What is the number of species present in an ecological community known as?

The correct answer is - species richness.

The species richness is a term that represents the number of the species that are living in a certain ecological community, a region, or a landscape. This term is strictly focused on the number of species. Unlike the biodiversity, the species richness doesn't take into account the density of the populations of the species, their distribution, their numbers within the species.

In a way, this term can be a bit misleading, because it can shows an abundance of species living somewhere, but all of those species might be endangered and the information for that will not be present, so the perception may be that the species are abundant and with high numbers of individuals as well.