Broadly distributed species often span a large range of environmental conditions, which pose contrasting physiological challenges. Such species are thought to persist across this heterogeneity, either by locally adapting or by evolving wide environmental tolerances via phenotypic plasticity or maintaining high genetic variation. The extent to which populations display local adaptation, phenotypic plasticity, and high within-population genetic variation will have large impacts on species responses to climate change. Large- scale habitat fragmentation impedes migration making plasticity and adaptation important mechanisms for in situ persistence. Using common gardens with reciprocal plantings we investigated the consequences of changes in water availability in the broadly distributed tropical live oak, Quercus oleoides. Chapter 1 examines the relationship among seed production timing, germination and seedling fitness at the local scale in dry forests of NW Costa Rica. In chapter 2, I investigate the extent to which four populations of Q. oleoides from regions with contrasting rainfall patterns exhibit local adaptation and the role of changes in water availability on seedlings fitness. In chapter 3, I examine the extent that populations exhibit differentiation in traits related to carbon and water use. Chapter 3 also investigates the role of trait plasticity in seedling responses to changes in seasonal water availability and the patterns of phenotypic selection on traits. Results from these studies show that local-scale differences in seed production timing have significant consequences for germination and seedling fitness. At a larger spatial scale, results of this work indicate that the broadly distributed Q. oleoides does not consist of a series of locally adapted populations, but rather, of populations with wide environmental tolerances. Seedlings from all populations show similar physiological and morphological responses to changes in water availability and differences among garden sites. Trait plasticity contributes more to phenotypic trait variation than within-population genetic differences. Overall, populations of Q. oleoides lineage represent a lineage well-adapted to drought. Populations are able to maintain fitness with changes in water availability in the short-term through plasticity but may be limited in their long-term adaptive capacity to future changes in rainfall patterns due to low within-population genetic variation for physiological traits.
University of Minnesota Ph.D. dissertation. June 2015. Major: Plant Biological Sciences. Advisor: Jeannine Cavender-Bares. 1 computer file (PDF); xiv, 244 pages.
Physiological and fitness consequences of seasonal rainfall variation in neotropical live oak seedlings (Quercus oleoides): implications for global change.
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