Determining the manner in which plant species shift their flowering times in response to climatic conditions is essential to understanding and forecasting the impacts of climate change on the world's ...flora. The limited taxonomic diversity and duration of most phenological datasets, however, have impeded a comprehensive, systematic determination of the best predictors of flowering phenology. Additionally, many studies of the relationship between climate conditions and plant phenology have included only a limited set of climate parameters that are often chosen a priori and may therefore overlook those parameters to which plants are most phenologically sensitive. This study harnesses 894,392 digital herbarium records and 1,959 in situ observations to produce the first assessment of the effects of a large number (25) of climate parameters on the flowering time of a very large number (2,468) of angiosperm taxa throughout North America. In addition, we compare the predictive capacity of phenological models constructed from the collection dates of herbarium specimens vs. repeated in situ observations of individual plants using a regression approach—elastic net regularization—that has not previously been used in phenological modeling, but exhibits several advantages over ordinary least squares and stepwise regression. When herbarium‐derived data and in situ phenological observations were used to predict flowering onset, the multivariate models based on each of these data sources had similar predictive capacity (R2 = 0.27). Further, apart from mean maximum temperature (TMAX), the two best predictors of flowering time have not commonly been included in phenological models: the number of frost‐free days (NFFD) and the quantity of precipitation as snow (PAS) in the seasons preceding flowering. By vetting these models across an unprecedented number of taxa, this work demonstrates a new approach to phenological modeling.
This study harnesses 894,392 digital herbarium records and 1,959 in situ observations to produce the first assessment of the effects of a 25 of climate parameters on the flowering time of 2,468 of angiosperm taxa throughout North using a regression approach—elastic net regularization—that has not previously been used in phenological modeling, but exhibits several advantages over ordinary least squares and stepwise regression. Multivariate models based on herbarium‐derived data and in situ phenological observations had similar predictive capacity. By vetting these models across an unprecedented number of taxa, this work demonstrates a new approach to phenological modeling.
In the face of recent wildfires across the Western United States, it is essential that we understand both the dynamics that drive the spatial distribution of wildfire, and the major obstacles to ...modeling the probability of wildfire over space and time. However, it is well documented that the precise relationships of local vegetation, climate, and ignitions, and how they influence fire dynamics, may vary over space and among local climate, vegetation, and land use regimes. This raises questions not only as to the nature of the potentially nonlinear relationships between local conditions and the fire, but also the possibility that the scale at which such models are developed may be critical to their predictive power and to the apparent relationship of local conditions to wildfire. In this study we demonstrate that both local climate-through limitations posed by fuel dryness (CWD) and availability (AET)-and human activity-through housing density, roads, electrical infrastructure, and agriculture, play important roles in determining the annual probabilities of fire throughout California. We also document the importance of previous burn events as potential barriers to fire in some environments, until enough time has passed for vegetation to regenerate sufficiently to sustain subsequent wildfires. We also demonstrate that long-term and short-term climate variations exhibit different effects on annual fire probability, with short-term climate variations primarily impacting fire probability during periods of extreme climate anomaly. Further, we show that, when using nonlinear modeling techniques, broad-scale fire probability models can outperform localized models at predicting annual fire probability. Finally, this study represents a powerful tool for mapping local fire probability across the state of California under a variety of historical climate regimes, which is essential to avoided emissions modeling, carbon accounting, and hazard severity mapping for the application of fire-resistant building codes across the state of California.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Context
Just as the timing of the vegetative growing season affects a host of ecological processes, the seasonality of floral availability impacts ecological processes from nectar availability and ...allergen production to competition for pollinator attention. However, no existing methodology is capable of evaluating multi-species bloom phenology in a standardized fashion across multiple ecosystems or compositionally distinct local flora. Thus, the manner in which the onset of the bloom season (during which the majority of species flower) differs along climate gradients and among distinct local flora remains largely unknown.
Objectives
This study evaluates differences in the timing of the bloom season throughout the western United States, and the relationship of the bloom season to the vegetative growing season and to local climate conditions.
