Fantasy series - Main character finds himself in a world facing invasion/extermination from horse riding reptilian invaders - swords and sorcery-esque - read this in the early 2000s

[Garrett]

Have a vague recollection (possibly getting wires crossed with Raymond E. Feist books) of use of portals to allow travel between different worlds.

[Garrett]

The main character ends up helping the race or group of people currently facing the invasion (i believe they may also have been a race of reptilians although smaller than the invaders) but ultimately i believe they are wiped out by the invaders.

I also recall that the invaders are driven by need as the planet seems to be dying with resources becoming every more scarce.