Environmental resistance - Supposedly makes hostile environments easier to live in. I read somewhere on this forum that every 5 points of this trait improves the effective conditions of any planet by 1 point, though. (10 points = 1 level, I think.)
Each 5 points of ER equals 1 point of Reproduction, and a small amount of Happiness. You have to change ER by a full 5 points to see an affect. Lowering it to 86 has no affect. Rasing it to 104 has no affect.
The best thing to do is lower ER to 81, raise Reproduction to 103 and Happiness to 107. You will see absolutely no affect upon your empire, except possibly slightly improved happiness, and you will get 100s of free racial points.
You likely recall the results of my tests on this trait many months ago.
