What is a keystone species?
(a) a species which makes up only a small proportion of the total biomass of a community, yet has a huge impact community’s organization and
(b) a common species that has plenty of biomass yet has a fairly low impact on the community organization
(c) a rare species that has minimal impact on the biomass and on other species in the community
(d) a dominant species that constitutes a large proportion of the biomass and which affects many other species.