One sixth of Amazonian tree diversity is dependent on river floodplains

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.

Consistent patterns of common species across tropical tree communities

Trees structure the Earth's most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1-6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth's 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world's most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.

Mapping density, diversity and species-richness of the Amazon tree flora

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution.

More than 10,000 pre-Columbian earthworks are still hidden throughout Amazonia

Indigenous societies are known to have occupied the Amazon basin for more than 12,000 years, but the scale of their influence on Amazonian forests remains uncertain. We report the discovery, using LIDAR (light detection and ranging) information from across the basin, of 24 previously undetected pre-Columbian earthworks beneath the forest canopy. Modeled distribution and abundance of large-scale archaeological sites across Amazonia suggest that between 10,272 and 23,648 sites remain to be discovered and that most will be found in the southwest. We also identified 53 domesticated tree species significantly associated with earthwork occurrence probability, likely suggesting past management practices. Closed-canopy forests across Amazonia are likely to contain thousands of undiscovered archaeological sites around which pre-Columbian societies actively modified forests, a discovery that opens opportunities for better understanding the magnitude of ancient human influence on Amazonia and its current state.

Biased-corrected richness estimates for the Amazonian tree flora

Amazonian forests are extraordinarily diverse, but the estimated species richness is very much debated. Here, we apply an ensemble of parametric estimators and a novel technique that includes conspecific spatial aggregation to an extended database of forest plots with up-to-date taxonomy. We show that the species abundance distribution of Amazonia is best approximated by a logseries with aggregated individuals, where aggregation increases with rarity. By averaging several methods to estimate total richness, we confirm that over 15,000 tree species are expected to occur in Amazonia. We also show that using ten times the number of plots would result in an increase to just ~50% of those 15,000 estimated species. To get a more complete sample of all tree species, rigorous field campaigns may be needed but the number of trees in Amazonia will remain an estimate for years to come.

Rarity of monodominance in hyperdiverse Amazonian forests

Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such “monodominant” forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.

Species Distribution Modelling: Contrasting presence-only models with plot abundance data

Species distribution models (SDMs) are widely used in ecology and conservation. Presence-only SDMs such as MaxEnt frequently use natural history collections (NHCs) as occurrence data, given their huge numbers and accessibility. NHCs are often spatially biased which may generate inaccuracies in SDMs. Here, we test how the distribution of NHCs and MaxEnt predictions relates to a spatial abundance model, based on a large plot dataset for Amazonian tree species, using inverse distance weighting (IDW). We also propose a new pipeline to deal with inconsistencies in NHCs and to limit the area of occupancy of the species. We found a significant but weak positive relationship between the distribution of NHCs and IDW for 66% of the species. The relationship between SDMs and IDW was also significant but weakly positive for 95% of the species, and sensitivity for both analyses was high. Furthermore, the pipeline removed half of the NHCs records. Presence-only SDM applications should consider this limitation, especially for large biodiversity assessments projects, when they are automatically generated without subsequent checking. Our pipeline provides a conservative estimate of a species’ area of occupancy, within an area slightly larger than its extent of occurrence, compatible to e.g. IUCN red list assessments.

Estimating the global conservation status of more than 15,000 Amazonian tree species

Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict that most of the world's >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century.

Hyperdominance in the Amazonian tree flora

The vast extent of the Amazon Basin has historically restricted the study of its tree communities to the local and regional scales. Here, we provide empirical data on the commonness, rarity, and richness of lowland tree species across the entire Amazon Basin and Guiana Shield (Amazonia), collected in 1170 tree plots in all major forest types. Extrapolations suggest that Amazonia harbors roughly 16,000 tree species, of which just 227 (1.4%) account for half of all trees. Most of these are habitat specialists and only dominant in one or two regions of the basin. We discuss some implications of the finding that a small group of species--less diverse than the North American tree flora--accounts for half of the world's most diverse tree community.

Changes in structure and composition of evergreen forests on an altitudinal gradient in the Venezuelan Guayana shield

