Amy Doster

I think this question depends heavily on what definition of keystone species you use, and how you use it. One definition I found uses it as such: “a species that has a disproportionate effect on its environment relative to its biomass”. In this case, it seems like humans would be an obvious keystone species, as we affect things in a much broader scale than maybe should be possible for a species of our biomass. Humans have far-reaching effects, in nearly every area of the earth, and now even on other planets and our moon. Since this definition doesn’t imply a positive or negative connotation on the term “keystone”, it is then permissible to assume that humans are. However, when other definitions are used, many of which imply a positive impact of the species in question, most people then agree that humans are not. With a definition such as “plays a role analogous to the role of a keystone in an arch; the arch still collapses without it”, it seems like humans would then not be keystone. Humans have far-reaching effects, but many of them impact the other species and the environment in very negative ways. Overall, I think it is more correct to generalize that humans are not keystone, in that although we may affect the world around us in many ways, it tends to be in negative ways, and this is not the connotation often associated with the term “keystone species”.

Definitions from Wikipedia - Keystone Species article