Ph.D. - Botanical Sciences (Botany)
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ItemPlant Invasion Success: Investigating the Roles of Herbivory and Plant-Soil Feedbacks([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05)Understanding why some non-native plants become successful invaders while most fail to invade can help in assessing risks of invasion. Plants that have evolved defensive traits to resist and/or tolerate herbivory may be more successful invaders since herbivory can potentially prevent species from establishing or regulate existing populations. Plant-soil feedbacks may also enhance dominance of invasive species through allelopathy, changes in soil chemical properties, and interactions with soil biota that promote their own growth and suppress recruitment and growth of co-occurring species. I investigated herbivory as barrier to post-establishment invasion success by conducting three sets of experiments that compared invasive and non-invasive woody species in Hawaii. I measured: seedling acceptability to two generalist herbivores in laboratory no-choice feeding trials, foliar herbivory on seedlings in a field common garden, and seedling tolerance to simulated foliar herbivory in a greenhouse. I also investigated the role plant-soil feedbacks play in the dominance of an invasive tree in Hawaii, Ardisia elliptica, by conducting greenhouse soil feedback experiments to determine if A. elliptica positively impacts its own growth and suppresses growth of two co-occurring species. I found that: 1. There was no general difference in resistance to herbivores between invasive and non-invasive species in feeding trials or the common garden experiment. 2. There was no general difference in tolerance to simulated herbivory between invasive and non-invasive species. 3. There was no evidence of positive soil feedbacks promoting A. elliptica growth. 4. Soil taken from beneath A. elliptica did not suppress growth of two co-occurring species. Thus, herbivory and plant-soil feedbacks do not appear to be playing a strong role in post-establishment invasion success of the species I investigated, suggesting that we still lack a comprehensive understanding of what factors drive invasion success or failure.
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ItemPopulation Divergence and Evolution of the Endangered Sesbania tomentosa (Fabaceae)([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05)Sesbania tomentosa (Fabaceae) is an endemic flowering plant primarily adapted to coastal strand and dry lowland habitat in the Hawaiian Islands, now extant in relicts of its former range. Efforts have been made to delineate distinct taxa from among the remaining populations. In the most recent treatment of Hawaiian Fabaceae, however, S. tomentosa was recognized as a single variable species. In an attempt to address issues of taxonomy, the present study compared phylogenetic hypotheses of Hawaiian Sesbania determined by morphological markers with those determined by molecular analyses (DNA sequence and microsatellite marker variation) and assessed their relative level of congruence. A complete lack of variation between eight putative taxa from six islands at two nuclear DNA regions (1035 bp) contrasts with the highly differentiated population structure of the nine microsatellite loci sampled, while confidence in the relationships proposed in morphological phylogenies based on putative taxonomy was low. Instead, Bayesian genetic clustering assignments and associated private alleles occurred in a distinct phylogeographic pattern. As a result, populations from Nihoa, Kaua„i and O„ahu are distinguished as a separate subspecies of S. tomentosa, populations from Maui Nui and Hawai„i Island (respectively) form two additional subspecies, and a fourth subspecies endemic to SE Moloka„i distinguishes itself from the rest of Maui Nui. Naturally-occurring populations of Sesbania tomentosa plus a substantial number of outplanted individuals were analyzed for levels of allelic diversity, heterozygosity and inbreeding. Evidence of genetic bottlenecks in populations was also investigated, as well as an analysis of population sub-structuring. Natural ecological dynamics affecting population differentiation often leave lasting genetic signatures, and are addressed alongside contemporary impacts on plant habitat when discussing the divergence of plant population remnants. The molecular data can be interpreted to support the hypothesis that distinctive-appearing remnant populations of this highly variable species have diverged at an accelerated rate due to human induced habitat fragmentation within the larger context of the speciation process itself. This study also provides examples of increasing genetic diversity in outplantings when intentional mixing of populations to augment diversity was practiced, as well as in situations where the genepools of natural populations are dynamic over time.
