<P> Peaches, for example, originated in China, and have been carried to much of the populated world . Tomatoes are native to the Andes . Squash (pumpkins), maize (corn), and tobacco are native to the Americas, but were introduced to the Old World . Many introduced species require continued human intervention to survive in the new environment . Others may become feral, but do not seriously compete with natives, but simply increase the biodiversity of the area . </P> <P> Dandelions are also introduced species to North America . </P> <P> A very troublesome marine species in southern Europe is the seaweed Caulerpa taxifolia . Caulerpa was first observed in the Mediterranean Sea in 1984, off the coast of Monaco . By 1997, it had covered some 50 km2 . It has a strong potential to overgrow natural biotopes, and represents a major risk for sublittoral ecosystems . The origin of the alga in the Mediterranean was thought to be either as a migration through the Suez Canal from the Red Sea, or as an accidental introduction from an aquarium . Another troublesome plant species is the terrestrial plant Phyla canescens, which was intentionally introduced into many countries in North America, Europe, and Africa as an ornamental plant . This species has become invasive in Australia, where it threatens native rare plants and causes erosion and soil slumping around river banks . It has also become invasive in France where it has been listed as an invasive plant species of concern in the Mediterranean region, where it can form monocultures that threaten critical conservation habitats . </P> <P> Japanese knotweed grows profusely in many nations . Human beings introduced it into many places in the 19th century . It is a source of resveratrol, a dietary supplement . </P>

Which of the following is not a way that two populations of the same species