We don't know that for sure though. All it takes is a single seed in an ideal condition. And that condition could've probably happened in a way that the pear wouldn't have the advantage that's caused some to name it "invasive".
But also, left alone, nature tends to rebalance on its own. Any species with a dominant advantage will eventually lose that advantage, given a few generations. Well, except for humans, who continually fight the natural rebalancing, and are only succeeding in increasingly destroying that which sustains life on this planet.
But also, left alone, nature tends to rebalance on its own. Any species with a dominant advantage will eventually lose that advantage, given a few generations. Well, except for humans, who continually fight the natural rebalancing, and are only succeeding in increasingly destroying that which sustains life on this planet.