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1.
Summary Since the mid 1990s, there has been a significant increase in the area of semi‐arid grasslands included in the National Reserve Systems in the Victorian Riverine Plain. This expansion has not been matched by an improved understanding of the alternate disturbance regimes that might produce better outcomes for native ecosystem conservation. Over the past 150 years, stock grazing has completely replaced fire in these grasslands. As a result, the impact of fire on native (and exotic) plant biodiversity is little understood. This study compared the current grazing regime (i.e. ‘status quo’) with burning and the removal of grazing (‘deferred’ management) across three grasslands in the Victorian Riverine Plain to determine the effects of short‐term exposure to alternate disturbances on community structure. Our results showed little change in species density, composition or abundance under the three disturbance treatments. A long exposure to stock grazing may have reduced the abundance of species likely to respond positively to burning. The cover of the biological soil crust responded positively to fire; such changes are known to significantly influence establishment and the functional composition of communities. As such, further investigation of the functional attributes of these communities may broaden our understanding of short‐term responses to alternate disturbance events. To better understand the utility of fire as a management tool, a long‐term commitment to expanding the implementation of this regime from its current extent will greatly increase the understanding of alternate disturbances in this landscape. 相似文献
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根据2006年在杭州湾北岸大型围隔海域进行的生态调查数据,利用EwE软件构建围隔海域人工生态系统的能量流动模型.模型由13个功能组构成,分别是肉食性鱼类、底栖捕食鱼类、浮游动物性鱼类、草食性鱼类、蟹类、虾类、软体动物、底栖动物、肉食性浮游动物、植食性浮游动物、大型藻类、浮游植物和有机碎屑,每一组都代表在生态系统中具有相似地位的有机体,基本覆盖了该人工生态系统能量流动的主要过程.能量流动分析表明,围隔海域人工生态系统中能量流动主要以碎屑食物链途径为主,其中植食性浮游动物在能量从低级向高层次转换中起关键作用.人工生态系统的营养级范围为1.00～3.90级,系统的能量流动主要有6级,来自初级生产者的能流效率为9.4%,来自碎屑的转换效率为9.8%,平均能量转换效率为9.6%.经生态网络分析,直接来源于碎屑的比例占总流量的57%,而直接来源于初级生产者的比例为43%,生态系统特征参数:总初级生产计算量/总呼吸量(TPP/TR)、系统物质和能量循环率(FCI)和系统聚合度(A)值分别为2.672、0.25、0.315,表明围隔海域人工生态系统目前正处于发育时期.该研究为首次利用Ecopath模型分析大型围隔海域人工生态系统的结构和能量流动,旨在为富营养化近岸海域的生态修复提供理论依据. 相似文献
3.
R.J. Morris M.J. McCartney I.R. Joint G.A. Robinson 《Journal of experimental marine biology and ecology》1985,86(2):151-170
A detailed characterization is presented of the spring diatom bloom which occurred in the enclosed experimental ecosystem bags at Loch Ewe, Scotland, during March–April 1983. The nutrient condition and bacterial biomass of the water column, phytoplankton species distribution, gross biochemical composition and detailed lipid composition (lipid class, fatty acid and free sterol) of the phytoplankton are reported throughout the bloom period. The results are compared with results from previous years. The conclusions are that major changes take place in the biochemical composition of a rapidly growing diatom population which affect both the gross composition and also the more detailed lipid composition. Such changes can take place over a matter of days and appear to be very dependent upon available growth conditions. Both carbohydrate and lipids levels increase towards the end of the bloom as nitrate and silicate levels are depleted in the water. Neutral lipids are shown to be important lipid components of the phytoplankton populations and long-chain ω3 polyunsaturated fatty acids are found to be only minor components of the structural polar lipids. The fatty acid and sterol data are discussed in relation to present knowledge concerning phytoplankton lipid composition. 相似文献
4.
