Helen Miller Alexander - Plant Population Biology
Professor
Ph.D., Duke University, 1982
7006 Haworth
Phone: (785) 864-3221
Fax: (785) 864-5321
Introduction: As a population biologist, I am intrigued both by the factors that affect the size and spactial distribution of populations (population ecology) and by the reasons for changes in the genetic composition of populations (population genetics). Nearly all my research has examined the population biology of plants; plants are often wonderful study organisms because they are easy to census and can be readily manipulated in experiments. I find plant population biology to be both of intrinsic interest and relevant to many applied questions. For example, this discipline is central to understanding why rare species may decline in numbers while invasive, weedy species can have explosive population growth.
My research is focused in three areas:
Ecological and genetic interactions between plants and fungal pathogens:Throughout my career, a major focus of my research has explored how components of the biotic environment, in particular fungal pathogens, affect the population biology of plants. Although the effects of disease are well known in agriculture, much less is known about the interactions between plants and fungi in non-agricultural settings. In Virginia, I have examined an unusual floral fungal disease of the plant Silene alba where spores are spread by insects that contact the infected flowers. I found that host populations can be genetically variable for disease resistance, explored how floral characteristics affect disease transmission, and evaluated different mechanisms of spore dispersal. Other studies in my laboratory with this host-pathogen system have focused on the fungus, such as theoretical work on inferring diploid genotypes using haploid progeny and explorations of patterns of mating types (effectively "sexes") of the fungus. In contrast to this work on a disease of reproductively mature plants, I have also examined fungal diseases of seeds and seedlings. For instance, my collaborator and I found that the effect of disease on an annual legume population depended not only on the degree to which the pathogens decrease the probability of survival of individual plants, but also on whether other plants in the population can compensate for such losses. Many of the seed and seedling diseases are caused by fungi that live in the soil. These soil-borne diseases are relatively unknown to ecologists, and thus I found it useful to collaborate with both theoretical ecologists and a plant pathologist on models of population dynamics of these interactions. Recent work in my laboratory focused on the sedge Carex blanda, which is infected by both a smut fungus (Anthracoidea blanda) and a rust fungus (Puccinia sp.). Using field and herbarium surveys across Kansas, we have shown that host populations at the edge of their range are more likely to be disease-free. In an ongoing study, we are examining the sunflower rust pathogen on wild sunflower species.
Population biology of wild sunflowers: biology of an annual disturbance specialist and potential ecological consequences of crop-wild hybridization: My recent research has emphasized the population biology of wild annual sunflowers, Helianthus annuus. These plants are fascinating because the annual habit is unusual for prairie plants and because sunflowers have become a model system for investigating ecological concerns about "crop-wild hybridization". With regard to the latter, it is likely that introduction of genetically engineered genes for pest resistance into crops would lead to spread of these genes via pollen to related wild plant populations. A relevant question is therefore whether subsequent reduction of pest levels in the wild populations is likely to create "superweeds" -i.e. wild populations that are no longer kept "in check" by insect herbivores or pathogens. Our laboratory group and collaborators have studied the survival, reproduction, and levels of seed predation in crop-wild hybrids in relationship to wild plants, and showed that ecological information could be used to predict changes in crop allele frequencies over time in experimental field populations. We have also focused on the ecological implications of seed dormancy in H. annuus. These studies have examined the persistence of seeds in the seed bank, the contribution of the seed bank to population dynamics, and how different types of soil disturbance affects the formation of the seed bank. One of our long term goals is to evaluate the degree to which increases in seed production in local populations affects the regional abundance of plants. To explore large scale patterns of distribution and dynamics, we have taken survey data for several years on roadside sunflower populations. These survey data have also been used to explore the scale-dependency of colonization and extinction and to develop ecological niche models of sunflowers. We are currently studying wild and crop-wild sunflowers with Drs. Kristin Mercer and Allison Snow at Ohio State; this study focuses on how differences in seed dormancy and competitive interactions between crop-wild hybrid seedlings and wild seedlings may affect introgression patterns.
