Rare, alpine, endemic species are particularly at risk for extinction. Alpine environments are especially vulnerable to climate change and human impacts, such as ski resort development and snowmaking. Draba asterophora Payson is a rare, alpine species that occurs only in three disjunct mountain-top regions surrounding Lake Tahoe. It is currently threatened by human impacts, such as ski resorts, as well as indirect influences of climate change and therefore in need of better understanding for conservation purposes. Draba asterophora may be able to serve as a case study for other similarly vulnerable, rare, alpine, endemic species with conservation needs. We utilized demographic, ecological, phylogenetic, and cytogenetic data to better understand D. asterophora's life history, habitat requirements, and delineate species boundaries. Draba asterophora occurs in three population clusters surrounding Lake Tahoe, segregated into two varieties, variety asterophora in the north (N) and south (S) and variety macrocarpa C. L. Hitchcock in the southwest (Sw). Populations exist on ski resort property in the north and south (variety asterophora) regions and thus face more threats. Therefore, these regions were the focus of long-term monitoring over a four year period. We assessed various morphological traits, survivorship and density estimates in these two population clusters (north and south). We created projection matrices for each population cluster and calculated finite rates of increase (λ), as well as reproductive and survivorship rates. The population projection matrices estimated growth rates close to 1.00 for both clusters (S: λ=0.977; N: λ=1.014), although neither cluster had reached a stable population structure. Plants in the north tended to be more robust, having more rosettes, inflorescences, flowers and fruits than the plants in the south. However, the plants in the northern population cluster did not have significantly higher brood sizes and the southern plants actually had larger seed to ovule ratios than those in the north ((S: x = 0.387l; N: x = 0.346). These results may be in part influenced by habitat differences (e.g. greater water availability in the north), specific site microclimate/microhabitat differences, genetic drift, and/or possibility polyploidy vigor (the northern cluster is tetraploid). However, as an autopolyploid, the NE cluster may have some difficulties with pairing in meiosis which could also contribute to its reduced seed to ovule ratios. Although the populations were found to be fairly stable currently, D. asterophora var. asterophora is potentially quite vulnerable to disturbance. All of the monitored populations in both clusters existed in small populations with low local densities confined to narrow geographic boundaries, and exhibit low fecundity. Because the taxon relies on survivorship of adults for population stability rather than new recruits, it is crucial to maintain stable adult populations in conservation efforts. Draba asterophora is similar to other alpine species tend, exhibiting high adult survivorship with low fecundity. We also examined the habitat requirements of D. asterophora by characterizing the abiotic habitat (soil chemical and texture analysis and site features such as aspect, slope, elevation) and the vegetative communities in D. asterophora sites. Draba asterophora sites all have fairly similar abiotic and biotic habitats despite large geographical separation, although some specific sites have unique characteristics as well. Draba asterophora habitats consist of steep, granitic slopes in the subalpine conifer zone with little understory. Draba asterophora's community may be facilitated by the diversity-stability hypothesis, as D. asterophora abundance (cover and/or frequency) was positively correlated with species richness and diversity, but negatively correlated with total vegetative cover (relative cover). In addition, D. asterophora has greater seed production (both seed/ovule ratio and brood size) in areas with greater species diversity. Draba asterophora does not appear to have many specific soil composition requirements or specific interspecific interactions, but generally occurs in diverse communities, albeit somewhat sparsely populated, in relatively open north-facing alpine habitats on steep granitic slopes. Changes in vegetation, topology and/or snow cover, due to disturbances such as grading, erosion, or snowmaking, may be detrimental to D. asterophora by rendering its habitat unsuitable. Therefore, D. asterophora habitat should be protected from further human impacts. Draba; the largest and most diverse genus in Brassicaceae, the mustard family, has complex phylogenetics due to its high degree of reticulate evolution, polyplodization, rarity and endemism. The D. asterophora complex has not been included in previous phylogenetic analyses. Only he northern population has been examined cytologically (2n=40). Thus, its taxonomy is poorly understood. We utilized one nuclear molecular marker, ITS, as well as two new chloroplast markers, trnS-G and trnH-psbA, to help resolve complex phylogenetic relationships and delimitation species boundaries within the D. asterophora complex. In addition, we examined the cytogenetics of all three population clusters to determine any differences in ploidy levels exist. The D. asterophora complex appears to be composed of three separately evolving trajectories differentiated by separate geographic regions surrounding Lake Tahoe, CA/NV. This is supported by both phylogenetic analyses as well as cytology. The combined DNA concatenated analysis demonstrated that all three regions form separate branches within the D. asterophora clade. Cytologically, chromosome counts were distinct in all three regions, with the southern cluster being a diploid (2n=20), the northern cluster an autotetraploid (2n=40), and the cluster in the southwest ( variety macrocarpa) an autooctoploid (2n=80). Based on these findings, we recommend that the three population clusters be treated as distinct taxonomic entities for conservation purposes. This demonstrates the importance of considering phylogenetics and ploidy levels, even of autopolyploids, in determining taxonomy, especially for rare, endemic species with disjunct habitats. Overall, this research suggests that the three geographic regions of the D. asterophora complex are distinct demographically and on own their evolutionary trajectories. Conservation efforts need to be targeted towards separate management of each population cluster. Maintaining stable adult populations, diverse plant communities, and preventing further destruction of habitat are the key conservation suggestions for D. asterophora.



College and Department

Life Sciences; Plant and Wildlife Sciences



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Draba asterophora, demography, ecology, habitat, phylogenetics, cytogenetics conservation