Vincent Omondi Odongo Christiaan van der Tol Robert Becht Joost C. B. Hoedjes Chandra Prasad Ghimire Zhongbo Su 《Ecohydrology》2016,9(7):1358-1375
This paper reports on the energy balance and partitioning analysed from 3‐year micrometeorological flux measurements of energy and water fluxes over a heterogeneous semi‐arid shrubland ecosystem in Lake Naivasha basin. The measurements enabled the characterization of the seasonal and interannual variability of the energy and water fluxes of the ecosystem covering two wet years (2012 and 2013) and one drought year (2014). On an annual scale, more than 60% of net radiation (Rn) was partitioned as latent (LE) and sensible (H) energy flux, with the latter being the larger consumer of Rn (~34%) and dominant for most months. The transition from H to LE dominance occurred from early noon to late afternoon in the wettest months of April and May. The residual energy balance closure term (C) accounted for between 25 and 40% of the Rn with the imbalance tending to be highest during periods of high insolation. Annual evapotranspiration was estimated at 873 mm, 632 mm and 537 mm for year 2012, 2013 and 2014 respectively. This accounted for at least 80% of the annual precipitation received for the respective years. Surface conductance (gs) scaled significantly with leaf expansion and Priestley–Taylor α coefficient, but was limited during periods of drought because of inadequate soil moisture suggesting that, change in LE was paralleled by changes in green leaf area index. Low values of decoupling coefficient (Ω) during these periods indicated that evapotranspiration was strongly controlled by gs and vapour pressure deficit (VPD). However, under non‐limiting moisture conditions evapotranspiration was decoupled from the atmosphere. This suggested that during the dry seasons and periods of prolonged drought, a lack of moisture in combination with high VPD leads to significant decreases in stomatal conductance that eventually limits partitioning of available energy into LE in the semi‐arid ecosystem part of the Lake Naivasha basin. However, during wet season these factors are non‐limiting and radiation is the dominant control of energy partitioning into LE in the ecosystem. The coupling and decoupling pattern provide insights towards formulating models that quantify evapotranspiration for ecosystems that experience seasonal shifts in controlling factors. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Sébastien Descamps Jon Aars Eva Fuglei Kit M. Kovacs Christian Lydersen Olga Pavlova Åshild Ø. Pedersen Virve Ravolainen Hallvard Strøm 《Global Change Biology》2017,23(2):490-502
The Arctic is warming more rapidly than other region on the planet, and the northern Barents Sea, including the Svalbard Archipelago, is experiencing the fastest temperature increases within the circumpolar Arctic, along with the highest rate of sea ice loss. These physical changes are affecting a broad array of resident Arctic organisms as well as some migrants that occupy the region seasonally. Herein, evidence of climate change impacts on terrestrial and marine wildlife in Svalbard is reviewed, with a focus on bird and mammal species. In the terrestrial ecosystem, increased winter air temperatures and concomitant increases in the frequency of ‘rain‐on‐snow’ events are one of the most important facets of climate change with respect to impacts on flora and fauna. Winter rain creates ice that blocks access to food for herbivores and synchronizes the population dynamics of the herbivore–predator guild. In the marine ecosystem, increases in sea temperature and reductions in sea ice are influencing the entire food web. These changes are affecting the foraging and breeding ecology of most marine birds and mammals and are associated with an increase in abundance of several temperate fish, seabird and marine mammal species. Our review indicates that even though a few species are benefiting from a warming climate, most Arctic endemic species in Svalbard are experiencing negative consequences induced by the warming environment. Our review emphasizes the tight relationships between the marine and terrestrial ecosystems in this High Arctic archipelago. Detecting changes in trophic relationships within and between these ecosystems requires long‐term (multidecadal) demographic, population‐ and ecosystem‐based monitoring, the results of which are necessary to set appropriate conservation priorities in relation to climate warming. 相似文献
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Hongyan Liu A. Park Williams Craig D. Allen Dali Guo Xiuchen Wu Oleg A. Anenkhonov Eryuan Liang Denis V. Sandanov Yi Yin Zhaohuan Qi Natalya K. Badmaeva 《Global Change Biology》2013,19(8):2500-2510
Forests around the world are subject to risk of high rates of tree growth decline and increased tree mortality from combinations of climate warming and drought, notably in semi‐arid settings. Here, we assess how climate warming has affected tree growth in one of the world's most extensive zones of semi‐arid forests, in Inner Asia, a region where lack of data limits our understanding of how climate change may impact forests. We show that pervasive tree growth declines since 1994 in Inner Asia have been confined to semi‐arid forests, where growing season water stress has been rising due to warming‐induced increases in atmospheric moisture demand. A causal link between increasing drought and declining growth at semi‐arid sites is corroborated by correlation analyses comparing annual climate data to records of tree‐ring widths. These ring‐width records tend to be substantially more sensitive to drought variability at semi‐arid sites than at semi‐humid sites. Fire occurrence and insect/pathogen attacks have increased in tandem with the most recent (2007–2009) documented episode of tree mortality. If warming in Inner Asia continues, further increases in forest stress and tree mortality could be expected, potentially driving the eventual regional loss of current semi‐arid forests. 相似文献
8.
