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Phillips, Randall
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Photoperiodic regulation of the seasonal pattern of photosynthetic capacity and the implications for carbon cycling
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Although temperature is an important driver of seasonal changes in photosynthetic physiology, photoperiod also regulates leaf activity. Climate change will extend growing seasons if temperature cues predominate, but photoperiod-controlled species will show limited responsiveness to warming. We show that photoperiod explains more seasonal variation in photosynthetic activity across 23 tree species than temperature. Although leaves remain green, photosynthetic capacity peaks just after summer solstice and declines with decreasing photoperiod, before air temperatures peak. In support of these findings, saplings grown at constant temperature but exposed to an extended photoperiod maintained high photosynthetic capacity, but photosynthetic activity declined in saplings experiencing a naturally shortening photoperiod; leaves remained equally green in both treatments. Incorporating a photo- periodic correction of photosynthetic physiology into a global-scale terrestrial carbon-cycle model significantly improves predictions of seasonal atmospheric CO2 cycling, demonstrating the benefit of such a function in coupled climate system models. Accounting for photo- period-induced seasonality in photosynthetic parameters reduces modeled global gross primary production 2.5% (∼4 PgC y−1), result- ing in a >3% (∼2 PgC y−1) decrease of net primary production. Such a correction is also needed in models estimating current carbon up- take based on remotely sensed greenness. Photoperiod-associated declines in photosynthetic capacity could limit autumn carbon gain in forests, even if warming delays leaf senescence.
day length | gross primary productivity | carbon sequestration | leaf area index | evapotranspiration
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Phylogenetic and functional diversity in large carnivore assemblages
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Large terrestrial carnivores are important ecological components and promi- nent flagship species, but are often extinction prone owing to a combination of biological traits and high levels of human persecution. This study com- bines phylogenetic and functional diversity evaluations of global and continental large carnivore assemblages to provide a framework for conser- vation prioritization both between and within assemblages. Species-rich assemblages of large carnivores simultaneously had high phylogenetic and functional diversity, but species contributions to phylogenetic and func- tional diversity components were not positively correlated. The results further provide ecological justification for the largest carnivore species as a focus for conservation action, and suggests that range contraction is a likely cause of diminishing carnivore ecosystem function. This study high- lights that preserving species-rich carnivore assemblages will capture both high phylogenetic and functional diversity, but that prioritizing species within assemblages will involve trade-offs between optimizing contempor- ary ecosystem function versus the evolutionary potential for future ecosystem performance. Carnivora, predation, ecosystem function, conservation priorities, biodiversity
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Phylogenetic patterns of species loss in Thoreau’s woods are driven by climate change
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Climate change has led to major changes in the phenology (the
timing of seasonal activities, such as flowering) of some species but
not others. The extent to which flowering-time response to temperature
is shared among closely related species might have
important consequences for community-wide patterns of species
loss under rapid climate change. Henry David Thoreau initiated a
dataset of the Concord, Massachusetts, flora that spans !150 years
and provides information on changes in species abundance and
flowering time. When these data are analyzed in a phylogenetic
context, they indicate that change in abundance is strongly correlated
with flowering-time response. Species that do not respond to
temperature have decreased greatly in abundance, and include
among others anemones and buttercups [Ranunculaceae pro parte
(p.p.)], asters and campanulas (Asterales), bluets (Rubiaceae p.p.),
bladderworts (Lentibulariaceae), dogwoods (Cornaceae), lilies (Liliales),
mints (Lamiaceae p.p.), orchids (Orchidaceae), roses (Rosaceae
p.p.), saxifrages (Saxifragales), and violets (Malpighiales).
