Explanation:
Geographical isolation - Geographical isolation is the separation of related organisms by geographical barriers such as mountains, valleys, deserts, water bodies, glaciers, forests etc. sea water isolator the islands from mainland land separate aquatic fauna and flora of lakes and ponds. High mountains isolate adjacent lands while mountains are separated from one are another by valleys. Geographical isolation is a very important factor in production of new species so, Darwin's finches living on Galapagos islands differ not only among themselves but also from mainland finches in size, colour, beak and food habits due to environmental conditions and Geographical barriers or isolation.