Population Growth Curves
- Populations don’t grow indefinitely.
- Over time, they follow a sigmoid growth curve, which consists of three distinct phases: rapid growth, slowed growth, and stabilization.
- This curve explains how populations interact with their environment and the limits imposed by resources, competition, predators, and diseases.
Recall that a population is a group of organisms of the same species living in a specific area.
Phases of the Sigmoid Growth Curve
1. Exponential Growth Phase:
Population grows rapidly due to:
- Abundant resources (e.g., food, space).
- Few limiting factors like predators or diseases.
Bacteria in a nutrient-rich petri dish double every few hours during this phase
Example- Think of a population of rabbits introduced to a new area with plenty of food and no predators.
- The population will grow quickly as each pair of rabbits produces offspring.
2. Transitional Phase
Growth slows as resources become limited, leading to:
- Increased competition for food, space, and water.
- Higher mortality rates as some individuals cannot survive or reproduce.
This phase marks the beginning of environmental resistance, where factors like competition and predation start to limit growth.
3. Plateau Phase
Population size stabilizes near the carrying capacity because:
- Birth and death rates are roughly equal.
- Resources are insufficient to support further growth.
Recall that carrying capacity refers to the maximum population size that an environment can sustainably support.
Example- A forest can only support a certain number of deer based on the availability of food and space.
- Once this limit is reached, the population stabilizes.
Factors Affecting Population Growth Curves
1. Predation
- Impact: Predators control prey populations by hunting them.
- Effect on Curve: The curve fluctuates as prey population declines, followed by predator decline, then recovery.
In predator-prey cycles, an increase in foxes leads to fewer rabbits, which in turn reduces fox numbers.
