Negative Feedback Control of Population Size by Density-Dependent Factors
- Populations don’t grow forever, as numbers increase, food shortages, predation, and disease act as natural limits.
- These density-dependent factors create a negative feedback loop, stabilizing population size near its carrying capacity.
Negative feedback is a stabilizing force, ensuring populations don’t spiral out of control.
What is Negative Feedback in Population Control?
- Negative feedback is a process where changes trigger responses that counteract the change, maintaining stability.
- In ecology, negative feedback prevents populations from exceeding the carrying capacity, the maximum number of individuals an environment can support.
- In a forest, if deer populations rise, food becomes scarce, leading to competition and malnutrition.
- This reduces population size, restoring balance.
Density-Dependent Factors: The Key Players
- Density-dependent factors are environmental pressures that intensify as population size increases.
- These include:
- Competition for Resources
- Predation
- Disease and Parasitism
- Avoid confusing density-dependent and density-independent factors.
- Density-dependent factors increase in effect as population grows (e.g., competition, disease).
- Density-independent factors affect populations regardless of size (e.g., natural disasters).
These factors create a negative feedback loop, pushing populations back toward stability.
1. Competition for Resources
- As populations grow, individuals compete for food, water, and space.
- More competition = fewer resources per individual.
- Survival of the fittest, only those best adapted can reproduce and pass on their genes.
- Population decline occurs as weaker individuals die off, reducing competition.
In a forest, deer compete for grazing areas. When food is scarce, weaker deer may starve, reducing the population until resources are sufficient again.
2. Predation: The Predatory-Prey Cycle
Predators help regulate prey populations, creating a natural balance.
- More prey = more food for predators → Predator numbers increase.
- Increased predation = fewer prey → Prey numbers decline.
- Fewer prey = predator decline → Prey population recovers.
The classic example of lynx and snowshoe hares demonstrates this cycle. When hare populations rise, lynx numbers follow, but as hares become scarce, lynx populations decline, allowing hares to rebound.
