Research on eye movement control during first language (L1) reading has long since established that (i) words are read most efficiently when the first saccade into the word lands near its center, (ii) words are refixated more often when landing positions deviate from the center of the word, and (iii) relatively proficient readers' saccades land closer to this center position. Eye-tracking studies of second language (L2) reading tend to compare participant groups based on their language background (L1 vs L2) rather than L2 proficiency. As of yet, there has been no comparison of these approaches. This study reports a comparative analysis of the Multilingual Eye-movement COrpus (MECO), which contains data on English text reading and its component skills from 543 participants representing 12 different L1s. Analyses of the distributions of initial landing positions and refixation probabilities establish that the gradient measure of proficiency in English (as L1 or L2) has a greater explanatory power than categorical contrasts between language backgrounds. We also found that English proficiency has a gradient effect on efficiency of saccadic targeting: more proficient readers landed their initial saccades closer to the word's center. However, more proficient readers of English were also less accurate in their saccadic targeting, showing greater dispersion of initial landing positions. We link this puzzling finding to the observation that landing in a suboptimal position comes with a much higher processing cost (refixation probability) for less proficient readers. This study discusses theoretical and methodological implications of the novel findings for reading research. / Thesis / Master of Science (MSc) / When we read text, we do not continuously move our eyes across it, but we make a series of rapid eye fixations on different parts of the text. Scientists know that if we fixate our eyes on a center of a word rather than on its beginning or end, we will understand that word the fastest. Highly skilled readers make the first fixation on any word in a more optimal place compared to less skilled readers. Making such optimal fixations allows highly skilled readers to understand each word they encounter faster, which makes them better readers and leads to more successful outcomes later in life. In this research project we were interested in how reader's proficiency in reading related skills affects the efficiency of their eye-movements during reading English as a first and second language. The results found that more proficient readers were found to have a lighter penalty to the speed of their reading when fixating their eyes farther away from the optimal position in words. Additionally, the results demonstrated that proficiency in reading related skills is a better indicator of the efficient eye-movement behavior than native language of the reader.

Causes and consequences of woody encroachment into grass dominated systems have been widely studied, however functional mechanisms which promote encroachment are largely unknown. Many expansive woody species are shrubs with rhizobial or actinorhizal N-fixing symbiotic associations. Morella cerifera L. (Myricaceae) is an actinorhizal N-fixing shrub which rapidly expands into grasslands on the barrier islands off the coast of Virginia, USA. The objective of this research was to determine physiological drivers of woody encroachment resulting in increased woody cover of M. cerifera on Southeastern, US barrier islands. Variations in physiology and resource use efficiencies (RUE) of M. cerifera and co-occurring shrubs were determined, and edaphic characteristics beneath shrub thicket canopies and in open areas were quantified as indications of resource availability. Analysis of dune vegetation and soils showed severe freshwater limitation and reduced plant height of dune forbs suggesting dunes represent an upper elevational boundary for M. cerifera distribution. Soil N availability was higher beneath shrubs compared to open areas, and both physiology and isotope effects showed facilitation of the non-fixing shrub, Baccharis halimifolia, by M. cerifera which may lead to increased rates of woody encroachment as B. halimifolia colonizes expanding thicket edges. Morella cerifera and other N-fixers had higher %refixation within stems which resulted in higher carbon use efficiency (CUE) and water use efficiency of N-fixing shrubs compared to non-fixers. Results of an N-fertilization experiment suggest B. halimifolia has higher dependence on and demand for soil nutrients compared to M. cerifera. Morella cerifera showed no signs of resource deficiency or reduced physiological capacity even at 0 ppm total Nsoil. Morella cerifera transitioned from utilizing solely fixation derived N to soil N as N concentrations increased providing another mechanism leading to increased CUE and, indirectly, overall RUE. In summary greater RUE, lower resource demand, and greater resource availability for M. cerifera compared to co-occurring shrubs may result from symbiotic root associations with bacteria and fungi. While expansion of M. cerifera thickets is limited to lower elevational interdunal depressions, expansion may continue and result in increased rates of woody encroachment through facilitation of co-occurring shrubs.

I quantified seasonal variations in corticular photosynthesis in 1st through 5th order branches of Myrica cerifera L. (Myricaceae) in order to determine whether corticular photosynthesis contributes to whole plant carbon gain by reducing respirational CO2 loss. Maximum % refixation was 110 ± 39 % of CO2 efflux in the dark (Rd) in 1st order branches during winter, minimum was 18 ± 3 % in 5th order branches during summer. Variations in % refixation paralleled changes in photosynthetically active radiation (PAR). As light attenuated with increasing branch order % refixation decreased. Increased PAR in the winter due to a more sparse canopy lead to increases in % refixation. Total chlorophyll content and chlorophyll a:b ratios were consistent with shade acclimation as branch order increased. Corticular photosynthesis may be a mechanism to enhance shrub expansion due to increased whole plant carbon use efficiency (CUE) and water use efficiency (WUE) attributed to refixation.

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