Density-dependence in Salvia lyrata L.

PhD dissertation, Duke UniversityOne of the central puzzles in ecology is what determines the size of populations in nature. Strident debate between those claiming precedence of density-independent factors over density-dependent ones, and vice versa, has subsided with the realization that both may play a role in limiting population size of any species. Nevertheless, very few attempts have been made to directly assess the effect of density on population growth in nature. This is particularly disturbing, because theoretical ecology 1s largely based on the density-dependent population growth routinely documented in laboratory experiments. Similarly, explanations of the existence of variation in life history among and within species, in particular the weedy vs. non-weedy habit, have invoked density-dependent selection. Yet such selection has never been demonstrated in nature, and thus its efficacy in maintaining genetic variation is unknown. The experiments reported here were devised to determine the extent to which density limits growth of a population of Salvia lyrata L., an herbaceous perennial plant common in North Carolina grasslands, and whether density-dependent selection structures its genetic variation. The local density of Salvia was altered by sowing in seed at different densities, and by transplanting or removing established individuals. In most cases, these manipulations elicited weak or conflicting responses; however density-dependent mortality and stunting of seedlings was evident at unnaturally high densities of sowing. Thus density is rarely sufficient to limit an individual's contribution to this population, but density effects can limit population size at extreme seedling densities. In additional experiments, evidence of genetic variation in density response was sought by planting individuals of known genetic origin into arrangements of varying density. An experiment in protected conditions showed variation among families in the response of flowering probability to density, but not in survival nor in the number of seeds produced. A field experiment showed variation among families in the reponse of a size trait, number of leaves, to density. Given that survival and fecundity are size-dependent, as documented in observations of the natural population, this result suggests the potential for density-dependent selection in nature

Pollinator Selection, Quantitative Genetics, and Predicted Evolutionary Responses of Floral Traits in Penstemon Centranthifolius (Scrophulariaceae)

Much of the remarkable diversity of angiosperm flowers is thought to have evolved in response to selection by animal pollinators. Selection during pollination can readily be documented, but the extent to which it leads to evolutionary change depends on the genetic basis of floral traits. Here we combine estimates of genetic variance and covariance for several traits of flowers and inflorescences in a wild plant species, with estimates of natural selection by hummingbird pollinators. Analysis of phenotypic selection through two components of pollination success indicates direct selection of plants toward larger size and toward bearing shorter flowers that produce more nectar. Predictions of selection response that account for genetic correlations among traits generally exceed the simple predictions based on apparent selection and heritabilities of single traits. This underscores the importance of genetic correlations and demonstrates that univariate, strictly phenotypic, analyses of natural selection can be misleading. A sample of fruits from one of the two years of our study also indicates that total selection at the end of the reproductive cycle is weaker than selection during pollination. Thus a second caution is in order, against relying too strongly on differential pollination success as an estimate of overall selection

Commentary on Lande-Arnold Analysis

1 online resource (PDF, 24 pages

Supporting Data Analysis for a talk to be given at Evolution 2008 University of Minnesota, June 20-24

1 online resource (PDF, 24 pages

Aster Models with Random Effects and Additive Genetic Variance for Fitness

1 online resource (PDF, 11 pages

Chemical vapor deposition growth

The objective was to investigate and develop chemical vapor deposition (CVD) techniques for the growth of large areas of Si sheet on inexpensive substrate materials, with resulting sheet properties suitable for fabricating solar cells that would meet the technical goals of the Low Cost Silicon Solar Array Project. The program involved six main technical tasks: (1) modification and test of an existing vertical-chamber CVD reactor system; (2) identification and/or development of suitable inexpensive substrate materials; (3) experimental investigation of CVD process parameters using various candidate substrate materials; (4) preparation of Si sheet samples for various special studies, including solar cell fabrication; (5) evaluation of the properties of the Si sheet material produced by the CVD process; and (6) fabrication and evaluation of experimental solar cell structures, using impurity diffusion and other standard and near-standard processing techniques supplemented late in the program by the in situ CVD growth of n(+)/p/p(+) sheet structures subsequently processed into experimental cells

Aster Models for Life History Analysis

1 online resource (PDF, 65 pages

Strong ecological but weak evolutionary effects of elevated CO2 on a recombinant inbred population of Arabidopsis thaliana

Summary • Increases in atmospheric CO 2 concentration have an impact on plant communities by influencing plant growth and morphology, species interactions, and ecosystem processes. These ecological effects may be accompanied by evolutionary change if elevated CO 2 (eCO 2 ) alters patterns of natural selection or expression of genetic variation. • Here, a statistically powerful quantitative genetic experiment and manipulations of CO 2 concentrations in a field setting were used to investigate how eCO 2 impacts patterns of selection on ecologically important traits in Arabidopsis thaliana ; heritabilities, which influence the rate of response to selection; and genetic covariances between traits, which may constrain responses to selection. • CO 2 had strong phenotypic effects; plants grown in eCO 2 were taller and produced more biomass and fruits. Also, significant directional selection was observed on many traits and significant genetic variation was observed for all traits. However, no evolutionary effect of eCO 2 was detected; patterns of selection, heritabilities and genetic correlations corresponded closely in ambient and elevated CO 2 environments. • The data suggest that patterns of natural selection and the quantitative genetic parameters of this A. thaliana population are robust to increases in CO 2 concentration and that responses to eCO 2 will be primarily ecological

Aster Models with Random Effects via Penalized Likelihood

1 online resource (PDF, 61 pages