Summary
Population growth at a constant per capita rate, producing a J-shaped curve in unlimited conditions.
In depth
dN/dt = rN: growth is proportional to the population, producing a J-shaped curve. It occurs when resources are unlimited, such as bacteria in fresh medium or invading species.
It cannot continue indefinitely.
Doubling time = ln2/r. Early invaders and recovering populations can show exponential phases. Boom and bust patterns are seen in lemming and insect outbreaks.
Remember: exponential growth means growth rate per individual is constant.
The per capita rate r equals births minus deaths per individual, and doubling time is about 0.69 divided by r. Bacteria in ideal conditions may double every 20 minutes; at that rate, one cell would produce a mass exceeding the Earth in days, which shows why exponential growth cannot last. Examples in nature include invasive species during early spread, recovery of protected whale populations and algal blooms.
Exponential growth appears on a semi-log plot as a straight line. In epidemics, the early spread of a pathogen is exponential with R0 above 1, until immunity or interventions slow it.
Key idea: this pattern is limited to short periods or low densities, before resources or other factors limit the population.
Frequently asked questions
What is Exponential Growth?
Population growth at a constant per capita rate, producing a J-shaped curve in unlimited conditions.
Which area of biology covers Exponential Growth, and how advanced is it?
Exponential Growth is one of the 54 topics in Ecology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Allee Effect, Logistic Growth, Population.
Can you give an example of Exponential Growth?
The human population grew nearly exponentially during the 20th century, from 1.6 to 6 billion.
What should I learn before Exponential Growth?
Work through the Beginner topics in Ecology first, such as Ecology, Ecosystem, Biotic and Abiotic Factors, then return to Exponential Growth. Intermediate topics assume the Beginner vocabulary.
What topics are related to Exponential Growth?
The closest topics to Exponential Growth are Allee Effect, Logistic Growth, Population, Limiting Factors. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Exponential Growth?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Exponential Growth. To practise the whole of Ecology, use the Ecology quiz.
How is Exponential Growth different from Allee Effect?
Exponential Growth: Population growth at a constant per capita rate, producing a J-shaped curve in unlimited conditions. Allee Effect: At low density, individual fitness declines, so small populations may fail to recover. Read both side by side and note what each one explains.
How should I study Exponential Growth step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Allee Effect and explain the difference aloud. Finally, take the Ecology quiz and come back to this page for any question you miss.