We propose a hypothesis to explain the very abrupt terminations that end most of the glacial episodes. During the last glaciation, the buildup and southerly expansion of large continental ice-sheets ...in the Northern Hemisphere and extensive cover of sea ice in the N. Pacific and the N. Atlantic imposed a much more zonal climatic circulation system than exists today. We hypothesize that this, in combination with the frigid (dry) polar air led to a significant decrease in freshwater runoff into the Arctic Ocean. In addition the freshwater contribution of the fresher Pacific water was completely eliminated by the emergence of the Bering Strait (sill depth 50 m). As the Arctic freshwater input was depleted, regions of the Arctic Ocean lost surface stability and eventually overturned, bringing warmer deep water to the surface where it melted the overlying sea ice. This upwelled water was quickly cooled and sank as newly formed deep water. For sustained overturn events, such as might have occurred during the peak of very large glacial periods (i.e. the last glacial maximum), the voluminous deep water formed would eventually overflow into the Nordic Seas and North Atlantic necessitating an equally voluminous rate of return flow of warmer surface waters from the North Atlantic thus breaking down the Arctic's zonal isolation, melting the expansive NA sea ice cover and initiating oceanic heating of the atmosphere over the ice-sheets bordering the NA. We suggest that the combined effect of these overturn-induced events in concert with a Milankovitch warming cycle, was sufficient to drive the system to a termination. We elaborate on this proposed sequence of events, using the model for the formation of the Weddell Sea polynya as proposed by Martinson et al. (1981) and various, albeit sparse, data sets from the circum-Arctic region to apply and evaluate this hypothesis to the problem of glacial terminations. PUBLICATION ABSTRACT
An abrupt drowning of the Black Sea shelf Ryan, William B.F.; Pitman, Walter C.; Major, Candace O. ...
Marine geology,
April 1997, 1997-04-00, 19970401, Letnik:
138, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
During latest Quaternary glaciation, the Black Sea became a giant freshwater lake. The surface of this lake drew down to levels more than 100 m below its outlet. When the Mediterranean rose to the ...Bosporus sill at 7,150 yr BP11Unless otherwise noted, all dates reported are raw carbon-14 ages before reservoir corrections (460 yr) and thus are compatible with previously published dates., saltwater poured through this spillway to refill the lake and submerge, catastrophically, more than 100,000 km2 of its exposed continental shelf. The permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of Europe at that time.
Neutral models are often used as null models, testing the relative importance of niche versus neutral processes in shaping diversity. Most versions, however, focus only on regional scale predictions ...and neglect local level contributions. Recently, a new formulation of spatial neutral theory was published showing an incompatibility between regional and local scale fits where especially the number of rare species was dramatically under‐predicted. Using a forward in time semi‐spatially explicit neutral model and a unique large‐scale Amazonian tree inventory data set, we show that neutral theory not only underestimates the number of rare species but also fails in predicting the excessive dominance of species on both regional and local levels. We show that although there are clear relationships between species composition, spatial and environmental distances, there is also a clear differentiation between species able to attain dominance with and without restriction to specific habitats. We conclude therefore that the apparent dominance of these species is real, and that their excessive abundance can be attributed to fitness differences in different ways, a clear violation of the ecological equivalence assumption of neutral theory.
