共查询到20条相似文献，搜索用时 15 毫秒
1.
Ronald H. Towner 《Evolutionary anthropology》2002,11(2):68-84
Dendrochronology, the science of tree‐ring dating, is the most accurate and precise nondocumentary dating method available to researchers studying the recent past. Tree‐ring dates are accurate and precise to the year and sometimes the season, and have no associated statistical uncertainty or standard error. Other prominent archeological dating techniques that use natural materials (for example, radiocarbon and archeomagnetism) have been calibrated using dendrochronological samples. 1 It is this precision and accuracy that has allowed archeologists working in the southwestern United States to construct the most detailed chronologies in the world, and to explore a plethora of environmental, social, and behavioral questions regarding past human adaptation to the region. 相似文献
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以小兴安岭典型阔叶红松林大面积固定样地(9hm2)为对象,分析不同地形下粗木质残体(CWD)的数量、存在形式、腐烂程度,探讨其与主要地形因子的相互关系.随着坡位的上升,CWD的密度和胸高断面积逐渐增加;从阴坡、半阴、半阳到阳坡,CWD的密度、胸高断面积和体积都呈现递减的趋势;CWD的数量分布随着样方坡度的增加没有呈现出明显的趋势.对不同地形下CWD的分布进行x2检验,各地形因子对CWD密度分布均差异显著,山脊、阴坡和坡度16～25°分别是CWD易发生的地形.在不同的地形中,CWD主要以干基折断、干中折断和枯立木3种形式存在.从谷地到山脊以拔根倒存在的CWD密度、胸高断面积和体积呈逐渐减少的趋势,而干中折断、根桩、枯立木和干基折断的密度大体上表现出增加的趋势;拔根倒的密度随坡度的上升逐渐减少,而枯立木则增加;由阳坡到阴坡枯立木的密度逐渐减少.不同存在形式的倒木,其树倒方向与坡向和风向均没有显著的相关性(p>0.05).不同地形下的各腐烂等级的CWD大致呈正态分布,且主要分布在2、3腐烂等级上,说明阔叶红松林不同地形的CWD输入和输出相对稳定. 相似文献
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Assembly history, or the order of species arrival, can have wide-ranging effects on species, communities and ecosystems. However, it remains unclear whether assembly history primarily affects individual species, with effects attenuating at the level of communities and ecosystems or, alternatively, has consistent effect sizes across increasing levels of ecological organisation. We address this question using a field-based manipulation of assembly history of wood-inhabiting fungi. The largest effect sizes were observed for the frequency of some individual species, and mean effect sizes were lower for community metrics of fungi immigrating from the regional species pool. There was little evidence, however, of attenuation in effect sizes at the ecosystem level (carbon, nitrogen, decomposition) in comparison to the species or community level. These results indicate that assembly history can have strong effects on ecosystem properties even under natural levels of environmental variability. 相似文献
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LENE BERGE DAVID E. BIGNELL HOMATHEVI RAHMAN DAVID F. R. P. BURSLEM 《Insect Conservation and Diversity》2008,1(2):85-94
Abstract.
- 1 A line intersection method was used to estimate abundance (technically linear abundance: m1 m−2), biovolume (m3 ha−1) and size class distribution (defined by diameter) of lying dead wood in tropical forest. Additional semi‐quantitative protocols assessed decay state (4 classes), termite attack (5 classes) and live termite occupancy (3 classes).
- 2 Three forest types (kerangas, alluvial and sandstone) were sampled in the Kabili‐Sepilok Forest Reserve of Eastern Sabah, using plots of 30 × 30 m. Approximately 50 man‐hours were required per site, at a replication of three plots per site and three well‐separated sites per forest type.
