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161.
基于温度-植被-降水的综合干旱指数(TVPDI)、地表径流、植被净初级生产力和粮食产量等数据,利用数据空间化方法、Slope趋势分析及Pearson相关分析等方法,探究了黄河流域从2001~2020年这20年间干旱时空变化特征以及对水资源、粮食资源和植被资源的影响,试图探究干旱与关键资源之间的相互影响.结果表明:①黄河流域干旱空间分布由东南向西北呈阶梯状加重,全流域有60.6 %的区域处于干旱状态;从变化看全流域干旱整体上呈逐年下降趋势,有94 %的区域由干旱逐渐向湿润转变,从春季到冬季干旱呈现先减轻后加重的趋势.②从流域重要资源的时空变化看,起关键作用的地表径流量有53 %的区域呈现增加趋势,且主要分布在流域西南地区;表征植被资源的植被净初级生产力(NPP)及表征粮食资源的粮食产量亦呈增长趋势.③干旱与3类资源呈现显著的空间关联度,干旱程度越高对地表径流量、植被生产力和粮食产量产生的影响越显著,但近年来变湿的地区,其重要资源并未显著增加,这说明干旱对3类重要资源的影响具有时间滞后性,且其滞后性在空间分布上具有显著差异性和地域分异规律.研究对于黄河流域农业生产和抗旱减灾、生态保育具有重要理论意义. 相似文献
162.
Structure of the social network and its influence on transmission dynamics in a honeybee colony 总被引:4,自引:3,他引:1
Dhruba Naug 《Behavioral ecology and sociobiology》2008,62(11):1719-1725
Infectious processes in a social group are driven by a network of contacts that is generally structured by the organization
arising from behavioral and spatial heterogeneities within the group. Although theoretical models of transmission dynamics
have placed an overwhelming emphasis on the importance of understanding the network structure in a social group, empirical
data regarding such contact structures are rare. In this paper, I analyze the network structure and the correlated transmission
dynamics within a honeybee colony as determined by food transfer interactions and the changes produced in it by an experimental
manipulation. The study demonstrates that widespread transmission in the colony is correlated to a lower clustering coefficient
and higher robustness of the social network. I also show that the social network in the colony is determined by the spatial
distribution of various age classes, and the resulting organizational structure provides some amount of immunity to the young
individuals. The results of this study demonstrates how, using the honeybee colony as a model system, concepts in network
theory can be combined with those in behavioral ecology to gain a better understanding of social transmission processes, especially
those related to disease dynamics. 相似文献
163.
In the course of their foraging bouts, bees frequently encounter spider webs among the vegetation. The ability to see and
avoid these webs is vital for the success of the individual bee’s foraging bout. In this study, we report on the response
of stingless bees (Trigona carbonaria) towards the webs of the St. Andrew’s Cross spider (Argiope keyserlingi). We studied the ability of bees to avoid webs in different contexts: when bees were on their foraging path or when they
were returning to the hive as well as when they were flying North or South. We show that the probability of a bee being able
to avoid a web depends on the context of the bee’s flight rather than the visual appearance of the web. Furthermore, the presence
of the spider seems to alert the bee to the web, resulting in bees being more able to avoid capture. We show, specifically,
that the probability of being captured is higher when the bee is returning to the hive compared with when the bee is foraging.
The likelihood of avoiding a web is also influenced by the compass direction of the flight, although to a lesser extent. Our
results indicate that the context of the predator–prey encounter has a significant influence on a bee’s ability to escape
interception by a spider web. 相似文献
164.
Stefanie Trapmann Nestor Etxebarria Heide Schnabl Karl Heinz Grobecker 《Environmental science and pollution research international》1998,5(1):17-20
Chloroplast thylakoids are used as biological units to determine herbicides in different kinds of water samples as well as
in aqueous extracts of compost, soil or food samples. The thylakoid bioassy shows clearly inhibition of fluorescence yield
in the presence of photosystem II specific herbicides. Due to this method the ecotoxicological effect of samples with unknown
pollutants can be tested fast and cost effective. It has been proven that all photosynthetic active compounds are recorded
at the same time because only additive interactions occur. Therefore, the contamination level can be expressed as cumulative
parameter for photosystem II active substances. Application was improved clearly by the addition of the radical scavenger
sodium ascorbate to the isolation media and by a higher concentration of the measuring medium. A new data evaluation method
is described yielding in a lower detection limit of 0.4 μg diuron/1. The guidelines for the quality of water for human consumption
with an allowable concentration of pesticides in groups is 0,5 μg/1 [1,2] and can be controlled with the thylakoid bioassay
without performing any preconcentration steps. 相似文献
165.