Amazonian forests are the largest and most diverse in the tropics, and much of the mystery surrounding their ecology can be traced to attempts to understand them through tiny local inventories. In ...this paper we bring together a large number of such inventories scattered across immense areas of western Amazonia in order to address simple questions about the distribution and abundance of tropical tree species in lowland terra firme forests there. The goal is to describe patterns of commonness and rarity at local (1 ha), landscape (∼ 104km2), and regional $(>10^6 km^2)$ scales, and to fuse the results into a more complete picture of how tropical tree communities are structured. We present estimates of landscape-scale densities for ∼1400 taxa, based on data from tree plots scattered over large tracts of terra firme forest in eastern Ecuador and southeastern Peru. A database of morphological, ecological, and other traits of >1000 of these species compiled from the taxonomic literature is then used to explore how species that are common in the inventories differ from species that are rare. Although most species show landscape-scale densities of <1 individual/ha, most trees in both forests belong to a small set of ubiquitous common species. These common species combine high frequency with high local abundance, forming predictable oligarchies that dominate several thousand square kilometers of forest at each site. The common species comprising these oligarchies are a nonrandom subset of the two floras. At both sites a disproportionate number of common species are concentrated in the families Arecaceae, Moraceae, Myristicaceae, and Violaceae, and large-statured tree species are more likely to be common than small ones. Nearly a third of the 150 most common tree species in the Ecuadorean forest are also found among the 150 most common tree species in the Peruvian forest. For the 254 tree species shared by the two data sets, abundance in Ecuador is positively and significantly correlated with abundance ∼1400 km away in Peru. These findings challenge popular depictions of Amazonian vegetation as a small-scale mosaic of unpredictable composition and structure. Instead, they provide additional evidence that tropical tree communities are not qualitatively different from their temperate counterparts, where a few common species concentrated in a few higher taxa can dominate immense areas of forest. We hypothesize that most Amazonian forests are dominated at large scales by oligarchies similar in nature to the ones observed in Ecuador and Peru, and we argue that the patterns are more indicative of regulation of relative abundances by ecological factors than of nonequilibrium chance-based dynamics. The paper concludes with a discussion of the practical applications of predictable oligarchies over large areas of unexplored forest.
Research to date on Amazonian swamps has reinforced the impression that tree communities there are dominated by a small, morphologically specialized subset of the regional flora capable of surviving ...physiologically challenging conditions. In this paper, using data from a large‐scale tree inventory in upland, floodplain, and mixed palm swamp forests in Amazonian Ecuador, we report that tree communities growing on well‐drained and saturated soils are more similar than previously appreciated. While our data support the traditional view of Amazonian swamp forests as low‐diversity tree communities dominated by palms, they also reveal four patterns that have not been well documented in the literature to date: 1) tree communities in these swamp forests are dominated by a phylogenetically diverse oligarchy of 30 frequent and common species; 2) swamp specialists account for < 10% of species and a minority of stems; 3) most tree species recorded in swamps (> 80%) also occur in adjacent well‐drained forest types; and 4) many tree species present in swamps are common in well‐drained forests (e.g. upland oligarchs account for 34.1% of all swamp stems). These observations imply that, as in the temperate zone, the composition and structure of Amazonian swamp vegetation are determined by a combination of local‐scale environmental filters (e.g. plant survival in permanently saturated soils) and landscape‐scale patterns and processes (e.g. the composition and structure of tree communities in adjacent non‐swamp habitats, the dispersal of propagules from those habitats to swamps). We conclude with suggestions for further research to quantify the relative contributions of these factors in structuring tree communities in Amazonian swamps.
Background
99m
TcTilmanocept, a novel CD206 receptor-targeted radiopharmaceutical, was evaluated in an open-label, phase III trial to determine the false negative rate (FNR) of sentinel lymph node ...biopsy (SLNB) relative to the pathologic nodal status in patients with intraoral or cutaneous head and neck squamous cell carcinoma (HNSCC) undergoing tumor resection, SLNB, and planned elective neck dissection (END). Negative predictive value (NPV), overall accuracy of SLNB, and the impact of radiopharmaceutical injection timing relative to surgery were assessed.
Methods and Findings
This multicenter, non-randomized, single-arm trial (ClinicalTrials.gov identifier NCT00911326) enrolled 101 patients with T1–T4, N0, and M0 HNSCC. Patients received 50 µg
99m
Tctilmanocept radiolabeled with either 0.5 mCi (same day) or 2.0 mCi (next day), followed by lymphoscintigraphy, SLNB, and END. All excised tissues were evaluated for tissue type and tumor presence.
99m
TcTilmanocept identified one or more SLNs in 81 of 83 patients (97.6 %). Of 39 patients identified with any tumor-positive nodes (SLN or non-SLN), one patient had a single tumor-positive non-SLN in whom all SLNs were tumor-negative, yielding an FNR of 2.56 %; NPV was 97.8 % and overall accuracy was 98.8 %. No significant differences were observed between same-day and next-day procedures.
Conclusions
Use of receptor-targeted
99m
Tctilmanocept for lymphatic mapping allows for a high rate of SLN identification in patients with intraoral and cutaneous HNSCC. SLNB employing
99m
Tctilmanocept accurately predicts the pathologic nodal status of intraoral HNSCC patients with low FNR, high NPV, and high overall accuracy. The use of
99m
Tctilmanocept for SLNB in select patients may be appropriate and may obviate the need to perform more extensive procedures such as END.
