CLIMATIC ASEASONALITY, PHENOLOGICAL DIFFERENTIATION AND SPECIATION IN TREES

Abstract

Nearly everywhere in the world, plant phenology is tightly linked with climatic seasonality. When all the individuals of a species flower at the same time each year, they are genetically linked to each other by cross-pollination. Phenological conformity maintains the genetic integrity that defines a species. Where the climate allows individuals of a species to flower at different times, individuals and subpopulations of a species may get reproductively isolated from each other. Since reproductive isolation is the essential first step for the evolution of a new species from a pre-existing one, it may be argued that wherever the climate is least effective in regimenting phenological behaviour, there would be maximum opportunities for phenological differentiation and reproductive isolation, and maximum opportunities for sympatric speciation. Data from the Malay Peninsula is presented to support this hypothesis. The Malay Peninsula has an exceptionally large number of species in relation to its land area, a wider range of well-documented phenological expressions than any other region of the world, and what appears to be the least seasonal of all climates.