Why most of the species live near the equator?
The geographical pattern of increasing biodiversity from the poles to the equator is one of the most pervasive features of life on Earth. Many ‘historical’ and ‘ecological’ hypotheses have been proposed and debated, but there is still little consensus.
This idea is also referred to as the latitudinal diversity gradient, meaning that as you move from the equator towards the poles.
There are multiple theories as to why this is the case.
The Equator is relatively stable in terms of an environment when compared to polar regions has also been suggested as a reason for increased biodiversity at the equator.
One of the more recent studies on this issue concluded that species turnover is higher in temperate regions. Some also believe greater primary productivity at the equator has lead to greater biodiversity. Having more energy available in this area means more consumers can be supported.
Biologists have long noted that life's majesty grows closer you are to the equator. There are not only more species in the tropics, but there are also more potential medicines, fruits, cultures, and languages. The gradient in diversity that Humboldt detected shapes human life, from our economies to our well-being. There are a variety of competing hypotheses to explain the pattern. One, in essence, attributes it to random chance. Another argues that more solar energy is received around the equator, allowing for greater species richness. The third point out that equatorial tropics are the largest biome, so it makes sense that there would be more specific. A fourth contends that competition, predation, mutualism, and parasitism are more prevalent in the tropics, and these interactions lead to greater speciation.
Locations on the Equator experience the quickest sunrises and sunsets because the sun moves nearly perpendicular to the horizon for most of the year. The length of daylight (sunrise to sunset) is almost constant throughout the year; it is about 14 minutes longer than nighttime due to atmospheric refraction and the fact that sunrise is begun (or sunset is ended) as the upper edge, not the center, of the Sun’s disk crosses the horizon.
Populations having less massive individuals are more often found in warm climates near the equator, while those with greater bulk, or mass, are found further from the equator in colder regions. This is due to the fact that big animals generally have larger body masses which result in more heat being produced. The greater amount of heat results from there being more cells. A normal byproduct of metabolism in cells is heat production. Subsequently, the more cells an animal has, the more internal heat it will produce. When the air temperature is consistently high, people usually have low body mass. Similarly, when the temperature is low, they have high mass. However, there are exceptions. Cold adaptation is usually more difficult physiologically for humans.
Another idea is geographical isolation due to changes in sea level, glaciation, and other factors: Some of the speciations which occurred in Amazonia and other tropical regions may have been due to warmer periods during which the sea level rose sufficiently to isolate fragments of these regions. In these cases, speciation would have been driven by geographical isolation.
The climate near the equator is more stable year around. You tend to see more organisms of the same type where there are seasons because there are certain attributes they all need to have to survive- steering evolution in a common direction.
Biodiversity generally tends to cluster in hotspots, and has been increasing through time, but will be likely to slow in the future.