For this reason, the seeds and pollinators must be able to fly throughout the area where these plants grow. If several small areas where such plants grow are too far away from one another for seeds and pollen to be carried from one to another, then they cannot cross pollinate or seed each other. Animals and plants such as bison and big bluestem need not only large amounts of space, but large amounts of unbroken space. If there is something, such as a farm, that prevents bison from getting to the food that they need or the seeds from getting to the ground where they can grow, then the populations may decline or even go extinct . Birds that cannot find suitable forest habitat to live in are susceptible to cow birds, which steal nests from other birds and lay their own eggs in them.
Cow birds find nests by looking in trees at the edges of forests.
Explain to the students that the settlement of the Midwest with large farms has caused the declines of many kinds of animals and plants. Cutting down forests not only destroys the forest habitat in the place where the timber was cut, but it also often increases the total length of forest edges and opens up corridors for invaders, such as the brown-headed cowbird, allowing predators to get to the animals that once found refuge among the trees. When farmers fill or drain wetlands, several kinds of birds lose their habitats, and the function of flood mitigation and water filtering is lost, which threatens the surrounding habitats with more devastating floods and contaminated water supplies. When farms are placed in the middle of a large area that was used by a population, the two smaller areas that remain on the opposite sides of the farm may not be sufficiently large to support the populations. For this reason, using a small amount of land may have disastrous consequences for a large number of living things.