Why are topographic maps useful? Give an example of how one might be used. PLEASE HELP

If you are using them for navigation, they can show you where easier paths might be.

They show us natural water features that we can use to find our way. Water features are in blue. Direction of stream travel can be determined by how the stream encounters the contour lines; the contour lines point upstream. In the example below, the stream runs from east (right) to west (left). The green arrow points at the head of the stream.

Hope this helps

One such situation would be that
"A fierce predator is removed from the ecosystem."

 A removal of such a predator would mean that the population of the animals it is eating would increase, which would in turn decrease the population of the animals or plants that those animals are eating, which would generally decrease the stability of the system.