New palaeoecological evidence for the potential role of fire in the Gran Sabana, Venezuelan Guayana, and implications for early human occupation

The neotropical Gran Sabana region of Venezuela is dominated by apparently anomalous vegetation types, treeless savannas and savanna-forest mosaics, considering the present-day warm and wet bioclimatic conditions. Past climatic changes and fire have been proposed as the more probable causes. Recent palynological studies show that savanna vegetation has been present since the beginning of the Holocene, but the earliest fires recorded so far only go back to 3,800 cal years b.p. This paper uses pollen and charcoal analyses to show the existence of early Holocene regional fires in the Gran Sabana, and to show the intimate connection between the proxies for fire (charcoal) and savanna vegetation (pollen) throughout the Holocene. Although the cause of such fires is not yet known, the possibility of early Holocene human occupation of the Gran Sabana is suggested.     

Unexpected biodiversity loss under global warming in the neotropical Guayana Highlands: a preliminary appraisal

The fully vegetated summits of the table mountains that form the Guayana Highlands (GH), in northern South America, hold amazing biodiversity and endemism levels, and unique vegetation types. In spite of their present‐day healthy appearance, their biota is seriously threatened of habitat loss by upward displacement, because of the projected warming for the end of this century. Available data are still insufficient for a definite assessment, but preliminary estimations based on representative endemic vascular plant species show that roughly one‐tenth to one‐third of them would loss their habitat with the 2–4°C temperature increase predicted for the region by AD 2100. Given the underlying endemism, the eventual loss of biodiversity will be of global nature. Other mountain ranges around the world with similar characteristics of the GH, namely topographical isolation, high endemism and absence of nival stage because of the lower altitude, would be under similar unexpected risk, and should be urgently considered for conservation purposes.     

Mammalian responses to Middle Holocene climatic change in the Great Basin of the western United States

In spite of decades of intense research directed toward understanding the climates and ecology of the Great Basin (western United States) during the past 10,000 years, the responses of mammals to the extreme aridity of the Middle Holocene (c. 8000–5000 years ago) in this region have been poorly understood. Using a well‐dated small mammal sequence from Homestead Cave, north‐central Utah, I show that the Middle Holocene small mammal faunas of this area underwent a decrease in species richness and evenness, driven largely by a series of local extinctions and near‐extinctions coupled with a dramatic increase in the abundance of taxa well‐adapted to xeric conditions. At the end of this period, some taxa that require relatively mesic habitats began to increase in abundance immediately, others did not rebound in abundance until several thousand years later, while still others have not returned at all. This suite of responses has been difficult to detect because climatic change at the beginning of the Middle Holocene was so much more substantial than that which occurred toward its end.     

Ocean cleaning stations under a changing climate: biological responses of tropical and temperate fish‐cleaner shrimp to global warming

Cleaning symbioses play an important role in the health of certain coastal marine communities. These interspecific associations often occur at specific sites (cleaning stations) where a cleaner organism (commonly a fish or shrimp) removes ectoparasites/damaged tissue from a ‘client’ (a larger cooperating fish). At present, the potential impact of climate change on the fitness of cleaner organisms remains unknown. This study investigated the physiological and biochemical responses of tropical (Lysmata amboinensis) and temperate (L. seticaudata) cleaner shrimp to global warming. Specifically, thermal limits (CTMax), metabolic rates, thermal sensitivity, heat shock response (HSR), lipid peroxidation [malondialdehyde (MDA) concentration], lactate levels, antioxidant (GST, SOD and catalase) and digestive enzyme activities (trypsin and alkaline phosphatase) at current and warming (+3 °C) temperature conditions. In contrast to the temperate species, CTMax values decreased significantly from current (24–27 °C) to warming temperature conditions (30 °C) for the tropical shrimp, where metabolic thermal sensitivity was affected and the HSR was significantly reduced. MDA levels in tropical shrimp increased dramatically, indicating extreme cellular lipid peroxidation, which was not observed in the temperate shrimp. Lactate levels, GST and SOD activities were significantly enhanced within the muscle tissue of the tropical species. Digestive enzyme activities in the hepatopancreas of both species were significantly decreased by warmer temperatures. Our data suggest that the tropical cleaner shrimp will be more vulnerable to global warming than the temperate Lysmata seticaudata; the latter evolved in a relatively unstable environment with seasonal thermal variations that may have conferred greater adaptive plasticity. Thus, tropical cleaning symbioses may be challenged at a greater degree by warming‐related anthropogenic forcing, with potential cascading effects on the health and structuring of tropical coastal communities (e.g. coral reefs).     

