Diatoms are among the most abundant phytoplankton that inhabit coastal ecosystems, forming large blooms that fuel coastal food webs. Although diatoms are often large and morphologically distinct, many are small or morphologically cryptic making it difficult to understand the temporal dynamics of whole diatom communities and the environmental factors that drive them. Here, we investigated diatom diversity and its environmental correlates using 6 yr of monthly surface water samples from the Narragansett Bay Plankton Time Series to investigate the seasonal and annual variability of diatom species occurrence. High‐throughput amplicon sequencing of filtered biomass yielded 658 diatom amplicon sequence variants (ASVs), of which 347 were identified to species. Of the 49 diatom genera in the sequencing dataset, 33% had never been observed in the time series using microscopy (1959–2014). We observed a weak quadratic relationship between ASV richness and chlorophyll‐
- NSF-PAR ID:
- 10158825
- Date Published:
- Journal Name:
- Biology
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2079-7737
- Page Range / eLocation ID:
- 19
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract a concentrations, suggesting that richness decreases during blooms. There was a significant difference in diatom ASV richness by season and we identified distinct assemblages associated with different seasons. These assemblages were remarkably synchronous, exhibiting a sinewave‐like pattern, over 6 yr with an annual periodicity that correlated significantly with seasonal changes in temperature, light, and dissolved inorganic nitrogen. The annual cycle of diatom assemblages suggests stability in a key component of the estuarine food web known to influence ecosystem resilience and function. Deviations from the annual cycle of recurrence could be used to distinguish between changes in community structure driven by annual fluctuations in the environment and those driven by climate‐change stressors. -
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Abstract The interior of Dronning Maud Land (DML) in East Antarctica is one of the most data-sparse regions of Antarctica for studying climate change. A monthly mean near-surface temperature dataset for the last 30 years has been compiled from the historical records from automatic weather stations (AWSs) at three sites in the region (Mizuho, Relay Station, and Dome Fuji). Multiple AWSs have been installed along the route to Dome Fuji since the 1990s, and observations have continued to the present day. The use of passive-ventilated radiation shields for the temperature sensors at the AWSs may have caused a warm bias in the temperature measurements, however, due to insufficient ventilation in the summer, when solar radiation is high and winds are low. In this study, these warm biases are quantified by comparison with temperature measurements with an aspirated shield and subsequently removed using a regression model. Systematic error resulting from changes in the sensor height due to accumulating snow was insignificant in our study area. Several other systematic errors occurring in the early days of the AWS systems were identified and corrected. After the corrections, multiple AWS records were integrated to create a time series for each station. The percentage of missing data over the three decades was 21% for Relay Station and 28% for Dome Fuji. The missing rate at Mizuho was 49%, more than double that at Relay Station. These new records allow for the study of temperature variability and change in DML, where climate change has so far been largely unexplored.
Significance Statement Antarctic climate change has been studied using temperature data at staffed stations. The staffed stations, however, are mainly located on the Antarctic Peninsula and in the coastal regions. Climate change is largely unknown in the Antarctic plateau, particularly in the western sector of the East Antarctic Plateau in areas such as the interior of Dronning Maud Land (DML). To fill the data gap, this study presents a new dataset of monthly mean near-surface climate data using historical observations from three automatic weather stations (AWSs). This dataset allows us to study temperature variability and change over a data-sparse region where climate change has been largely unexplored.
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Abstract Aim Tropical regions harbour over half of the world's mammals and birds, but how their communities have assembled over evolutionary timescales remains unclear. To compare eco‐evolutionary assembly processes between tropical mammals and birds, we tested how hypotheses concerning niche conservatism, environmental stability, environmental heterogeneity and time‐for‐speciation relate to tropical vertebrate community phylogenetic and functional structure.
Location Tropical rainforests worldwide.
Time period Present.
Major taxa studied Ground‐dwelling and ground‐visiting mammals and birds.
Methods We used in situ observations of species identified from systematic camera trap sampling as realized communities from 15 protected tropical rainforests in four tropical regions worldwide. We quantified standardized phylogenetic and functional structure for each community and estimated the multi‐trait phylogenetic signal (PS) in ecological strategies for the four regional species pools of mammals and birds. Using linear regression models, we test three non‐mutually exclusive hypotheses by comparing the relative importance of colonization time, palaeo‐environmental changes in temperature and land cover since 3.3 Mya, contemporary seasonality in temperature and productivity and environmental heterogeneity for predicting community phylogenetic and functional structure.