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ItemEcophysiological Repsonses of Macroalgae to Submarine Groundwater Discharge in Hawai`i([Honolulu] : [University of Hawaii at Manoa], [May 2015], 2015-05)Submarine groundwater discharge (SGD) is a ubiquitous process that delivers significant amounts of nutrients and other solutes to coastal ecosystems worldwide. Although the quality and quantity of SGD has been characterized at many sites, the biological implications of this process remain poorly understood. The objective of this work was to compare the physiological response of macroalgae and benthic community structure across gradients of SGD and nutrient loading in Hawai‘i. Common marine algae were collected and/or deployed at several sites on O‘ahu, and Maui. Selection of sites was informed by adjacent land use, known locations of wastewater injection wells, and previous estimates of environmental risk due to onsite sewage disposal systems (OSDS). For deployed samples, initial values of algal tissue nitrogen (N) parameters were determined after pretreatment in low nutrient conditions. At all locations, algal tissue nitrogen (N) parameters (δ15N, N %, and C:N) were compared with the N parameters (δ15N and N concentration) of coastal groundwater , marine surface water, or groundwater simulations. Algal tissue N was highest (> 2 %) in samples located nearshore at sites adjacent to coastal aquifers enriched with anthropogenic sources of N. The lowest tissue N values (< 1 %) were found offshore or at relatively unimpacted sites. In general, the δ15N values of algal tissues and water samples were highest (9 - 18 ‰) at sites adjacent to high-volume wastewater injection wells and high densities of OSDS; lowest values (< 4 ‰) were observed in samples adjacent to sugarcane fields. Benthic diversity was greatest in locations with low anthropogenic impact. In contrast, highly impacted locations were dominated by opportunistic species. This work advances the use and interpretation of algal bioassays by highlighting the importance of onshore-offshore trends, and deviations from initial N parameter values, for the detection of N source and relative N availability. Wastewater was detectable and a major source of N at many locations. These results support recent studies that indicate SGD is a significant transport pathway for anthropogenic pollutants with important biogeochemical implications. Minimizing contaminant loads to coastal aquifers will reduce pollutant delivery to nearshore reefs in areas with SGD flux.
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ItemPopulation ecology of Metrosideros Polymorpha and some associated plants of Hawaiian volcanoes( 1993)Metrosideros polymorpha is the dominant tree of Hawaiian rain forests and lava flows. Research was undertaken to explain: the pattern of Metrosideros forest development on lava flows; the role seed ecology plays in maintaining Metrosideros populations; and the relationships between Metrosideros and associated species. Long-term rain forest development was inferred from measurements of population structure for Metrosideros, other trees, and tree ferns on a chronosequence of five lava flows (aged 47-3000 yr; Mauna Loa). Metrosideros comprised ≥ 70% of the tree basal area at each site. Although Metrosideros basal area increased with flowage, population densities peaked on the 137 yr flow, then declined, apparently through self-thinning. On the older flows, a dense tree fern canopy may have inhibited regeneration of Metrosideros. Dominance shifted from pubescent to glabrous varieties of Metrosideros as flow age increased. Seed dispersal data, collected on a lava flow downwind of Metrosideros forest, indicated that seed density decreased from 5580 m- 2yr- 1 at the forest edge, to 20 m-2yr-1 250 m away. However, seedling density did not decrease across the flow, suggesting that recruitment is not limited by seed rain. In the laboratory, Metrosideros seeds germinated over a wide range of temperatures and light qualities. Germination in the dark and emergence after burial were poor. The light requirement was not overcome by a fluctuating thermoperiod. Seeds from glabrous and pubescent plants differed in their germination characteristics. In a Kilauea forest, abundances were quantified for seed plants in the vegetation, seed rain, and seed bank. The seed rain and vegetation were more similar to each other than either was to the seed bank. Metrosideros dominated the vegetation and seed rain, but formed only a pseudo-persistent seed bank. Native species dominated the vegetation and seed rain, but alien species dominated the seed bank, suggesting that aliens may replace many of the natives if the forest is disturbed. Metrosideros seeds are produced in great numbers, are widely dispersed, and can germinate under diverse environmental conditions. These attributes contribute to the success of Metrosideros as an early colonizer of new substrates and should also promote regeneration in established forests.
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