The expected sample variance of uncorrelated random variables with a common mean and applications in unbalanced random effects models

There is a little-known but very simple generalization of the standard result that for uncorrelated variables with a common mean and variance, the expected sample variance is the marginal variance. The generalization justifies the use of the usual standard error of the sample mean in possibly heteroscedastic situations and motivates some simple estimators for unbalanced linear random effects models. The latter is illustrated for the simple one-way context. --

Calibration, error analysis, and ongoing measurement process monitoring for mass spectrometry

We consider problems of quantifying and monitoring accuracy and precision of measurement in mass spectrometry, particularly in contexts where there is unavoidable day-to-day/period-to-period changes in instrument sensitivity. First we consider the issue of estimating instrument sensitivity based on data from a typical calibration study. Simple method-of-moments methods, likelihood-based methods, and Bayes methods based on the one-way random effects model are illustrated. Then we consider subsequently assessing the precision of an estimate of a mole fraction of a gas of interest in an unknown. Finally, we turn to the problem of ongoing measurement process monitoring and illustrate appropriate set-up of Shewhart control charts in this application. --

Assessing Microsite and Regeneration Niche Preferences When Introducing Endangered Species

As pressures from development and climate change grow, land managers are turning to introductions/assisted migrations to prevent rare species extinctions. When introducing a species, it is important that propagules survive long enough to reproduce and recruits establish and reproduce themselves. If the target specie's specific microsite and regeneration requirements are unknown, one can use experimental introductions to learn demographic information while attempting to create a new population. Planting into three distinct microsites within its native habitat, I used the introduction of the endangered plant, Tephrosia angustissima var. corallicola, as an opportunity to answer microsite-specific questions while attempting to establish a new population. Results showed the highest transplant and recruit growth, flowering, and survival occurred in shady, dry microsites; recruits germinated in shadier locations than where adults were planted. Lessons learned from introduction successes and failures are essential to building the scientific base needed for rare species conservation and policy decisions

Availability growth modeling

In reliability modeling, the term availability is used to represent the fraction of time that a process is operating successfully. Several different definitions have been proposed for different types of availability. One commonly used measure of availability is cumulative availability, which is defined as the ratio of the amount of time that a system is up and running to the total elapsed time. During the startup phase of a process, cumulative availability may be treated as a growth process. A procedure for modeling cumulative availability as a function of time is proposed. Estimates of other measures of availability are derived from the estimated cumulative availability function. The use of empirical Bayes techniques to improve the resulting estimates is also discussed

Stepe i suhi travnjaci panonskog područja

Klimazonalna stepska vegetacija južne Rusije doseže panonsko područje na edafski specifičnim staništima usred srednjoevropskih listopadnih šuma. Na tim posebnim staništima na nagnutim kao i na ravnim položajima može se uočiti određeni slijed vegetacije od kserotermnih stepa preko stepskih travnjaka na plitkoj i šumostepa na srednje dubokoj podlozi do mezofilnih stepskih šuma na dubljim profilima

Evaluating plant community response to sea level rise and anthropogenic drying: Can life stage and competitive ability be used as indicators in guiding conservation actions?

Increasing sea levels and anthropogenic disturbances have caused the world’s coastal vegetation to decline 25-50% in the past 50 years. Future sea level rise (SLR) rates are expected to increase, further threatening coastal habitats. In combination with SLR, the Everglades ecosystem has undergone large-scale drainage and restoration changing Florida’s coastal vegetation. Everglades National Park (ENP) has 21 coastal plant species threatened by SLR. My dissertation focuses on three aspects of coastal plant community change related to SLR and dehydration. 1) I assessed the extent and direction coastal communities—three harboring rare plant species—shifted from 1978 to 2011. I created a classified vegetation map and compared it to a 1978 map. I hypothesized coastal communities transitioned from less salt- and inundation-tolerant to more salt- and inundation-tolerant communities. I found communities shifted as hypothesized, suggesting the site became saltier and wetter. Additionally, all three communities harboring rare plants shrunk in size. 2) I evaluated invading halophyte (salt-tolerant) plant influence on soil salinity via a replacement series greenhouse experiment. I used two halophytes and two glycophytes (non-salt-tolerant) to look at soil salinity over time under 26 and 38‰ groundwater. I hypothesized that halophytes increase soil salinity as compared to glycophytes through continued transpiration during dry, highly saline periods. My results supported halophytic influence on soil salinity; however, not from higher transpiration rates. Osmotic or ionic stress likely decreased glycophytic biomass resulting in less overall plant transpiration. 3) I assessed the best plant life-stage to use for on-the-ground plot-based community change monitoring. I tested the effects of increasing salinity (0, 5, 15, 30, and 45‰) on seed germination and seedling establishment of five coastal species, and compared my results to salinity effects on one-year olds and adults of the same species. I hypothesized that seedling establishment was the most vulnerable life-stage to salt stress. The results supported my hypothesis; seedling establishment is the life-stage best monitored for community change. Additionally, I determined the federally endangered plant Chromolaena frustrata’s salinity tolerance. The species was sensitive to salinity \u3e5‰ at all developmental stages suggesting C. frustrata is highly threatened by SLR