From previous testing I've done, Env. Resist. has only shown to have an effect on growth rate, independant of anything else.
Every 5 points in it raises growth by 1%. I tested this for Unpleasant and up, so if someone wants to double check this for worse conditions, be my guest.
Unfortunately, this appears to be a case where it'd make sense for it to affect how well your population handled poor conditions, people assumed that's what it did, and the misinformation spread...
FYI, I basically had several growth tables laid out with the percentage increase charted for variations in condition, Env. Resist. values, and reproduction values. In every case across the board, the 5% to 1% ratio held true. The border is between 0/1 and 5/6, so you can reduce your starting % to 96% with no ill effect. I'd suggest making it 81% and using the points in reproduction to compensate - it's cheaper until you hit the breakpoint for repro.