The Arctic tundra has extremely cold winter temperatures and short winter days. In contrast, summer days are long and moderately warm. Small cushion plants, blueberries, birch, and willow, which grow in a thin layer of soil atop permanently frozen soils, form the base of the food chain. Lichens are also abundant on the tundra. The plants and lichens are eaten by caribou, pika, moose, and grizzly bear. Grizzly bears also eat the caribou, pika, and moose. Which items are part of the Arctic tundra ecological community