Human beings cannot be called a keystone species because our influence on nature is not disproportionately large compared to our abundance (population size). Our cities, roads, and technologies, however, have altered nearly every ecosystem on Earth.
I’ve been thinking about the human niche or role in wider ecosystems and aside from the wide savannah style plains on which we evolved it seems we are a keystone species in most other ecosystems, but not quite.
If a keystone or engineer species is one which, through its actions is able to create habitats, control water/moisture/nutrient cycles, maintain species composition etc like Grey Wolves, Sea Otters or Beavers, then humans are like a keystone species BUT – we act to create ecosytems which are for us, instead of for other species. We control megafauna, use fires to ensure grazing grounds, remove unwanted predators, hunt top through bottom of the food web, create spaces for species which benefit ourselves. In short we are more like a ‘mirror’ species – one which always acts to recreate the world in our own image.
Agriculture, horticulture, permaculture, control through fire and hunting, pseudo-herding of grazing animals etc. These are all strategies to make the ecosystem for us, not for others.