Why is there a natural decrease in the number of plant and animal species from the equator to the poles?

The uneven distribution of animals and plants on Earth is one of the forms of manifestation of the zoning of nature (the main geographical pattern). Depending on the changing ratio of heat and moisture, the species composition of animals and plants decreases in the direction from the equator to the poles. Climate change is the main factor that determines the presence of more than ten large natural zones (taiga, tundra, savannah, deserts, steppes, arctic deserts, etc.), elongated like belts on the surface of our planet and replacing each other from the equator to the poles. Each of these zones has its own characteristics of flora and fauna.