Ecosystems: Food Chains & Energy Flow

• Ecosystems are complex systems of organisms and their interactions, including feeding for energy.
• Food chains represent who eats whom in an ecosystem, illustrating feeding interactions.
• In a freshwater lake ecosystem, a food chain example is: aquatic plants → stonefly larva → bluegill → osprey.

Energy Flow in Ecosystems

• Energy is transferred from organism to organism through feeding.
• In the freshwater lake example, aquatic plants use solar energy for photosynthesis and create food.
• The stonefly larva then eats the aquatic plants, transferring energy.
• Energy flows upward to the bluegill when it eats the stonefly larva, and then to the osprey when it consumes the bluegill.
• Energy flows in one direction as each organism consumes the one below it in the chain.

Food Chain and Trophic Levels

• Trophic levels classify an organism's position in an ecosystem and how they contribute to energy flow.
• Energy flows from producers to consumers as organisms at higher levels eat those at lower levels.
• Aquatic plants are at the base of the pyramid.
• Energy moves upward to aquatic insects (primary consumers), then to bluegill (secondary consumers), and finally to osprey (tertiary/quaternary consumer).

Producer

• Producers (autotrophs) form the base of the trophic pyramid.
• Autotrophs create their own food through photosynthesis (using solar energy) or chemosynthesis (using chemical energy).
• Examples of producers include algae, phytoplankton, and plants like duckweed or grass.

Primary Consumer

• Primary consumers feed on producers.
• They are exclusively herbivores, like grasshoppers.
• Primary consumers occupy the second trophic level.

Secondary Consumer

• Secondary consumers feed on primary consumers.
• They can be carnivores or omnivores, such as robins.
• Predators start appearing in the third trophic level.

Tertiary Consumer

• Tertiary consumers feed on secondary consumers.
• Typically predators, they can be carnivores or omnivores, such as rat snakes.
• Occupy the fourth trophic level.

Quaternary Consumers

• Quaternary consumers are apex predators that feed on tertiary consumers.
• Typically carnivores, they can be omnivores, such as hawks.
• Sit at the top of the trophic pyramid with few predators.

Herbivores, Carnivores, and Omnivores

• Organisms that cannot produce their own food eat others for energy.
• These describe the typical diet of an organism and which trophic level they occupy.

Herbivores

• Herbivores feed exclusively on plant matter like grasshoppers.
• Energy transfers from plants to the herbivore.
• Herbivores are primary consumers of plant-produced energy.

Carnivores

• Carnivores feed exclusively on meat.
• Rat snakes are carnivores.
• Carnivores feed at the secondary consumer level or above.

Omnivores

• Omnivores eat both plants and meat.
• Due to their diet, omnivores can feed at all trophic levels from primary to quaternary consumers.

Food Web Energy Flow

• Food webs represent all interconnected food chains within an ecosystem.
• They show how feeding relationships between organisms are connected.
• Energy flows upward from producers to quaternary consumers, and can also flow between organisms in different food chains.

10% Rule

• Only about 10% of energy transfers from one trophic level to the next.
• The remaining energy is lost through heat, metabolism, or unconsumed matter.
• For example, if a grasshopper has 100 kJ of energy, only 10 kJ is transferred to a robin that eats it (100 kJ x 0.10 = 10 kJ).
• The remaining 90 kJ is lost to heat, metabolism, or unconsumed matter.

Explore energy transfer in ecosystems through food chains. Understand how energy flows from producers to consumers, illustrated by a freshwater lake ecosystem example. Learn about trophic levels and organism roles.