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Multi-empirical investigations on the population genetic structure, ecological niche, and regeneration of Ivesia webberi with conservation implications
AuthorBorokini, Israel Temitope
Ecology, Evolution and Conservation Biology
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Ecosystems often contain a few cosmopolitan species and a large number of rare species. Despite their relative low abundance and biomass, rare species support the multifunctionality and resilience of ecosystems. Therefore, empirical studies on rare and range-restricted species can increase our understanding of eco-evolutionary underpinnings of species and ecosystem persistence, and generate sufficient knowledge to design effective conservation programs. These research studies can also benefit conservation programs for rare and range-restricted species, which are often prioritized. This research focuses on Ivesia webberi, a federally threatened perennial forb and the vegetative communities that harbor the species. Specifically, empirical studies investigated the following: (1) species-environment relationship of I. webberi using iterative and multi-year ecological niche modeling with complementary model-guided sampling, to describe and predict suitable habitats; (2) the relationship between soil seed bank and aboveground vegetation in plant communities where I. webberi is found, to understand the regeneration niche of I. webberi and assess ecological resilience of the vegetative communities; (3) genetic diversity, structure, and functional connectivity among I. webberi populations in order to characterize genetic resources and therefore evolutionary potential; (4) the relationships between genome size variation and bioclimatic variables within I. webberi and among Ivesia taxa; and (5) seed viability of I. webberi, including spatiotemporal variability and storage behavior.Findings from the 5-year iterative niche modeling study resulted in the discovery of seven novel populations, an expansion of the known species distribution range, and identification of important environmental drivers of the ecological niche of I. webberi. Native species richness was higher in aboveground vegetation in the sampled sites where I. webberi occurs while the soil seed bank is dominated by invasive annual grasses. This resulted in low floristic similarity between the aboveground vegetation and the soil seed bank, and highlights the importance of seeding with native plants and control of invasive plant species to maintain the ecological legacies of these sites in the Great Basin Desert. Genetic diversity is relatively low across I. webberi populations and exhibited significant spatial genetic structure; functional connectivity was influenced by synergistic effects of geographic distance and landscape features. However, I. webberi exhibits a significant temporal, not geographical, variation in seed viability, and seed viability potentially reduces with storage time suggesting a recalcitrant behavior. Seed viability can be reliably estimated and monitored using non-destructive x-ray imagery and multispectral imaging techniques. An 8-fold variation in genome size of 31 Ivesia taxa was observed, ranging from 0.73 pg/2C in I. baileyi var. beneolens to 5.91 pg/2C in I. lycopodioides ssp. megalopetala. This genome size variation significantly correlated with actual evapotranspiration and seed size. Inference from genome size suggest that all sampled Ivesia are diploid with 28 chromosomes. Similar significant correlations between intraspecific genome size variation in I. webberi and evapotranspiration and seed size were observed; genome size was larger in I. webberi populations closer to the species’ range center and smaller towards the margin. Relatively small genome sizes and their correlations with functional trait and energy availability indicate that genome size has adaptive significance for these desert-adapted species. Overall, the findings of these studies have advanced scientific knowledge on the eco-evolutionary processes in a range-restricted plant species in the Great Basin Desert, and provide useful information to design effective conservation programs.