Gradually,Asian Carp edge out the other native species in the river until they are one of the only kinds of fish left.

VOA: standard.2010.07.20

You can imagine that this can only happen gradually; none of this happens overnight.

你可以想象得出,这种变革,只能缓慢的进行,并不能一蹴而就

耶鲁公开课 - 古希腊历史简介课程节选