The gray wolf, also known as the timber wolf, is the largest of about 41 wild species within the dog family. Recognized subspecies of the gray wolf number 24 from the New World and eight from the Old World. Wolves are able to live in habitats ranging from Arctic tundra to forest and prairie, as long as suitable prey is present. At one time wolves occurred throughout most of the Northern Hemisphere from about south central Mexico to the Arctic. The wolf social unit is the pack, which normally is between two and eight animals but may range up to 36. Each pack has its own area, which may vary from 50 to 5,000 square miles (130-13,000 sq km), and will defend the area against intruders. When two wolves meet, each shows its relationship to the other by indicating dominance or submission through facial expression and posture. Additional modes of wolf communication are vocalizations (including howling) and scent marking.