Master of Science, Miami University, 2014, Botany

The objectives of my study were (1) to determine the spatial distribution of four invasive species; Rubus phoenicolasius, Berberis thunbergii, Rosa multiflora, and Lonicera japonica in a mature forest; (2) to investigate the role of propagule rain from a road, logged forest, and floodplain on these distributions, and (3) to explore the role of treefall gaps as a facilitator of invasion. The importance of propagule rain was indicated by higher densities of R. multiflora near the floodplain and R. phoenicolasius and climbing L. japonica near the road. Based on higher frequency and density, gaps are important for the establishment, growth, and reproduction of R. phoenicolasius, growth of R. multiflora and L. japonica, and reproduction of B. thunbergii.

Committee: David Gorchov PhD (Advisor); Thomas Crist PhD (Committee Member); M. Henry H. Stevens PhD (Committee Member); Jing Zhang PhD (Committee Member); Ziying Jiang PhD (Committee Member) Subjects: Botany; Ecology; Geographic Information Science

Master of Science in Biological Sciences, Youngstown State University, 2010, Department of Biological Sciences and Chemistry

A biological community can become invaded by non-resident species when the resources necessary for establishment and growth coincide with invader propagules. There are many ecological factors that affect below- and aboveground resource availability in a community and this research integrates both spatially and temporally varying components. In a managed grassland, we measured the interactive effects of disturbance patch size (DPS), grazing intensity (GI), and soil resource availability (SRA) on the invasion success of smooth pigweed Amaranthus hybridus (L.) and velvetleaf Abutilon theophrasti (L.). Importantly, we considered two life history stages of each focal invader (i.e., emerged and established seedlings) because invasion success may depend on when resource shifts coincide with particular life history stages. Our empirical data generally support the following predictions: 1) thresholds in ISP exist across DPS, the magnitude of which increases with higher SRA levels, 2) the life history stage of the invader strongly affects ISP in smaller sized patches containing high SRA, 3) regardless of invader size, grazing effects are large in small DPSs in high SRA area 4), in the absence of grazing, SRA within a given DPS can have opposing effects on ISP. Integrating disturbance type and intensity across other ecological dimensions is important in elucidating the mechanisms of community invasibility as well as offering sound recommendations to managers of native grassland communities.

Committee: Ian Renne PhD (Advisor); Thomas Diggins PhD (Committee Member); Felicia Armstrong PhD (Committee Member) Subjects: Agriculture; Biology; Ecology; Plant Propagation

Doctor of Philosophy, Miami University, 2008, Botany

What causes change of community diversity, stability, or invasibility is of long-standing interest to ecologists. Despite the attention focused on these essential themes, the roles of resource availability in connecting these broad ecological topics, or helping find potential mechanisms underlying observed patterns are still unclear. My studies focus on a resource-based view of these ecological themes using laboratory microcosms as model systems, with specific questions surrounding each theme addressed. In the diversity-resource theme, I focused on the relation between species richness (most empirical and theoretical studies use richness as a measure of diversity) and productivity (manipulated by changing the nutrient concentration of a standard growth medium). Specifically, I tested whether the productivity-richness relation varied with different observational scale and ecosystem size, and whether the relation between productivity and compositional dissimilarity was modified when historical effects were minimized. Results showed that the productivity-richness relation varied with observational scale, but was unrelated to ecosystem size. Also, there was a different form of scale dependence than previous field research reported. In the stability-resource theme, I tested the effects of two types of resources, nutrients and space, and of one aggregate community property, richness, on stability. Since richness is known to affect stability and be affected by both nutrient and space, I did not manipulate richness, but instead allowed it to be determined by the combining effects of nutrients and space. Results showed that the effects of nutrients and space on stability were generally mediated by their effects on richness, and the focal level of biological organization at which stability was measured would determine their relative power in predicting stability. In the invasibility-resource theme, I provided an empirical test of the fluctuating resource hypothesis by creat (open full item for complete abstract)

Committee: M. Henry H. Stevens (Advisor); Michael Vanni (Committee Member); Nancy Smith-Huerta (Committee Member); Richard Moore (Committee Member); Thomas Crist (Committee Chair) Subjects: Ecology

Master of Science in Biological Sciences, Youngstown State University, 2012, Department of Biological Sciences and Chemistry

Numerous investigations have elucidated patterns and processes which govern community invasibility but relatively few have examined invasibility in a successional context. Explored here is the potential for biotic resistance to reduce invasibility of riparian successional forests at the landscape scale (~100ha) and address the following: 1) Does exotic species richness and percent cover change across successional time? 2) What is the relationship between native and non-native diversity and does that relationship change through succession? Vegetation surveys were conducted to quantify plant species richness on four raised terraces (understory reinitiation to multi-age old growth), six lower terraces (stem exclusion to understory reinitiation), and seven active channel margins, mid-channel islands, or abandoned channels (stand initiation). Exotic species richness and cover declined throughout succession and no exotic species were found on landforms greater than 136 years of age. However, although native richness remained constant throughout succession, native assemblages changed markedly. Thus landform diversity patterns in Zoar Valley likely reflect contemporary and/or past states of high community invasibility, which suggests that invasibility either does not change throughout succession, or that the regional species pool of native species adapted to particular successional stages is similar in size. This finding suggests that minimally invaded, closed canopy forests is due to a lack of exotic species in the regional species pools that are well adapted for establishing in forest understories and opposes the view that these communities are intrinsically less invasible. Future studies of community invasibility, in forests and other systems, may be better served by examining the traits and life-history strategies to which a community is susceptible to being invaded by.

Committee: Thomas Diggins Ph.D. (Advisor); Ian Renne Ph.D. (Committee Member); Carl Chuey (Committee Member) Subjects: Biology; Ecology; Forestry; Plant Biology