Populations in nearly every ecosystem have shifted in response to human introductions of formerly isolated species from other regions. The change really is dra

Populations in nearly every ecosystem have shifted in response to human introductions of formerly isolated species from other regions. The change really is dramatic - in the last two hundred years the northeastern US forests, which I've studied somewhat, have completely lost the dominant overstory plant, the American Chestnut (introduced fungi), and have lost a many-inches-thick layer of topsoil debris with resident moss & fungus populations (introduced earthworms). That's in the ones that have recovered from the agricultural/logging clearcuts and that weren't affected by the fire suppression.