Accommodating problems of rarity definition and phylogeny in assessing common-rare differences in reproductive effort: opportunities provided by the Cape Flora

Owing to the existence of numerous large genera with clusters of closely re lated species with different population sizes and distribution ranges, the Cape Flora provides exceptional opportunities for accommodating problems of rarity definition and phylogenetic relatedness in assessing common-rare di fferences. Here we report on progress in exploiting these opportunities by presenting date on a measure of reproductive effort (seed:ovule ratio) for six closely related plant species pairs in the Proteaceae. The species pair s were equally divided between the widespread/common-restricted/common and widespread/common-restricted/rare categories, and all grow in the species-r ich fynbos landscapes of South Africa's Cape Floristic Region. The pairs in cluded five genera and spanned a range of growth forms and reproductive bio logies. All pairs had overlapping reproductive phenologies and similar biol ogies, and were broadly matched for habitat requirements. Rare species did not have significantly different seed:ovule ratios than common congeners. H owever, all three restricted/rare species had significantly higher seed:ovu le ratios than their widespread/common congeners. No significant results we re recorded for the widespread/common-restricted/common comparisons. Our fi ndings indicate that by selecting a large number of closely related species pairs, and categorizing them according to different forms of rarity, the c ontradictory results inherent in the literature on common-rare comparisons can be resolved. The study system offers great potential for further resear ch on the causes and consequences of different forms of plant rarity.