There have been several ecological studies in forests of the Guayana Shield, but so far none had examined the changes in structure and composition of evergreen forests with altitude. This study describes and analyzes the structure, species composition and soil characteristics of forest stands at different altitudinal zones in Southeastern Venezuelan Guayana, in order to explain the patterns and the main factors that determine the structure and composition of evergreen forests along the altitudinal gradient. Inventories of 3 948 big (>10cm DBH) and 1 328 small (5-10cm DBH) woody stems were carried out in eleven plots, ranging from 0.1 to 1.0ha, along a 188km long transect with elevations between 290 and 1 395masl. It has been found that 1) hemiepihytes become more dominant and lianas reduce their dominance with increasing altitude and 2) the forest structure in the study area is size-dependent. Five families and 12 genera represented only 9% of the total number of families and genera, respectively, recorded troughout the gradient, but the two groups of taxa comprised more than 50% of the Importance Value (the sum of the relative density and the relative dominance) of all measured stems. Moreover, the results suggest that low species richness seems to be associated with the dominance of one or few species. Stand-level wood density (WD) of trees decreased significantly with increasing elevation. WD is an indicator of trees'life history strategy. Its decline suggests a change in the functional composition of the forest with increasing altitude. The Canonical Correspondence Analysis (CCA) indicated a distinction of the studied forests on the basis of their altitudinal levels and geographic location, and revealed different ecological responses by the forests, to environmental variables along the altitudinal gradient. The variation in species composition, in terms of basal area among stands, was controlled primarily by elevation and secondarily by rainfall and soil conditions. There are other interacting factors not considered in this study like disturbance regime, biological interactions, productivity, and dispersal history, which could affect the structure and composition of the forests in the altitudinal gradient. In conclusion, it appears that the structural and floristic variability observed in the studied transect is produced by a combination of different climates and randomly expressed local processes interacting across a complex physical landscape.

Continental-scale patterns of canopy tree composition and function across Amazonia

The world's greatest terrestrial stores of biodiversity and carbon are found in the forests of northern South America, where large-scale biogeographic patterns and processes have recently begun to be described. Seven of the nine countries with territory in the Amazon basin and the Guiana shield have carried out large-scale forest inventories, but such massive data sets have been little exploited by tropical plant ecologists. Although forest inventories often lack the species-level identifications favoured by tropical plant ecologists, their consistency of measurement and vast spatial coverage make them ideally suited for numerical analyses at large scales, and a valuable resource to describe the still poorly understood spatial variation of biomass, diversity, community composition and forest functioning across the South American tropics. Here we show, by using the seven forest inventories complemented with trait and inventory data collected elsewhere, two dominant gradients in tree composition and function across the Amazon, one paralleling a major gradient in soil fertility and the other paralleling a gradient in dry season length. The data set also indicates that the dominance of Fabaceae in the Guiana shield is not necessarily the result of root adaptations to poor soils (nodulation or ectomycorrhizal associations) but perhaps also the result of their remarkably high seed mass there as a potential adaptation to low rates of disturbance.

Successfully establishing laparoscopic surgery programs in developing countries. Clinical results and lessons learned

BACKGROUND

Laparoscopic surgery has not been widely established in developing countries due to the lack of access to training and lack of money. We describe our experience using on-site training programs to efficiently teach and propagate laparoscopic surgery in Leon, Nicaragua; La Paz, Bolivia; and Santa Cruz, Bolivia.

METHODS

A group of well-trained and motivated local surgeons was identified in each country as the initial target for teaching. Participants were taught basic and advanced laparoscopic surgery during on-site didactics, animal laboratories, and proctoring sessions. Follow-up courses were held until the target group of surgeons was capable of independently teaching and supervising laparoscopic surgery among other surgeons in each country.

RESULTS

Multiple technical and logistic difficulties were encountered. In Leon, Nicaragua, and La Paz, Bolivia, a total of eight surgeons were fully trained and proctored in laparoscopic cholecystectomy. In La Paz and Santa Cruz, Bolivia, a total of seven surgeons were instructed in advanced laparoscopic procedures. To date, over 180 patients have undergone laparoscopic cholecystectomy or advanced procedures with a morbidity similar to that reported in literature series in the United States.

CONCLUSIONS

Our experience demonstrates that in spite of numerous limitations, basic and laparoscopic surgery can be efficiently and safely taught in developing countries. Many lessons were learned in how to safely and efficiently use laparoscopic equipment and instruments within strict financial constraints.

Operative enteroscopy. A useful tool in the evaluation and intervention of bilioenteric anastomoses

Roux-en-Y hepaticojejunostomy is the procedure of choice in the management of patients with major bile duct injuries. In instances of anastomotic stricture, this anastomosis is inaccessible to conventional endoscopy. A technique is described for assessment and intervention of bilioenteric anastomoses that escape the reach of conventional endoscopy. Three cases are presented illustrating the feasibility of open and laparoscopic-assisted small-bowel endoscopy. All patients presented with recurrent cholangitis and had multiple interventions in their biliary tree prior to referral. At operation, the limb of jejunum going to the bilioenteric anastomosis was identified, an enterotomy was made, and a flexible endoscope was passed to evaluate the anastomosis. In two cases the anastomosis was revised by endoscopically excising scar tissue. In the third case the anastomosis was patent and unnecessary intervention was avoided. There was no morbidity or mortality and the patients had complete resolution of their symptoms. Operative endoscopy appears to be useful in the evaluation and intervention of bilioenteric anastomoses that cannot be evaluated by conventional endoscopy.

