1,721,007 research outputs found
Climate variability and stress exposure alter evolutionary responses across populations of Mimulus cardinalis
No full textWe are just beginning to understand population-level responses to extreme climatic events. Populations of the same species from differing climatic regions can have different traits and adaptations that have locally evolved, and this can alter their evolutionary trajectories when exposed to similar selection pressures. My thesis examines how populations of Mimulus (Erythranthe) cardinalis (scarlet monkeyflower) from historically different climates respond to a severe drought, using a resurrection approach to grow ancestral (pre-drought) and descendant (peak-drought) individuals in a common environment and growing them in either wet or dry treatments. In chapter two, I report that populations in the north (historically wetter and less variable) did not show evolutionary changes at the macro-morphological scale (e.g., date of flowering, specific leaf area), while southern populations (historically drier and more variable) evolved toward trait values that promote dehydration avoidance. In chapter three, I find that macro-morphological changes (or lack thereof) can be better understood by examining more cryptic micro-morphological alterations in leaf architecture and physiology. Here, northern populations evolved greater plasticity in mesophyll composition, stomatal density and assimilation rate, trending toward dehydration avoidance and potentially allowing macro-morphological traits to remain stabilized. Southern populations began with trait values that were more drought avoidant and evolved further along this trajectory, resulting in a trade-off for photosynthesis under wet conditions. Finally, differences in evolutionary trajectories between northern and southern populations can also be attributed to phenotypic legacies from non-genetic inheritance. In chapter four, I grew northern and southern populations for 3 generations under either wet or dry treatments to assess epigenetic stress memory. Northern populations exhibited greater epigenetic-attributed plasticity than the southern populations, but the southern populations evolved epigenetic plasticity, which likely assisted in vegetative avoidance of drought. Thus, although at the macro-scale northern populations did not show a clear trend, anatomical features and grandparental histories show both regions rapidly evolve toward dehydration avoidance and non-genetically respond to drought stress, but through different mechanisms. These results indicate that northern populations are becoming more like ancestral southern populations, while southern populations might be nearing the edge of their adaptive capacity. Science, Faculty ofBotany, Department ofGraduat
Herbivory and climate as drivers of plant population and range dynamics
No full textClimate change should be shifting species' ranges upslope and poleward as they track their
suitable climates. However, many species' ranges are not shifting, with researchers struggling to
accurately predict species' sensitivity to climate change. These unexpected responses to climate
change could be due to the temporal scale species respond to climate or the role of species'
interactions, such as herbivory, in shaping species ranges. My thesis explores how climate and
herbivory interact to shape species ranges, providing insights into how these ranges may respond to climate change. First, I test whether the lack of range shifts for many species is because they respond to warming on longer timescales than we measure range shifts. Using a 25-species seed addition experiment, I compared seedling recruitment patterns with adult climatic ranges. I found evidence of a delayed sensitivity to climate change, where range shifts are likely occurring, but responses are delayed and slower than the pace of climate change. Second, I test the assumption that species interactions, like herbivory, are more prevalent towards species' lower range limits and, thus, primarily shape lower over higher limits. While I found herbivory on Lupinus latifolius increases towards warmer temperatures, I also identified herbivore-guild specific precipitation patterns in herbivory. Thus, non-temperature variables can explain unexpected range patterns in species interaction intensity. Finally, I assessed how climate and herbivory jointly influence population dynamics across the range of L. latifolous. Through a field
experiment manipulating temperature and herbivory, I found that the strongest effects of
herbivory on population dynamics were towards lower elevations. Herbivory effects on
populations were driven by a compounding effect of herbivory intensity and climatic stress,
which together made plants more vulnerable to herbivory than either factor alone. Overall, my
thesis suggests that unexpected species responses to climate change are partly explained by (1) the temporal scale species respond and (2) indirect effects of climate change, where climatic
stress makes plants more vulnerable to herbivory. My research advances our knowledge of
interacting mechanisms underlying species' population and range dynamics to inform temporal
and spatial responses to climate change.Science, Faculty ofBotany, Department ofGraduat
Demographic pathways and genetic consequences of range expansion
No full textSpecies range expansions exist at the interface of ecology and evolutionary biology and the iterative interactions between eco-evolutionary theory and observational and experimental tests in nature. Understanding the demographic pathways and genetic consequences of range expansion has important implications for interpreting spatial patterns in biodiversity in the context of historical processes, managing invasive species, and forecasting species range shifts. Range expansion theory makes robust predictions about how genetic diversity, fitness, and traits should change over space and time due to serial founder events characterizing the demographic pathways underlying the history of colonization, but empirical results do not always match theoretical expectations. In this thesis, I use a combination of theoretical and empirical work to investigate the demographic pathways and genetic consequences of post-glacial species range expansions. First, I investigate whether density-dependent selection on loci underlying relevant life-history traits at the low-density range edge may be an important factor explaining discrepancies between theoretical and empirical studies of the predicted negative genetic consequences of range expansion. I find expressed genetic load is dependent on the population density in which fitness is measured. Next, I investigate patterns of genetic diversity through space and time in the context of colonization following alpine glacier recession to understand whether dispersal limitation (i.e., serial founder events) also characterizes expansions across this relatively understudied smaller spatiotemporal scale. I find that shorter spatiotemporal scales of range expansion do not appear to be limited by dispersal at the range edge, suggesting levels of population genetic diversity are not reduced post-expansion. Finally, I investigate how mating system diversity is maintained within a species, specifically testing how historical range expansion can influence contemporary biogeographic patterns in species traits. I detect, on average, a pattern of increased probability of selfing and clonal propagation with increased distance from putative historical refugia. This pattern suggests selection for both sexual and asexual reproductive assurance occurred in colonizing populations during range expansion. Together, these studies provide a better understanding for how range expansion in ecologically complex simulated and natural environments can shape spatial patterns in biodiversity we see today.Science, Faculty ofBotany, Department ofGraduat
Simulated invasion suggests rapid evolution of biotic resistance to a range-shifting competitor
No full textClimate change is driving species ranges both polewards and upslope in elevation. These shifts may differ in rate or magnitude among species, leading to novel community formations and species interactions. Most research has focused on predicting range shifts and elucidating the evolutionary dynamics of range expansions for species on the move (range-shifting invaders).
