The relationship between the length of flowering periods and the distribution ranges of plant species in eastern South Africa.

Abstract

Flowering is one of the most important stages in determining the successful survival and spread in plants. The duration of the flowering period is closely associated with successful reproduction, making it essential to understand the importance and effects of the length of flowering on various macroecological variables across plant species. The effects of the length of flowering periods on the distribution range size of species have seldom been investigated. This project aims to identify any macroecological relationship that may exist between the length of flowering periods and the distribution ranges of plant species endemic to the eastern part of South Africa, a region well known for its floral diversity. Range size and flowering phenology data were collected for several genera that are centred in the region (Cussonia, Gymnosporia, Searsia, Streptocarpus, Pavetta, Plectranthus, Crinum, Eulophia, Gladiolus, Kniphofia, Satyrium, Watsonia and Zantedeschia). At genus level, the relationship varied considerably. While significant correlations between the two variables were retrieved in four genera, the meaning of these patterns differed. In some cases, these suggested that a larger range was achieved through successful pollination due to extended flowering periods, whereas in others, it is probably just an effect of different flowering seasons in different areas where the range is large enough to comprise diverse climates. When incorporating variables such as growth form (narrowly and broadly-defined) and genus identity in analyses of covariance between flowering durations and various measures of distribution, the association of genera was far greater than that of growth form. It can be concluded that both range size and the length of the flowering season are the result of numerous factors acting jointly, which differ across plant groups and are likely to be susceptible to changes in climate and biological invasions. This means that the relationship between range size and flowering period is driven by different factors in different genera, suggesting that the conservation of plant diversity in the face of global change will have to consider the complexity of flowering patterns, and it is likely that lineage-specific approaches for different plant groups will be necessary.