The interaction between dioecious plants and their associating pollinators is poorly known, especially in Arctic ecosystems where plants and insects are extremely sensitive to potential spatial and temporal mismatches. Dioecism in flowering plants is a sexual system where a plant bears either female or male flowers, which allows for the selection of the most favourable genetic combination. For many dioecious plants, the males and females in a population are observed to segregate from each other along an environmental gradient. One of the proposed selective mechanisms causing this spatial segregation of sexes consists of the differences in reproductive investments between males and females [1]. Females require and spend more resources and energy on the productions of ovaries, fruits, and seeds than males that invest primarily on pollen grains. This major difference in reproduction biology indicates that females are more likely to occupy resource-rich habitats than males, resulting in spatial segregation of sexes. The proposed project will select a dioecious plant species and study the biotic and abiotic variations within and between several populations. The variations include female to male ratios, phonological and morphological differences between females and males during the growing season, the resulting fruit set and seed set at the end of the growing season, and the surrounding abiotic environmental factors. The information will be tested for their associations with pollinator richness to determine the effects of pollinator abundance and diversity on the reproductive successes of dioecious females.
In addition to understanding the pollination ecology of dioecious plants, the proposed project will also aim to address the status of pollinators in natural ecosystems across northern Canada. Pollination is an extremely valuable ecosystem service carried out by managed and wild pollinators for many agricultural crops and wild plants. Without pollinators and the plants that depend on them, ecosystems will be reduced or lost, and food security for humans will become seriously jeopardized. Most insect pollinators worldwide are in a state of decline and, because of their importance, there is a growing concern in the ecological community to not only determine the potential drivers causing the declines, but to also develop mitigating solutions [2]. One of the main potential drivers of global pollinator declines is climate change [2]. However, studies pertaining to the effects that climate change has on pollinators in the Arctic, one of the world’s most important ecotones, remains scant. Therefore, the proposed project will also establish baseline knowledge on pollinator abundance and diversity in northern Canada by trapping and identifying pollinators that visit the dioecious plant species of interest.
To fully account for wild pollinator abundance and diversity Arctic ecosystems, the proposed project will be carried out in Ivvavik National Park of northern Yukon: a unique region in the Arctic ecosystem that was unglaciated during the Ice Ages and now has distinct landscapes and biodiversity. The plant species in study will be Shepherdia canadensis, one of the dioecious plant species in the Arctic whose berries are consumed by local First Nations people as well as by wildlife such as grizzly bears. Very little is known about the pollination biology of S. canadensis and the associating pollinators, however, especially given Arctic’s short growing season. Overall, I hypothesize that along an elevation gradient where harsher environmental conditions are found in higher elevations than lower elevations, female S. canadensis will be more dominant in lower elevations and vice versa for the males. Furthermore, I hypothesize that pollinator abundance and diversity will also differ along the elevational gradient and result in different reproductive success rates, such as fruit set and seed set, of the females.
My objectives are to: 1. Establish a baseline inventory of pollinator abundance and diversity in Ivvavik National Park; 2. Determine the sex ratio and sexual dimorphism of dioecious S. canadensis populations in Ivvavik National Park along an environmental gradient (e.g. elevation gradient); and 3. Examine the effects of pollinator abundance and diversity on the reproductive success rates (e.g. fruit set and seed set) of S. canadensis plants in different populations along the environmental gradient. This project is important and relevant in terms of its fundamental goals of understanding the effects of sexual selection by pollinators on the ecology and evolution of dioecious plants and the impacts of climate change on wild pollinators and plants in Arctic ecosystems.
[1] Bierzychudek, P, Eckhart, V. 1988. Am. Naturalist. 132: 34; [2] Potts, S. et al. 2011. TREE. 25: 345.
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