fv11 - food chains

AP Environmental Science: Unit 1 – The Living World: Ecosystems

Topic: 1.11 Food Chains and Food Webs

Page 1: Energy Transfers in Ecosystems

• Food Chain Definition

  • A linear representation of how organisms depend on each other for food.

  • Example: In a grassland ecosystem:

    • Grass (Producer) → Rabbit (Primary Consumer) → Hawk (Secondary Consumer).

• Limitations of Food Chains

  • Oversimplified model; does not account for multiple prey or predators.

  • Example: Both owls and hawks can eat the same rabbit.

• Food Webs

  • A more complex representation showing all feeding relationships in an ecosystem.

  • Allows observation of trophic cascades—how populations at one level affect others.

• Trophic Cascade Example

  • In a marine ecosystem:

    • Increased sea otter population → Decreased sea urchin population → Increased kelp growth.

  • Ripple effects can lead to habitat changes for other species.

Page 2: Response to Disturbance

• Feedback Mechanisms

  • Natural systems maintain a steady state through feedback.

  • Two types of feedback: Negative and Positive.

• Negative Feedback Loops

  • Common in ecosystems; aim to return to original state.

  • Example: Drought reduces lake size, leading to decreased evaporation.

Page 3: Population Dynamics

• Herbivore Population Example

  • Increased herbivore population (e.g., deer) → Decreased plant population → Decreased herbivore population.

  • Prevents dominance of a single species.

• Positive Feedback Loops

  • Changes amplify rather than stabilize.

  • Example: Global warming leads to ice cap melting, exposing darker ground, which absorbs more heat and accelerates melting.

• Invasive Species Example

  • Brown tree snakes in Guam:

    • No natural predators → Exponential population growth → Decline of native bird species.

Page 4: Ecosystem Impact

• Impact of Species Removal or Addition

  • Changes in one species can affect the entire food web.

  • Introduction of a new apex predator can alter primary consumer populations.

Page 5: Key Terms to Review

• Food Chain: Linear sequence of energy transfer from producers to top consumers.

• Food Web: Complex network of interconnected food chains.

• Invasive Species: Non-native species that disrupt ecosystems.

• Negative Feedback Loops: Mechanisms that stabilize ecosystems by counteracting changes.

• Positive Feedback Loops: Cycles that amplify changes, potentially destabilizing ecosystems.

• Primary Consumer: Organisms that feed directly on producers.

• Producer: Organisms that convert sunlight into energy through photosynthesis.

• Secondary Consumer: Organisms that feed on primary consumers.

• Trophic Cascade: Ecological changes resulting from alterations at one trophic level.

• Trophic Interactions: Feeding relationships that describe energy flow in ecosystems.