Because flowering-time response traits are shared among closely
related species, our findings suggest that climate change has
affected and will likely continue to shape the phylogenetically
biased pattern of species loss in Thoreau’s woods
PNAS ! November 4, 2008 ! vol. 105 ! no. 44 ! 17029–17033
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Phylogenetic trees and the future of mammalian biodiversity
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Phylogenies describe the origins and history of species. However, they can also help to predict species’ fates and so can be useful tools for managing the future of biodiversity. This article starts by sketching how phylogenetic, geographic, and trait information can be combined to elucidate present mammalian diversity patterns and how they arose. Recent diversification rates and standing diversity show different geographic patterns, indicating that cra- dles of diversity have moved over time. Patterns in extinction risk reflect both biological differences among mammalian lineages and differences in threat intensity among regions. Phylogenetic com- parative analyses indicate that for small-bodied mammals, extinc- tion risk is governed mostly by where the species live and the intensity of the threats, whereas for large-bodied mammals, eco- logical differences also play an important role. This modeling approach identifies species whose intrinsic biology renders them particularly vulnerable to increased human pressure. We outline how the approach might be extended to consider future trends in anthropogenic drivers, to identify likely future battlegrounds of mammalian conservation, and the likely casualties. This framework could help to highlight consequences of choosing among different future climatic and socioeconomic scenarios. We end by discussing priority-setting, showing how alternative currencies for diversity can suggest very different priorities. We argue that aiming to maximize long-term evolutionary responses is inappropriate, that conservation planning needs to consider costs as well as benefits, and that proactive conservation of largely intact systems should be part of a balanced strategy.
extinction risk latent risk mammals
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Physical Laws Shape Biology
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IN THE PERSPECTIVE “A DYNAMICAL-SYSTEMS VIEW OF STEM CELL
biology” (12 October 2012, p. 215), C. Furusawa and K. Kaneko discuss
the relevance of dynamic systems biology approaches and the
concept of “attractors” to understand cell differentiation and proliferation.
We share their excitement in using computational models that
apply physical laws to cell fate decision.
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Physically based assessment of hurricane surge threat under climate change
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Storm surges are responsible for much of the damage and loss of life associated with landfalling hurricanes. Understanding how global warming will affect hurricane surges thus holds great interest. As general circulation models (GCMs) cannot simulate hurricane surges directly, we couple a GCM-driven hurricane model with hydrodynamic models to simulate large numbers of synthetic surge events under projected climates and assess surge threat, as an example, for New York City (NYC). Struck by many intense hurricanes in recorded history and prehistory, NYC is highly vulnerable to storm surges. We show that the change of storm climatology will probably increase the surge risk for NYC; results based on two GCMs show the distribution of surge levels shifting to higher values by a magnitude comparable to the projected sea-level rise (SLR). The combined effects of storm climatology change and a 1 m SLR may cause the present NYC 100-yr surge flooding to occur every 3–20 yr and the present 500-yr flooding to occur every 25–240 yr by the end of the century.
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Physiological plasticity increases resilience of ectothermic animals to climate change
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Understanding how climate change affects natural populations remains one of the greatest challenges for ecology and management of natural resources. Animals can remodel their physiology to compensate for the effects of temperature variation, and this physiological plasticity, or acclimation, can confer resilience to climate change1,2. The current lack of a comprehensive analysis of the capacity for physiological plasticity across taxonomic groups and geographic regions, however, constrains predictions of the impacts of climate change. Here, we assembled the largest database to date to establish the current state of knowledge of physiological plasticity in ectothermic animals. We show that acclimation decreases the sensitivity to temperature and climate change of freshwater and marine animals, but less so in terrestrial animals. Animals from more stable environments have greater capacity for acclimation, and there is a significant trend showing that the capacity for thermal acclimation increases with decreasing latitude. Despite the capacity for acclimation, climate change over the past 20 years has already resulted in increased physiological rates of up to 20%, and we predict further future increases under climate change. The generality of these predictions is limited, however, because much of the world is drastically undersampled in the literature, and these undersampled regions are the areas of greatest need for future research efforts.
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Physiology and Climate Change
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Studies of physiological mechanisms are needed to predict climate effects on ecosystems at species and community levels.
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Phytoplankton Calcification in a High-CO2 World
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Ocean acidification in response to rising atmospheric CO2 partial pressures is widely expected to reduce calcification by marine organisms. From the mid-Mesozoic, coccolithophores have been major calcium carbonate producers in the world’s oceans, today accounting for about a third of the total marine CaCO3 production. Here, we present laboratory evidence that calcification and net primary production in the coccolithophore species Emiliania huxleyi are significantly increased by high CO2 partial pressures. Field evidence from the deep ocean is consistent with these laboratory conclusions, indicating that over the past 220 years there has been a 40% increase in average coccolith mass. Our findings show that coccolithophores are already responding and will probably continue to respond to rising atmospheric CO2 partial pressures, which has important implications for biogeochemical modeling of future oceans and climate.
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