UNDERSTANDING RARITY IN A NARROW ENDEMIC <em>BEGONIA</em> THROUGH BIOLOGICAL COMPARISON WITH A COMMON SPECIES

Abstract

Rare endemics usually have high risk of threats and extinction and often require conservation urgency. Hence, understanding the causes and consequences of rarity is the basis for sound conservation efforts. Here, we compare the reproductive fecundity, mating system, morphological traits, demography, microclimate and genetic diversity between a rare (Begonia herveyana) and a common (B. maxwelliana) herbaceous congener to investigate whether these attributes contribute to rarity in Begonia. The reproductive fecundity, mating system, microclimate and demographic structure of both species were similar and thus, did not explain well the causes of rarity. Both species recorded fruit sets of 55–67%, adopted a mixed-mating system with outcrossing rates of approximately 90%, established at microsites of high humidity and low light intensity, and showed a J-shaped demographic structure. However, both species differed in plant size and the level of genetic diversity. The plant size was bigger in B. maxwelliana and the genetic diversity of B. herveyana (H_E = 0.113) was lower than that of B. maxwelliana (H_E = 0.415). Rarity in B. herveyana could possibly be explained by the low level of genetic diversity, population decline and limited dispersal.