87. Food Chains and Predator-Prey Cycles

Food chains are simplified diagrams that show the flow of energy through an ecosystem by identifying what eats what.

Every food chain follows a specific order of energy transfer:

Producers: These are always at the start of the chain. They are photosynthetic organisms (like green plants or algae) that use sunlight to create glucose. This glucose is used to build biological molecules, which we call biomass.
Primary Consumers: These are the organisms that eat the producers (herbivores).
Secondary Consumers: Predators that eat the primary consumers.
Tertiary Consumers: Predators that eat the secondary consumers.
Energy Flow: Arrows in a food chain point in the direction of energy transfer (from the organism being eaten to the consumer). Most energy is lost at each level; for example, if a producer has 1,000 units of energy, the primary consumer might only receive 100 units.

In a stable community, the numbers of predators and prey rise and fall in a predictable pattern called a predator-prey cycle.

Low Predator Numbers: When there are few predators, the prey population increases because they are not being hunted as much.
Increasing Predator Numbers: As the prey population grows, there is more food for predators, so the predator population begins to increase.
Decreasing Prey Numbers: High numbers of predators eventually eat so many prey that the prey population begins to fall.
Decreasing Predator Numbers: With fewer prey available as food, the predator population starts to decline, which then allows the prey population to recover and restart the cycle.

The Lag Time: The predator population always peaks after the prey population. This is because it takes time for a population to increase through breeding, even when food is plentiful.
Interdependence: These cycles demonstrate how closely tied the survival of one species is to another within an ecosystem.