Population dynamics of a long-lived prairie perennial, the Mead’s milkweed: The majority of the plant species I have studied over my career have been short-lived, weedy plants. However, most plant species that are native to the Great Plains are perennials and may live for decades. I have thus gained new perspectives by working with others on a long-term study of the Mead's milkweed, a rare, long-lived prairie species. In this research, we have documented the survival and reproduction of plants in an unusually large population. Since characteristics of this plant and its habitat make it difficult to census, we developed quantitative approaches to estimate population size that are extensions of "mark-recapture" techniques used by animal ecologists. Our data set is now 20 years long, and thus provides an unusually comprehensive view of the biology of this species. Information about this species can also be found at the following site: http://www.ksr.ku.edu/Mmilkweed/index.htm
Conclusions and Collaborators: In addition to the population biology focus, there are two themes relevant to much of my research. First, I enjoy the interplay between observational studies, experimentation, and modeling and other quantitative approaches. Second, I am stimulated by collaborative investigations. My past and present collaborators include researchers at University of Kansas as well as at other institutions, such as Jeanne Mihail (University of Missouri) and James Bever (Indiana University) [soil pathogen work]; Allison Snow and Kristin Mercer (Ohio State University), Loren Rieseberg (Indiana University), Diana Pilson (University of Nebraska), and Janis Antonovics (University of Virginia) [sunflower studies], and Karen Garrett (Kansas State University) [prairie disease studies]. An important part of my research approach has also been the active involvement of graduate and undergraduate students in the design and implementation of research projects.
Alexander, H.M., N. Slade, W.D. Kettle, and G.L. Pittman, Detection, survival rates, and dymanics of a cryptic plant, Asclepias meadii; applications of mark-recapture models to longterm monitoring studies. In review (Journal of Applied Ecology).
Collins, C* and H.M. Alexander. Statistics in an Alien World: a Final Assesment Project for Biostatistics Laboratories. In review (Journal of Statistics Education)
Moody-Weis*, J., J. Antonovics, H.M. Alexander, and D. Pilson. 2008. Predicting local colonization and extinction dymanics from coarser-scale surveys. Ecography (in press).
Moody-Weis*, J. and H. M. Alexander. 2007. The mechanisms and consequences of seed bank formation in wild sunflowers (Helianthus annuus) Journal of Ecology 95: 851-864.
Alexander, H. M., S. Price**, R. Houser, D. Finch* and M. Tourtellot. 2007. Is there reduction in disease and predispersal seed predation at the border of a host plant’s range? – field and herbarium studies of Carex blanda. Journal of Ecology 95: 446-457.
Grman, E.** and H. M. Alexander. 2005. Factors limiting fruit production in Asclepias meadii in Northeastern Kansas. American Midland Naturalist 153:245-256.
Thrall, P. H., L. G. Barrett, J. J. Burdon, and H. M. Alexander. 2005. Variation in pathogen aggressiveness within a metapopulation of the Cakile maritime-Alternaria brassicicola host-pathogen association. Plant Pathology 54:265-274.
Garrett, K. A., S. P. Dendy, A. G. Power, G. K. Blaisdell, H. Alexander, and J. K. McCarron. 2004. Barley yellow dwarf luteovirus (BYOV) in natural populations of dominant tallgrass prairie species. Plant Disease 88:574.
Pilson, D., A. A. Snow, L. H. Rieseberg, and H. M. Alexander. 2003. Effects of a Bacillus thuringiensis (Bt) transgene on the fecundity and abundance of weeds: a case study of sunflower. Pages 173-189 in T. Lelley, E. Balaz, and M. Tepfer (Eds.), Ecological Impact of GMO Dissemination in Agro-Ecosystems. Proceedings of an OECD Workshop in Grossrssbach, Austria, Sept. 27-28, 2002, Facultas Verlags- und Buchhandels AG, ISBN 3-85076-631-4.