Methods
This study estimated the season during which all but the earliest and latest 5 % of local species flower (the bloom season) using digital herbarium records. Bloom season timing was compared to land surface phenology, SI-x phenoclimate metrics, and PRISM climate normals.
Results
Local differences in mean temperature of the coldest month explained 76 % of observed variation in bloom season onset. Variation in land surface phenology explained 50 % of observed variation, while SI-x Bloom estimates explained 64 % of observed variation in bloom season onset.
Conclusions
These results confirm that bloom season phenology is distinct from the vegetative growing season, and that local temperature is a good predictor of bloom season onset. This work represents a new modality for studying multi-taxa flowering phenology at landscape and regional scales.
Context
This study provides a unified, holistic framework for predicting the dynamics of shrub-grass conversion throughout Mediterranean-climate shrublands. This work focuses specifically on the ...California chaparral, which until recently has been considered resistant to invasion by exotic grasses, but in recent years appears to have undergone substantial type conversion.
Objectives
To synthesize current understanding of the feedbacks and anthropogenic impacts that both enhance and reduce the susceptibility of southern California chaparral to invasion and its corresponding ability to recolonize invaded areas.
Methods
We review the existing literature pertaining to the factors that enhance or reduce the susceptibility of chaparral to invasion, and organize these factors and their interactions into a single unified framework of environmental drivers, ecological interactions, and historical legacies associated with the distribution and rate of such invasion.
Results
A myriad of processes interact to mediate the invasion of exotic grasses into intact chaparral. In addition, we demonstrate that feedbacks exist within both chaparral shrublands and exotic grasslands that modify the landscape in ways that can enhance their own survival, act as barriers to conversion into alternate cover types, and in some cases weaken the resistance of adjacent vegetation to invasion. We posit a methodological framework from which the many climatic, anthropogenic, edaphic, and biotic feedbacks that determine the mosaic of invasion can be modeled.
Conclusions
This study demonstrates that substantial conversion of chaparral into deciduous grasslands has recently occurred in southern California and presents a unified framework for forecasting the dynamics of shrub-grass conversion throughout Mediterranean-climate shrublands.
AIMS: Flowering phenology is well documented to restrict the distribution of many plant species. However, community‐level shifts in flowering time may occur either through exclusion of species with ...unsuitably early or late flowering for local conditions (composition‐derived phenological shifts) or through intraspecific phenological responses to climate variations over space. Although these mechanisms have quite different ecological implications, the relative contribution of composition‐derived phenological shifts remains largely unknown. Therefore, determining the magnitude of composition‐derived phenological variation is crucial for understanding the relationship between phenology and community assemblage over space, and for predicting the impacts of future climate change. This study will evaluate the contributions of compositional differences to spatial variation in community‐level flowering times throughout the early, mid and late portions of the growing season and across a variety of temperate environments. LOCATION: Continental United States. METHODS: This study develops novel herbarium‐based methods to separate intraspecific phenological variations over space from changes in flowering time derived from differences in community composition. RESULTS: Although typically smaller than intraspecific variations, composition‐derived shifts in flowering time explained up to 49.3% of overall phenological variation. Composition‐derived changes in flowering time among late‐flowering species also explained the greatest proportion of overall variation and were the most responsive to differing climate conditions. Xeric regions also exhibited composition‐derived phenological shifts that were stronger and more closely tied to climate conditions (R² up to 0.553) than other regions. MAIN CONCLUSIONS: These results indicate that interspecific differences in flowering time play a significant role in determining the composition of the plant community over space. However, the impact of flowering phenology on community assemblage varies considerably among seasons and climate regions, and appears to be strongest among xeric regions and among late‐flowering species.
