A dominant species in an ecosystem is the most abundant species present. It makes up the highest percentage of the total biomass in the system. A keystone species is one that has the greatest effect on all of the other species in an ecosystem. If removed from a system, its loss will have large and lasting negative impacts on the rest of the community. Both are similar in that they are both species and they are both very important to a given ecosystem either through ecological importance or sheer numbers. They are different in that they have different levels of impact. A dominant species may be the most visible in a given area but if it is removed it may not have any significant impacts on the system as a whole. A keystone species, on the other hand, may not be particularly visible in a system but its removal would have devastating effects on the ecosystem.
Wow thank you so much! :)