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Oligocene CO2 Decline Promoted C4 Photosynthesis in Grasses
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C4 photosynthesis is an adaptation derived from the more common C3 photosynthetic pathway that con- fers a higher productivity under warm temperature and low atmospheric CO2 concentration [1, 2]. C4 evolution has been seen as a consequence of past atmospheric CO2 decline, such as the abrupt CO2 fall 32–25 million years ago (Mya) [3–6]. This relationship has never been tested rigorously, mainly because of a lack of accurate estimates of divergence times for the different C4 lineages [3]. In this study, we inferred a large phylogenetic tree for the grass family and es- timated, through Bayesian molecular dating, the ages of the 17 to 18 independent grass C4 lineages. The first transition from C3 to C4 photosynthesis occurred in the Chloridoideae subfamily, 32.0–25.0 Mya. The link between CO2 decrease and transition to C4 pho- tosynthesis was tested by a novel maximum likeli- hood approach. We showed that the model incorpo- rating the atmospheric CO2 levels was significantly better than the null model, supporting the importance of CO2 decline on C4 photosynthesis evolvability. This finding is relevant for understanding the origin of C4 photosynthesis in grasses, which is one of the most successful ecological and evolutionary innovations in plant history.
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Olson 1969.pdf
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TRB Library
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NIC-PEK
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Olson Unionidae.pdf
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TRB Library
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NIC-PEK
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On a collision course: competition and dispersal differences create no-analogue communities and cause extinctions during climate change
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Most climate change predictions omit species interactions and interspecific variation in dispersal. Here, we develop a model of multiple competing species along a warming climatic gradient that includes temperature- dependent competition, differences in niche breadth and interspecific differences in dispersal ability. Competition and dispersal differences decreased diversity and produced so-called ‘no-analogue’ commu- nities, defined as a novel combination of species that does not currently co-occur. Climate change altered community richness the most when species had narrow niches, when mean community-wide dispersal rates were low and when species differed in dispersal abilities. With high interspecific dispersal variance, the best dispersers tracked climate change, out-competed slower dispersers and caused their extinction. Overall, competition slowed the advance of colonists into newly suitable habitats, creating lags in climate tracking. We predict that climate change will most threaten communities of species that have narrow niches (e.g. tropics), vary in dispersal (most communities) and compete strongly. Current forecasts probably underestimate climate change impacts on biodiversity by neglecting competition and dispersal differences.
Keywords: climate change; competition; dispersal; community ecology; movement ecology; thermal performance breadth
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On the forest cover–water yield debate: from demand- to supply-side thinking
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Several major articles from the past decade and beyond conclude the impact of reforestation or afforestation on water yield is negative: additional forest cover will reduce and removing forests will raise downstream water availability. A second group of authors argue the opposite: planting additional forests should raise downstream water availability and intensify the hydrologic cycle. Obtaining supporting evidence for this second group of authors has been more dif- ficult due to the larger scales at which the positive effects of forests on the water cycle may be seen. We argue that for- est cover is inextricably linked to precipitation. Forest-driven evapotranspiration removed from a particular catchment contributes to the availability of atmospheric moisture vapor and its cross-continental transport, raising the likelihood of precipitation events and increasing water yield, in particular in continental interiors more distant from oceans. Sea- sonal relationships heighten the importance of this phenomenon. We review the arguments from different scales and perspectives. This clarifies the generally beneficial relationship between forest cover and the intensity of the hydro- logic cycle. While evidence supports both sides of the argument – trees can reduce runoff at the small catchment scale – at larger scales, trees are more clearly linked to increased precipitation and water availability. Progressive deforesta- tion, land conversion from forest to agriculture and urbanization have potentially negative consequences for global precipitation, prompting us to think of forest ecosystems as global public goods. Policy-making attempts to measure product water footprints, estimate the value of ecosystem services, promote afforestation, develop drought mitigation strategies and otherwise manage land use must consider the linkage of forests to the supply of precipitation.
