For example, after a glacier retreats the environment is very harsh. Over time, lichens begin to grow on rocks providing food for animals like caribou. Predators like wolves follow caribou herds and humans follow both species hunting them for meat and hides. Hunting big game like caribou or mastodon requires big stone tipped spears, like Clovis points. As time went by, the climate on Long Island warmed and the caribou headed north. Walnut, chestnut and beech trees established themselves and soon deer and turkey became abundant. Fishing became a reliable way to provide food. Big spears were traded for smaller weapons, harpoons, nets and fish hooks. As the climate changed so did the animals, plants and human ways of life.