Group foraging, patch exploitation time and the finder's advantage

 We use a combination of the marginal value theorem (MVT) of Charnov (1976), and a group foraging model featuring information sharing to address patch residence in an environment where food occurs in discrete patches. We shall show that among equal competitors the optimal patch time for the individual that finds the food patch is shorter than that for the non-finder among equal competitors, T _E < T _N. This is the case if the patch-finder commences food harvesting in the patch earlier and manages to monopolise a fraction of the prey items (finder's advantage) before the other individuals come to take their benefit. When individuals differ in their food-searching abilities so that some of them (producers) contribute proportionally more to food-searching than others (scroungers), and differ in ability to compete for the food found, a difference emerges between producer and scrounger individuals in the optimal patch time. Within a patch we always have the finder's advantage (T _E < T _N) regardless of phenotype. Between patches a suite of optimal patch times for encountering individuals emerges depending on the performance of producers and scroungers when changing from solitary feeding to feeding in a group. The optimal patch time for individuals that are affected more severely by competition is shorter than that for individuals of the phenotype with better competitive ability. When both phenotypes are affected similarly no difference in optimal patch times emerges. Received: 13 February 1996 / Accepted after revision: 28 September 1996     

Intrapopulation spatial segregation in bream (<Emphasis Type="Italic">Abramis brama</Emphasis>) and roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>) in the Rybinsk Reservoir

In the course of studies on mass fish species (bream and roach) in water bodies of the Upper Volga basin, intraspecific groups of individuals have been distinguished. Conditions and possible mechanisms of spatial differentiation of these groups are considered. The intrapopulation divergence of individuals by some adaptive characters, primarily behavioral, enables them to utilize alternative resources, which provides for more efficient use of the environment by populations.     

Exposure estimates to Fusarium mycotoxins through cereals intake

Mycotoxins are harmful substances produced by fungi in several commodities with a widespread presence in foodstuffs. Human exposure to mycotoxins occurs mainly by contaminated food. The quantitation of mycotoxins in cereal-based food, highly consumed by different age population, is of concern. In this survey, 159 cereal-based samples classified as wheat, maize and rice-based, have been evaluated for the occurrence of patulin, deoxynivalenol, 3-acetyl-deoxynivalenol, fusarenon-X, diacetoxyscirpenol, nivalenol, neosolaniol, HT-2, T-2 and zearalenone by gas chromatography–tandem mass spectrometry. Intakes were calculated for average consumers among adults, children and infants and compared with the tolerable daily intakes (TDI). Data obtained were used to estimate the potential exposure levels. 65.4% of the samples were contaminated with at least one mycotoxin and 15.7% of the analyzed samples showed co-occurrence of mycotoxin. The dietary exposure to HT-2 and T-2 toxins was estimated as 0.010 and 0.086 μg kg⁻¹ bw d⁻¹, amounting to 10% and 86% of the TDI, for adults and infants respectively. These results back up the necessity to take a vigilant attitude in order to minimize human intake of mycotoxins.     

Women NGOs and rural women empowerment activities in the Niger Delta, Nigeria

The study attempted to document beneficiaries’ perceptions on the contributions of Women NGOs (WNGOs) to the socio-economic empowerment of rural women in Akwa Ibom State, Nigeria. The specific objectives of the study included: an assessment of WNGOs contributions to improvements’ in beneficiaries’ socio-economic activities and constraints affecting beneficiaries’ participation in WNGOs activities. An attempt was also made to determine the existence of a significant relationship between the pre and post-participation income of WNGOs beneficiaries. A sample size of 240 respondents from 48 Local Women Groups (LWGs), which are affiliated to three active WNGOs in four states of the Niger Delta were utilized for the study. Findings revealed that WNGOs cater for a broad spectrum of rural women. WNGOs were revealed to affect beneficiaries’ socio-economic statuses through increased income generation, health awareness and acquisition of food processing skills. Constraints affecting beneficiaries’ participation in WNGOs activities include: inadequate credit facilities, and poor utilization of credit advances, resulting in poor loan repayment levels. A direct relationship was also revealed to exist between increased beneficiary exposures to WNGOs credit facilities and increased beneficiary income. It is believed that WNGOs are capable of more effective inputs into human and community development activities. Recommendations are proffered in this respect. Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.     

