If humans have caused great changes in the distribution and composition of communities over the past several millenia, we are also certain to see great changes in the future. There is, however, an important difference. Past human-caused changes were local or regional. With the dramatic increase in the scale of human activities since the Industrial Revolution, human-caused changes are now global. We'll return to this topic in about a week and a half, when we devote a full lecture to talking about climate change and its impacts.