Results Phylogenetic and functional structure showed non‐significant yet varying tendencies towards clustering or dispersion in all communities. Mammals had stronger multi‐trait PS in ecological strategies than birds (mean PS: mammal = 0.62, bird = 0.43). Distinct dominant processes were identified for mammal and bird communities. For mammals, colonization time and elevation range significantly predicted phylogenetic clustering and functional dispersion tendencies respectively. For birds, elevation range and contemporary temperature seasonality significantly predicted phylogenetic and functional clustering tendencies, respectively, while habitat diversity significantly predicted functional dispersion tendencies.
Main conclusions Our results reveal different eco‐evolutionary assembly processes structuring contemporary tropical mammal and bird communities over evolutionary timescales that have shaped tropical diversity. Our study identified marked differences among taxonomic groups in the relative importance of historical colonization and sensitivity to environmental change.
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Abstract The historical rise of irrigation has profoundly mitigated the effect of drought on agriculture in many parts of the United States. While irrigation directly alters soil moisture, meteorological drought indices ignore the effects of irrigation, since they are often based on simple water balance models that neglect the irrigation input. Reanalyses also largely neglect irrigation. Other approaches estimate the evaporative fraction (EF), which is correlated with soil moisture under water-limited conditions typical of droughts, with lower values corresponding to drier soils. However, those approaches require satellite observations of land surface temperature, meaning they cannot be used to study droughts prior to the satellite era. Here, we use a recent theory of land–atmosphere coupling—surface flux equilibrium (SFE) theory—to estimate EF from readily available observations of near-surface air temperature and specific humidity with long historical records. In contrast to EF estimated from a reanalysis that largely neglects irrigation, the SFE-predicted EF is greater at irrigated sites than at nonirrigated sites during droughts, and its historical trends are typically consistent with the spatial distribution of irrigation growth. Two sites at which SFE-predicted EF unexpectedly rises in the absence of changes in irrigation can be explained by increased flooding due to human interventions unrelated to irrigation (river engineering and the expansion of fish hatcheries). This work introduces a new method for quantifying agricultural drought prior to the satellite era. It can be used to provide insight into the role of irrigation in mitigating drought in the United States over the twentieth century.
Significance Statement Irrigation grew profoundly in the United States over the twentieth century, increasing the resilience of American agriculture to drought. Yet observational records of agricultural drought, and its response to irrigation, are limited to the satellite era. Here, we show that a common measure of agricultural drought (the evaporative fraction, EF) can be estimated using widespread weather data, extending the agricultural drought record decades further back in time. We show that EF estimated using our approach is both sensitive and specific to the occurrence of irrigation, unlike an alternative derived from a reanalysis.
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Abstract Tropical mountains feature marked species turnover along elevational gradients and across complex topography, resulting in great concentrations of avian biodiversity. In these landscapes, particularly among morphologically conserved and difficult to observe avian groups, species limits still require clarification. One such lineage is Scytalopus tapaculos, which are among the morphologically most conserved birds. Attention to their distinctive vocal repertoires and phylogenetic relationships has resulted in a proliferation of newly identified species, many of which are restricted range endemics. Here, we present a revised taxonomy and identify species limits among high-elevation populations of Scytalopus tapaculos inhabiting the Peruvian Andes. We employ an integrated framework using a combination of vocal information, mitochondrial DNA sequences, and appearance, gathered from our own fieldwork over the past 40 yr and supplemented with community-shared birdsong archives and museum specimens. We describe 3 new species endemic to Peru. Within all 3 of these species there is genetic differentiation, which in 2 species is mirrored by subtle geographic plumage and vocal variation. In a fourth species, Scytalopus schulenbergi, we document deep genetic divergence and plumage differences despite overall vocal similarity. We further propose that an extralimital taxon, Scytalopus opacus androstictus, be elevated to species rank, based on a diagnostic vocal character. Our results demonstrate that basic exploration and descriptive work using diverse data sources continues to identify new species of birds, particularly in tropical environs.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/biology9010019
