Grass from the old world and the new world 

A colleague told me the differences between grasses from the new world and the grasses from the old world. For grasses from the new world, less nutrient is stored in roots and more nutrient is stored in grass blades. These grasses grow faster for their leaves are better at absorbing solar energy. But they are less resistant to grazing. When grass blades are eaten, little nutrient is left to regenerate.

For grasses from the old world, more nutrient is stored in roots and less nutrient is stored in grass blades. These grasses grow not as fast. But they are more resistant to grazing. When grass blades are eaten, much nutrient is still intact at the roots. This helps them to regenerate.

The differences are caused by different selection pressures. Crows in Canada are much bigger than those in China. If crows are so big in China, they would be hunted down actively. In general, life from the old world grow slower but are more resilient.