Margaret E.K. Evans

Oenothera

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population and range modeling | comparative analysis of niche evolution | evolutionary ecology | conservation ecology

Population and Range Modeling
Kent Holsinger, Eric Menges, and I developed a novel approach to population viability analysis (PVA): we built a hierarchical Bayesian (hB) model that draws upon data from all parts of the life cycle simultaneously to estimate vital rates and their covariation as a function of time-since-fire and random year effects. A unique feature of this model is a year effect that connects five submodels (generalized linear mixed models) into a single large model (with ~1,340 parameters). This work has appeared in Population Ecology, Ecological Monographs, and Theoretical Population Biology. Future work includes the development of multi-species PVA, using data on three endangered species of Dicerandra. With Brian Enquist and Sean McMahon, I am developing hB, process-based models of range dynamics of North American trees facing climate change.

 

Comparative Analysis of Niche Evolution
With Michael Donoghue and Stephen Smith, I combined niche models and phylogenies to examine climatic niche evolution and its role in the diversification of the “bird-cage” evening primroses (Evans et al. 2009; 2010 Presidential Award, American Society of Naturalists). By mapping phylogeny in climate space, we were able to visualize the remarkable radiation of climatic niche in this group (below). David Ackerly created the R function traitgram {picante} based on this work. Christoph Heibl's R function plotAncClim {phyloclim} recreates the below figure. With Sebastien Lavergne, Wilfried Thuiller, and Frederic Jiguet, I analyzed the relationship between past niche evolution in European birds and their current population trends. I am currently working on niche evolution in the Malagasy endemic family Sarcolaenaceae and in Malagasy Euphorbia’s (with Thomas Haevermans and Xavier Aubriot), and in Schefflera (with Pete Lowry and Greg Plunkett).

 

Evolutionary Ecology
Bet Hedging

Bet-hedging traits are interesting because they seem maladaptive – mean fitness (i.e., fitness if the organism were to constantly experience the average environment) is sacrificed in favor of reduced variance in fitness, because this leads to higher long-term fitness. I’ve documented that seed banking has these effects, using demographic data collected from natural populations of two desert plants. I’ve also discussed the consequences of seed banking for genetic diversity, the dynamics of allele frequencies, traits, population persistence, and species coexistence. I remain interested in ho
w temporal and spatial heterogeneity shape species and how species’ responses to heterogeneity in turn influence their persistence and coexistence in communities.

Life History Evolution
New PhytologistWhy reproduce once vs. more than once per lifetime? – it’s a fundamental question of life history theory. Using a comparative analysis of life history, I found support for the notion that the annual life history (monocarpy, also known as semelparity) evolves where adult survival is low and juvenile survival high.

Breeding System Evolution
Stebbins (1950) predicted that the evolution of selfing should be associated with climatic extremes, but this pattern had not been documented. With Kent Holsinger, Kathyrn Theiss, and Michael Donoghue, I found self-compatibility to be associated with the coldest and mildest winter temperatures, as well as the strongest and weakest drought, experienced by species in a clade of evening primroses. With Warren Wagner, we will explore the pattern in further detail.

Extreme environments select for reproductive assuranceextreme environments select for reproductive assurance

Conservation Ecology
I’ve contributed to basic knowledge, either in terms of demography, reproductive biology, or genetic diversity, of the following rare plants: Asimina obovata (Annonaceae), Cimicifuga elata (Ranunculaceae), Dicerandra frutescens and D. christmanii (Lamiaceae), Eryngium cuneifolium (Apiaceae), Hypericum cumulicola (Hypericaceae), Liatris ohlingerae (Asteraceae), Nolina brittoniana (Asparagaceae), and Warea carteri (Brassicaceae). Most of these are plants endemic to Florida scrub that I worked with at Archbold Biological Station.

Top row, L to R: Asimina obovata (Michelle Rensel), Cimicifuga elata , Dicerandra frutescens (Reed Bowman), Eryngium cuneifolium (Steve Shirah), Hypericum cumulicola (Matt Trager)
Bottom row, L to R: Liatris ohlingerae (Sarah Haller), Nolina brittoniana, and Warea carteri (Shirley Denton)


mekevans@email.arizona.edu

Laboratory of Tree Ring Research
University of Arizona
Bryant Bannister Building
1215 East Lowell St.
Tucson, Arizona 85721
520·621·0778 (ph) · 520·621·8229 (fax)

Department of Ecology and Evolutionary Biology
University of Arizona
BioSciences West Room 310
1041 East Lowell St.
Tucson, Arizona 85721
520·626·4741 (ph) 520·621·9190 (fax)

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