Latitudinal and altitudinal gradients: Temperature, precipitation, distance from the equator (latitudinal gradient), altitude from sea level (altitudinal gradient) are some of the factors that determine biodiversity distribution patterns. The most important pattern of biodiversity is latitudinal gradient in diversity. This means that there is an increasing diversity from the poles to equator. Diversity increases as one moves towards the temperate zones and reaches the maximum at the tropics.
Thus, tropics harbour more biodiversity than temperate or polar regions, especially between the latitudes of . ⁰ N and . ⁰ S (Tropic of Cancer to the Tropic of Capricorn). Harsh conditions exist in temperate areas during the cold seasons while very harsh conditions prevail for most of the year in polar regions.
Columbia located near the equator (0⁰) has nearly species of birds while New York at 41⁰N has species and Greenland at 71⁰N has species. India, with much of its land area in the tropical latitudes, is home for more than species of birds. Thus it is evident that the latitude increases the species diversity. Decrease in species diversity occurs as one ascends a high mountain due to drop in temperature (temperature decreases @ .5⁰C per Km above mean sea level) The reasons for the richness of biodiversity in the Tropics are: • Warm tropical regions between the tropic of Cancer and Capricorn on either side of equator possess congenial habitats for living organisms.
• Environmental conditions of the tropics are favourable not only for speciation but also for supporting both variety and number of organisms. • The temperatures vary between 25⁰C to 35⁰C, a range in which most metabolic activities of living organisms occur with ease and efficiency. • The average rainfall is often more than mm per year. • Climate, seasons, temperature, humidity, photoperiods are more or less stable and encourage both variety and numbers.
• Rich resource and nutrient availability.