How do r selected populations differ from K selected populations?

In a nutshell, R selected populations are more "YOLO" type while K selected populations are more "dig in and play for the future" type.

Let me tell you what I mean.

Basically, R selected populations are species that have very high mortality rates amongst their young. In other words they lose a lot of their young. Hence, these species are mostly tuned to endorse in a lot of reproduction, and spend less energy in parenting. For example, flies just have a ton of offspring, and don't really care about nurturing them. As a result, not a lot of them survive. In a nutshell, R selected populations focus on quantity over quality. They are mostly geared towards the time of repopulation, when an ecosystem needs to be "filled up" again.

K selected populations, on the other hand, are species that have very low mortality rates at childbirth. They have few offspring, but put more energy into nurturing them. For example, humans usually have about 2-3 offspring on average, but we nurture them very well (at least most of the time), and prepare them to endure the world and live a long life. Therefore, you could say that K selected populations go for quality over quantity. These are mostly geared towards surviving for long periods of time, and thriving in stable ecosystems.

Hope that helped :)