The natural vegetation in an area provides a food source to omnivores and herbivores; if the natural vegetation is altered, species numbers can decline or the species may die out. When animals do not have enough food, they may try to move to other areas, impacting the ecosystem in that area as well.
The natural vegetation of an area is affected by the climate, soil and amount of precipitation in an area. One reason global warming is worrisome is because it changes the characteristics of the environment. Different characteristics may not support the natural vegetation that the animals in the area are accustomed to. The animals that feed on herbivores are left with a smaller food source that affects their population as well.