An evaluation of the Lost World and Vertical Displacement hypotheses in the Chimantá Massif, Venezuelan Guayana

Aim To document the occurrence of vertical displacements of vegetation in the high plateaus of the Venezuelan Guayana (tepuis) over the last c. 6000 years, and to discuss their significance for the origin of their flora, especially the endemism patterns observed in their flat summits. Two hypotheses have been proposed for the origin of the summit flora. One (the Lost World hypothesis) proposes a long history of evolution in isolation from the surrounding plains, while the other (the Vertical Displacement hypothesis) suggests that vertical movements of vegetation during the Pleistocene glacial‐interglacial cycles would have resulted in floristic mixing within the lowlands, and genetic interchange among plateau summits. Location This work has been conducted on the flat summit of the Churí‐tepui, in the Chimantá massif, at 5°15′ Lat. N and 62°01′ Long. W, around 2250 m altitude. Methods Pollen analysis and radiocarbon dating of two peat outcrops, using modern analogue technique and numerical methods for palaeoecological interpretation were used. Results The replacement of a high‐altitude plant community (a paramoid Chimantaea shrubland) by a lower elevation (< 2300 m) Stegolepis meadow, occurred about 2500 years before present (yr bp ). This vegetation change is inferred to have resulted from a regional climatic shift to higher temperature and moisture. A subsequent decrease in temperature and moisture led to the establishment of present conditions after about 1450 yr bp . Main conclusions The highland vegetation of the tepuis responded to climate shifts with vertical displacements, supporting the hypothesis of vertical mixing. However, a physiographical analysis shows that around half of the tepuis would never have been connected by lowlands. Therefore, both hypotheses are needed to explain the origins of the summit flora in the tepuis.     

Temperature dependence of stream benthic respiration in an Alpine river network under global warming

1. Global warming has increased the mean surface temperature of the Earth by 0.6 °C in the past century, and temperature is probably to increase by an additional 3 °C by 2100. Water temperature has also increased, which in turn can affect metabolic rate in rivers. Such an increase in metabolic rate could alter the role of river networks in the global C cycle, because the fraction of allochthonous organic C that is respired may increase. 2. Laboratory‐based incubations at increasing water temperature were used to estimate the temperature dependence of benthic respiration in streams. These experiments were performed on stones taken from seven reaches with different thermal conditions (mean temperature ranging 8–19 °C) within the pre‐alpine Thur River network in Switzerland, June–October 2007. 3. The activation energy of respiration in different reaches along the river network (0.53 ± 0.12 eV, n = 94) was similar, indicating that respiration was constrained by the activation energy of the respiratory complex (E = 0.62 eV). Water temperature and the thickness of the benthic biofilm influence the temperature dependence of respiration and our results suggest that an increase of 2.5 °C will increase river respiration by an average of 20 ± 1.6%.     

