primary productivity of these areas compare.

More on Species Richness Species richness is not only affected by primary productivity. It is also affected by: Area Habitat destruction and/or fragmentation reduces species richness “Key stone” Predators If certain predators are removed or low in numbers it reduces species richness in the lower trophic levels. Introduction of “foreign” species By either competing with endemic species or preying upon them, some endemic species go extinct and/or their populations are drastically reduced.

Reintroduction of Gray Wolves led to increased species richness