Food Chains & Predator-Prey Cycles

Energy Flow in Ecosystems

• Definition of Food Chain

  • A food chain illustrates the linear flow of energy within an ecosystem.

  • It simplifies the complex interactions shown in a food web by focusing on a single chain of consumption.

• Producers

  • Define producers as organisms that perform photosynthesis, converting sunlight into glucose for energy.

  • Example: Grassia (a type of green plant or alga).

  • Importance of Photosynthesis: They create biomass, which consists of all biological molecules formed through this process.

• Consumers in the Food Chain

  • Primary Consumers

    • Organisms that eat producers; also referred to as herbivores.

    • Example: Mice, rabbits, aphids.

  • Secondary Consumers

    • Organisms that eat primary consumers; always a type of predator.

    • Example: Owls that feed on mice.

  • Tertiary Consumers

    • Organisms that consume secondary consumers.

    • Predatory role continues; may lead to more levels (quaternary consumers) in some ecosystems, but not in all.

• Energy Transfer Through the Food Chain

  • Energy is lost at each trophic level as it transfers upwards in the food chain.

  • Example of Energy Loss:

    • If the producer (grass) provides 1,000 joules of energy:

      • Primary consumer (mice) receives approximately 100 joules.

      • Secondary consumer (owl) receives about 20 joules.

  • Representation of Energy Flow:

    • Arrows between trophic levels in food chains indicate the direction of energy flow.

    • These arrows should be reversed to correctly represent the energy loss.

Predator-Prey Relationships

• Definition of Predator-Prey Cycle

  • This cycle describes the dynamic relationship between predator and prey populations over time.

  • Graphical representation shows fluctuations in the populations of both groups.

• Characteristics of Predator-Prey Cycles

  • Observations: Both species' populations cycle up and down, but predator population lags behind prey population.

  • Example Analysis:

    • The peak of the mouse population occurs before the peak of the owl population, indicating a phase difference.

• Dynamics of Population Changes

  • Initial Phase:

    • Low owl population allows mouse population to increase as predation pressure is low.

  • Subsequent Phase:

    • Increased mouse population provides ample food for owls, resulting in an increase in the owl population.

  • Decline Phase:

    • High owl population leads to over-predation, causing a decline in the mouse population.

    • Decreasing mouse population reduces food availability for owls, leading to a decline in the owl population.

  • Recovery Phase:

    • Lower owl populations allow mouse populations to rebound, repeating the cycle.

• Reasons for Cycles

  • Natural lag in population response: It generally takes several generations for populations to increase or decrease in response to food availability.

  • Example: Owls need multiple breeding cycles to significantly increase their population in good feeding conditions.