To make a fair game between old and new tribes, tcause the dinosaurs to grow old (die of old age) and for some level of generation to be infertile.
This will cause 2 side effects
1 - Large tribes will lose dinosaurs, closing the gap a little with new tribes. Today it is absolutely impossible to compete with a base that has been well established on the map for years.
2 - The late game will need to recover the experience of tame new dinos every time, to expose the players to enviroment and pvp and keep the tribe entreted.
I will suggest the same for structures:
1. Decreases damage resistance over time to constantly need repairs to get back to 100%. VERY BIG bases will need more work, keep players entertained in maintaining the base structures and defenses making a chance for new and regular tribes to exploit these weaknesses against less frequent large/old tribes.