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AP Enviro



Unit 3

3.2 K-Selected r-Selected Species

2 min readdecember 19, 2020

Karla Jauregui Sandoval

The rate of population for species depends on the reproductive strategies that they use and can be compared using a spectrum between k and r selected species.  There are a number of factors that are used to compare their reproductive strategies.

  • Average Size of species 

  • How much time goes into parental care for offspring 

  • Family Size of Species (how much offspring do they produce) 

  • How much competition is there for resources 

  • What role do they play in ecological succession 

  • Are they invasive species or do they get affected by invasive species? 


Image Courtesy of Pixabay

Characteristic of K-selected species 

A K selected species can be described as generally larger species and tend to be terrestrial mammals. They invest a lot of parental care to their offspring which is why their family sizes are smaller. Because time, energy and resources are invested into child rearing, K -selected species tend to have a Type 1 and Type 2 survivorship curve. Offspring live longer lives and grow slowly until their habitat hits the carrying capacity. 

In K selected species a population may increase then hit a carrying capacity for their habitat which means that their habitat can reach the limit of population their resources can support. 


Image Courtesy of Pixabay

Characteristic of R-selected species 

R selected species are generally small and parents invest little time and energy into parental care. The family size of these species is large! R selected species have a large amount of offspring per reproductive age. However they have a Type 3 survival curve which means that most of the offspring die off during their early ages and the few live to their old age. 

During their lifetime they have low competition for resources because of their quick adaptability to their habitat.


K - Selected 



Generally larger as species (terrestrial mammals)

Generally small 


LOTS of parental care ➪time, energy and resources in child rearing 

Parents invest a little amount of time. energy  and resources in children 

Family Size 

Small  ➪ few offspring per reproductive event 

 ➪ long lifespans 

 ➪ grow slowly until they hit carrying capacity 

Large offspring per reproductive event 

 ➪ short lifespan 

 ➪ fast sexual maturity 

 ➪ grow quickly but followed by overshoots and die-offs - predator prey relationships 


Highly competitive for resources (crowded niches)

Low competition for resources ➪  adapt quickly 

Eco. Succession

Late stage successors 

Pioneer species

Invasive species 

Mostly affected by invasive species 

Most invasive species are r selected because they reproduce quickly 


Humans, eagles, elephants, parrots, bison, bears. 

Insects, mice, bacteria, grasses, 

🎥 Watch this video here at 34 minutes to discuss this key topic more!


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