This video, we're going to talk about r and k selection. And so recall from our previous lesson videos that different species actually vary in how they allocate their time, energy, and resources to survival growth and reproduction. And how a species actually goes about doing so is what we refer to as the life history of that species. Now natural selection, we know, is a major mechanism of evolution, and it has shaped 2 life history outcomes that are actually on opposite ends of a spectrum. And, of course, we're referring to r and k selection, which are really just another aspect of life history.
Now because r and k selection are on opposite ends of a spectrum, of course, this means that many organisms fall in between these two opposite ends of a spectrum. But what exactly is r and k selection? Well, k selection, as its name implies, is when natural selection optimizes fitness at high population densities that are near the carrying capacity or near k. And this is where k selection gets its name from. Now k-selected species are adapted to stable environments, intense competition, and they tend to have stable populations that are near the carrying capacity or near k.
Now on the other hand, r selection, as its name implies, is when natural selection optimizes fitness at low population densities that are not near the carrying capacity. And r selection maximizes the per capita population growth rate or maximizes the value of r, which is where r selection gets its name from. Now unlike k-selected species, r-selected species are adapted to unstable environments, and they often experience what are known as boom and bust cycles, which are characterized by rapid population growth followed by rapid population crashes. And so let's take a look at this image down below, which should look a little familiar to you since we're showing you this trade-off between fecundity and survivorship, where organisms that have high fecundity tend to have low survivorship. And so, the left-hand side of this spectrum here is representing our selection, and so notice that we're using the Monarch butterfly to represent our r-selected species.
And so organisms that fall into this r-selected category tend to have high fecundity, low survivorship. They also tend to produce many offspring, 100 or thousands of offspring in many cases, and they have a very low investment into each offspring. So there's not usually a lot of parental care. And so these r-selected species tend to exhibit type 3 survivorship curves, which recall from our previous lesson videos are characterized by really high mortality rates and low survivorship early on in life, where most organisms that are born will not survive long enough to adulthood. But once the organisms reach a certain age in adulthood, they tend to have lower mortality rates and higher survivorship.
Now the right side of this spectrum over here has organisms that have high survivorship and low fecundity, and we're using the Orca here to represent these k-selected species or k selection. And they tend to produce very few offspring, and they tend to have a high investment into each offspring, usually offering pretty good parental care. And these organisms tend to exhibit type 1 survivorship curves, which recall from our previous lesson videos are characterized by very low mortality rates and very high survivorship early on in life where most organisms that are born will survive to adulthood. But then later in life, the mortality rates increase, and the survivorship drops. And so this here concludes our brief lesson on r and k selection, and we'll be able to apply these concepts and problems moving forward.
So I'll see you all in our next video.
