Natures limiting factors

I was thinking about natures limiting factors and one of the big ones is how many kids your body produces and how long they live. If you look at things the shorter the life span and the more predators you have the more babies you produce. Look at mice. They have a large amount of babies but their life spans are short. Humans have usually one or two babies but our life spans are much longer. So for those paranormal creatures that can reproduce and life a very long life span it shouldn't be a huge surprise that most of them have trouble having babies. I mean if you have a vampire like creature who could give birth all the time to large groups of babies humans would be hunter out of existence. Even if they didn't purposely kill their food the population just couldn't keep up with that kind of attention. Another limiting factor is the bigger a predator you are the fewer kids you seem to have. Look at bears. Usually bears only have a few kids. So is it a surprise that werewolves have trouble having kids. I think a lot of that has to do with the stress you're putting on the body as well as the fact that if you had to many the population just couldn't support it. I would also think that were babies would hit the ground almost ready to get going like puppies. Within a short period of time they can walk. They can't maybe say fight but they aren't helpless. Unlike human babies who would die within a day if they don't have someone to take care of them. Just a thought from the book I'm reading now. Have fun.