Reproduction and establishment of two endangered African cedars, Widdringtonia cedarbergensis and Widdringtonia whytei

In this thesis I determine the effect of population decline on reproduction for two critically endangered African cedars. Widdringtonia whytei (Mulanje cedar) endemic to Mt Mulanje, in Malawi and Widdringtonia cedarbergensis (Clanwilliam cedar) endemic to the Cedarberg Mountains in the Western Cape Province of South Africa. Populations of both species have declined dramatically in the recent past and both show evidence of insufficient recruitment. Recent research has shown that a reduction in population density may limit pollen dispersal, reduce seed viability and increase self-pollination rates, causing an inbreeding depression, resulting in less fit offspring. Based on this research, I hypothesise that pollen transfer in Widdringtonia is distance-dependant and therefore populations with greater distances to the nearest adult neighbour will have lower seed viability, due to pollination failure. I also hypothesise, that trees which receive less outcross pollen due to distance-dependant pollination will have higher rates of self-pollination. I further hypothesise that seed viability may also increase with increased soil nutrients and more amenable climate differences linked to changes in altitude. To test these hypotheses, I determine the extent to which reduced population density has resulted in a decline in viable seed using germination experiments, followed by cut tests and tetrazolium chloride tests. For W. cedarbergensis seedling survival was determined in a greenhouse and self-pollination was assessed with ISSR markers, using DNA extracted from parent and offspring. My results show that seed viability for both W. cedarbergensis and W. whytei is not significantly correlated with distance to nearest-neighbour, altitude or soil nitrogen, carbon or phosphorus. These results suggest that current population densities are not effecting the reproduction either of W. whytei or W. cedarbergensis. My results for population genetics show relatively low levels of genetic variation in W. cedarbergensis typical of endangered and endemic species. The genetic differentiation between populations is low, suggesting that pollen flow between populations is adequate and populations are not genetically isolated. I conclude that there is no evidence that population decline is causing any noticeable limitations on pollen transfer and reproduction in Widdringtonia

Shade or light? : size class distribution and δ¹³C values as clues to the recruiting environment of Widdringtonia whytei

In order to determine the recruitment environment of the endangered Mulanje Cedar, Widdringtonia whytei, size class distributions were measured for six populations on Mount Mulanje, Malawi. Carbon isotope ratios were also collected from leaf tissue in trees of varying height in order to determine the effects of positioning within or below the canopy. Carbon isotope ratios were also taken from wood cores and the δ¹³Cvalues for the innermost and outermost wood were compared for two sites. Size class :frequency distributions had a tendency to be normally distributed but one site showed skewed values towards seedling and another showed a flat distribution, possibly due to continual logging of the trees. Height correlated well with leaf δ¹³Cvalues. Sombani and Bvunje showed the same current (outer wood) δ¹³Cvalues but different recruitment (inner wood) δ¹³Cvalues. Results indicate that Bvunje trees recruited in the shade and Sombani recruited in the sunlight. There is ambiguity in both size class data and carbon isotope data and therefore either Widdringtonia whytei is able to recruit in a variety of manners and environments or other factors are influencing the results

Certain syndrome or complex conundrum? : the pollination of Erica lanuginosa

The flower of Erica lanuginosa has a tightly closed corolla, held in place by hinged sepals. with a dull reddish-pink colour which makes make it hard to determine a likely pollinator. Rodent trapping and pollen analysis of faecal matter showed it unlikely to be pollinated by a rodent. Flowers excluded from external pollination showed no seed set, hence it is not considered to be self-pollinated. Nectar analysis are inconclusive as an indicator of pollination syndrome. Entomophily by a robust insect with a medium length proboscis is considered unlikely due to phenology and morphology of the flower. Omothiphily is a possibility as stem thickness correlates with previous studies investigating the correlation between stem thickness and pollination syndromes. The pollination syndrome of Erica lanuginosa remains indeterminate by I hypothesize that, due to phenology, thick supportive, stem and large quantities of nectar and close-formed flower, which needs to be manoeuvred open, its pollinator is likely a short-billed generalist-feeding bird restricted by food choice during the winter months