However, slower-moving (resident) species could also evolve when competing with range-shifting invaders. This could result in the evolution of increased resident biotic resistance, impeding the invader’s growth, as seen in biological invasions. Range-shifting invaders, however, may differ from invasive species in their selective impacts on resident competitors. Therefore, it remains unknown whether biotic resistance can also evolve in residents facing range-shifting invaders driven by climate change. Here we construct populations of eight duckweed genotypes (Lemna minor = resident), from various localities near and beyond the range edge of a potential range-shifting competitor, Spirodela polyrhiza (invader), and invade them with one genotype of S. polyrhiza. Such a scenario could occur in Northern Europe where climate change may propel S. polyrhiza to repeatedly invade L. minor populations inexperienced to competition with S. polyrhiza. Following 14 weeks of lab-simulated invasion, we observed significant rapid evolution and morphological plasticity in L. minor. Selection favoured faster growth rates and
genotypes with less geographic proximity to (less co-evolutionary history with) S. polyrhiza. Morphological plasticity was inconsistent across L. minor genotypes, but some genotypes developed longer roots and larger raft sizes in invaded populations. Finally, we observed weak evidence for increased biotic resistance in L. minor when S. polyrhiza was re-introduced to previously invaded (experienced) L. minor populations. Collectively, rapid evolution and plasticity created subtle phenotypic differences in L. minor populations with invaders compared to those without, which may have driven increased biotic resistance to invasion in L. minor. Our results indicate that range-shifting species, even at low densities, may drive evolution, plasticity, and
increased biotic resistance in resident competitors that could feed back to influence range expansion by the invader.Science, Faculty ofBotany, Department ofGraduat
Experimental evolution of species ranges and coexistence using competing duckweed species
No full textUnderstanding the evolution of species distributions is a fundamental goal of evolutionary ecology. With global change comes new challenges in predicting the movement of species ranges and the re-assembly of ecological communities. Importantly, these rapid changes in species distributions can provide unique opportunities for ecology to shape evolution, and for evolution to govern population and community dynamics across space and time. However, much remains unknown about how rapid feedbacks between population ecology and genetics (i.e., eco-evolutionary feedbacks) scale up to govern species distributions and community patterns. To make progress, this thesis tests a series of predictions on how evolution can alter species distributions and community assembly, using the evolution of duckweed species in experimental mesocosms. In Chapter 2, I test how evolution during range expansion alters our ability to predict population spread. With selection from an environmental gradient in space, I found that range expansion speed was more variable, and hence less predictable, across replicate populations. This occurred despite slower population spread and higher population densities at the range front – conditions in which models otherwise predict less variable range expansion speeds due to greater selection over genetic drift. In Chapter 3, I test how community context, specifically interspecific competition, alters adaptation during climate-driven range shifts. I found feedbacks between competition and evolution differed across a species experimental range, with competition limiting adaptive evolution at the range core, but promoting adaptation to climate stress at the range edge. I suggest that competition therefore has the potential to promote evolutionary rescue in response to global change. Lastly, in Chapter 4, I test whether and how mechanisms of coexistence evolve over time, from identical lineages to distinct species. I parametrized coexistence of genetically divergent lineages within and across duckweed species to show that coexistence mechanisms evolve in concert with lineage divergence. While evolutionary biology has mainly focused on mechanisms of genetic isolation, I suggest that feedbacks between genetic isolation and ecological differentiation is key for the origins of coexisting species. Overall, my thesis unpacks the diverse, and often surprising, pathways by which eco-evolutionary feedbacks govern population and community trajectories across space and time.Science, Faculty ofBotany, Department ofGraduat
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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