The human populations are not limited by the carrying capacity of their ecosystems, and they are the only species on Earth that are able to perform such a thing. The main reason for this is that the humans are able to transport resources of all sorts and for all needs from very distant places. Even if there's a very large population surrounded by desert, the humans are still able to survive by simply bringing in the necessary things from other places throughout he means of transportation. Another reason is that the humans are able to change and manipulate their environment to certain extent, being able to provide for themselves even in ecosystems that naturally are nowhere near close to provide those things for them.