RELATIVE LEACHING POTENTIALS ESTIMATED FROM HYDROLOGIC SOIL GROUPS1

Leaching of soils with water can be both beneficial and hazardous in the same instance, removing salts harmful to plants and contributing dissolved substances to groundwater. The leaching potential of a given soil is difficult to assess, even with complex instrumentation. This paper suggests that the final infiltration rates associated with the Hydrologic Soil Groups used by the USDA Soil Conservation Service in watershed planning may provide a useful guide in estimating quantities of leaching water moving through soil profiles.     

民窿空区群级联失稳评价

民窿空区群已构成了许多矿山安全生产的极大隐患。针对民窿空区群的特点，运用重整化群方法，从整体的角度对民窿空区群系统的稳定性问题进行了研究，得到了空区群变尺度级联失稳迭代函数。给出了判别空区群系统整体失稳的临界概率，将空区群系统失稳的复杂判别转化为单元失稳概率与临界概率大小的比较问题，同时给出了计算实例，以供参考。所建立的方法可以为大规模民窿空区群范围内的工程施工以及民窿所在矿山空区群整体稳定性评价提供参考，同时也为认识一般空区群系统的失稳机理开辟了一条新的途径。     

大型综合性企业集团安全生产发展战略编制技术

针对由总论、安全生产理念、战略目标、管理体系、运营机制、绩效考核、保障建设和附则8部分组成的企业安全生产发展战略的体系框架,系统阐述企业安全生产发展战略编制的核心内容,剖析了企业安全生产理念的内涵,并分析企业设立安全生产战略目标的层次和内容,在企业安全生产管理体系、运营机制、绩效考核、风险管理、保障建设等方面详细解析安全生产发展战略编制的路径。     

New directions in Mexican environmental policy

Since taking office 1 December 1988, Mexico's incumbent president, Carlos Salinas de Gortari, has introduced important innovations in environmental policy that distinguish his administration from those of his predecessors. Greater administrative continuity, improved regulatory capacity achieved through statutory change, focused priorities centering on pollution abatement in Mexico City, and an aggressive search for external financing for pollution control are hallmarks of Salinas' approach. The success of these environmental reforms depends heavily on economic recovery, however, and environmental policy still suffers from underfunding, bureaucratic fragmentation, and heavy reliance on voluntarist enforcement mechanisms. Recently, U.S. congressional debate on a proposed free trade agreement with Mexico has been a factor in spurring the Salinas government to take new antipollution and conservation measures. Mexico's growing environmental movement is also an important force behind the government's new responsiveness in environmental matters. The Salinas administration recognizes the issue's political salience and has sought to defuse environmental criticism using a large arsenal of resources at its disposal. Salinas' environmental policy strategy may thus be characterized as both proactive and reactive in nature. While the reforms are evidence that Mexico is beginning to take environmental matters more seriously, economic recovery and sustained environmental activism remain vital to further progress.     

DETRITUS ABUNDANCE AND BENTHIC INVERTEBRATE CATCH IN ARTIFICIAL SUBSTRATE SAMPLES FROM MOUNTAIN STREAMS1

ABSTRACT: Artificial substrates were designed using rock filled polyethylene bags which were perforated with holes. The substrates trapped waterborne sediment and detritus which enhanced microhabitat complexity. Colonization was compared in side-by-side tests with multiple plate samplers in mountain streams ranging from second to seventh order. After 41 days the bag samples contained more sediment and detritus and more animals than did multiple plates. Plastic bags exceeded multiple plate samples by a factor of nearly 8 for individuals and 1.5 for taxa expressed as numbers/sampler. Although detritus amounts differed significantly between samplers, catch composition was similar in habitat preference and functional groups. Most taxa were “lotic erosional” or “lotic erosional-depositional” detritivores. The plastic bags better represented the streambed fauna judged by their greater similarity to dip net samples. Bag samplers had 4.5 × the colonization area of multiple plates, hence would be expected to support more species. Catch/m² of colonization area was not significantly different between samplers. Functionally the plastic bags act as detritus retention devices, offering a diverse, highly dynamic microhabitat for colonization. Results are interpretable in terms of research on microdistribution of stream benthos and the river continuum model. This study supports the conclusion that stream benthos abundance and diversity are related to the amount of detritus. Maximum diversity and numbers of individuals occurred in samples from third and fourth order streams. Grazers reached peak abundances in the same streams where the continuum model predicts P>R Shredders reached maximum abundances in third and fourth order streams where the riparian canopy was greatest. Predator abundance changed little with stream size. Although bag samples required more sorting time, the samplers are catch effective, inexpensive, and adaptable.