长江口拟长脚数量变化和对环境变暖的响应

据1959年和2002年在长江口29°00′～32°00′ N, 122°00′～123°30′ E海域四季调查资料,研究结合拟长脚丰度和同步水温资料进行曲线拟合、构造数学模型和计算最适温度.分析拟长脚(Parathemisto gaudichaudi)的生态类型、空间分布、数量动态以及对变暖趋势的响应.结果表明:长江口海域拟长脚平均丰度和出现率都表现为夏秋季较低和冬春季较高.1959年春季平均丰度最高,为1.8 ind/m3;1959年秋季平均丰度最低,为0.03 ind/m3.1959年春季出现率最高,为62.96%;1959年秋季出现率最低,为6.90%.长江口拟长脚在1959年春季丛生指标最大(7.12),在1959年秋季最小(-1.00).这说明该种春季在长江口海域有明显的集群性,秋季集群性则不明显.温度是影响拟长脚季节变化和年间变化的主要因素.长江口海域拟长脚丰度和同步温度资料曲线拟合结果符合Yield Density模型,最适温度是17.0 ℃,置信度分析和拟合统计结果均有非常高的置信度.综合拟长脚最适温度和季节变化特征,可认为该种是暖温种.近年来在春季长江口水域的拟长脚丰度有所降低,这种数量年间变化趋势应与全球气候变暖相关.该种可作为海洋变暖长期变化的指示种.     

Impact of global warming on the tree species composition of boreal forests in Finland and effects on emissions of isoprenoids

This study aims to identify how climate change may influence total emissions of monoterpene and isoprene from boreal forest canopies. The whole of Finland is assumed to experience an annual mean temperature (T) increase of 4 °C and a precipitation increase of 10% by the year 2100. This will increase forest resources throughout the country. At the same time, the proportions of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) in southern Finland (60°≤ latitude < 65°N) will be reduced from the current 40–50% to less than 10–20%, with increased dominance of birches (Betula pendula and Betula pubescens). In northern Finland (65°≤ latitude < 70°N), the proportions of Norway spruce and Scots pine will be balanced at a level of about 40% as the result of an increase in Norway spruce from the current 21% to 37% and a concurrent reduction in Scots pine from 63% to 40%. The proportion of birches is predicted to increase from the current 17% to 23%, but these will become the dominant species only on the most fertile sites. Total mean emissions of monoterpene by Scots pine will be reduced by 80% in southern Finland, but will increase by 62% in the north. Emissions from Norway spruce canopies will increase by 4% in the south but by 428% in the north, while those from birch canopies will increase by about 300% and 113%, respectively. Overall emissions of monoterpene over the whole country amount to about 950 kg km^?2 y^?1 under current temperature conditions and will increase by 17% to 1100 kg km^?2 y^?1 with elevated temperature and precipitation, mainly because of an increase at northern latitudes. Under current conditions, emissions of isoprene follow the spatial distribution of spruce canopies (the only isoprene‐emitting tree species that forms forests in Finland) with four times higher emissions in the south than in the north. The elevated temperature and the changes in the areal distribution of Norway spruce will result in increases in isoprene emissions of about 37% in southern Finland and 435% in northern Finland. Annual mean isoprene emissions from Norway spruce canopies over the whole country will increase by about 60% up to the year 2100.     

长江口强壮箭虫和肥胖箭虫的丰度变化对环境变暖的响应

根据1959年和2002年在长江口28°00′～32°00′N,122°00′～123°30′E海域4个季节8个航次海洋调查资料,分析强壮箭虫(Sagitta crassa)和肥胖箭虫(Sagitta enflata)丰度的平面分布和季节变化特征,并结合同步的温度资料分析不同生态类群的强壮箭虫和肥胖箭虫对环境变暖的响应.结果表明:长江口水域春、夏、秋3季强壮箭虫平均丰度均小于1.00 ind/m3,出现率低,无集群性.1959年冬季平均丰度达3.24 ind/m3,出现率较高,有明显的集群性,而2002年冬季平均丰度锐减为0.001 ind/m3,几无分布.肥胖箭虫夏季平均丰度、出现率和集聚强度明显高于其它季节.2002年夏季平均丰度达16.06 ind/m3,较1959年增加3.71 ind/m3,且分布区明显扩大.可见,暖温种强壮箭虫和暖水种肥胖箭虫对长江口海域变暖的响应不同,可作为长江口海洋变暖长期变化的重要指示种.     

