The history of South American tropical precipitation for the past 25,000 years

Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.     

Dissecting amazonian biodiversity

Biogeographical and biodiversity studies in Iowland Amazonian rain forests typically refer to observed or postulated distribution barriers such as past unfavorable climates, mountains, rivers, and river floodplains that divide the uniform tierra firme (noninundated) forest. Present-day ecological heterogeneity within tierra firme has hardly been discussed in this context, although edaphic differences are known to affect species distribution patterns in both inundated areas and tierra firme. Quantification of landscape heterogeneity in Peruvian Iowland Amazonia (500,000 kilometers squared), based on field studies and satellite image analysis, shows that Peruvian Amazonia is considerably more heterogeneous than previously reported. These observations have implications for the research, management, and conservation of Amazonian biodiversity.     

Indigenous worldviews and Western conventions: <Emphasis Type="Italic">Sumak Kawsay</Emphasis> and cocoa production in Ecuadorian Amazonia

This article explores the role of conventions in the normalization of cocoa production in Ecuadorian Amazonia. Convention theory provides key theoretical tools for understanding coordination among agents. However, conventions must be understood as cultural constructions with a strong Eurocentric background that must be substantially modified in originally non-European contexts. A creative application of convention theory can partially overcome bifurcation among Western and non-Western rationalities. First, it shows that Western values and forms of coordination are heterogeneous, conflictive and opposing. Second, it provides key insight for understanding the transformation of subaltern subjectivities generated from non-Western rationalities that are closely associated with subjugated knowledges. Third, in applying the concept of compromise, it allows one to understand cognitive hybridization and coordination among indigenous and Western agents and thus the complexities of processes of resistance, subversion and empowerment carried by indigenous communities. This article is focused on how cocoa production in Ecuadorian Amazonia serves as an example of the confluence and coordination of indigenous (using the concept of “Good Living” or Sumak Kawsay) and Western conventions. The assertion of Sumak Kawsay is understood as a relevant transformation of Ecuadorian post-colonial relations. It is shown that relevant industrial upgrading processes are justified by, among others, Sumak Kawsay repertoires. Additionally, dialogue on knowledge and compromise among conventions, and especially concerning Sumak Kawsay and the market, have been key facets shaping the development of a differentiated quality strand that has promoted relevant changes in the subaltern positioning of indigenous farmers in the cocoa commodity chain.     

Millennial-scale dynamics of southern Amazonian rain forests

Amazonian rain forest-savanna boundaries are highly sensitive to climatic change and may also play an important role in rain forest speciation. However, their dynamics over millennial time scales are poorly understood. Here, we present late Quaternary pollen records from the southern margin of Amazonia, which show that the humid evergreen rain forests of eastern Bolivia have been expanding southward over the past 3000 years and that their present-day limit represents the southernmost extent of Amazonian rain forest over at least the past 50,000 years. This rain forest expansion is attributed to increased seasonal latitudinal migration of the Intertropical Convergence Zone, which can in turn be explained by Milankovitch astronomic forcing.     

Amazonia through time: Andean uplift, climate change, landscape evolution, and biodiversity

The Amazonian rainforest is arguably the most species-rich terrestrial ecosystem in the world, yet the timing of the origin and evolutionary causes of this diversity are a matter of debate. We review the geologic and phylogenetic evidence from Amazonia and compare it with uplift records from the Andes. This uplift and its effect on regional climate fundamentally changed the Amazonian landscape by reconfiguring drainage patterns and creating a vast influx of sediments into the basin. On this "Andean" substrate, a region-wide edaphic mosaic developed that became extremely rich in species, particularly in Western Amazonia. We show that Andean uplift was crucial for the evolution of Amazonian landscapes and ecosystems, and that current biodiversity patterns are rooted deep in the pre-Quaternary.     

The 2010 Amazon drought

In 2010, dry-season rainfall was low across Amazonia, with apparent similarities to the major 2005 drought. We analyzed a decade of satellite-derived rainfall data to compare both events. Standardized anomalies of dry-season rainfall showed that 57% of Amazonia had low rainfall in 2010 as compared with 37% in 2005 (≤-1 standard deviation from long-term mean). By using relationships between drying and forest biomass responses measured for 2005, we predict the impact of the 2010 drought as 2.2 × 10(15) grams of carbon [95% confidence intervals (CIs) are 1.2 and 3.4], largely longer-term committed emissions from drought-induced tree deaths, compared with 1.6 × 10(15) grams of carbon (CIs 0.8 and 2.6) for the 2005 event.     

