Why are there fewer top carnivores than herbivores in most land ecosystems?

This is because of the energy transfer within the food chain

Explanation:

When energy is passed in food chain only a small amount of the energy becomes new body mass (or is used in metabolic processes) and the rest of the energy is lost as waste.  So, this means that a carnivore has to eat many herbivores  that are below them in food pyramid in order to get enough energy for survival and growth.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.