Alexander, H. M., and A. M. Schrag. 2003. Role of soil seed banks and newly dispersed seeds in population dynamics of the annual sunflower, Helianthus annuus. Journal of Ecology.
Slade, N. A., H. M. Alexander, and W. Dean Kettle. 2003. Estimation of population size and probabilities of survival and detection in a population of Mead's milkweed. Ecology 84:791-797.
Cummings*, C. L. and H. M. Alexander. 2002. Population ecology of wild sunflowers: effects of seed density and post-dispersal vertebrate seed predation on numbers of plants per patch and seed production. Oecologia 130:272-280.
Cummings*, C. L., H. M. Alexander, A. A. Snow, L. H. Rieseberg, M. J. Kim, and T. M. Culley*. 2002. Fecundity selection in a sunflower crop-wild study: can ecological data predict crop allele changes? Ecological Applications 12:1661-1671.
Alexander, H. M., C. L. Cummings*, L. Kahn* and A. A. Snow. 2001. Seed size variation and predation of seeds produced by wild and crop-wild sunflowers. American Journal of Botany 88:623-627.
Snow, A. A., L. H. Rieseberg, H. M. Alexander, C. Cummings* and D. Pilson. 2001. Assessment of gene flow and potential effects of genetically engineered sunflowers on wild relatives. Pp. 19-25 in J. Schiemann (ed.), The Biosafety Results of Field Tests of Genetically Modified Plants and Microorganisms: Fifth International Symposium, Biologischen Bundesanstalt f?r Land-und Forstwirtschaft, Berlin and Braunschweig.
Alexander, H.M. and J.D. Mihail. 2000. Seedling disease in an annual legume: consequences for seedling mortality, plant size, and population seed production, Oceologia 122: 346-353.
Holah*, J. and H. M. Alexander. 1999. Soil pathogenic fungi have the potential to afffect the coexistence of two tallgrass prairie species. Journal of Ecology 87: 598-608.
Cummings*, C. L., H. M. Alexander and A. A. Snow. 1999. Increased pre-dispersal seed predation in sunflower crop-wild hybrids. Oceologia 121: 330-338.
Slade, N. A., R. Gomulkiewicz and H. M. Alexander. 1998. Alternatives to Robinson and Redford: assessing overharvest from incomplete demographic data. Conservation Biology 12: 148-155.
Oudemans, P. V., H. M. Alexander, J. Antonovics, S. Altizer*, P. H. Thrall and L. Rose**. 1998. The distribution of mating type bias in natural populations of anther-smut Ustilago violacea (= Microbotryumviolaceum) on Silene alba (= S.Latifolia) in Virginia. Mycologia 90:372-381.
Mihail, J. D., H. M. Alexander and S. J. Taylor. 1998. Interactions between root infecting fungi and plant density in an annual legume. Journal of Ecology 86:739-748.
Alexander, H. M. and Holt, R. D. 1998. The interaction between competition and plant disease. Perspectives in Plant Ecology, Evolution , and Systematics 1/2: 206-220.
Alexander, H.M., N.A. Slade and W.D. Kettle. 1997. Application of mark-recapture models to estimation of the population size of plants. Ecology 78:1230-1237.
Thrall, P.H., J.D. Bever, J.D. Mihail and H.M. Alexander. 1997. The population dynamics of annual plants and soil-borne fungal pathogens. Journal of Ecology 85:313-328.
Alexander, H. M., P. H. Thrall, J. Antonovics, A. M. Jarosz and P. V. Oudemans. 1996. Population dynamics and genetics of plant disease: a case study of anther-smut disease of Silene alba caused by the fungus Ustilago violacea. Ecology 77:990-996.
Davelos*, A. L., H. M. Alexander and N. A. Slade. 1996. Ecological genetic interactions between a clonal host plant (Spartina pectinata) and associated rust fungi (Puccinia seymouriana and Puccinia sparganiodes). Oceologia 105: 205-213.
(*graduate student authors, **undergraduate student authors)
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