全球气候变暖对“植物-害虫-天敌”互作系统的影响

全球气候变化是近来人类关注的焦点问题,其最显著的特征是气候变暖。因为昆虫具有生活周期短、繁殖率高等特点,所以,气候变暖对昆虫的发育、繁殖和存活会产生强烈的直接影响。气候变暖促使一些昆虫提前春天的物候现象,向高纬度或高海拔地区迁移。然而,昆虫在自然界并非孤立地存在,它们与寄主植物和自然天敌相互联系、相互作用,并在长期的进化过程中逐渐适应特定区域的气候条件。因此,全球气候变暖对"植物-害虫-天敌"的种间关系必然产生直接或间接的影响,导致不同昆虫之间以及昆虫与其相关营养层的物种之间的相互关系在气候变化下呈现出时间上的异步性和空间上的错位,从而影响植物的适应性和抗虫性、害虫的发生规律和危害程度以及天敌的种群消长和控害效能。昆虫除了可以通过休眠或滞育的方式在时间上避开高温的影响外,还可以通过迁飞或移动的方式在空间上避开高温的影响,在这种迁移和扩散不同步的情况下可能使害虫食性和取食植物的害虫及其天敌的种类发生变化,从而改变生物群落的组成与结构,影响生态系统的服务和功能。     

Potential response of dark carbon fixation to global warming in estuarine and coastal waters

Dark carbon fixation (DCF), through which chemoautotrophs convert inorganic carbon to organic carbon, is recognized as a vital process of global carbon biogeochemical cycle. However, little is known about the response of DCF processes in estuarine and coastal waters to global warming. Using radiocarbon labelling method, the effects of temperature on the activity of chemoautotrophs were investigated in benthic water of the Yangtze estuarine and coastal areas. A dome-shaped thermal response pattern was observed for DCF rates (i.e., reduced rates at lower or higher temperatures), with the optimum temperature (T_opt) varying from about 21.9 to 32.0°C. Offshore sites showed lower T_opt values and were more vulnerable to global warming compared with nearshore sites. Based on temperature seasonality of the study area, it was estimated that warming would accelerate DCF rate in winter and spring but inhibit DCF activity in summer and fall. However, at an annual scale, warming showed an overall promoting effect on DCF rates. Metagenomic analysis revealed that the dominant chemoautotrophic carbon fixation pathways in the nearshore area were Calvin-Benson-Bassham (CBB) cycle, while the offshore sites were co-dominated by CBB and 3-hydroxypropionate/4-hydroxybutyrate cycles, which may explain the differential temperature response of DCF along the estuarine and coastal gradients. Our findings highlight the importance of incorporating DCF thermal response into biogeochemical models to accurately estimate the carbon sink potential of estuarine and coastal ecosystems in the context of global warming.     

Radiation and speciation of pelagic organisms during periods of global warming: the case of the common minke whale, Balaenoptera acutorostrata

How do populations of highly mobile species inhabiting open environments become reproductively isolated and evolve into new species? We test the hypothesis that elevated ocean‐surface temperatures can facilitate allopatry among pelagic populations and thus promote speciation. Oceanographic modelling has shown that increasing surface temperatures cause localization and reduction of upwelling, leading to fragmentation of feeding areas critical to pelagic species. We test our hypothesis by genetic analyses of populations of two closely related baleen whales, the Antarctic minke whale (Balaenoptera bonaerensis) and common minke whale (Balaenoptera acutorostrata) whose current distributions and migration patterns extent are largely determined by areas of consistent upwelling with high primary production. Phylogeographic and population genetic analyses of mitochondrial DNA control‐region nucleotide sequences collected from 467 whales sampled in four different ocean basins were employed to infer the evolutionary relationship among populations of B. acutorostrata by rooting an intraspecific phylogeny with a population of B. bonaerensis. Our findings suggest that the two species diverged in the Southern Hemisphere less than 5 million years ago (Ma). This estimate places the speciation event during a period of extended global warming in the Pliocene. We propose that elevated ocean temperatures in the period facilitated allopatric speciation by disrupting the continuous belt of upwelling maintained by the Antarctic Circumpolar Current. Our analyses revealed that the current populations of B. acutorostrata likely diverged after the Pliocene some 1.5 Ma when global temperatures had decreased and presumably coinciding with the re‐establishment of the polar–equatorial temperature gradient that ultimately drives upwelling. In most population samples, we detected genetic signatures of exponential population expansions, consistent with the notion of increasing carrying capacity after the Pliocene. Our hypothesis that prolonged periods of global warming facilitate speciation in pelagic marine species that depend on upwelling should be tested by comparative analyses in other pelagic species.     

