European pied flycatcher
Oaks are keystone species in a wide range of habitats from Mediterranean semi-desert to subtropical rainforest. For example, oak trees are important components of hardwood forests, and certain species are particularly known to grow in associations with members of the Ericaceae in oak–heath forests. A number of kinds of truffles, including the two well known varieties, the black Périgord truffle and the white Piedmont truffle, have symbiotic relationships with oak trees. Similarly many other mushrooms such as "Ramaria flavosaponaria" also associate with oaks. The European pied flycatcher is an example of an animal species that often depends upon oak trees.