r-strategist species maximize rapid population growth in unpredictable or disturbed environments, whereas K-strategist species invest more resources in fewer offspring and are better adapted to stable environments near carrying capacity. These are endpoints on a continuum, not rigid categories.
This is an HL-only concept linking population ecology in Subtopic 2.1 to succession in Subtopic 2.5. In the syllabus, it is specified directly in understanding 2.5.11.
How the Strategies Differ
The letter r represents the intrinsic rate of population increase. Selection favours early reproduction and many offspring when mortality is high or resources are temporarily abundant.
The letter K represents the carrying capacity of an environment. Near carrying capacity, competition for limited resources favours organisms whose fewer offspring have a greater chance of surviving.
| Feature | r-strategist species | K-strategist species |
|---|---|---|
| Typical environment | Unstable, disturbed or unpredictable | Relatively stable and predictable |
| Offspring | Many, usually small | Few, usually larger |
| Parental care | Little or none | Considerable |
| Maturity and lifespan | Early maturity; shorter lifespan | Later maturity; longer lifespan |
| Population pattern | Rapid growth and large fluctuations | Slower growth near carrying capacity |
| Succession | Common in pioneer communities | Common in later seral or climax communities |
| Example | Common dandelion (Taraxacum officinale) | African elephant (Loxodonta africana) |
During succession, disturbed habitats initially favour r-strategists because they disperse and reproduce rapidly. As biomass increases and resources become more strongly contested, K-strategists can gain an advantage through competitive ability and greater investment in survival.
