Ants, pigeons, rats, and cockroaches are some of the important urban migrants, and are a universal result of urbanization. Thus today various nations are rushing to create national parks and preserves, with one of the goals being to preserve a pristine environment for animals in the wild.
生物學者喜歡用地形縱剖面來說明野生動物的生態變遷。由平地到海拔五百公尺是台灣植被最豐富、生態最多樣、氣候最溫暖的地方，餵養的動物種類、數量也最多。