Explain why most species with a high capacity for population growth tend to have small individuals, while those with a low capacity for population growth

Species with a high capacity for population growth like bacteria, for example,
tend to be small because they don't wast time and their energy into growth, but rather in reproduction. They start reproducing  sonly after they are born.
On the other hand, bigger species like us humans, have time to grow larger, mature in a complex organism and spend less energy and  time in reproducing a lot.