A herd of alpine ibex (Capra ibex) struggles through deep snow. A recent study examined 45 years of census data for a population of alpine ibex in Gran Paradiso National Park in northwestern Italy. Researchers found that in the absence of natural predators and human hunting, density dependence and the severity of winter weather limit the population’s size. Severe winter weather affects population size by decreasing juvenile survival. During severe winters, the probability of starvation increases for juveniles through the higher energy costs of thermoregulation and decreased food available due to deep snow. This photograph originally appeared on the cover of Ecology (85:6) in June of 2004.