Summary
r-strategists reproduce quickly with many offspring; K-strategists have few offspring and invest heavily in each.
In depth
r-selected species (insects, weeds, bacteria) live in unstable environments with early maturity and many small offspring. K-selected species (elephants, humans) live in stable ones with later maturity, few offspring and parental care. Most species lie on a continuum.
It is a continuum and many species are intermediate. Life history theory expands the idea with age at maturity and parental care.
Remember: r-selected species do well in disturbed habitats; K-selected in stable ones.
The r/K idea (MacArthur and Wilson) is a continuum rather than two categories. Many species show mixtures, such as trees producing many seeds but living long. Grime proposed a similar scheme for plants: competitors, stress-tolerators and ruderals. Newer life-history theory also stresses mortality schedules (Pianka, Grime, Stearns) and the fast-slow continuum.
r-selected species recolonise disturbed areas quickly and are often pests, while K-selected species are vulnerable to overharvesting because they recover slowly: whales, sharks and elephants. Parental care is more prevalent in K strategists.
Remember: r stands for the intrinsic rate of increase and K for the carrying capacity.
Frequently asked questions
What is r and K Strategies?
r-strategists reproduce quickly with many offspring; K-strategists have few offspring and invest heavily in each.
Which area of biology covers r and K Strategies, and how advanced is it?
r and K Strategies 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 Survivorship Curves, Ecological Succession, Island Biogeography.
Can you give an example of r and K Strategies?
A dandelion versus an oak.
What should I learn before r and K Strategies?
Work through the Beginner topics in Ecology first, such as Ecology, Ecosystem, Biotic and Abiotic Factors, then return to r and K Strategies. Intermediate topics assume the Beginner vocabulary.
What topics are related to r and K Strategies?
The closest topics to r and K Strategies are Survivorship Curves, Ecological Succession, Island Biogeography, Niche Partitioning. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand r and K Strategies?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for r and K Strategies. To practise the whole of Ecology, use the Ecology quiz.
How is r and K Strategies different from Survivorship Curves?
r and K Strategies: r-strategists reproduce quickly with many offspring; K-strategists have few offspring and invest heavily in each. Survivorship Curves: Graphs of the proportion of a cohort surviving by age, classified as type I, II or III. Read both side by side and note what each one explains.
How should I study r and K Strategies 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 Survivorship Curves and explain the difference aloud. Finally, take the Ecology quiz and come back to this page for any question you miss.