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Africa, as temperatures can vary in the region at any given time. Therefore flowering durations may be similar, but the timing slightly altered as a result of differing temperatures, particularly from low-lying coastal areas to the inland plateau. Plectranthus species which have longer flowering durations from late spring until end of summer, such as P. saccatus (subsp. saccatus) and P. purpuratus (subsp. purpuratus), which occur in the coastal areas of eastern South Africa, in comparison to species such as P. ramosior and P. xerophilus, which occur in the Highveld areas and flower over late summer into autumn for significantly shorter periods. Therefore, the variation of temperature across geographic ranges amongst various species from coastal to Highveld areas, may act as an influence. Though these patterns may not be blatantly obvious it does suggest that variability in geographic range is one of many key drivers of timing, duration and variability in flowering seasons.
In order to support some of these points, however, it is important to do extensive field research on the various flowering phenologies of these genera, and investigate the possible community-level interactions that may exist. The results of this study, based on secondary data, of selected genera has limited application. The patterns identified may obscure a great amount of variation, especially intra-specific. Field work is needed to validate these observed patterns. Identifying particular flowering patterns at given localities would also allow for the identification of inter-specific similarities, such as synchronized or prolonged flowering seasons or even increases in pollinator availability.
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narrow range, with a few species having larger distributional ranges, depicted by outliers on the box-and-whisker plot (Figure 4.2b.).
The range size patterns of the monocotyledonous geophytic herbs and dicotyledonous woody species indicate that these lineages or taxa have a wider distribution in comparison to dicotyledonous herbs, though among geophytes larger ranges are mostly noted in Zantedeschia and Kniphofia. These patterns may be determined by factors such as dispersal mechanisms, as geophytes seldom have specialised long-distance dispersal (but Zantedeschia fruit is fleshy and is presumably bird-dispersed). Dicotyledonous woody species may rely more often on generalist pollinators, rather than specific pollinators and this may allow them to achieve wider distributional ranges. Dicotyledonous herbaceous species may also have smaller range sizes because of reliance on specific pollinators. Kelly and Woodward (1996) found that wind-pollinated species in British flora had greater range sizes in comparison to non-wind pollinated species.
Subdividing broad growth forms into narrow growth forms showed that, in woody plants, both trees and shrubs have the greatest distributional ranges, with trees having slightly larger range sizes. Kelly and Woodward (1996) also identified this in the British flora, where trees had larger range sizes than woody shrubs. Besides, woody species in general are less likely to be susceptible to factors such as predation and fires once established. In the box-and-whisker plot Streptocarpus is the dicotyledonous herb that consists of numerous narrowly distributed species (Figure 4.2c.). However, in contrast, the range size patterns of other dicotyledonous herbs are similar to those of the monocotyledonous geophytic herbs.
Similarly, when considering variation in the range size patterns at genus level, it is essential to consider specific factors that might determine range sizes in particular genera. It is clear that Cussonia species have the largest range sizes amongst the included genera (Figure 4.2c.). It may be argued that patterns such as these can be related to niche breadth. According to Williams et al. (2006), species with broad ecological niches are likely to have wide distributional ranges, as these species are likely to be well adapted to a variety of environments. Species such as those in the genus Cussonia could be adapted to establish and survive in a broad range of environmental conditions, resulting in larger range sizes. Niche breadth could perhaps also describe why genera such as Zantedeschia, Streptocarpus, Eulophia and Watsonia have such narrowly distributed species. These species may require
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specific environmental conditions, which may only occur in a highly localised (small) area, to establish and survive. The specific niche dimensions involved may vary from one genus to another, or even within genera. The resources species require to expand their respective range sizes could span a number of different factors, from pollinators to nutrients or even water availability.
The seed size of species is another aspect that could partly explain the range size patterns seen at genus level. The smaller the seed size, the greater the potential dispersal range, which allows species to expand the geographic ranges in which they occur (Westoby et al., 1996).
The broad range sizes of some Searsia, Satyrium, Kniphofia and Gladiolus species could be a result of this. Additionally, the link between seed size and range size it is dependent on how many seeds a plant produces that are distributed and establish successfully. This factor, however, may have to be disregarded in the case of Cussonia. If this assumption were valid for all genera, then Cussonia species may produce high numbers of small-sized seeds, which are easily dispersed and established successfully. However, the association between seed size and geographic range may not necessarily be the only determinant and would have to be considered with other biotic and abiotic factors.
Many of these possible geographic range size determinants have not been accounted for in the data set or even in this discussion section, but may represent explanations of the patterns that are being observed in the genera considered here. Many of the determinants described so far are extrinsic factors, part of the environment in which the species exist. However, from an intrinsic perspective, two of the most important determinants of range size patterns are phylogenetic relatedness and phenotypic plasticity across genera and species. The latter could be linked to the concept of niche breadth. Species with greater phenotypic plasticity have greater chances of evolving adaptations in new environments, therefore allowing the geographic range of the species to expand (Pohlman et al., 2005). Kelly and Woodward (1996) believe that phylogenetic relatedness is an important aspect of ecological explanations of range size patterns or other traits that may be identified.
Despite the fact that phylogenetics was not taken into account in this study, the relationship that possibly exists between the flowering patterns and range size patterns can still be explained and understood from various other perspectives. Thus it is still essential to
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understand all the possible contributing factors that have been discussed thus far, and how these factors influence the main findings of this study.