The numbers of deer, because there was nothing to hunt them, had built up and built up in the Yellowstone Park, and despite efforts by humans to control them, they'd managed to reduce much of the vegetation there to almost nothing, they'd just grazed it away.
因为没有天敌追逐它们 黄石公园里鹿的数量不断增加 尽管人类作出努力想去控制它们 但它们已经将很多植被 食用殆尽