- 3 Mean biovolume of lying dead wood exceeded 8 × 103 m3 ha−1 in kerangas (= heath) forest, with lower values in other types. Large items (> 19 cm diameter) were less than 10% of total abundance, but represented the largest biovolume, exceeding (alluvial) or equalling (kerangas) the total biovolumes of smaller categories combined. Most items (not less than 75%) were present as small wood (< 10 cm diameter). Items in the highest decay class had the highest biovolume.
- 4 Termite attack was greater in the kerangas, where nearly 90% of items showed evidence of consumption, compared with 58% in the alluvial and 40% in the sandstone forests. Over 40% of items in the kerangas contained live termites compared with 25% in the alluvial and 15% in the sandstone. Items in the highest attack class (= almost total internal destruction) represented about one‐half of the total biovolume available in the alluvial and kerangas forest types, and about one‐third in the sandstone.
7.
Eric Harvey Isabelle Gounand Chelsea J. Little Emanuel A. Fronhofer Florian Altermatt 《Ecology and evolution》2017,7(15):5724-5731
In many natural systems, the physical structure of the landscape dictates the flow of resources. Despite mounting evidence that communities’ dynamics can be indirectly coupled by reciprocal among ecosystem resource flows, our understanding of how directional resource flows might indirectly link biological communities is limited. We here propose that differences in community structure upstream should lead to different downstream dynamics, even in the absence of dispersal of organisms. We report an experimental test of the effect of upstream community structure on downstream community dynamics in a simplified but highly controlled setting, using protist microcosms. We implemented directional flows of resources, without dispersal, from a standard resource pool into upstream communities of contrasting interaction structure and then to further downstream communities of either one or two trophic levels. Our results demonstrate that different types of species interactions in upstream habitats may lead to different population sizes and levels of biomass in these upstream habitats. This, in turn, leads to varying levels of detritus transfer (dead biomass) to the downstream communities, thus influencing their population densities and trophic interactions in predictable ways. Our results suggest that the structure of species interactions in directionally structured ecosystems can be a key mediator of alterations to downstream habitats. Alterations to upstream habitats can thus cascade down to downstream communities, even without dispersal. 相似文献
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Abstract Chill‐susceptible insects are able to improve their survival of acute cold exposure over both the short term (i.e. hardening at a relatively severe temperature) and longer term (i.e. acclimation responses at milder temperatures over a longer time frame). However, the mechanistic overlap of these responses is not clear. Four larval stages of four different strains of Drosophila melanogaster are used to test whether low temperature acclimation (10 °C for 48 h) improves the acute cold tolerance (LT90, ～2 h) of larvae, and whether acclimated larvae still show hardening responses after brief exposures to nonlethal cold or heat, or a combination of the two. Acclimation results in increased cold tolerance in three of four strains, with variation among instars. However, if acclimation is followed by hardening pre‐treatments, there is no improvement in acute cold survival. It is concluded that short‐term thermal responses (e.g. hardening) may be of more ecological relevance to short‐lived life stages such as larvae, and that the mechanisms of low temperature hardening and acclimation in D. melanogaster may be antagonistic, rather than complementary. 相似文献
10.
Cohen-Hadar N Wine Y Nachliel E Huppert D Gutman M Frolow F Freeman A 《Biotechnology and bioengineering》2006,94(5):1005-1011
Protein crystals, routinely prepared for the elucidation of protein 3D structures by X-ray crystallography, present an ordered and highly accurate 3D array of protein molecules. Inherent to the 3D arrangement of the protein molecules in the crystal is a complementary 3D array of voids made of interconnected cavities and exhibiting highly ordered porosity. The permeability of the porosity of chemically crosslinked enzyme protein crystals to low molecular weight solutes, was used for enzyme mediated organic synthesis and size exclusion chromatography. This permeability might be extended to explore new potential applications for protein crystals, for example, their use as bio-templates for the fabrication of novel, nano-structured composite materials. The quality of composites obtained from \"filling\" of the ordered voids in protein crystals and their potential applications will be strongly dependent upon an accurate preservation of the order in the original protein crystal 3D array during the \"filling\" process. Here we propose and demonstrate the feasibility of monitoring the changes in 3D order of the protein array by a step-by-step molecular level monitoring of a model system for hydrogel bio-templating by glutaraldehyde crosslinked lysozyme crystals. This monitoring is based on step-by-step comparative analysis of data obtained from (i) X-ray crystallography: resolution, unit cell dimensions and B-factor values and (ii) fluorescence decay kinetics of ultra-fast laser activated dye, impregnated within these crystals. Our results demonstrated feasibility of the proposed monitoring approach and confirmed that the stabilized protein crystal template retained its 3D structure throughout the process. 相似文献
11.
