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How do predator-prey relationships create cycles in population size?
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population ecology
A herd of common wildebeest (Connochaetes taurinus) migrating across a dusty savanna in Africa. The animal is a keystone species (i.e., a species with a disproportionately large effect on its biological community) in plains and acacia savanna ecosystems from southeastern Africa to central Kenya.
In population ecology, predator-prey relationships create cycles in population size through reciprocal feedback loops, which can be modeled mathematically using the Lotka-Volterra equations.
These cycles occur because the growth rate of each population is dependent on the other:
- Prey Dynamics: The prey population growth is reduced by its interaction with predators. When prey are abundant, the predator population has more food, allowing it to increase.
- Predator Dynamics: The predator population growth is increased by its interaction with prey. As predators increase, they consume more prey, eventually causing the prey population to decline.
- Cyclical Feedback: As the prey population drops due to high predation, the predator population eventually declines due to a lack of food. Once the predator population decreases, the prey population is released from predation pressure and can begin to recover, restarting the cycle.1
These interactions are fundamental to understanding predation and the broader structure of food chains, where changes in top predator numbers can trigger trophic cascades that ripple through an entire ecosystem.2