Sigmoid volvulus in the high altitude of the Andes. Review of 230 cases

Sigmoid volvulus (SV) is uncommon in the United States. Little has been published in the English literature about the high incidence of SV among rural areas of the Bolivian and Peruvian Andes at 13,000 feet above sea level. A review of 230 cases of SV in a Bolivian hospital is presented. SV accounted for 79 percent of all intestinal obstructions. Nonoperative reduction was attempted in all patients except those with peritonitis. Nonoperative reduction alone was performed in 31 percent of the patients, and 69 percent underwent surgical intervention, 66 percent as an emergency and 3 percent electively. Surgical treatment consisted of sigmoidectomy and primary anastomosis (50 percent), Hartmann's procedure (12 percent), and operative detorsion with sigmoid plication (38 percent). Overall mortality was 13.5 percent. Fifty-seven of the surgically treated patients developed significant complications. The etiology of SV is unclear. High altitude, along with other etiologic factors, may play an important role in SV. To our knowledge, this series represents the highest incidence of SV in bowel obstruction.

Heparin effect on plasma fibrinogen in the thrombophilic syndrome

The effects of heparin were studied in a group of 42 patients with preinfarction angina (PA) and acute myocardial infarction (AMI) whose plasma fibrinogen was increased. Plasma fibrinogen was measured by the turbidimetric method in timol turbidimetric units. Statistically significant results proved that heparin reduces the plasma fibrinogen progressively over a treatment period of 6 weeks. During the first three weeks a dose of 1 cc (50 mg or 5000 IU) was given by intravenous injection at 6-h intervals, this was followed by a dose of 2 cc (100 mg or 10,000 IU) given by subcutaneous injection at 12-h intervals for a further three weeks. Hyperfibrinogenemia is perhaps one of the most important factors in the thrombophilic syndrome, and at the same time it is one of the fundamental physiopathological alterations observed in AMI and PA. Because heparin reduces hyperfibrinogenemia it has a beneficial effect in these diseases.

Use of flecainide acetate in the treatment of premature ventricular contractions

Flecainide acetate, a new benzamide antiarrhythmic agent, was studied after single-dose intravenous administration to 35 male and female patients with nonlife-threatening premature ventricular contractions (PVCs). Prior Holter monitoring established that each patient had "stable" PVCs of at least 600/12 hr. PCV in 80% of the patients was attributed to underlying coronary heart disease and/or Chagas' disease. After bolus injections of flecainide acetate, cardiac rhythm was again monitored by Holter ECG recording for 24 hours. All patients had 100% suppression of PVCs, ranging from 60 to 1440 minutes in duration. The average duration of suppression for all patients was more than 8 hours (498 minutes). Follow-up at 6, 12, 18, and 24 hours showed statistically significant PVC reductions (p less than 0.01) when compared with control rates. Side effects were trivial. The extended half-life of this new agent (about 20 hours in cardiac patients) may allow a convenient twice-daily dosage schedule.

Heparin effect on blood viscosity

The effect of heparin on blood viscosity was investigated in a group of patients with acute myocardial infarction (AMI) and preinfarction angina (PA), whose blood viscosity was elevated. Viscosity was measured with Cannon, Fenske, and Routine viscometers. Kinematic viscosity, bath and whole blood, plasma, and serum viscosity were determined as well as dependent parameters (fibrinogen, serum proteins, number of platelets, and hematocrit). All of them were found to increase, and it was significantly proved that intravenous heparin immediately decreased plasma viscosity, but has a lesser effect on serum and whole blood viscosity. A dose of 1 cc = 50 mg = 5000 IU intravenous heparin, will maintain this decrease for a month. In our four-week-study, 1 cc i.v. heparin was administered at 6-hour intervals for the first 2 weeks, and 2 cc heparin subcutaneous injections were administered at 12-hour intervals for the next 2 weeks. We found that heparin also decreased fibrinogen, hematocrit, serum alpha 2 globulin, and number of platelets. Hyperviscosity, hypercoagulability, and the increase of platelet adhesiveness arae some of the most important physiopathological alterations of AMI and PA. The decrease of blood viscosity due to heparin is one of the most important and beneficial effects of it in this pathology.