地膜覆盖和施氮量对旱作春玉米农田净温室效应的影响

以旱作雨养条件下的春玉米为试验对象,在长武黄土高原农业生态试验站进行田间试验,研究了地膜覆盖和施氮量对农田净温室效应和温室气体排放强度的影响.结果表明:采用地膜覆盖与增加施氮量都会影响净温室效应与温室气体排放强度,地膜覆盖条件下(FM),不同施氮量的春玉米产量为1643~16699 kg·hm-2,净温室效应(CO_2当量,下同)为595~4376 kg·hm^-2·a^-1,温室气体排放强度为213~358 kg·t^-1;无覆膜条件下(UM),不同施氮量的春玉米产量为956~8821 kg·hm-2,净温室效应为342~4004 kg·hm^-2·a^-1,温室气体排放强度为204~520 kg·t^-1.研究表明,对于旱作春玉米农田系统,地膜覆盖可以有效降低温室气体排放强度,增加作物产量,地膜覆盖下施氮250 kg·hm-2可以实现高产与降低环境代价的双赢.     

Possible impact of global warming on cabbage root fly (Delia radicum) activity in the UK

A program for simulating the patterns of egg-laying by populations of the cabbage root fly was used to model the effects of global warming on future cabbage root fly attacks. An increase of 3°C in mean daily temperature would cause the cabbage root fly to become active about a month earlier in the year than at present. Under such conditions, the emergence of flies from the overwintering population would be less synchronised, as the completion of diapause and post-diapause development would occur at the same time in different individuals within the population. However, there would continue to be only three generations of fly each year, even in the south of England. With temperature increases of 5°C or 10°C, the fly would complete four generations each year and aestivation would seriously disrupt egg-laying. These rises in temperature would have a major impact on cabbage root fly activity and would require new strategies for controlling this pest.     

Advances in understanding the impacts of global warming on marine fishes farmed offshore: Sparus aurata as a case study

Monitoring variations in proteins involved in metabolic processes, oxidative stress responses, cell signalling and protein homeostasis is a powerful tool for developing hypotheses of how environmental variations affect marine organisms' physiology and biology. According to the oxygen- and capacity-limited thermal tolerance hypothesis, thermal acclimation mechanisms such as adjusting the activities of enzymes of intermediary metabolism and of antioxidant defence mechanisms, inducing heat shock proteins (Hsps) or activating mitogen-activated protein kinases may all shift tolerance windows. Few studies have, however, investigated the molecular, biochemical and organismal responses by fishes to seasonal temperature variations in the field to link these to laboratory findings. Investigation of the impacts of global warming on fishes farmed offsore, in the open sea, can provide a stepping stone towards understanding effects on wild populations because they experience similar environmental fluctuations. Over the last 30 years, farming of the gilthead sea bream Sparus aurata (Linnaeus 1758) has become widespread along the Mediterranean coastline, rendering this species a useful case study. Based on available information, the prevailing seasonal temperature variations expose the species to the upper and lower limits of its thermal range. Evidence for this includes oxygen restriction, reduced feeding, reduced responsiveness to environmental stimuli, plus a range of molecular and biochemical indicators that change across the thermal range. Additionally, close relationships between biochemical pathways and seasonal patterns of metabolism indicate a connection between energy demand and metabolic processes on the one hand, and cellular stress responses such as oxidative stress, inflammation and autophagy on the other. Understanding physiological responses to temperature fluctuations in fishes farmed offshore can provide crucial background information for the conservation and successful management of aquaculture resources in the face of global change.     