Sparse pre-Columbian human habitation in western Amazonia

Locally extensive pre-Columbian human occupation and modification occurred in the forests of the central and eastern Amazon Basin, but whether comparable impacts extend westward and into the vast terra firme (interfluvial) zones, remains unclear. We analyzed soils from 55 sites across central and western Amazonia to assess the history of human occupation. Sparse occurrences of charcoal and the lack of phytoliths from agricultural and disturbance species in the soils during pre-Columbian times indicated that human impacts on interfluvial forests were small, infrequent, and highly localized. No human artifacts or modified soils were found at any site surveyed. Riverine bluff areas also appeared less heavily occupied and disturbed than similar settings elsewhere. Our data indicate that human impacts on Amazonian forests were heterogeneous across this vast landscape.     

Amazon deforestation and climate change

A coupled numerical model of the global atmosphere and biosphere has been used to assess the effects of Amazon deforestation on the regional and global climate. When the tropical forests in the model were replaced by degraded grass (pasture), there was a significant increase in surface temperature and a decrease in evapotranspiration and precipitation over Amazonia. In the simulation, the length of the dry season also increased; such an increase could make reestablishment of the tropical forests after massive deforestation particularly difficult.     

The response of vegetation on the Andean flank in western Amazonia to Pleistocene climate change

A reconstruction of past environmental change from Ecuador reveals the response of lower montane forest on the Andean flank in western Amazonia to glacial-interglacial global climate change. Radiometric dating of volcanic ash indicates that deposition occurred ~324,000 to 193,000 years ago during parts of Marine Isotope Stages 9, 7, and 6. Fossil pollen and wood preserved within organic sediments suggest that the composition of the forest altered radically in response to glacial-interglacial climate change. The presence of Podocarpus macrofossils ~1000 meters below the lower limit of their modern distribution indicates a relative cooling of at least 5°C during glacials and persistence of wet conditions. Interglacial deposits contain thermophilic palms suggesting warm and wet climates. Hence, global temperature change can radically alter vegetation communities and biodiversity in this region.     

Climate change, deforestation, and the fate of the Amazon

The forest biome of Amazonia is one of Earth's greatest biological treasures and a major component of the Earth system. This century, it faces the dual threats of deforestation and stress from climate change. Here, we summarize some of the latest findings and thinking on these threats, explore the consequences for the forest ecosystem and its human residents, and outline options for the future of Amazonia. We also discuss the implications of new proposals to finance preservation of Amazonian forests.     

The greenhouse theory of climate change: a test by an inadvertent global experiment

Since the dawn of the industrial era, the atmospheric concentrations of several radiatively active gases have been increasing as a result of human activities. The radiative heating from this inadvertent experiment has driven the climate system out of equilibrium with the incoming solar energy. According to the greenhouse theory of climate change, the climate system will be restored to equilibrium by a warming of the surfacetroposphere system and a cooling of the stratosphere. The predicted changes, during the next few decades, could far exceed natural climate variations in historical times. Hence, the greenhouse theory of climate change has reached the crucial stage of verification. Surface warming as large as that predicted by models would be unprecedented during an interglacial period such as the present. The theory, its scope for verification, and the emerging complexities of the climate feedback mechanisms are discussed.     

Late miocene tidal deposits in the amazonian foreland basin

Late Miocene tidal sediments of Acre, Brazilian Amazonia, were deposited in an embayment or interior seaway located in the sub-Andean zone. This late Tertiary embayment system may once have connected the Caribbean with the South Atlantic. The tidal coasts of the embayment-seaway have provided an avenue for the earliest waif (over water) dispersal phases of the great American biotic interchange in the late Miocene. The subsequent change from semimarine to terrestrial environments is of value in assessing the importance of earlier hypotheses on the evolution of the westem Amazonian landscape and gives insight into the formation of several observed biogeographic patterns, especially of aquatic biota.     

