Population growth
With no limits, a population grows exponentially, faster and faster. In reality, limits such as food and space slow it down, and it levels off at the carrying capacity (K), the largest population the environment can support. This S-shape is logistic growth.
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Analogy
A bath filling: fast at first, then the plughole and overflow set a limit.
Example
Start: 100 bacteria.Double each hour.After 5 hours: 100 x 2^5= 3,200.
In practice
A few rabbits introduced to an island boom, then food runs short and numbers level off.
Practice
Flashcards
- What is carrying capacity?The maximum population size an environment can support over time.
Interview questions
- Describe logistic population growth and explain the factors that set the carrying capacity.
- Initial exponential growth
- Resources limit growth
- Population levels at K
- Density-dependent factors such as food, space, disease
Questions people ask
What are density-dependent factors?
These are limits whose effect becomes stronger as a population becomes more crowded, such as competition for food, disease and predation. Density-independent factors, such as a storm or a fire, harm a population regardless of its size. Both shape how populations grow.
What is the difference between r-selected and K-selected species?
r-selected species, such as insects and weeds, have many young, grow fast and give little care. K-selected species, such as elephants and humans, have few young, take time to grow and invest heavily in each. Most species lie somewhere between the two.