Well it really depends on what kind of change there is. For this I'll use a drought as an example. If a drought occurs in an area the plant life and vegetation will start to die off in that area. From there, primary consumers would run out of food. then secondary consumers, and so forth and so on. it'd be like putting a cow in a field of dirt with no food and a large bucket of water. Eventually the cow will die of starvation. Now apply this to all of the animals in that ecosystem.
