A physical barrier is a tangible obstacle that prevents movement or access between two areas. Examples include walls, fences, and natural formations like mountains or rivers. These barriers can serve various purposes, such as protecting property, controlling wildlife, or defining boundaries. In ecology, physical barriers can influence the distribution of species. For instance, a river may separate two populations of animals, leading to different evolutionary paths. Similarly, mountains can limit the spread of certain plants and animals, affecting biodiversity in the region.