Evan H. answered • 10/02/19
PhD Student of Ecology
Humans could be considered a keystone species as we do have a disproportionate impact on ecosystem structure based on our population size (although this definition is complicated by the fact that there are a remarkable amount of humans compared to other large mammals). However, when thinking about keystone species, it is generally accepted that a keystone species is important for the maintenance of it's native habitat. Human beings occupy the entire planet and thus, are outside of the natural native range of the species. We also are very destructive to the condition of ecosystems around the world, including in our original native range. Biodiversity would generally be better off without human influence in most places where humans exist, so if you are thinking of natural systems, it is better to think of humans as invasive species. We consume resources across a broad spectrum of biomes without any significant predators or competitors (predator and competition release). Indeed, when this happens, systems can fall apart and we have seen this throughout the world as landscapes change to benefit humans.
However, there is one type of system I would say that humans are truly keystone species. The urban environment. Homo Sapiens have create a landscape type that had not previously existed. While this landscape is inhospitable for lots of forms of life, many species are better off because of it. Pigeons, rats, raccoons, lice, etc all thrive in the urban ecosystems in the world. For these organisms, for this system, humans are keystone species by taking the role of ecosystem engineers.
