Final answer:
Temperature stability is the factor that contributes to a higher diversification rate in the tropics, promoting speciation by providing stable conditions for the development of specialized niches and promoting complex ecosystems.
Step-by-step explanation:
The factor proposed to contribute to a higher species diversification rate in the tropics is temperature stability. Temperature stability in the tropics leads to environmental consistency, which may promote speciation by providing stable conditions that allow for the development of highly specialized niches.
Additionally, the greater energy input from the sun provides a high amount of solar energy, which sustains complex ecosystems with a high diversity of life. This complexity increases habitat heterogeneity and the number of ecological niches, further encouraging the process of speciation and the emergence of new species.