Oocyte development was aborted and full maturity did not occur in virgin female sea bass Dicentrarchus labrax unless they remained in water above 10° C during the main period of gonad development. There was no difference in the condition factors of females with high or low I G values in March, which indicates that retarded gonadal development was not necessarily due to poor body condition or nutritional state. It is suggested that the extended duration of the adolescent phase of female bass around southern Britain is a response to their environment, rather than an intrinsic aspect of the species'biology. 相似文献
9.
The present study was carried out to assess the possible role of mitogen-activated protein kinase (MAPK) in the meiosis-inducing action of the AMP-activated protein kinase (AMPK) activator, 5-aminoimidazole-4-carboxamide 1-beta-ribofuranoside (AICAR). Cumulus cell-enclosed oocytes (CEO) or denuded oocytes (DO) from immature, eCG-primed mice were cultured 4 hr in Eagle's minimum essential medium containing dbcAMP plus increasing concentrations of AICAR or okadaic acid (OA). OA is a phosphatase inhibitor known to stimulate both meiotic maturation and MAPK activation and served as a positive control. Both OA and AICAR were potent inducers of meiotic resumption in mouse oocytes and brought about the phosphorylation (and thus, activation) of MAPK, but by different kinetics: MAPK phosphorylation preceded GVB in OA-treated oocytes, while that resulting from AICAR treatment appeared only after GVB. The MEK inhibitors, PD98059 and U0126, blocked the meiotic resumption induced by AICAR but not that induced by OA. Although the MEK inhibitors suppressed MAPK phosphorylation in both OA- and AICAR-treated oocytes, meiotic resumption was not causally linked to MAPK phosphorylation in either group. Furthermore, AICAR-induced meiotic resumption in Mos-null oocytes (which are unable to stimulate MAPK) was also abrogated by PD98059 treatment. A non-specific effect of the MEK inhibitors on AICAR accessibility to the oocyte was discounted by showing that they failed to suppress either nucleoside uptake or AICAR-stimulated phosphorylation of acetyl CoA carboxylase (ACC), a substrate of AMPK. The suppression of AICAR-induced maturation by MEK inhibitors must, therefore, be occurring by actions unrelated to MEK stimulation of MAPK; consequently, it would be prudent to consider this possible non-specific action of the inhibitors when they are used to block MAPK activation in mouse oocytes. 相似文献
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Ephemeral cropping systems are characterized by frequent disturbances of ecological processes, which may compromise the conservation of plant and arthropod diversity and the ecosystem services they may provide. Conservation biological control practices include habitat manipulations that provide non‐pest resources and selectively enhance natural enemies' effectiveness. This study, conducted in eight commercial fields of organically grown tomato, compared the effectiveness of sown flower strips with semi‐natural margins in regulating natural enemy abundance, biocontrol, and crop damage. During repeated visits, the abundance of different arthropod groups was recorded. Crop surveys included measurement of aphid abundance, parasitism, and leaf and fruit damage from sap‐sucking and lepidopteran pests. Semi‐natural habitats were associated with higher vegetation diversity, but natural enemies were more strongly associated with sown strips during flowering. Sap‐sucking pests were always recorded in higher abundance in flower strips, but crop damage in the plots adjacent to these strips was lower, suggesting that these strips may act as a trap‐crop. The inclusion of floral supplements enhanced the parasitism rate of aphids in the crop, and reduced the rate of increase of lepidopteran‐caused foliar damage with time. Early in the growing season, semi‐natural strips showed significantly lower levels of crop damage and aphid counts, suggesting that these habitats may be important during early crop colonization by natural enemies. These results indicate that the inclusion of flower strips enhances the conservation of arthropod functional diversity in ephemeral crops, and that diverse mechanisms are important for controlling different pests. However, the efficacy of habitat manipulation is likely to be greater when it is complemented with the conservation of diverse semi‐natural vegetation in the pre‐existing field margin. 相似文献
12.
