That takes a million years - what happens in the short run is a certain type of species well adapted to our changes will take over the roles in a less specialized capacity. What type? Well,

1. They will be adapted to living in close contact with humans.

2. They will be dietary opportunists (since they must have had a latent ability to eat an extinct species' diet once it got freed up)

3. They will be small, since large animals can't live in the tiny, divided-up parcels of land that we create with roads and fences.

Therefore they will be what we consider pests! Enjoy living in your rat and roach infested world, fellow humans, you've selected them to inherit the earth from wolves, lions and eagles. :/

Plenty of other wildlife manages to live in cities alongside humans, including songbirds and squirrels.

Small, opportunistic omnivores who are adapted to close contact with humans.

I believe that’s how mammals started - small, opportunistic creatures living near dinosaurs.

We're already modifying genes just fine; what makes you think it would take millions of years? Maybe a few hundred.

Natural selection is a far different process than humans selectively editing genes. Even if we gained a perfect understanding of every species on earth (we haven't even come close to finding them all) and were somehow able to scale this to impact the entire planet's genome, the idea that humans are somehow going to be able to select traits better and orders of magnitude faster than nature is the absolute height of arrogance and this comment is a good example of the exact reason we are screwed.

Humans are amazingly adaptable in the environments they can live in from the Antarctic to the Sahara. Humans will definitely go on in any future climatic situation, but it would be much easier if there were lots of temperate arable land and we hadn't killed off 80% of all known species.

I am assuming humans don't go extinct but if the global economic system collapses then yes, the 3rd option is essentially extinction or at the very least an extremely drastic reduction of the human population.

Humans better hope the things they eat will adapt fast enough.