Why is there a change in natural zones in the mountains, what determines their number?

Natural zones are formed under the influence of climate, since the different plants and animals that make up them are adapted to certain temperatures. And in the mountains, as you know, the temperature decreases with height, and those living organisms that exist at the foot of the mountain cannot exist in the cold conditions of its middle part. And this is how vertical natural zones appear. Their number depends on where the mountain is and what its height is. In the high mountains of the tropics there are all existing zones.