▁pressure ▁was ▁a ▁force ▁that ▁sh aped ▁the ▁e col ogy ▁of ▁the ▁Great ▁Pla ins ▁as ▁strongly ▁as ▁periodic ▁pra irie ▁fires ▁and ▁which ▁were ▁central ▁to ▁the ▁surv ival ▁of ▁many ▁American ▁Indians ▁of ▁the ▁Great ▁Pla ins . ▁To ▁the ▁corn - g row ing ▁village ▁Indians , ▁it ▁was ▁a ▁val ued ▁second ▁food ▁source . ▁However , ▁there ▁is ▁now ▁some ▁controvers y ▁over ▁their ▁interaction . ▁Charles ▁C . ▁Mann ▁wrote ▁in ▁ 1 4 9 1 : ▁New ▁Re vel ations ▁of ▁the ▁Amer icas ▁Before ▁Columb us , ▁pages ▁ 3 6 7 ▁ff , ▁" H ern ando ▁De ▁S oto ' s ▁expedition ▁st agger ed ▁through ▁the ▁S out heast ▁for ▁four ▁years ▁in ▁the ▁early ▁ 1 6 th ▁century ▁and ▁saw ▁h ord es ▁of ▁people ▁but ▁apparently ▁didn ' t ▁see ▁a ▁single ▁b ison ." ▁Mann ▁discussed ▁the ▁evidence ▁that ▁Native ▁Americans ▁not ▁only ▁created ▁( by ▁select ive ▁use ▁of ▁fire ) ▁the ▁large ▁grass lands ▁that ▁provided ▁the ▁b ison ' s ▁ideal ▁habitat ▁but ▁also ▁kept ▁the ▁b ison ▁population ▁reg ulated . ▁In ▁this ▁theory , ▁it ▁was ▁only ▁when ▁the ▁original ▁human ▁population ▁was ▁dev ast ated ▁by ▁wave ▁after ▁wave ▁of ▁ep ide mic ▁( from ▁dise ases ▁of ▁Europe ans ) ▁after ▁the ▁ 1 6 th ▁century ▁that ▁the ▁b ison ▁her ds ▁propag ated ▁wild ly . ▁In ▁such ▁a ▁view , ▁the ▁se as ▁of ▁b ison ▁her