In recent decades, the final frost dates of winter have advanced throughout North America, and many angiosperm taxa have simultaneously advanced their flowering times as the climate has warmed. ...Phenological advancement may reduce plant fitness, as flowering prior to the final frost date of the winter/spring transition may damage flower buds or open flowers, limiting fruit and seed production. The risk of floral exposure to frost in the recent past and in the future, however, also depends on whether the last day of winter frost is advancing more rapidly, or less rapidly, than the date of onset of flowering in response to climate warming. This study presents the first continental‐scale assessment of recent changes in frost risk to floral tissues, using digital records of 475,694 herbarium specimens representing 1,653 angiosperm species collected across North America from 1920 to 2015. For most species, among sites from which they have been collected, dates of last frost have advanced much more rapidly than flowering dates. As a result, frost risk has declined in 66% of sampled species. Moreover, exotic species consistently exhibit lower frost risk than native species, primarily because the former occupy warmer habitats where the annual frost‐free period begins earlier. While reducing the probability of exposure to frost has clear benefits for the survival of flower buds and flowers, such phenological advancement may disrupt other ecological processes across North America, including pollination, herbivory, and disease transmission.
In recent decades, the final frost dates of winter have advanced throughout North America, and many angiosperm taxa have simultaneously advanced their flowering times as the climate has warmed. This study presents the first continental‐scale assessment of recent changes in frost risk to floral tissues, using digital records of 475,694 herbarium specimens representing 1,653 angiosperm species collected across North America from 1920 to 2015. Across the majority of sampled species (1,092 of 1,653 species), rates of last frost have advanced much more rapidly than flowering dates. As a result, frost risk has declined in association with recent warming.
Understanding the effects of climate change on the phenological structure of plant communities will require measuring variation in sensitivity among thousands of co‐occurring species across regions. ...Herbarium collections provide vast resources with which to do this, but may also exhibit biases as sources of phenological data. Despite general recognition of these caveats, validation of herbarium‐based estimates of phenological sensitivity against estimates obtained using field observations remains rare and limited in scope. Here, we leveraged extensive datasets of herbarium specimens and of field observations from the USA National Phenology Network for 21 species in the United States and, for each species, compared herbarium‐ and field‐based estimates of peak flowering dates expected under standardized temperature conditions, and of sensitivity of peak flowering time to geographic and interannual variation in mean minimum temperatures (TMIN). We found strong agreement between herbarium‐ and field‐based estimates for standardized peak flowering time (r = 0.91, p < 0.001) and for the direction and magnitude of sensitivity to both geographic TMIN variation (r = 0.88, p < 0.001) and interannual TMIN variation (r = 0.82, p < 0.001). This agreement was robust to substantial differences between datasets in 1) the long‐term TMIN conditions observed among collection and phenological monitoring sites and 2) the interannual TMIN conditions observed in the time periods encompassed by both datasets for most species. Our results show that herbarium‐based sensitivity estimates are reliable among species spanning a wide diversity of life histories and biomes, demonstrating their utility in a broad range of ecological contexts, and underscoring the potential of herbarium collections to enable phenoclimatic analysis at taxonomic and spatiotemporal scales not yet captured by observational data.
Aim
Climate affects the flowering time of many species. Little is known, however, about how climate influences the properties of regional floras, including the rate at which taxa flower sequentially ...throughout the flowering season. This study is the first to detect geographical variation in this rate across North America. In addition, we tested for the independent effects of intraspecific variation in flowering time and taxonomic composition on the rate of sequential flowering among regional floras distributed across a temperature gradient.
Location
North America.
Time period
This study examined >59,000 herbarium specimens that were collected in flower from 1901 to 2013.
Major taxa studied
2,803 angiosperm taxa.
Methods
We identified 51 climatically homogeneous regions across the continental, mostly western states of the USA, in each of which ≥100 species were represented by herbarium specimens. We then examined the effects of mean annual temperature (MAT) on the rate of sequential flowering among species in each region. We also evaluated whether geographical variation in the rate of sequential flowering was attributable to intraspecific variation in the flowering time and/or the taxonomic composition of regional floras.
Results
As MAT increased over space, the rate of sequential flowering (standardized by the absolute length of the flowering season in each region) increased among relatively early‐flowering taxa but decreased among the latest‐flowering taxa. Both intraspecific variation and shifts in taxonomic composition among floras contributed to this pattern.
Main conclusions
Among floras throughout North America, the rate of sequential flowering among co‐occurring taxa changes with MAT. Intraspecific phenological variation primarily affects the rate of sequential flowering during the first half of the growing season, consistent with the inference that future warming will most strongly affect flowering synchrony among early‐flowering taxa.
