Hunters: The Defender

Colorado based forest ranger survives posioning of earth by alien invaders who eventally stock the earth with a variety of nasty animals from across the universe. Aliens use captured humans for labor and bait. Ranger attacts a few survivors who learn to avoid alien detection by various means. Generations pass as humans sink deeper in degradation. Eventally a great grandson of the original forest ranger sets out to explore and eventually gains the skill and self confidence to attack the alien's huge basecamp with assorted human remnants he has gathered along the way. They catch the aliens off guard and deal a devastating blow to their base. The end. It was a pretty good book by Lovejoy. I bought it years ago, the year it was published. Always thought it was ripe for a sequal.