This video, we're going to talk about the demographic information in survivorship curves. A survivorship curve is really just a graphical representation of a life table, and it is a graph of the number of living individuals in a cohort, which we plot on the y-axis of the curve, surviving to each age group, which we plot on the x-axis of the curve. Now the y-axis of a survivorship curve is often expressed on a logarithmic scale, which is important because it allows for a wide range of values to be plotted onto the same graph. There are only 3 general shapes of survivorship curves, which we call type 1, type 2, and type 3 survivorship curves, and we can see them down below in this graph. Notice that the blue curve that we're showing you here represents a type 1 survivorship curve.

In a type 1 survivorship curve, there is very low mortality rates early on in life, allowing most individuals that are born to survive to adulthood. But then later in life, the mortality rates increase significantly. An example of a species that exhibits a type 1 survivorship curve is human beings like you and me. A type 2 survivorship curve is being shown here in red. Instead of having low and then high mortality rates, with a type 2 survivorship curve, the mortality rates are pretty similar throughout the entire species' lifetime, creating a straight line as you can see here.

An example of a species that displays a type 2 survivorship curve is the northern cardinal that you can see here. Lastly, we have a type 3 survivorship curve, which is essentially the opposite of a type 1 survivorship curve. Instead of having very low mortality rates early in life, there are very high mortality rates early in life, and so most individuals that are born will not survive to adulthood. But then once the individuals reach a certain age, the mortality rates decrease significantly, and very few of them can actually reach adulthood and, you know, older ages of life. An example of a species that displays a type 3 survivorship curve is the American bullfrog that you can see here.

Down below, we do have a very important note, which is that survivorship is actually a spectrum, and so most populations actually exhibit characteristics that fall somewhat in between these three classic types, type 1, type 2, and type 3. These are just very recognizable survivorship curves. But, again, species in reality can display all kinds of different shapes, and so they can fall in between these values. This here concludes our lesson on survivorship curves, and we'll be able to get some practice moving forward. I'll see you in our next video.