The reasons for the diversity are as follows:
- Over geological times the tropics have had more stable climate than the temperatezones. In tropics, therefore, local species continued to live there itself, whereas intemperate they tend to disperse to other areas.
- Tropical communities are older than temperate one’s and therefore there has beenmore time for them to evolve. This could have allowed them greater degree ofspecialization and local adaptation to occur.
- Warm temperatures and high humidity in most tropical areas provide favourableconditions for many species that are unable to survive in temperate areas.
- In tropics there is greater pressure from pests, parasites and diseases. This does notallow any single species to dominate and thus there is opportunity for many species toco-exist. On the contrary in temperate zones there is reduced pests pressure due to
- cold, and there is one or few dominating species that exclude many other species.
- Among plant, rates of out-crossing appear to be higher in tropics, which may lead tohigher levels of genetic variability.
- Tropical areas receive more solar energy over the year. Thus tropical communities aremore productive or greater resource base that can support a wider range of species.