True, Eric, my favourite example is rhododendron ponticum which was introduced into this country as rapid growing cover for game birds, but now a lot of trouble and expense is being put into eradicating it as an invasive exotic species. The sting in the tail is that fossil evidence shows that it was once a native to this country but was wiped out by the ice age that sterilised Britain, no wonder it is doing so well, it is reclaiming its home territory!
As you say, nature is never frozen in time, it adapts to changes just as at present it is adapting to climate change. We are part of nature (some would dispute that!) and are very successful at adapting to change.