Is there a distinction between bears and chubbies or chubby chasers?
Yes, a bear is a gay man with facial and body hair. The stereotypical bear is a big man -- not necessarily fat -- but a large, bear-like furry guy. However, the bear community has expanded into different kinds of bears. Bear cubs are younger men, daddy bears are older men (generally seniors), chubby bears are portly guys, and muscle bears are hairy guys with big arms and chests. Otters are bears who are more slender than the average bear; wolves are skinny guys with hair.
It often seems that the chubby chaser movement has completely overtaken the bear movement. Bears were never just supposed to be "fat guys," but people often -- wrongly -- see bears as men who are quite obese or even morbidly obese. These, of course, are chubby bears, not regular bears. (And let's face it, most muscle bears are really chubby bears, their bellies being a much more distinctive feature than the size of their arms.)
When it comes to bears I think a hairy body (as well as a beard or goatee) matters much more than the size of the belly.