植物与病原菌互作理论研究进展

植物病原菌与其寄主相互作用过程中,关于病原菌操控植物和植物又反抗病原菌侵染的作用机制,学术界存在多种模型和假说,从最早的Flor"基因对基因"假说到警戒假说,再从警戒假说到"诱饵"假说,再到目前学术界较为认同的Zigzag理论。对这些植物与病原菌互作理论进行了总结,着重介绍了"诱饵"假说和Zigzag理论。     

论我国种植业、畜牧业技术进步的测定

在分析广义农业技术进步基本理论的基础上，对四种农业技术进步的测定模型、方法进行比较分析，从中选择出增长速度方程模型是现阶段比较理想的测定种植业和畜牧业技术进步的方法。最后，利用此模型对我国“八五”期间种植业、畜牧业技术进步率进行实际测定。     

会计目的：会计理论体系的起点

】会计理论体系的结构及起点问题,一直是会计界争论的焦点。该文拟就从会计产生和发展的角度,按照逻辑与历史相统一的原则和矛盾发展规律,在分析目标起点论、环境起点论、假设起点论、多元论之不足的基础上,阐述会计理论体系的起点应是会计目的。进而以会计目的为起点,推导出逻辑一贯的、完整的、开放的、动态的、与会计实践紧密相联的理论体系。     

金元中医学史中的“王道”学派探析

中医发展历史中,出现了繁多的学派。而至金元时期,战争病疫绵多。这一时期的医学学派中金元四大家精心研究前人的医学理论文献,且结合各自的临床实践,提出各自的医学理论。其中＂王道＂医学派——李杲、朱震亨的＂补土＂、＂滋阴＂理论的提出,丰富和发展了祖国医学宝库,留下了值得我们思考的医学思想和医学理论。     

Advent and course of pastoralism in the kalahari

It has long been thought that farming and herding were comparatively recent introductions into the Kalahari and that it has been a preserve of foraging "Bushmen" for thousands of years. Agropastoral Bantu-speakers were thought to have entered this region only within the last two centuries. However, fully developed pastoralism and metallurgy are now shown to have been established in the Kalahari from A.D. 500, with extensive grain agriculture and intracontinental trade added by A.D. 800. Archeological, linguistic, and historical evidence delineates the continuation of mixed economies in the region into the present. Consequences of this revised view for anthropological theory and for policy planning concerning contemporary Kalahari peoples are indicated.     

Explaining the abundance of ants in lowland tropical rainforest canopies

The extraordinary abundance of ants in tropical rainforest canopies has led to speculation that numerous arboreal ant taxa feed principally as "herbivores" of plant and insect exudates. Based on nitrogen (N) isotope ratios of plants, known herbivores, arthropod predators, and ants from Amazonia and Borneo, we find that many arboreal ant species obtain little N through predation and scavenging. Microsymbionts of ants and their hemipteran trophobionts might play key roles in the nutrition of taxa specializing on N-poor exudates. For plants, the combined costs of biotic defenses and herbivory by ants and tended Hemiptera are substantial, and forest losses to insect herbivores vastly exceed current estimates.     

Orbital forcing of the marine isotope stage 9 interglacial

Milankovitch orbital forcing theory has been used to assign time scales to many paleoclimate records. However, the validity of this theory remains uncertain, and independent sea-level chronologies used to test its applicability have been restricted largely to the past approximately 135,000 years. Here, we report U-series ages for coral reefs formed on Henderson Island during sea-level high-stands occurring at approximately 630,000 and approximately 330,000 years ago. These data are consistent with the hypothesis that interglacial climates are forced by Northern Hemisphere summer solar insolation centered at 65 degrees N latitude, as predicted by Milankovitch theory.     

A model for plate tectonic evolution of mantle layers

In plate tectonic theory, lithosphere that descends into the mantle has a largely derivative composition, because it is produced as a refractory residue by partial melting, and cannot be resorbed readily by the parent mantle. We suggest that lithosphere sinks through the asthenosphere, or outer mantle, and accumulates progressively beneath to form an accretionary mesosphere, or inner mantle. According to this model, there is an irreversible physicochemical evolution of the mantle and its layers. We make the key assumption that the rate at which mass has been transferred from the lithosphere to the mesosphere is proportional to the rate of radiogenic heat production. Calculations of mass transfer with time demonstrate that the entire mass of the present mesosphere could have been produced in geologically reasonable times (3 x 10(9) to 4.5 x 10(9) years). The model is consistent with the generation of the continental crust during the last 3 x 1O(9) years and predicts an end to plate tectonic behavior within the next 10(9) years.