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Assessing the Effects of Biotic and Abiotic Factors on Ephedra viridis Seed Size
AuthorHickey, Andrew Christopher
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Seeds are the first stage of life for most plants and not all seeds are created equal. Several pre-dispersal and post-dispersal environmental factors affect the quality of seeds plants produce, the seeds available for dispersal, and the likelihood of seedling establishment/survivability. In this dissertation, I utilized the desert shrub Ephedra viridis to investigate three topics regarding: 1) Intraspecific seed preferences of harvester ants (Pogonomyrmex occidentalis) across varying microhabitat regimes, 2) Intraspecific plant response through seed size evolution to recent climate trends, and 3) Neighboring shrub influence on seed size across environmental gradients.The primary findings from each of my three chapters are:1) The likelihood of harvester ants harvesting seeds decreases with increasing intraspecific seed mass and increases in microhabitat cover. However, harvester ant intraspecific seed size preference did not change across environmental gradients.2) Seasonally, increases in soil water availability and nitrogen were correlated with increases in E. viridis seed mass. E. viridis residing in regions where there have been decreases in water availability over time and lower average water availability have larger relative seed mass than E. viridis in wetter regions. Lastly, E. viridis residing in regions where there have been increases in high temperature over time have larger relative seed mass than E. viridis in more temperate regions.3) E. viridis with larger relative neighbor influence (i.e. larger/closer neighboring shrubs) produce smaller seeds than E. viridis with lower relative neighbor influence regardless of the abiotic environment. However, the relevance of this relationship ecologically is most likely not significant.This dissertation further knowledge in realms involving harvester ant seed harvesting behavior, intraspecific seed response to climate change, and the influence of plant-plant interactions on seed size across environmental gradients.