Post-doctoral Research: I will be investigating the ecological and evolutionary processes that maintain continuous color variation and the existence of extremely dark flowers in the native endemic Royal Irises (Iris section Oncocyclus) in the lab of Dr. Yuval Sapir. I am looking forward to exploring the evolutionary ecology of plants and the interface of genetics and ecology.
Doctoral Research: Plant-pollinator interactions and environmental change: Effects of experimental changes in phenology and water availability on a montane wildflower
Recent changes in climate are altering ecosystems worldwide. Environmental changes may disrupt ecological relationships, including those between plants and pollinators. Plant-pollinator mutualisms are vital to maintaining ecosystems and supporting global crop production. Warmer springs are changing the timing of plant reproduction and pollinator emergence (i.e. phenology). Earlier snowpack melting is likely altering soil water availability during the growing season. As individual species respond to climatic shifts, ecological relationships may be disrupted, potentially altering community composition and ecosystem functioning.
With an estimated 87.5% of flowering plants depending on animal pollination for sexual reproduction, including approximately 70% of the world’s leading food crops (Aizen et al. 2009, Ollerton et al. 2011), understanding the mechanisms behind observed declines in pollinators and insect-pollinated plants is a critical scientific and societal challenge. Yet despite a growing interest in addressing this challenge (IPCC 2014), we still know relatively little about the mechanisms underlying climate-driven changes in plant-pollinator interactions.
Research Objectives: I investigated the mechanisms driving plant-pollinator responses to changes in water availability and phenology associated with warmer springs and early snowmelt. Specifically, I examined the extent which floral traits, pollination, and seed set of the tall-fringed bluebell, Mertensia ciliata (Boraginaceae), respond to changes in soil moisture and flowering phenology in the sub-alpine meadows around the Rocky Mountain Biological Laboratory (Gothic, CO):
(I) Effects of variation in water availability. Reduction in soil moisture due to early snowmelt may affecta plants capacity to produce a floral display that is attractive to pollinators, (e.g., by reducing flower number, size, or reward). I hypothesized that reducing soil water availability would decrease the capacity of plants to attract pollinators, resulting in lower pollination success and seed set. Results of my three year water manipulation experiment show that water reduction negatively impacts M. ciliata flower size (corolla width and length), nectar production, pollinator visits, seed set and seed mass. I also found that pollinators are less likely to visit narrow flowers compared to wide ones, but that visit rates are not influenced by nectar volume.
(II) Effects of variation in flowering phenology. Between 1973-2006, mean spring temperatures in this area have increased by 2℃ and the average date of first bloom for the native M. ciliata has advanced by more than a week. I hypothesized that differences in the timing of plant reproduction alters the visitation rate and the community of potential pollinators, resulting in lower pollination success and seed set. To test this, I experimentally manipulated M. ciliata phenology by inducing propagules to flower at different times using temperature and light variation along an elevation gradient, and then placed flowering plants in the field in experimental arrays and observing pollinator visits. I found that pollination rates (number of flowers visited/flowers available per hour of observations) declined over the course of the summer. The composition of pollinators also changed over time, shifting from a diverse array of solitary bees, flies, and bumblebee queens to 100% worker bumblebees by the final week of observations. Contrary to my hypothesis, however, differences in flowering timing had no impact on seed set.
(III) Interactive effects of variation in water availability and flowering phenology. Both shifts in water availability and phenology have important effects on pollinator visitation and plant reproductive success. Changes in water availability directly affect floral morphology and nectar rewards, and these changes in turn, influence pollinator visitation rates (H1, see above). Plants that differ in the timing of flowering may experience different pollinator visitation rates and a different community of pollinators (H2). Moreover, there is strong evidence to suggest that pollinator effectiveness varies considerably between early and late-season visitors (H2, see above). Changes in water availability and flowering phenology, however, are unlikely to occur in isolation, and so it is important to test the potential interactive effects that these two ecological drivers may have on plant-pollinator mutualisms. I hypothesized that the effect that differences in flowering phenology have on the diversity and number of pollinator visits a plant receives varies with changes in water availability. To test this hypothesis, we manipulated flowering phenology and soil moisture in a factorial experiment with the subalpine perennial Mertensia ciliata (Boraginaceae) and measured effects on floral traits, pollinator visitation and identity, and seed set. Plants in the water addition treatment made larger flowers and more nectar than those in the drought treatment. The probability of receiving a visit declined after week two, and coincided with a decline in floral abundance in the arrays, which suggests that pollinators were attracted to arrays based on the overall floral abundance. Among plants receiving visits, both the visitation rate and percent of non-bumblebee visitors declined after the first week and remained consistently low until the final week, when drought treatment plants alone experienced a resurgence in visits by solitary bees and flies. Seed set and seed mass were positively affected by increased water availability and differed among phenology weeks. In this system differences in flowering phenology had greater effects on pollinator visitation than changes in water availability, but the reverse was true for seed production. Our results indicate that the effects of changes in water availably and phenological shifts associated with anthropogenic climate change are more likely to have interactive effects for zoophilous plant species that have wide variety of potential pollinators than species in serviced by specialized pollinators. Taken together, these results highlight the importance of assessing how co-occurring ecological responses to changes in climate may affect plant reproductive success.
References:
Aizen, M. A., Garibaldi, L. A., Cunningham, S. A., & Klein, A. M. (2009). How much does agriculture depend on pollinators? Lessons from long-term trends in crop production. Annals of Botany, 103(9), 1579-1588.
IPCC [INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE]. (2014). Climate change 2014: Impacts, adaptation, and vulnerability. Summary for policymakers. Cambridge University Press, New York, New York, USA.
Ollerton, J., Winfree, R., & Tarrant, S. (2011). How many flowering plants are pollinated by animals?. Oikos, 120(3), 321-326.