Ecozones are defined by the evolutionary history of the biolife they contain, rather than of the locational convenience in the continental listing scheme. The distribution of life forms in these ecozones was originally determined by the early continental drift driven by the plate tectonics process.
One of the warning signs that climate change is happening, is the degree to which animal migrations between ecozones is occurring. These migrations can be expected, for example, in ecozones undergoing persistent warming or drought conditions.
Changing the migration times and location destinations interfere with a species' sheltering, food supply availability, and breeding cycles, thus decreasing species survival possibilities. Animals failing to migrate may face worst conditions in their natural regions due to climate change where regional temperature increases may decrease their food supply.
For example, Some butterflies and birds are not only starting their yearly migrations earlier but they also are migrating further North. In fact, the migration patterns of the state birds of Iowa, Georgia, Massachusetts, New Hampshire, Washington, Maryland, and California may change completely out of their home states by the end of this century according to a study by the National Wildlife Federation.