People often confuse the terms "game ranger" and "field guide". There is a difference, and here is why …
A game ranger is mainly responsible for the physical and resource management of national parks and private game reserves. S/he acts as a custodian of the wildlife and maintains the game reserve on which the wildlife is kept – the biological populations of the animals as well as roads, fencing, water resources, erosion control, alien plant control, burning programmes, population control and bush clearing, among other tasks.
A field guide interacts with the tourists visiting national parks and private game reserves, sharing his/her knowledge about nature and the environment with these visitors. These guiding experiences are either conducted in a vehicle or on foot. A field guide acts as an interpreter between the environment and the guest, with the ultimate intention of promoting conservation and environmental protection to the tourists through instilling an appreciation for nature in them.
"Nature guide" is a synonym for "field guide" – it refers to exactly the same concept.