Effect of Altitude and Co-occurring Species on Sequential Reproductive Stages in a Grassland Harebell.
Sawrey, Olivia Rose Pamela
Understanding reproductive capabilities of individual species along altitudinal gradients is increasingly important in light of changes in habitat that are predicted with climate change. Alpine plants can be considered particularly at risk from climate-change as they occupy what are in effect habitat islands. Up until recently New Zealand’s alpine flora has been assumed to be largely self compatible with high levels of generalised pollinator relationships. However recent evidence has found this not to be the case suggesting that reproduction in New Zealand alpine plants may be more sensitive to changes in climate and pollinator availability than previously thought. Of particular interest is an alpine bellflower, which is self-incompatible and has a short duration of stigma receptivity. This plant, Wahlenbergia albomarginata Hook., ranges in flower size and petal colour can vary from light blue to white, with extreme blue flowers being more attractive to pollinators en masse. The central aim of this study was to discover if changes in environment over W. albomarginata’s wide altitudinal range affect its reproductive characteristics namely: flower size, colour, pollen delivery and seed set.The effect of environmental factors associated with altitude and soil chemistry on flower colour (reflectance 450:550 nm ratio) and flower size were compared in over three hundred flowers among three locations: the Blue Mountains(with sites ranging from 650m-1000m), The Remarkables (with sites ranging from 990m-1650m) and the Pisa Range (with sites ranging from 886m-1705m). Additional work tested for changes in flower colour over time and in restricted soil moisture. The effect of altitude on pollen load at the Blue Mountains was determined. Forty thousand pollen grains were identified on sixty stigmas. The proportion of hetero-specific pollen was compared with immediate flowering neighbourhood and with previous work carried out at The Remarkables. Finally, the effect of altitude on seed set and mass was tested at The Remarkables. Fifteen thousand seeds were counted from seventy two capsules to test the effect of location between the Blue Mountains and Remarkables. Results showed environmental factors associated with altitude affected flower size at one of three locations. At the other two, significant variation in flower size between sites did not coincide with an altitudinal effect. This suggests flower size changes with environmental factors that do not always change with altitude. Flower colour was bluest in younger flowers, which is likely to enhance male fitness, by increasing pollen export by pollinators prior to gender phase change in this protandrous species. On average, eighty percent of pollen load on stigmas was exotic at the Blue Mountains. This was in stark contrast with previous findings at higher altitude at The Remarkables. Pollen load was not affected by altitude or immediate neighbourhood at the Blue Mountains, because the exotics, whose pollen was present on stigmas, were present at all sites. Seed set was not affected by altitude at Tithe Remarkables, despite this being the largest gradient, and the only location where flower size was affected.It can be concluded from this study that changes in flower size due to environment do not affect reproductive outcomes in the field. Changes in temperature associated with elevating altitude do not affect insect activity sufficiently to change pollen type or amount delivered to W. albomarginata, or seed set. Instead, location and different co-occurring species greatly affect the type of pollen delivered, but not overall seed set. This study shows that W. albomarginata has a high level of plasticity in floral characteristics that are dependent on abiotic conditions, and is able to maintain a consistent reproductive output, despite inhabiting areas with a variety of soil pH, soil moistures, soil nitrogen levels, temperatures, shelter and plant mosaics throughout its wide altitudinal range.
Advisor: Lord, Janice M
Degree Name: Master of Science
Degree Discipline: Botany
Publisher: University of Otago
Keywords: alpine; herb; grassland; New Zealand; stigma clogging; flower size; flower colour; wahlenbergia albomarginata; campanulaceae; pollination ecology; altitude gradient; exotic pollinators; native pollinators; Otago; seed set; soil chemistry; abiotic environment
Research Type: Thesis