Michelle J. Greenwood 《Austral ecology》2014,39(8):941-951
Community structure and dynamics can be influenced by resource transfers between ecosystems, yet little is known about how boundary structure determines both the magnitude of exchanges and their effects on recipient and donor communities. Aquatic and terrestrial ecosystems are often linked by resource fluxes and riparian vegetation is commonly affected by anthropogenic alterations to land use or river hydrological regime. I investigated whether shrubs at the freshwater–terrestrial interface alter the supply, distribution and importance of aquatic prey resources to terrestrial consumers. Shrubs were predicted to alter the larval community composition of aquatic insects and the emergence of winged adults, thus affecting aquatic prey subsidies to terrestrial consumers. In addition, shrubs were hypothesized to alter the microclimatic suitability of the riparian zone for adult aquatic insects, act as a physical barrier to their dispersal and affect terrestrial community composition, particularly the abundance and type of predators that could benefit from the aquatic prey resource. Stable isotope dietary analyses and a survey of shrub‐dominated and open grassland riparian habitats revealed that larval densities of aquatic insects (EPTM: Ephemeroptera, Plecoptera, Trichoptera and Megaloptera) were higher in shrub than grassland habitats; however, reduced emergence and lateral dispersal in shrub areas led to lower densities of adults. The temperature and relative humidity of the riparian zone did not differ between the habitats. Ground‐active terrestrial invertebrate communities had a higher proportion of cursorial spiders in grassland, coinciding with greater abundances of aquatic prey. Aquatic prey contribution to cursorial spider diet matched adult aquatic insect abundances. Overall, riparian shrubs reduced the magnitude, or at least altered the timing, of cross‐ecosystem subsidy supply, distribution and use by consumers through mechanisms operating in both the aquatic and terrestrial ecosystems. Thus, the structure of ecosystem boundaries has complex effects on the strength of biological interactions between adjacent systems. 相似文献
12.
Louise Mair Mari Jönsson Minna Räty Lars Bärring Gustav Strandberg Tomas Lämås Tord Snäll 《Diversity & distributions》2018,24(10):1416-1425
Aim
Climate change is expected to have major impacts on terrestrial biodiversity at all ecosystem levels, including reductions in species‐level distribution and abundance. We aim to test the extent to which land use management, such as setting‐aside forest from production, could reduce climate‐induced biodiversity impacts for specialist species over large geographical gradients.Location
Sweden.Methods
We applied ensembles of species distribution models based on citizen science data for six species of red‐listed old‐forest indicator fungi confined to spruce dead wood. We tested the effect on species habitat suitabilities of alternative climate change scenarios and varying amounts of forest set‐aside from production over the coming century.Results
With 3.6% of forest area set‐aside from production and assuming no climate change, overall habitat suitabilities for all six species were projected to increase in response to maturing spruce in set‐aside forest. However, overall habitat suitabilities for all six species were projected to decline under climate change scenario RCP4.5 (intermediate–low emissions), with even greater declines projected under RCP 8.5 (high emissions). Increasing the amount of forest set‐aside to 16% resulted in significant increases in overall habitat suitability, with one species showing an increase. A further increase to 32% forest set‐aside resulted in considerably more positive trends, with three of six species increasing.Main conclusions
There is interspecific variation in the importance of future macroclimate and resource availability on species occurrence. However, large‐scale conservation measures, such as increasing resource availability through setting aside forest from production, could reduce future negative effects from climate change, and early investment in conservation is likely to reduce the future negative impacts of climate change on specialist species. 相似文献13.