Trees of Amazonian Ecuador Andino, Juan Ernesto Guevara; Pitman, Nigel C. A.; Ulloaulloa, Carmen ...
Ecology,
12/2019, Letnik:
100, Številka:
12
Journal Article
Recenzirano
Odprti dostop
We compiled a data set for all tree species collected to date in lowland Amazonian Ecuador in order to determine the number of tree species in the region. This data set has been extensively verified ...by taxonomists and is the most comprehensive attempt to evaluate the tree diversity in one of the richest species regions of the Amazon. We used four main sources of data: mounted specimens deposited in Ecuadorian herbaria only, specimen records of a large‐scale 1‐hectare‐plot network (60 plots in total), data from the Missouri Botanical Garden Tropicos® database (MO), and literature sources. The list of 2,296 tree species names we provide in this data set is based on 47,486 herbarium records deposited in the following herbaria: Alfredo Paredes Herbarium (QAP), Catholic University Herbarium (QCA), Herbario Nacional del Ecuador (QCNE), Missouri Botanical Garden (MO), and records from an extensive sampling of 29,768 individuals with diameter at breast height (dbh) ≥10 cm recorded in our plot network. We also provide data for the relative abundance of species, geographic coordinates of specimens deposited in major herbaria around the world, whether the species is native or endemic, current hypothesis of geographic distribution, representative collections, and IUCN threat category for every species recorded to date in Amazonian Ecuador. These data are described in Metadata S1 and can be used for macroecological, evolutionary, or taxonomic studies. There are no copyright restrictions; data are freely available for noncommercial scientific use (CC BY 3.0). Please see Metadata S1 (Class III, Section B.1: Proprietary restrictions) for additional information on usage.
We inventoried two Amazonian tree communities separated by ~1400 km of continuous lowland tropical forest, in an effort to understand why one was more diverse than the other. Yasuní National Park, ...near the equator in eastern Ecuador, has one of the most diverse tree communities in the world. Manu National Park, at 12° S in Peru's Madre de Dios region, is only moderately diverse by upper Amazonian standards. Following the field inventories, a database of morphological, ecological, and other traits was compiled from the taxonomic literature for 1039 species from the plots. Our goals were (1) to describe how terra firme tree communities at the two sites differed in composition, diversity, and structure; (2) to characterize the "extra" species responsible for the higher diversity at Yasuní and (3) to assess, in the light of those observations, some explanations for why forests near the equator are so diverse. Yasuní has ~1.4 times as many tree species as Manu at all three spatial scales we examined: local (1 ha), landscape (<10 000 km2), and regional (<100000 km2). Yasuní samples contain more families and genera, more individual trees per unit area, and a larger proportion of small trees. Tree species at Yasuní have smaller stature, larger leaves, larger seeds, and smaller geographic and altitudinal ranges than those at Manu, and disproportionate increases in species diversity are observed within the Myrtaceae, Lauraceae, Melastomataceae, and several other families. Community structures were strikingly similar, with the same species (Iriartea deltoidea, a palm) dominating both sites at identical densities. Common species at Yasuní occur at the same densities as equally ranked species at Manu, but there are substantially more very rare species at Yasuní. The poorer tree flora is not a nested subset of the richer tree flora, though a majority of species in each inventory do occur at the other site. Several models that offer explanations for geographic variation in tropical tree species diversity are assessed in light of these data. Most do a poor job of accounting for the patterns revealed by the inventories. We speculate that the most important factor in producing the higher diversity in Yasuní is its rainier, aseasonal climate, and we discuss two specific rainfall-related mechanisms that appear to be supported by the data: (1) year-round water availability allowing more species to persist in the understory at Yasuní and (2) a newly described "mixing effect" related to the higher stem density there.
The Black Sea: A Freshwater Lake? Burkhard, Martin; William B. F. Ryan; Pitman, Walter C.
Science (American Association for the Advancement of Science),
04/1998, Letnik:
280, Številka:
5363
Journal Article
PDF
![[99mTc]Tilmanocept Accurate...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1068-9265_1534-4681/small "[99mTc]Tilmanocept Accurately Detects Sentinel Lymph Nodes and Predicts Node Pathology Status in Patients with Oral Squamous Cell Carcinoma of the Head and Neck: Results of a Phase III Multi-institutional Trial")
