Browsing by Subject "tallgrass prairie"

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    Estimating the capacity of Chamaecrista fasciculata to adapt to novel environments
    (2021-12) Peschel, Anna
    Tallgrass prairies are one of the most endangered ecosystems in North America with less than 1 percent of their original extent prior to European settlement remaining. Most tallgrass prairie has been razed for agriculture because they tend to exist on fertile soils. In Minnesota the tallgrass prairie once covered 18 million acres, but now only 200,000 acres remain—small, fragmented patches in a matrix of corn and soybean fields (Minnesota Prairie Plan Working Group 2018).Climate change poses new management challenges for extant tallgrass prairies. Given that the remaining prairies are small and severed from gene flow, they may lack sufficient genetic variation to adapt to climate change. If the standing genetic diversity within a population is insufficient for adaptive evolution, seed may need to be sourced from other populations to introduce alleles adaptive in environments predicted for the future. However, how tallgrass prairie plant populations will respond to climate change, and if they possess the capacity to adapt to climate change in situ, are open questions. With insight from prior research (Etterson 2004a,b; Sheth et al. 2018; Kulbaba et al. 2019), we investigate the capacity of the annual prairie legume, Chamaecrista fasciculata, to adapt to environments predicted for the future. The overarching aims of this research are to 1) estimate adaptive capacity in a population of C. fasciculata, 2) test fundamental evolutionary theory predicting a populations’ rate of adaptation, and 3) identify how key plant traits may respond to, and modulate a population’s response to, future climate change. Along with increasing temperatures, climate change in the Midwest is expected to increase the frequency and intensity of rainstorms (Angel et al. 2018). In Chapter 1, we asked if C. fasciculata has sufficient additive genetic variance for fitness to adapt to extreme rain. We also investigated how extreme rain affects plasticity of, selection on, and heritability of specific leaf area (SLA), a trait thought to mitigate water loss. We manipulated rainfall over a pedigreed population of C. fasciculata using rain shelters and found C. fasciculata possessed a significant capacity to adapt to anomalously wet environments. We also found plants to have thinner leaves in wet environments while selection favored thicker leaves, but fitness remained above replacement (mean lifetime fitness > 1, indicating population growth). In Chapter 2 we asked if C. fasciculata possesses the capacity to adapt to climate change, and how well predictions of the rate of adaptation match what is realized in the field. We planted a pedigreed population of C. fasciculata into three sites along an east to west aridity gradient. The eastern (home) site is predicted to have climate similar to the current climate of the western sites in 25-50 years, so comparisons of the rate of adaptation between the home and western sites will give insight into the capacity of this population to adapt to future climates. We detected significant additive genetic variance for fitness in all sites, which implies this population possesses the capacity to adapt to future climates. Predictions of progeny generation mean fitness were greater than what was realized in the field, and the progeny generation was maladapted. However, maladaptation was buffered by the environment at the home and westernmost site, as the fitness of these populations was above replacement. This work suggests C. fasciculata possesses significant genetic variance to adapt in situ to wetter environments, but a change in the selective environment between generations may cause maladaptation. In chapter 3 we used the experimental design of chapter 2 and asked how climate change alters plasticity of, selection on, and heritability of two key traits, SLA and corolla width, to investigate if changes in plasticity or selection on these traits affects the capacity of C. fasciculata to adapt to future climates. We found significant differences in selection on traits between sites, as well as significant selection for thicker leaves and larger flowers across sites. The plastic response was generally maladaptive (thinner leaves and smaller flowers). We did not find traits to be heritable, which may be a consequence of limited power. Mean fitness in the western most site was above replacement which implies adaptive phenotypic plasticity and adaptive evolution of SLA and corolla width may not be necessary for this population to increase in mean fitness. We detected abundant and significant additive genetic variance for mean lifetime fitness which suggests the populations of C. fasciculata used in this research possess the capacity to adapt to wetter environments. However, temporal environmental variation caused alleles selected by the environment in the parental generation to change frequency in a maladaptive direction, according to the environment in the progeny generation. While the progeny generation was maladapted, mean fitness remained above replacement which is a consequence of plasticity, not adaptive evolution. Mean fitness above replacement at the western most site suggests that this population of C. fasciculata may be able to persist in future climates without seed from other sites. However, the ability of plasticity to buffer populations from environmental change in the long term, as well as the long-term effects of fluctuating selection for demography and evolution, remain unclear and are future research directions. More studies employing the Fundamental Theorem of Natural Selection (FTNS) are needed so we can increase our predictive power of the adaptive capacity of populations in hopes of conserving populations at risk of extinction from climate change.
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    Harvesting native seed to supply landscape-scale restoration: evaluating risks and sustainable practices
    (2016-06) Meissen, Justin
    Seed supply limits large-scale restorations, which often rely on seed collection from remnant ecosystems. Overharvesting seed may deplete populations, exacerbate seed limitation, and jeopardize ecosystem integrity, but these risks have not been formally studied. Many life history traits are linked to species’ reliance on seed reproduction, and so may provide a useful framework to address seed harvest risks. I evaluated whether life history traits predict susceptibility to overharvest by comparing tallgrass prairies in Minnesota (USA) harvested at varying frequencies (every year, once per 3-5 years, unharvested). I identified species less likely to occur on frequently harvested sites then tested whether lifespan, clonality and seed production predicted harvest sensitivity. Short-lived, non-clonal species were sensitive to seed harvest while long-lived clonal species were not, suggesting that life history traits provide a means to predict seed harvest risk. To verify the predictive utility of life history traits and determine extinction risks from seed harvest over long restoration timeframes (25 years), I used matrix models of clonal Solidago canadensis and Anemone canadensis and non-clonal Rudbeckia hirta, Packera aureus, Zizia aurea, and Liatris ligulistylis to simulate seed harvest and extinction risk. I simulated 5 scenarios: no harvest; annual harvest at 50%/75% intensity; and triennial harvest at 50%/75% intensity. Non-clonal species were insensitive to triennial and 50% harvest, but susceptible to extinction risks of up to 92% with annual 75% harvest. Clonal species were insensitive to all harvest scenarios. To maintain populations of non-clonal species in the long-term, high intensity annual harvest should be avoided. To demonstrate the risk of overharvest in short-lived, non-clonal species and determine sustainable harvest regimes, I conducted a field experiment varying seed harvest intensity (0, 50%, or 100% seed removed) and management (burned or unburned) for R. hirta populations. I compared seedling recruitment and seed production among treatments, and found that seed production nearly doubled with burning. Moderate intensity harvest with burning allowed high levels of seedling recruitment, but high harvest intensity prevented recruitment, as predicted for a short-lived, non-clonal species. A regime combining moderate intensity harvest with fire management provides seeds while also conserving at-risk seed donor sources.