In Nigeria, the major climatic factor that determines the distribution of organisms is

In Nigeria, rainfall is the most significant climatic factor influencing the distribution of organisms. Nigeria's vegetation zones - from the mangrove swamps in the south to the Sahel savanna in the north - are primarily determined by the amount and pattern of annual rainfall rather than by any other single climatic variable.

The southern regions receive heavy rainfall (over 2,000 mm annually) and support dense tropical rainforests, while the northern regions receive progressively less rainfall (as low as 500 mm in the far north) and support savanna grasslands and semi-arid vegetation. This rainfall gradient directly controls which plant species can grow in each zone, and the plant communities in turn determine which animal species inhabit the area.

While temperature, humidity, and light also affect organisms, they do not vary as dramatically across Nigeria as rainfall does. Nigeria lies entirely within the tropics, so temperature remains relatively warm throughout the country year-round. Humidity and light intensity are themselves partly consequences of rainfall patterns. It is the marked north-south rainfall gradient, driven by the movement of the Inter-Tropical Convergence Zone (ITCZ), that creates the distinct ecological zones across the country.