I'm speculating that "slow down" in your first quote means "the flow doesn't plummet towards zero when it's busy" and in the second quote it means "reduce their

I'm speculating that "slow down" in your first quote means "the flow doesn't plummet towards zero when it's busy" and in the second quote it means "reduce their average velocity". So in that sense they don't slow down (i.e. the colony doesn't grind to a halt) because they slow down (i.e. literally slowing down) Again, I'm speculating about the meaning but if I'm right then it's a poor choice of words from the author.