Province: Scientists are warning that polar bears, which evolved quickly to dine mainly on seals, could face formidable competition as brown bears expand northward with global warming. The iconic white bruins exist almost entirely on a meat diet, while their omnivorous southern cousins will chow down on almost any animal flesh and gorge themselves on berries. In fact, one recent study predicts that polar bears may be forced to eat the eggs of snow geese to fill their bellies. Another study, published…