Why can the pyramid of numbers be straight and inverted?

If the reproduction rate of the prey population is high, then even with low biomass, such a population can be a sufficient food source for predators with a higher biomass but low reproduction rate. For this reason, pyramids of abundance or biomass may be inverted, i.e., low trophic levels may have lower density and biomass than higher levels.
For example, many insects (inverted number pyramid) can live and feed on one tree. The inverted pyramid of biomass is characteristic of marine ecosystems, where primary producers (phytoplanktonic algae) divide very quickly and their consumers (zooplanktonic crustaceans) are much larger, but they reproduce much more slowly. Marine vertebrates have an even greater mass and a long reproduction cycle.