Despite the profound impacts of drought on terrestrial productivity in coastal arid ecosystems, only a few studies have addressed how drought can influence ecological cascades across ecosystem boundaries. In this study, we examine the consequences of rainfall pulses and drought that subsequently impact the breeding success of a threatened nocturnal seabird, the Scripps's Murrelet (Synthliboramphus scrippsi). On an island off the coast of southern California, the main cause of reduced nest success for one of their largest breeding colonies is egg predation by an endemic deer mouse (Peromyscus maniculatus elusus). Mice on the island have an opportunistic diet of primarily terrestrial sources, but drastic declines in terrestrial productivity from drought might be expected to increase their reliance on marine resources, including murrelet eggs. We compiled data on terrestrial and marine productivity between 1983 and 2013 to determine how conditions in these ecosystems influence murrelet nest success. We found that the severity of drought had the strongest negative impact on murrelet nest success. We calculated that the reduction in fecundity during drought years due to increased egg predation by mice was substantial enough to produce a declining population growth rate. Nest success was much higher under normal or high rainfall conditions, depending on whether oceanic conditions were favorable to murrelets. Therefore, the more frequent and severe drought that is projected for this region could lead to an increased risk of murrelet population decline on this island. Our study highlights the need for understanding how species interactions will change through the effects of increasing drought and altered rainfall regimes under global change. 相似文献
14.
Panu Halme Noora Vartija Jukka Salmela Jouni Penttinen Veera Norros 《Insect Conservation and Diversity》2013,6(4):502-512
- Dead wood is a primary habitat for a large number of insects, including species from many nematoceran (Diptera) groups. The species living in dead wood must be adapted to the ephemeral and ever‐changing nature of their substrate. There is a growing body of knowledge about the effects of dead wood quality and the surrounding landscape on the saproxylic beetle community, but we know very little about the other saproxylic insects. Moreover, we know only very little about the variation in the insect community between different parts of decaying wood pieces.
- Using emergence traps, we studied the saproxylic nematoceran communities occupying different parts of decaying fallen aspen trunks in a boreal forest. To explain the variation in the detected assemblages, we also studied the variation in the physical environment in different parts of one of the studied trunks during the season.
- We found out that the overall variation in assemblages was very high and also the similarity between the base and top of the same trunk was usually low. Dissimilarity arose more from differences in species richness than from species turnover. The greatest contrasts in the physical conditions of the study trunk were between the inside and the upper and lower surface of the trunk base.
- Due to high variation within the trunks and especially between the trunks, the sampling effort in studies on the ecology of saproxylic insects should be high to have a reliable estimate of the local community.