Keywords: afforestation, climate change adaptation, forest ecosystem services, precipitation recycling, water yield
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On the Hydrologic Adjustment of Climate-Model Projections: The Potential Pitfall of Potential Evapotranspiration
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Hydrologic models often are applied to adjust projections of hydroclimatic change that come from climate models. Such adjustment includes climate-bias correction, spatial refinement (‘‘downscaling’’), and consideration of the roles of hydrologic processes that were neglected in the climate model. Described herein is a quantitative analysis of the effects of hydrologic adjustment on the projections of runoff change associated with projected twenty-first-century climate change. In a case study including three climate models and 10 river basins in the contiguous United States, the authors find that relative (i.e., fractional or percentage) runoff change computed with hydrologic adjustment more often than not was less positive (or, equivalently, more negative) than what was pro- jected by the climate models. The dominant contributor to this decrease in runoff was a ubiquitous change in runoff (median 211%) caused by the hydrologic model’s apparent amplification of the climate-model-implied growth in potential evapotranspiration. Analysis suggests that the hydrologic model, on the basis of the empirical, temperature-based modified Jensen–Haise formula, calculates a change in potential evapotranspiration that is typically 3 times the change implied by the climate models, which explicitly track surface energy budgets. In com- parison with the amplification of potential evapotranspiration, central tendencies of other contributions from hydrologic adjustment (spatial refinement, climate-bias adjustment, and process refinement) were relatively small. The authors’ findings highlight the need for caution when projecting changes in potential evapotranspiration for use in hydrologic models or drought indices to evaluate climate change impacts on water.
KEYWORDS: Hydrologic model; Climate change; Potential evapotranspi- ration
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On the Line-Survey Says... Apr 21, 2020
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While much is known about the science of wildland fire behavior, the same cannot necessarily be said about our understanding of the impacts that these blazes have upon those tasked with putting them out. Although that knowledge base is slowly building, much remains to be learned about the psychological and behavioral health of wildland firefighters (WLFF’s). Thanks to the recent research efforts of clinical psychology doctoral student Patty O’Brien (a former Lolo Hotshot, and now Dr. O’Brien), we now know a great deal more. Patty was able to survey over 2600 current or former wildland firefighters to learn more about their demographic, employment, and clinical characteristics, as well as their health behaviors. In this, the tenth and final podcast of On the Line season three, Patty and her doctoral advisor Dr. Duncan Campbell join host Charlie Palmer to discuss some of her groundbreaking findings, and to chart out a course for future steps.
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On the vapour trail of an atmospheric imprint in insects
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Terrestrial arthropods, at constant risk from desiccation, are highly sensitive to atmospheric temperature and humidity. A physiological marker of these abiotic conditions could highlight phenotypic adaptations, indicate niche partitioning, and predict responses to climate change for a group representing three-quarters of the Earth’s animal species. We show that the 18O composition of insect haemolymph is such a measure, providing a dynamic and quantitatively predictable signal for respiratory gas exchange and inputs from atmospheric humidity. Using American cockroaches (Periplaneta americana) under defined experimental conditions, we show that insects respiring at low humidity demon- strate the expected enrichment in the 18O composition of haemolymph because of evapor- ation. At high humidity, however, diffusional influx of atmospheric water vapour into the animal forces haemolymph to become depleted in 18O. Additionally, using cockroaches sampled from natural habitats, we show that the haemo- lymph 18O signature is transferred to the organic material of the insect’s exoskeleton. Insect cuticle, therefore, exhibits the mean atmospheric conditions surrounding the animals prior to moulting. This discovery will help to define the climatic tolerances of species and their habitat preferences, and offers a means of quantifying the balance between niche partitioning and ‘neutral’ processes in shaping complex tropical forest communities.
Keywords: stable isotopes; arthropods; niches; neutral theory; climate change
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