California sea lions have managed to maintain -- and, in the case of males, increase -- their average body size as their population grows and competition for food becomes fiercer. This is in contrast to other marine mammals, whose average body size tends to decrease as their numbers increase. Researchers report that sexual selection was a strong driving force for males to grow bigger and to strengthen muscles in their neck and jaw that help them fight for mates. Both male and female sea lions evaded food shortages by diversifying their diets and, in some cases, foraging further from the shore.
To explore how California sea lion ecology has changed as their population has grown, the researchers analyzed museum specimens of adult male and female California sea lions collected in central and northern California between 1962 and 2008. To estimate changes in body size, they compared the overall size of more than 300 sea lion skulls collected over the years. They also measured other skull features, such as the size of muscle attachment points, which allowed them to assess changes in sea lion neck flexibility and biting force.
Read more here.