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Many recent studies have demonstrated that propagule pressure is a useful predictor of patterns of invasions by non-native species. However, most of these studies have used only current, not historical, data to estimate propagule pressure. Recognizing the potential importance of propagule pressure over time, I used surrogate variables that represent both past and present propagule pressure, for example, the length of time a surrounding area had been developed. I quantified the relationships between these surrogate variables and the distribution and abundance of non-native woody plant species in central Texas. I constructed statistical models predicting native and non-native species richness and the occurrence of five common species using a set of six ecological and five development-related predictor variables. I compared all models using the corrected Akaike information criterion (AICc). Overall, age of residential development surrounding native woodlands was the best predictor, other than community type, of non-native species richness. As expected, areas near older developments had more non-native species than areas near newer developments. Surprisingly, age of development and average city age, two different measures of the length of time that landscaping (a major source of propagules of non-native woody species in this region) had been present nearby, were much better predictors than distance to source populations. Age of development and average city age (weighted by distance from the site) were also both correlated with distance to source populations; this may be true in other systems as well. This suggests that the reason distance to source population has been a successful predictor of invasion may be because it is a surrogate for an underlying causal variable, length of time of exposure to source populations. Future studies of non-native invasions would benefit from taking into account both past and present propagule pressure: age of residential development and city age could be useful surrogates in other systems. / text

Prior clinical studies have documented that high blood pressure is one of the prominent risk factors leading to cerebrovascular disease and subsequent cognitive impairment. The present study aims to examine the relationship between blood pressure and brain and cognitive function in a community sample. This study recruited 41 elderly persons aged 60–70. Multiple imaging modalities were adopted to assess white matter microstructure, regional brain volume, and resting-state neural activity while a set of neuropsychological tests was used to assess cognitive function. With blood pressure measured at clinical interview, correlation and regression analyses were performed. Results showed reduced white matter integrity with increased systolic blood pressure in the splenium of the corpus callosum and inferior longitudinal fasciculus in the absence of change in brain volume or neural activity. Also, increased systolic blood pressure was found to be correlated with poorer cognitive performance in information processing speed. The results held significant after controlling age, sex, and education. These observations of the subclinical sample suggest that high blood pressure relates to subtle changes in the brain and cognitive deficits. Blood pressure control, as a relatively modifiable factor, should be taken seriously in community-dwelling elderly. / published_or_final_version / Clinical Psychology / Doctoral / Doctor of Psychology

The purpose of this study was to assess the amount of sodium in the diet of normal adults. The population consisted of 86 adults, 49 females and 37 males, who were participants in the Family Heart Study (FHS). Of this population 26 were studied during the baseline assessment period and were just entering the program. The remaining 60 people were studied after participating in the FHS for one year. Three methods were used to assess sodium intake: a salt questionnaire, a salt preference test and the sodium content of a 24-hour urine collection. The salt questionnaire consisted of questions to assess the frequency of intake of high sodium foods and the use of salt at the table and in cooking. The salt preference test was done using a baked potato salted to taste by the participants. The salt questionnaire and salt preference test were compared to the amount of sodium in a 24-hour urine collection. There was no relationship among any of these measures of salt intake. The urinary analysis for sodium indicated that the participants in this study had a moderately high sodium intake (143 mEq/day), similar to other studies in the U.S. Males excreted more sodium than females. The group assessed at baseline and the group assessed after one year in the study both excreted the same amount of sodium. The year one group had switched to Lite salt and reduced their use of salt during cooking; however, they used salty foods with the same frequency as the baseline group. The urinalysis demonstrates that the changes made by the year one group were not significant in reducing their salt intake. The amount of sodium excreted showed no relationship to blood pressure. This finding is similar to other studies in the U.S. because most people consume over 70 mEq sodium/day, which is above the proposed threshold to prevent hypertension. The genetic variability in the U.S. population obscures any relationship of sodium intake to blood pressure. Some of the major problems in assessing sodium intake are the variability from day to day and the ubiquity of sodium in our foods. It was concluded that urinary assessment of sodium was the best method available at this time, although multiple collections are necessary to compensate for the variability of sodium intake. / Graduation date: 1981

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