Now listen to part of a lecture on this topic in a biology class.
Imagine there is a group of mice living in a large field and owls living nearby. Now owls eat mice. So the number of mice there are in any given time depends upon on the number of owls in the area, because the more owls there are, the more mice get eaten, right?
Now imagine one year there are more owls than usual. Since there are more owls in the area to eat the mice, what do you think will happen to the number of mice? As you can imagine, the number would drop. There would be fewer mice.
As far as the other factor, we can use rabbits to help understand this one. Imagine a population of rabbits living in an area. These rabbits usually start having their young at the end of winter, after the cold winter weather is gone. And they keep reproducing until the following winter when they will stop again while the cold winter weather lasts.
But let's say this year the winter season is very short, and you know, it starts getting warm much earlier than usual. Since winter this year is so short, the rabbits can start reproducing much earlier. That means the rabbits in that area will have at least one extra reproductive cycle, so of course one extra litter of baby rabbits. So the number of rabbits in that area would increase a lot.