Ecosystems: Food Chains and Energy Flow

• Ecosystems encompass all organisms in an area and their interactions.
• Food chains illustrate feeding relationships within an ecosystem, showing who eats whom.
• Food chains represent feeding interactions in an ecosystem when organisms eat or are eaten.

Food Chain Examples

• A freshwater lake food chain: aquatic plants → stonefly larva → bluegill → osprey.
• A terrestrial food chain: grass → plant-eating insects → meat-eating insects → frog → snake → bird of prey.
• A marine food chain: algae → plankton → crustaceans → fish → dolphin → shark.

Energy Flow

• Energy is transferred from organism to organism through feeding.
• In the freshwater lake example, the aquatic plants used energy from the sun to create food through photosynthesis. The stonefly larva ate the aquatic plants, which means that the energy that aquatic plants contained was transferred to the stonefly.
• Energy flows in one direction, from lower to higher levels in the food chain.

Trophic Levels

• Trophic levels classify an organism's position in an ecosystem and its role in energy flow.
• Energy flows from producers to consumers.
• In the freshwater lake example, the aquatic plants produce their own food and are at the lowest trophic level or the base of the pyramid. The energy then flows to the aquatic insects, then to the bluegill that eats the aquatic insects, and finally to the osprey that eats the bluegill.

Producers (Autotrophs)

• Producers create their own food through photosynthesis or chemosynthesis.
• Photosynthetic producers use solar energy; chemosynthetic producers use chemical energy.
• Examples include algae, phytoplankton, and plants like duckweed or grass.

Primary Consumers

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

Secondary Consumers

• Secondary consumers feed on primary consumers.
• They can be carnivores or omnivores.
• Predators start to appear at this level.
• They make up the third trophic level.

Tertiary Consumers

• Tertiary consumers feed on secondary consumers.
• They are typically predators, either carnivores or omnivores.
• These animals occupy the fourth trophic level.

Quaternary Consumers

• Quaternary consumers are apex predators that feed on tertiary consumers and below.
• They are typically carnivores but can be omnivores.
• They are at the top of the food chain with few predators.

Herbivores

• Herbivores eat exclusively plant matter.
• Grasshoppers are primary consumers of plants.

Carnivores

• Carnivores feed exclusively on meat (other animals).
• Rat snakes eating rodents, lizards, and frogs are carnivores.
• Carnivores feed at the secondary consumer level or above.

Omnivores

• Omnivores eat both plants and meat.
• They can feed at all trophic levels from primary to quaternary consumers.

Food Webs

• Food webs represent all interconnected food chains within an ecosystem.
• They show how feeding relationships between organisms in different food chains are interconnected.
• Energy flows from producers to quaternary consumers, but not always linearly.
• Energy can flow between organisms in different food chains.

Energy Transfer Efficiency

• Energy transfer between trophic levels is not perfectly efficient.
• Typically, only 10% of energy from a lower level transfers to the next.
• The remaining energy is lost as heat, used for metabolism, or unconsumed.
• Example: If a grasshopper with 100 kJ of energy is eaten by a robin, only 10 kJ is transferred (100 kJ x 0.10 = 10 kJ).