Susanna López‐Legentil Patrick M. Erwin Marta Velasco Xavier Turon 《Invertebrate Biology》2013,132(1):69-80
Relatively little is known about the life cycles of ascidians in temperate seas. Here, we investigated the biological cycle of the colonial ascidian Didemnum fulgens, a dominant species in some shallow localities of the NW Mediterranean Sea. Growth rates and frequencies of fission/fusion events were calculated over a period of 13 months, and the reproductive cycle determined after 32 months of observation. For analyses of reproduction, zooids were dissected in the laboratory and classified into five reproductive categories; these data were used to calculate a maturity index. For growth analyses, underwater photographs of marked colonies were used to estimate the surface area of D. fulgens colonies, calculate monthly growth rates, and document fusion and fission events. Clear seasonal patterns in reproduction and growth were observed, with distinct periods of investment into each function. Gonad maturation started in winter and larval release occurred in early summer, just before maximal sea temperatures were reached. After reproducing, colonies shrank and aestivated during the warmer summer months. Growth occurred during the cooler months, with maximal and minimal growth rates observed in winter and summer, respectively. Fusions and fissions occurred year‐round, although fissions were more frequent in fall (coincident with high growth rates) and fusions in spring (coincident with reproduction). These results add to the mounting evidence that ascidian life cycles in temperate seas are characterized by a trade‐off between investment in reproduction and growth, triggered by seasonal temperature shifts and constrained by resource availability during summer. 相似文献
13.
Michelle V. A. Ewacha Corris Kaapehi Jane M. Waterman James D. Roth 《African Journal of Ecology》2016,54(1):68-75
Burrowing and foraging of semi‐fossorial rodents can affect species distribution and composition. Ground squirrels dig large burrow systems for refuge from predators and temperature extremes. Burrowing and foraging around burrows by squirrels may affect habitat and resource distributions for other organisms. We examined the impact of Cape ground squirrels (Xerus inauris) on vegetation, small mammals and beetles during winter and summer in grasslands on the edge of the Namib Desert. At each burrow system and paired control site without burrows, we estimated plant cover and height using quadrats (N = 8 paired sites), small mammal abundance and species richness using mark‐recapture techniques (N = 8 paired sites) and beetle abundance and species richness using pitfall traps (N = 6 paired sites, winter only). Squirrel burrowing and foraging activities resulted in lower plant cover and height, higher small mammal abundance and lower beetle abundance and species richness. Squirrels also reduced more plant cover in winter compared to summer, but had no effect on small mammal species richness. Furthermore, plant cover and height were higher in summer, whereas small mammal abundance and species richness were higher in winter. Our results suggest that Cape ground squirrels are important ecosystem engineers that influence plant and animal communities in the Namib Desert grasslands. 相似文献
14.
