Carrying Capacity & Limiting Factors
- Define carrying capacity and describe overshoot and dieback
- Distinguish density-dependent from density-independent limiting factors
- Explain how resource availability drives populations toward carrying capacity
Carrying capacity, overshoot, and dieback
The carrying capacity (K) is the maximum population size an environment can sustain indefinitely given its resources. A population growing quickly can temporarily exceed K — an overshoot — usually because there is a lag before the effects of resource depletion catch up. Once resources run short, deaths surge and the population crashes below K in a dieback (population crash). Populations often oscillate around K rather than sitting exactly on it, and repeated overshoots can lower K by degrading the habitat.
Density-dependent limiting factors
Density-dependent factors grow stronger as the population becomes more crowded — their effect depends on density. Competition for food, water, and space intensifies; predators are attracted to dense prey; disease and parasites spread faster when individuals are packed together; and the buildup of waste worsens. These factors act as a brake that tightens as the population approaches K, which is exactly what bends the growth curve into its S-shape.
Density-independent limiting factors
Density-independent factors hit a population regardless of how crowded it is. A hurricane, flood, drought, wildfire, volcanic eruption, or a sudden cold snap kills roughly the same fraction of individuals whether the population is sparse or dense. These factors — mostly abiotic events, especially weather and natural disasters — can cause sharp, unpredictable crashes that have nothing to do with the population reaching its carrying capacity.
A deer herd on an island grows rapidly, exceeds the food supply, and then two-thirds of the deer starve over one harsh winter. Identify the carrying-capacity concept and classify the limiting factors involved.
- 1.The herd grew past what the food could support — this is an overshoot of the carrying capacity K.
- 2.The mass starvation that follows is a dieback (population crash) back below K.
- 3.Starvation from food shortage is worse because the herd is crowded — that is a density-dependent factor (competition for food).
- 4.The harsh winter itself, which strikes regardless of herd size, adds a density-independent factor (weather).
Which of the following is a DENSITY-DEPENDENT limiting factor?
Quick test: ask "would this factor hurt more if the population were more crowded?" If yes (competition, predation, disease) it is density-dependent. If it would kill the same fraction no matter how crowded (a storm, a freeze, a fire) it is density-independent.
A population briefly rises above its environment’s carrying capacity and then crashes sharply below it. This sequence is best described as:
On graphs, carrying capacity K appears as a horizontal line the population fluctuates around. If the curve shoots above the line then plunges, label it overshoot and dieback. If it rises and flattens smoothly onto the line, that is logistic growth reaching K.
Answer the 2 checkpoints as you read.
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