Main content
Survivorship curves and K-/r-selection
Review your understanding of survivorship curves, K-selected species, and r-selected species in this free article aligned to AP standards.
Key points
- Survivorship curves are graphs that show the proportion of a population that survives from one age to the next. These curves represent age-specific mortality in a group of organisms.
- To generate survivorship curves, ecologists typically collect age-specific survival rates for organisms within a cohort. A cohort is a group of individuals from the same population who are born at the same time. Survivorship data from a cohort can be representative of the larger population.
- In general, scientists divide survivorship curves into three types based on their shapes:
- Type I survivorship curves represent populations whose organisms tend to survive beyond their young and middle-ages and die when they become elderly. These organisms usually have small numbers of offspring and provide lots of parental care to make sure those offspring survive.
- Type II survivorship curves represent populations with a constant proportion of individuals dying at each age interval. Similar to species that exhibit Type 1 survivorship, these organisms usually have relatively few offspring and provide them with lots of parental care.
- Type III survivorship curves represent populations that have a high death rate among the young, but a relatively low death rate for those who survive into middle and old age. These organisms usually have lots of offspring at once, but don't provide them with much parental care.
- Type I and Type II curves represent typical survivorship patterns for K-selected species. Type III curves represent typical survivorship patterns for r-selected species.
- K-selected species have traits that are advantageous at high population densities. These species tend to have long lives, thrive under stable conditions, be large in size, produce few offspring, reproduce more than once in a lifetime, and provide lots of parental care to their offspring.
- r-selected species have traits that maximize reproductive success in uncrowded environments. These species are often found in disturbed environments, or other areas where competition is low. They tend to have short life spans, be small in size, mature early, have many offspring, and they may reproduce only once per lifetime.
- Most real populations show some mix of Types I, II, and III survivorship patterns. For example, juveniles of some species may display Type III survivorship, while adults of the same species display Type II survivorship.
Want to join the conversation?
- What are examples of Types 1, 2 and 3?(4 votes)
- Type 1: Humans. No explanation needed since I assume you are one?
Type 2: Certain lizards, perching birds, and rodents. [1] Songbirds are also an example of a Type 2 Survivorship Curve. In the songbird population there is no link between mortality and age. [2]
Type 3: Insects, fishes and turtles. Turtles are well known to hatch a lot of baby turtles, leaving them on beaches and let the lucky one to survive (You probably heard or seen some views like this). Here are two videos about it if you never heard about it before:
https://www.youtube.com/watch?v=HYF_vUBFSsA
https://www.youtube.com/watch?v=AkGnPl0QL6o
[1] https://www.britannica.com/science/Type-II-survivorship-curve
[2] https://study.com/academy/lesson/survivorship-curve-types-examples-quiz.html(4 votes)
- why is there so many types(4 votes)
- there are so many types , due to the mortality of the organism(3 votes)
- Can we get example of types of organism that would fit on each of the type?(4 votes)
- Which curve(s) would you expect to represent species whose offspring are subject to random predation throughout their life span?(1 vote)
- If each organism is susceptible to the same probability of predation at each stage of their life, it would follow a Type 2 path where the organisms of the species have a constant proportion of individuals dying at each stage of their life.
If they had more of a chance of predation at the beginning of their life span, it would follow a Type 3 trend. And, if they had more of a chance of predation at the end of their life span, it would follow a Type 1 trend.(4 votes)
- Are types 1, 2, and 3 related to the k and r related species?(1 vote)
- Yes. Type 1 describes K-selected species, while Type 3 describes r-selected species. Type 2 is something between those.(3 votes)
- i don´t understand this chart(0 votes)
- The y-axis scaling by x10 instead of +10 and represents the number of organisms alive. The x-axis basically represents age (but as a percent of how long they could possibly live, for example, if the maximum lifespan of a fish is 10 years, then the graph at 50% it shows the fish at age 5). This means that the graph shows the number of organisms alive at each age.(7 votes)
- Why is there so many types(2 votes)
- I'm curious on what meals type 1 had.(1 vote)
- I don't think there's a direct relation between type 1 and the food they eat.
For example, type 1 includes human and whales. I doubt whales eat pizza or drink tea.(2 votes)
- What was the number of organism surviving in type III species(1 vote)
- Are types 1, 2, and 3 related to the k and r related species?(1 vote)