Length and mass data for 1260 (536 females, 683 males, 41 sex unknown) striped marlin Kajikia audax were collected at the fish markets of Tungkang, Singkang and Nanfangao from July 2004 to September 2010. Of these samples, 534 gonads (236 females and 298 males) ranging from 95 to 206 cm in eye‐to‐fork length (L EF ) and 8 to 88 kg in round mass (M R), were collected. Chi‐square tests indicated sex ratios were homogeneous among months in 2004 and 2006–2008, but not in 2005, 2009 and 2010; and there were significant differences in sex ratio by size. The overall sex ratio (R S ) differed significantly from the expected 0·5. Kajikia audax are sexually dimorphic and the proportions of females increased with size between 140 and 210 cm L EF . Reproductive activity was assessed using a gonado‐somatic index (I G ), external appearance of the gonads and histological examination and results indicated that the spawning season occurred from April to August with a peak in June to July. Based on histological observations and the distribution of oocyte diameters, K. audax are multiple spawners and their oocytes develop asynchronously. The estimated length‐at‐50% maturity (L EF50 ) was c . 181 cm (c . 4·8 years of age) for females. The proportion of reproductively active females in the spawning season with ovaries containing postovulatory follicles (0·27) indicated that they spawned every 3·7 days on average. The hydrated oocyte method estimated mean ± S.D. batch fecundity (F B ) to be 4·4 ± 2·02 million eggs; average relative fecundity was 53·6 ± 13·9 oocytes g?1 M R; and the average annual fecundity was 181·3 ± 48·3 million eggs. The parameters estimated in this study are key information for stock assessments of K. audax in the north‐western and central Pacific and will contribute to the conservation, management and sustainable yield of this species. 相似文献
15.
北部湾生态通道模型的构建 总被引：13，自引：0，他引：13
根据1997年～1999年在北部湾进行的渔业资源和生态环境调查数据,利用EwE软件构建北部湾生态系统的营养通道模型,模型由16个功能组构成,包括了哺乳动物和海鸟,每一组都代表在生态系统中具有相似地位的有机体,基本覆盖了北部湾生态系统能量流动的主要过程.模型分析表明,北部湾生态系统的能量流动主要以捕食食物链途径为主,其中无脊椎动物在能量从低级向高层次转换中起关键作用.各功能组的营养级范围为1.00～4.04,哺乳动物占据了最高营养层.生态网络分析表明,系统的能量流动主要有6级,来自初级生产者的能流效率为12.2%,来自碎屑的转换效率为12.3%,平均能量转换效率为12.2%.模型估算的可利用的生物量密度为8.7 t·km-2,生态系统的生物生产量只占系统净初级生产力的1.81%.当前北部湾海洋生态系统处于不稳定状态. 相似文献
16.
Andrea Holzschuh Matteo Dainese Juan P. González‐Varo Sonja Mudri‐Stojnić Verena Riedinger Maj Rundlöf Jeroen Scheper Jennifer B. Wickens Victoria J. Wickens Riccardo Bommarco David Kleijn Simon G. Potts Stuart P. M. Roberts Henrik G. Smith Montserrat Vilà Ante Vujić Ingolf Steffan‐Dewenter 《Ecology letters》2016,19(10):1228-1236
Mass‐flowering crops (MFCs) are increasingly cultivated and might influence pollinator communities in MFC fields and nearby semi‐natural habitats (SNHs). Across six European regions and 2 years, we assessed how landscape‐scale cover of MFCs affected pollinator densities in 408 MFC fields and adjacent SNHs. In MFC fields, densities of bumblebees, solitary bees, managed honeybees and hoverflies were negatively related to the cover of MFCs in the landscape. In SNHs, densities of bumblebees declined with increasing cover of MFCs but densities of honeybees increased. The densities of all pollinators were generally unrelated to the cover of SNHs in the landscape. Although MFC fields apparently attracted pollinators from SNHs, in landscapes with large areas of MFCs they became diluted. The resulting lower densities might negatively affect yields of pollinator‐dependent crops and the reproductive success of wild plants. An expansion of MFCs needs to be accompanied by pollinator‐supporting practices in agricultural landscapes. 相似文献
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Robert A. Gregg Douglas A. Eagles 《Marine and Freshwater Behaviour and Physiology》2013,45(4):303-325
