Niche environments and more migration:

Based on how migrations of humans have happened, I would say the prime real estate would undergo a lot of shifting as different species and sub-species vied for control of territory. On Earth, most parts of the World have seen many ethnicities push each other around or absorb the other groups after conquering them. This can involve the disappearance of the Y chromosome specific to the displaced group - in other words, all the men are killed and all the children are descended from the invaders.

In a world where the invaded is a completely different species that is likely not compatible, it means species will often face extinction or migration. There will be lots of pressure on species to fight to the death or find new places to live, which often means displacing yet another species from territory THEY are in.

Species that thrive in less desirable niche environments where there is less competition will have refuges they can withdraw to and survive until in a position to reclaim territory. Elves and dwarves might want farm land, but if times are hard, they pull back to the mountains or the forests and kill everyone who sets foot there. This may allow them to stabilize their migration pattern and assert periodic control and expansion into the neighboring lands.

Other species will need to be more nomadic or come up with better strategies to stabilize their control. Orcs might be able to interbreed with everything and still give birth to orcs. Humans might be good castle builders and diplomats. Vampires may be able to infiltrate other species and adapt to whatever conqueror comes along.

• At a guess, species would tend to spread out and control preferred microenvironments, leading to dispersed races (possibly with quite distinct ethnicities) while more generalist species will spread widely as they are moved along by constant shifting migrations of other aggressive generalists.
• Lots of changing factors like disease, technology, symbiotic relationships, and new magical abilities or even the vagaries of the gods will alter this. Imagine a god tied to a certain region - invaders would be hard-pressed to invade the trollish land of Moloch worshippers, but a conversion of the hobgoblins to worshipping Moloch could leave the locals in real trouble. Dwarves friendly with humans might let humans migrate to lands cut off from others by mountain ranges. Elves in forests completely surrounding a large swamp might undergo speciation into swamp-elves after the fire-newts burn the woods to the ground. Rice production might mean lizard men thrive and dominate, until humans start growing rice and invading wetter areas for agriculture. The possibilities are endless.

Niche environments and more migration:

Based on how migrations of humans have happened, I would say the prime real estate would undergo a lot of shifting as different species and sub-species vied for control of territory. On Earth, most parts of the World have seen many ethnicities push each other around or absorb the other groups after conquering them. This can involve the disappearance of the Y chromosome specific to the displaced group - in other words, all the men are killed and all the children are descended from the invaders.

In a world where the invaded is a completely different species that is likely not compatible, it means species will often face extinction or migration. There will be lots of pressure on species to fight to the death or find new places to live, which often means displacing yet another species from territory THEY are in.

Species that thrive in less desirable niche environments where there is less competition will have refuges they can withdraw to and survive until in a position to reclaim territory. Elves and dwarves might want farm land, but if times are hard, they pull back to the mountains or the forests and kill everyone who sets foot there. This may allow them to stabilize their migration pattern and assert periodic control and expansion into the neighboring lands.

Other species will need to be more nomadic or come up with better strategies to stabilize their control. Orcs might be able to interbreed with everything and still give birth to orcs. Humans might be good castle builders and diplomats. Vampires may be able to infiltrate other species and adapt to whatever conqueror comes along.

• At a guess, species would tend to spread out and control preferred environments, leading to dispersed races (possibly with quite distinct ethnicities) while more generalist species will spread widely as they are moved along by constant shifting migrations of other aggressive generalists.
• Lots of changing factors like disease, technology, symbiotic relationships, and new magical abilities or even the vagaries of the gods will alter this. Imagine a god tied to a certain region - invaders would be hard-pressed to invade the trollish land of Moloch worshippers, but a conversion of the hobgoblins to worshipping Moloch could leave the locals in real trouble. Dwarves friendly with humans might let humans migrate to lands cut off from others by mountain ranges. Elves in forests completely surrounding a large swamp might undergo speciation into swamp-elves after the fire-newts burn the woods to the ground. Rice production might mean lizard men thrive and dominate, until humans start growing rice and invading wetter areas for agriculture. The possibilities are endless.