Abstract
Secretory proteins are an essential component of interorgan communication networks that regulate animal physiology. Current approaches for identifying secretory proteins from specific cell ...and tissue types are largely limited to in vitro or ex vivo models which often fail to recapitulate in vivo biology. As such, there is mounting interest in developing in vivo analytical tools that can provide accurate information on the origin, identity, and spatiotemporal dynamics of secretory proteins. Here, we describe
i
SLET (in situ Secretory protein Labeling via ER-anchored TurboID) which selectively labels proteins that transit through the classical secretory pathway via catalytic actions of Sec61b-TurboID, a proximity labeling enzyme anchored in the ER lumen. To validate
i
SLET in a whole-body system, we express
i
SLET in the mouse liver and demonstrate efficient labeling of liver secretory proteins which could be tracked and identified within circulating blood plasma. Furthermore, proteomic analysis of the labeled liver secretome enriched from liver
i
SLET mouse plasma is highly consistent with previous reports of liver secretory protein profiles. Taken together,
i
SLET is a versatile and powerful tool for studying spatiotemporal dynamics of secretory proteins, a valuable class of biomarkers and therapeutic targets.
The evolution of seed size may be influenced by intrinsic attributes of populations, such as mating system and extrinsic factors, such as climate. Several hypotheses propose that the evolution of ...self‐fertilization from an outcrossing progenitor will be accompanied by a reduction in seed size, but this prediction has not been rigorously tested. Many studies report that the mean seed size of populations or taxa is associated with long‐term climate conditions. Here, we examined the effects on seed size of both mating system and climate within a single genus.
In the California wildflower genus, Clarkia (Onagraceae), we sampled seeds from 58 populations representing three pairs of sister taxa; each pair included a predominantly outcrossing and a facultatively selfing taxon. We then examined the independent effects on population mean seed size of mating system, elevation, long‐term (30‐year) climate conditions, and climate anomalies (the deviation between conditions in the year of collection and the long‐term mean), focusing on maximum monthly temperature (Tmax), cumulative moisture deficit and cumulative precipitation (PPT) during Clarkia's growing season (fall, winter and spring).
In each taxon pair, the selfing taxon had smaller seeds than the outcrosser. Local, long‐term (1921–1980 and 1981–2000) mean Tmax, PPT and elevation were independently and negatively associated with seed size. Long‐term means for Tmax and PPT explain geographical variation in seed size better than climate anomalies in the year of collection.
Synthesis. We corroborated two key hypotheses concerning the drivers of geographical variation in mean seed size. Small seeds in Clarkia co‐evolve with selfing (although the mechanism remains elusive) and in response to chronically warm and wet conditions. The effect of long‐term mean precipitation on seed size differs qualitatively from the effect of precipitation anomalies; relatively large seeds are produced in populations experiencing wetter‐than‐normal years. Ongoing climate change may therefore generate conflicting selection on seed size in Clarkia: intensifying drought is likely to lead to an evolutionary increase in seed size due to its effects on seedling survivorship, while climate‐driven declines in pollinators or selection favouring more rapid reproduction may promote the evolution of self‐pollination, facilitating the evolution of smaller seeds.
We corroborated two key hypotheses concerning the drivers of geographical variation in mean seed size. Small seeds in Clarkia co‐evolve with selfing (although the mechanism remains elusive) and in response to chronically warm and wet conditions. The effect of long‐term mean precipitation on seed size differs qualitatively from the effect of precipitation anomalies; relatively large seeds are produced in populations experiencing wetter‐than‐normal years. Ongoing climate change may therefore generate conflicting selection on seed size in Clarkia: intensifying drought is likely to lead to an evolutionary increase in seed size due to its effects on seedling survivorship, while climate‐driven declines in pollinators or selection favouring more rapid reproduction may promote the evolution of self‐pollination, facilitating the evolution of smaller seeds. Image credit: Heather Schneider merits credit for the photo of Clarkia unguiculata, and Leah Dudley took the photo of Clarkia xantiana.
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