The regulatory contribution that preferential trade agreements (PTAs) make to global climate governance is assessed through an analysis of climate-related provisions found in 688 PTAs signed between 1947 and 2016. Provisions are analyzed along four dimensions: innovation, legalization, replication, and distribution. Innovative climate provisions are found in several PTAs that are in some cases more specific and enforceable than the Kyoto Protocol and the Paris Agreement. Nonetheless, these climate provisions offer limited progress because they remain weakly ‘legalized’, fail to replicate broadly in the global trade system, and were not adopted by the largest greenhouse gas emitters. Despite the inclusion of innovative climate provisions in a number of PTAs, their poor design and weak replication position them as some of the weakest environmental provisions within PTAs. 相似文献
166.
Species interactions such as predation or competition can have notable implications for fish population dynamics. Stock status and associated biological reference points can be misrepresented if these interactions are not considered. Here we present a multispecies, biomass production model (MS-PROD) developed by incorporating modifications to the Schaefer production model. The modifications explicitly emphasize a functional group approach, highlighting the effects of species interactions that include competition between species within a group, competition between groups, and predation. The mathematical formulation also includes constraints on carrying capacity for both the entire system and for individual groups. We applied the model as initialized to the Northeast U.S. Large Marine Ecosystem finfish community. We then executed simulations designed to explore the behavior of the model with respect to fishery exploitation and ecological interactions. Collectively, the results demonstrated the utility, and the need, for incorporating ecological effects into fisheries models. 相似文献
167.
A dynamic plot-scale model PROGRASS was developed to simulate the seasonal and inter-annual dynamics of productive, cut grass/clover mixtures in response to management, and specifically to examine the role of root development on grass/clover interactions. The model was parameterized by virtue of data for dry matter yield, leaf area index, root mass, soil mineral N uptake and biological N fixation from a long-term field trial in north-eastern Switzerland. It was tested using 5 years of independent data for yield and clover fraction from a field experiment with two management regimes carried out on the Swiss Central Plateau. The results of transient simulations indicated that under intensive fertilization grass dominance was initiated by preferential allocation of assimilates to the roots. The rapid growth of the grass root system lowered the substrate C:N ratio, favouring carbon allocation to the shoot, which eventually provided competitive advantages with respect to light interception. Under extensive management, limited N acquisition capacity of the grass root system maintained preferential allocation to the roots, limiting shoot development in the grass and leading to clover dominance. Co-existence regimes with dominance by one of the components were also found in equilibrium experiments, with a transition regime from clover to grass dominance for annual N applications in the range 100–200 kg N ha−1 y−1 that reflected adjustments of the root system to fertilization. It is concluded that the dynamics of grass/clover mixtures is driven by negative and positive feedbacks in the soil–plant system that are strongly controlled by root development and therefore by the allocation patterns of the grass component. 相似文献
168.
169.
ABSTRACT: Recharge is an important parameter for models that simulate water and contaminant transport in unconfined aquifers. Unfortunately, measurements of actual recharge are not usually available causing recharge to be estimated or possibly added to the calibration procedure. In this study, differences between observed water-table elevations and water-table elevations simulated with a model based on the one-dimensional Boussinesq equation were used to identify both the timing and quantity of recharge to an alluvial valley aquifer. Observed water table elevations and river stage data were recorded during a five-year period from 1991 to 1995 at the Ohio Management Systems Evaluation Area located in south-central Ohio. Direct recharge attributed to overbank flow during and shortly after flood conditions accounted for 65 percent of the total recharge computed during the five-year study period. Recharge of excess infiltration to the aquifer was intermittent and occurred soon after large rainfall events and high river stage. Specification of constant recharge with time values in ground-water simulation models seems inappropriate for stream-aquifer systems given the strong influence of the river on water table elevations in these systems. 相似文献
170.
Need and nestmates affect begging in tree swallows 总被引:3,自引:0,他引:3
We conducted an experiment on nestling tree swallows (Tachycineta bicolor) to examine predictions from signalling models for the evolution of conspicuous begging behaviour. Specifically, we examined
the relationship between (1) nestling begging intensity and hunger, (2) begging intensity and parental provisioning and (3)
begging intensity and nestmate condition. Forty broods of 9-day-old nestlings were removed from their nests for 1 h and assigned
to one of the following three treatments: (1) all nestlings in the brood deprived of food (n = 13), (2) all nestlings in the brood fed (n = 11) or (3) half the nestlings in the brood deprived and half fed (n = 16). Videotapes before and after the treatments showed that begging intensity increased in broods in which all of the nestlings
had been deprived and decreased in broods in which all of the nestlings had been fed. Deprived nestlings in the half-and-half
treatment did not change their begging intensity in response to treatment, while fed nestlings in this treatment group showed
a decrease in begging intensity. Parent tree swallows increased their feeding rate to deprived broods and decreased their
rate to fed broods. Within broods, parents decreased their feeding rate to fed nestlings, but showed no significant change
in feeding to deprived nestlings. Our results suggest that begging intensity is influenced by hunger and that parents appear
to respond to variation in begging intensity. The begging of nestmates also appears to influence begging independently of
need. These results are consistent with predictions derived from signalling models of begging.
Received: 20 June 1997 / Accepted after revision: 19 January 1998 相似文献