Question

The table below shows the number of species in different parts of the world. 

Name of Place	Number of Bird species
Columbia	1400
India	1200
Northern South America	1300
New York	105
Denmark	504

Identify the common factor in regions with a higher number of bird species and suggest at least two reasons for this greater diversity.

Answer 1

Greater diversity is seen in regions closer to the equator/tropics (latitudinal range of 23.5° N to 23.5° S), which harbor more species.

Reasons for this greater diversity are:

1. Speciation is generally a function of time. Unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus have had a long evolutionary time for species diversification.
2. Tropical environments, unlike temperate ones, are less seasonal and relatively more constant and predictable. Such constant environments promote niche specialisation and lead to greater species diversity.
3. There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.