Question

explain why an ecological pyramid is smaller at the top than at the bottom

Answer 1

because most things at the top are less hunted organisms, leaving it to be eaten less. Which will result in a smaller amount.
Rather than the rest of organisms, there are more and larger because they are the hunted.
Because of energy the bottom gets 100% of the energy the next only gets 10% then 1% then .1% and so on.

Answer 2

@tara777