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Ruchira Somaweera James Nifong Adam Rosenblatt Mathew L. Brien Xander Combrink Ruth M. Elsey Gordon Grigg William E. Magnusson Frank J. Mazzotti Ashley Pearcy Steven G. Platt Matthew H. Shirley Marisa Tellez Jan van der Ploeg Grahame Webb Rom Whitaker Bruce L. Webber 《Biological reviews of the Cambridge Philosophical Society》2020,95(4):936-959
Large‐bodied predators are well represented among the world's threatened and endangered species. A significant body of literature shows that in terrestrial and marine ecosystems large predators can play important roles in ecosystem structure and functioning. By contrast, the ecological roles and importance of large predators within freshwater ecosystems are poorly understood, constraining the design and implementation of optimal conservation strategies for freshwater ecosystems. Conservationists and environmentalists frequently promulgate ecological roles that crocodylians are assumed to fulfil, but often with limited evidence supporting those claims. Here, we review the available information on the ecological importance of crocodylians, a widely distributed group of predominantly freshwater‐dwelling, large‐bodied predators. We synthesise information regarding the role of crocodylians under five criteria within the context of modern ecological concepts: as indicators of ecological health, as ecosystem engineers, apex predators, keystone species, and as contributors to nutrient and energy translocation across ecosystems. Some crocodylians play a role as indicators of ecosystem health, but this is largely untested across the order Crocodylia. By contrast, the role of crocodylian activities in ecosystem engineering is largely anecdotal, and information supporting their assumed role as apex predators is currently limited to only a few species. Whether crocodylians contribute significantly to nutrient and energy translocation through cross‐ecosystem movements is unknown. We conclude that most claims regarding the importance of crocodylians as apex predators, keystone species, ecosystem engineers, and as contributors to nutrient and energy translocation across ecosystems are mostly unsubstantiated speculation, drawn from anecdotal observations made during research carried out primarily for other purposes. There is a paucity of biological research targeted directly at: understanding population dynamics; trophic interactions within their ecological communities; and quantifying the short‐ and long‐term ecological impacts of crocodylian population declines, extirpations, and recoveries. Conservation practices ideally need evidence‐based planning, decision making and justification. Addressing the knowledge gaps identified here will be important for achieving effective conservation of crocodylians. 相似文献
16.
Weizhi Lu Jingfeng Xiao Fang Liu Yue Zhang Chang'an Liu Guanghui Lin 《Global Change Biology》2017,23(3):1180-1198
Wetlands play an important role in regulating the atmospheric carbon dioxide (CO2) concentrations and thus affecting the climate. However, there is still lack of quantitative evaluation of such a role across different wetland types, especially at the global scale. Here, we conducted a meta‐analysis to compare ecosystem CO2 fluxes among various types of wetlands using a global database compiled from the literature. This database consists of 143 site‐years of eddy covariance data from 22 inland wetland and 21 coastal wetland sites across the globe. Coastal wetlands had higher annual gross primary productivity (GPP), ecosystem respiration (Re), and net ecosystem productivity (NEP) than inland wetlands. On a per unit area basis, coastal wetlands provided large CO2 sinks, while inland wetlands provided small CO2 sinks or were nearly CO2 neutral. The annual CO2 sink strength was 93.15 and 208.37 g C m?2 for inland and coastal wetlands, respectively. Annual CO2 fluxes were mainly regulated by mean annual temperature (MAT) and mean annual precipitation (MAP). For coastal and inland wetlands combined, MAT and MAP explained 71%, 54%, and 57% of the variations in GPP, Re, and NEP, respectively. The CO2 fluxes of wetlands were also related to leaf area index (LAI). The CO2 fluxes also varied with water table depth (WTD), although the effects of WTD were not statistically significant. NEP was jointly determined by GPP and Re for both inland and coastal wetlands. However, the NEP/Re and NEP/GPP ratios exhibited little variability for inland wetlands and decreased for coastal wetlands with increasing latitude. The contrasting of CO2 fluxes between inland and coastal wetlands globally can improve our understanding of the roles of wetlands in the global C cycle. Our results also have implications for informing wetland management and climate change policymaking, for example, the efforts being made by international organizations and enterprises to restore coastal wetlands for enhancing blue carbon sinks. 相似文献
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Maurice S Coroller L Debaets S Vasseur V Le Floch G Barbier G 《Journal of applied microbiology》2011,111(6):1436-1446
Aims: To predict the risk factors for building infestation by Serpula lacrymans, which is one of the most destructive fungi causing timber decay in buildings. Methods and Results: The growth rate was assessed on malt extract agar media at temperatures between 1·5 and 45°C, at water activity (aw) over the range of 0·800–0·993 and at pH ranges from 1·5 to 11·0. The radial growth rate (μ) and the lag phase (λ) were estimated from the radial growth kinetics via the plots radius vs time. These parameters were then modelled as a function of the environmental factors tested. Models derived from the cardinal model (CM) were used to fit the experimental data and allowed an estimation of the optimal and limit values for fungal growth. Optimal growth rate occurred at 20°C, at high aw level (0·993) and at a pH range between 4·0 and 6·0. The strain effect on the temperature parameters was further evaluated using 14 strains of S. lacrymans. The robustness of the temperature model was validated on data sets measured in two different wood‐based media (Quercus robur L. and Picea abies). Conclusions: The two‐step procedure of exponential model with latency followed by the CM with inflection gives reliable predictions for the growth conditions of a filamentous fungus in our study. The procedure was validated for the study of abiotic factors on the growth rate of S. lacrymans. Significance and Impact of the Study: This work describes the usefulness of evaluating the effect of physico‐chemical factors on fungal growth in predictive building mycology. Consequently, the developed mathematical models for predicting fungal growth on a macroscopic scale can be used as a tool for risk assessment of timber decay in buildings. 相似文献
19.