The patello‐tibial joint in the walking leg of the horseshoe crab can move in the flexion‐extension and promotion‐remotion planes with the freedom of movement of a ball‐and‐socket joint. Its mechanical status is represented by at least seven populations of sensory neurons and these include three different types of proprioceptors; articular membrane receptors, muscle length receptors and muscle tension receptors. A population of each of these types of proprioceptor is associated with structures on the anterior and posterior sides of each leg. In this report we describe the representation of joint movement in both planes by two populations of each type of proprioceptor. In general, the articular membrane receptors were most sensitive to joint flexion; receptors on the anterior side of the leg were biased toward promotion, while those on the posterior were biased toward remotion. Muscle length receptor activity was increased by joint extension and was slightly augmented, in posterior and anterior length receptors, by promotion and remotion, respectively. Length receptor tonic activity was a linear function of muscle length for extension but a non‐linear function of muscle flexion. Tension receptor activity was always highly dependent upon active muscular contraction. Tension receptors associated with posterior tibial flexor showed enhanced activity when the joint was promoted; the activity of those associated with the anterior flexor was enhanced by remotion. The relationships between tension receptor activity and muscle length, and between tension receptor activity and joint position, were also explored. While no single receptor population appears capable of representing the status of this joint in both planes, the output of all of the receptor populations studied appears to provide the CNS with unambiguous information about several parameters representing the status of this complex joint. 相似文献
19.
YUNHUI LIU JAN C. AXMACHER CHANGLIU WANG LIANGTAO LI ZHENRONG YU 《Insect Conservation and Diversity》2010,3(1):34-43
Abstract. 1. In the intensively cultivated major crop production areas of China, large knowledge gaps still prevail with regard to the current status of biodiversity in general, and especially in relation to agriculture management and planting patterns. Effective measures for species conservation are hence widely lacking. 2. The diversity of ground beetle (Coleoptera: Carabidae) assemblages was compared between intensively managed wheat/maize fields, cotton monocultures, lawns, orchards and semi‐natural woodland located in Quzhou county, a typical, intensively managed agricultural region in the North China Plain. 3. Although significant differences were found in species composition between different habitats, diversity of ground beetles in non‐cropping sites was not significantly higher than in intensively managed wheat/maize double‐cropping fields, while cotton monocultures had a significant lower carabid diversity. A combination of intensively managed wheat/maize double‐cropping fields with orchards appears to preserve substantial proportions of ground beetle diversity. 4. To conserve the full spectrum of beetle species currently observed in the agricultural landscape of the North China Plain, the creation of both diverse habitats and a diversity of cropping systems are important, which includes a strengthening of less intensive farming practices. 相似文献
20.
Tree hollows are a critical but diminishing resource for a wide range of fauna around the world. Conservation of these fauna depends on sustainable management of tree species that produce the hollows on which they depend. This study addressed the need for empirical data about intraspecific and interspecific variation in hollow occurrence and abundance in woodland trees in Australia. We measured and performed hollow surveys on 1817 trees of seven species of woodland Eucalyptus in central‐western New South Wales, Australia. Trees were surveyed at 51 one‐hectare sites and about 30% of trees surveyed had multiple stems. Generalized linear mixed models that accounted for nestedness of stems within trees and trees within sites detected a significant amount of variation in hollow occurrence and abundance. Models for individual tree stems of live trees showed hollow probability and abundance increased with diameter at breast height (DBH) and with increasing senescence (form). Stems of Eucalyptus microcarpa Maiden had a higher probability of having hollows than similar DBH stems of Eucalyptus camaldulensis Dehnh., Eucalyptus melliodora A.Cunn. ex Schauer or Eucalyptus populnea ssp. bimbil L.A.S.Johnson & K.D.Hill. Dead stems in live trees were more likely to have hollows than live stems of similar DBH. Each stem in a multi‐stemmed tree had a lower probability of hollow occurrence and lower abundance of hollows than single‐stemmed trees of similar DBH. For stems of dead trees, hollow occurrence and abundance increased with DBH and differed depending on stage of senescence. A comparison of our data with other studies indicates regional variation of hollow abundances within tree species. 相似文献