复合稻田生态系统温室气体交换及其综合增温潜势

研究稻田CO2、CH4、N2O等温室气体的综合增温潜势,有助于科学评价复合稻田生态系统在减少温室气体排放和减缓全球变暖方面的作用,为稻鸭、稻鱼复合种养模式的发展提供依据。2006年采用静态箱法研究了养鸭稻田（RD）、养鱼稻田（RF）和常规淹水稻田（CK）的CH4、N2O的排放量。水稻整个生育期间,RD、CK和RF的CH4排放量分别是19.11、26.71g/m^2和25.01g/m^2;N2O排放量分别是0.237、0.229、0.237g/m^2。采用干物质积累法测得,水稻整个生长期内RD处理地上稻株对CO2的净固定量为2766.4g/m2,RF为2759.59g/m^2,CK为2533.9g/m^2。采用土壤有机碳库的变化估算土壤CO2净交换通量,水稻整个生育期间,三类稻田土壤亚系统均表现为对CO2的净固定,相当于固定CO2量分别为RD675.55g/m^2、CK575.43g/m^2、RF562.62g/m^2。三类稻田温室气体的交换均表现为CO2的净吸收、CH4、N2O的净排放,综合增温潜势以RD为最低。稻田养鸭能显著减少甲烷排放,降低增温潜势,其减缓综合温室效应的潜力是常规淹水稻田的1.6倍左右。     

Changes in chromosomal polymorphism and global warming: The case of Drosophila subobscura from Apatin (Serbia)

In this study, chromosomal inversion polymorphism data for a natural population of Drosophila subobscura from a swampy region near the town of Apatin (Serbia) were compared with data for the same population collected approximately 15 years earlier. The pattern of chromosomal inversion polymorphism changed over time. There were significant increases in the frequency of characteristic southern latitude ("warm" adapted) chromosomal arrangements and significant decreases in the frequency of characteristic northern latitude ("cold" adapted) chromosomal arrangements in the O and U chromosomes. The chromosomal arrangements O(3+4) and O(3+4) (+) (22) (derived from the O(3+4) arrangement) showed significant increases in 2008 and 2009 with regard to the 1994 sample. There was also a significant increase (～50%) in the U(1) (+) (2) arrangement, while U(1+8) (+) (2) (a typical southern arrangement) was detected for the first time. Since the Apatin swampy population of D. subobscura has existed for a long time in a stable habitat with high humidity that has not been changed by man our results indicate that natural selection has produced chromosomal changes in response to the increase in temperature that has occurred in the Balkan Peninsula of central southeastern European.     

Predicted range expansion of the invasive fire ant, Solenopsis invicta, in the eastern United States based on the VEMAP global warming scenario

The red imported fire ant, Solenopsis invicta Buren, is an invasive pest from South America that currently occupies much of the south‐eastern USA. Global warming is likely to allow range expansion of many invasive species, including S. invicta. We used a dynamic, ecophysiological model of fire ant colony growth coupled with models simulating climate change to predict the potential range expansion of S. invicta in the eastern USA over the next century. The climate change scenario predicted by the Vegetation–Ecosystem Modelling and Analysis Project (VEMAP) was used in our analyses. Our predictions indicate that the habitable area for S. invicta may increase by c. 5% over the next 40–50 years (a northward expansion of 33 ± 35 km). As the pace of global warming is expected to quicken in the latter half of the century, however, the habitable area for S. invicta in 2100 is predicted to be > 21% greater than it currently is (a northward expansion of 133 ± 68 km). Because the black imported fire ant, S. richteri Forel, occupies higher latitudes than S. invicta, the overall area of the eastern USA infested with invasive Solenopsis species could be greater than that estimated here.