# r and K selection

**Channel:** Bozeman Science
**Source:** https://www.youtube.com/watch?v=Bu6ouKt9zhs
**Transcript page:** https://www.withtranscript.ai/video/Bu6ouKt9zhs

## Chapters

- 0:04 — Population Growth and Carrying Capacity
- 2:42 — Survivorship Curves in Species
- 4:05 — Traits of R Selected Species
- 5:31 — Traits of K Selected Species

## Transcript

**[0:04]:** hi it's Mr Anderson and in this podcast I'm going to talk about R and K selection or R selected and K selected species right here we've got a chameleon female that's just laid two eggs right here we have a frog that's just laid thousands of eggs one of these is an R selected one is a k selected if you know exactly which is which right now then you probably don't need to watch the rest of the video but for those of you that are now left let me talk about rnk selection basically we have to talk about population growth and so any population where you have a positive R and R stands for growth rate if you ever have it a positive R you're going to follow a curve that looks kind of like this you'll first of all have exponential growth and then eventually you'll run out of space or food there's going to

**[0:52]:** be competition and eventually you're going to hit what's called logistic growth and so we call this the j-shaped curve the exponential or the sigma or the s-shaped curve which is uh logarithmic and so what is n n is going to be the number of individuals in the population and so right here if we put n on this side and we put time on the x- axis as time goes on the numbers are going to increase so this would be a low n value right here and this would be a higher n value and this would be a really high n value and so it's important that you know what n is that's the number in the population R is the growth rate remember if it's ever positive and how do we calculate growth rate it's it's basically the number of people being born minus the number of people who die if we ever have a

**[1:35]:** positive one then we're going to get this curve now it's not always radical like this sometimes it's going to be really gradual like this sometimes it's going to be incredibly quick depending on what the R value is and then the last thing is uh k k stands for carrying let's try to spell that right capacity and so basically that means in an area for a certain group of Po or a certain population there's like a maximum amount that they can support and so we call that the carrying capacity and that's where the limit is it's eventually going to level out on that and so if I were to talk about in the real world because this is just a math uh formula basically in the real world we put wolves back in Yellowstone Park and so there was tons of food there not a lot of competition and so basically their growth rate went up

**[2:21]:** and then it's dropped and it's gone up and it's dropped and it's kind of Reach This carrying capacity a maximum number of wolves that you can have in Yellowstone Park and so it's not as smooth as that but it certainly has an R value the N value has increased and then it's reached kind of a k so it's important that you know what NR and KR another thing that's important is that you understand the way life

**[2:42]:** exists this is the story of life and death is going to vary and we really have three different types so you happen to be a type one survivorship curve and what that means is think about all the kids in your class or all the kids who were born on the same day that you were basically most of you are going to survive that first day and most of you are going to survive now a few people will die right away but most of you are going to survive you're going to make it through your teenage years and your Middle Ages and eventually you're going to drop off and all of you are going to die in these last 10 15 20 years that's because we're type one we're humans and we give a lot of you could see this right here parental care to our Offspring now if we look at a frog here's some

**[3:24]:** frog eggs down here they show what's called a type three survivorship curve on day one thousands of Little Frogs almost all of them die but a few of them survive and then they're going to level off and then they're eventually all going to die now we also have something in the middle type two we call that song birds are an example of that and so they're going to die off at a linear rate throughout their whole life cycle and so Robins are an example of that Robins on average live about a year but some live a few months and some live three years but on average they're just going of drop off until they're all dead the ones the cohort the ones that are born on that one specific day remember our Environ are going to differ sometimes we're going to live in environments that are relatively stable like a desert and sometimes not so

**[4:05]:** much like a rainforest or even a coral reef especially right now they're changing radically almost every day and so basically let's get to what an R selected species is our selected are going to be those that base their life on R and remember R is growth rate and so these are species that want to quickly grow and exploit a niche as as fast as they can and so these are things that normally live in an unstable environment um they have high facundity what does that mean facundity basically means is that they can make a lot of babies really really quickly in general these things are small they don't live that long and their offspring just kind of spread to the ends of the Earth and so an example of this would be a dandelion they show up really early in the spring they reproduce quickly if you've ever seen a a dandelion when it goes

**[4:52]:** to seeds the seeds are just spread out given very little parental care bacteria insects Dions which are alga or type of this or squid babies are essentially laid by the females males put sperm all over that you have these packets and then the parents just head away they just leave and then eventually all the squid are born most of them are food for fish but some of them are able to survive and so that's the are selected species you're putting your life in growth rate so what's K selected species well these things are going to put their lives basically around carrying capacity they're in it for the long haul then they're in it for exponential

**[5:31]:** and then that logistic growth they want to live a long time generally they live in a more stable environment they're larger as far as body size they're going to live a lot longer there's a lot of Parental care so you as as a human are going to be a k selected species if we look at plants compare this to the dandelion a tree like this some trees will live hundreds if not thousands of years or whales or an example of K selected species but you don't necessarily have to be big this is an Arctic turn that lives DEC ades and they have a lot of Parental care and so they're K selected species know this that in life it's not always one or the other there are some species that actually show a Continuum and so a sea turtle you might look at a sea turtle it's big lives a really long time you might

**[6:16]:** say well that's maybe a k selected species but then if you remember of how they're born they're just going to lay a bunch of eggs cover them up in hole and then just kind of swim away and all of these eggs are going to hatch these little baby sea turtles are kind of on their own and so that would be more of an R selected and so even within a lifetime you can be R and K selected and even by gender so if you think about it not not humans per se but in in animals males tend to live more of an R selected species produce as many as they can spread as much of their sperm as far as they can whereas females are more K selected investing a lot in those Offspring in that long Hall so let's go back and look at that first Slide the chameleon is it r or k

**[6:59]:** selected well it's investing in just these two eggs and so it's in it for the long haul where this would be an R selected species and I hope that's helpful