Elizabeth M. P. Madin Joshua S. Madin Aaron M. T. Harmer Neville S. Barrett David J. Booth M. Julian Caley Alistair J. Cheal Graham J. Edgar Michael J. Emslie Steven D. Gaines Hugh P. A. Sweatman 《Ecology and evolution》2020,10(14):6954-6966
The relative roles of top‐down (consumer‐driven) and bottom‐up (resource‐driven) forcing in exploited marine ecosystems have been much debated. Examples from a variety of marine systems of exploitation‐induced, top‐down trophic forcing have led to a general view that human‐induced predator perturbations can disrupt entire marine food webs, yet other studies that have found no such evidence provide a counterpoint. Though evidence continues to emerge, an unresolved debate exists regarding both the relative roles of top‐down versus bottom‐up forcing and the capacity of human exploitation to instigate top‐down, community‐level effects. Using time‐series data for 104 reef communities spanning tropical to temperate Australia from 1992 to 2013, we aimed to quantify relationships among long‐term trophic group population density trends, latitude, and exploitation status over a continental‐scale biogeographic range. Specifically, we amalgamated two long‐term monitoring databases of marine community dynamics to test for significant positive or negative trends in density of each of three key trophic levels (predators, herbivores, and algae) across the entire time series at each of the 104 locations. We found that trophic control tended toward bottom‐up driven in tropical systems and top‐down driven in temperate systems. Further, alternating long‐term population trends across multiple trophic levels (a method of identifying trophic cascades), presumably due to top‐down trophic forcing, occurred in roughly fifteen percent of locations where the prerequisite significant predator trends occurred. Such alternating trophic trends were significantly more likely to occur at locations with increasing predator densities over time. Within these locations, we found a marked latitudinal gradient in the prevalence of long‐term, alternating trophic group trends, from rare in the tropics (<5% of cases) to relatively common in temperate areas (~45%). Lastly, the strongest trends in predator and algal density occurred in older no‐take marine reserves; however, exploitation status did not affect the likelihood of alternating long‐term trophic group trends occurring. Our data suggest that the type and degree of trophic forcing in this system are likely related to one or more covariates of latitude, and that ecosystem resiliency to top‐down control does not universally vary in this system based on exploitation level. 相似文献
20.
Molecular tip dating of phylogenetic trees is a growing discipline that uses DNA sequences sampled at different points in time to coestimate the timing of evolutionary events with rates of molecular evolution. In this context, beast , a program for Bayesian analysis of molecular sequences, is the most widely used phylogenetic tool. Here, we introduce tipdatingbeast , an r package built to assist the implementation of various phylogenetic tip‐dating tests using beast . tipdatingbeast currently contains two main functions. The first one allows preparing date‐randomization analyses, which assess the temporal signal of a data set. The second function allows performing leave‐one‐out analyses, which test for the consistency between independent calibration sequences and allow pinpointing those leading to potential bias. We apply those functions to an empirical data set and supply practical guidance for results interpretation. 相似文献