Distribution,biology and hybridization of Scaphirhynchus albus and S. platorynchus in the Missouri and Mississippi rivers

Synopsis Scaphirhynchus albus and S. platorynchus were studied in Missouri during 1978–1979 to assess their distribution and abundance, to obtain information on their life histories, and to identify existing or potential threats to their survival. S. platorynchus was collected in substantial numbers (4355 specimens) at all 12 sampling stations in the Missouri and Mississippi rivers, while only 11 S. albus were captured from 6 stations. Twelve specimens identified in the field as hybrids between the two species were captured from 4 stations. Morphometric and meristic comparisons of presumed hybrids with the parent species, using cluster and principal components analyses, demonstrated intermediacy of most specimens identified in the field as hybrids. Aquatic insects comprised most of the diet of S. platorynchus and S. albus, but S. albus and the hybrids had consumed considerable quantities of fish. S. albus grew more rapidly than S. platorynchus, while the growth of hybrids was intermediate. Hybridization appears to be a recent phenomenon, resulting from man-caused changes in the big-river environment. Hybridization may be a threat to survival of S. albus in the study streams.     

Comparative ontogeny of photobehavioural responses of charrs (Salvelinus species)

Synopsis The development of photobehavioural responses in brook (Salvelinus fontinalis) and lake (S. namaycush) charr was studied by monitoring the intrasubstrate movements and concurrent photoresponse behaviour of incubated embryos and alevins. Photoresponse behaviour of both F-1 hybrids of the parent species was also recorded. All embryos initially moved downward in the substrate, however brook charr descended farther and faster into the substrate than did lake charr. Photoresponse tests demonstrated a similar pattern of photoresponse transformation from a photonegative to a photopositive state in both species. However, photoresponse reversal was faster, more extensive and occurred later in brook charr than in lake charr. Patterns of photoresponse change in F-1 hybrids were intermediate between those of the parent species. Photoresponse shifts preceded the onset of alevin emergence in both species. occurring when differential development of various morphological characters existed. Developmental states of characters were synchronously maximal towards the end of alevin emergence. Intermediate measures of morphological development were observed for F-1 hybrids. Possible functions and mechanisms of photoresponse transitions are discussed in relation to ecological differences between the species.     

Environmental structures and variation in coastal vegetation of the Golfe du Lion (France)

On the French Mediterranean seashore, the essential environmental factors are: salinity, humidity, human activity, instability, and nature of the soil. Each of these factors presents a large range of variation. According to the values and the rhythm of changes presented by each of them a hierarchy of impacts has been established. As a consequence one ecological impact or another may be the result of the occurrence of mosaìcs in the plant cover. Thus, to explain the structures observed, it is necessary to distinguish between homogeneous systems in the landscape characterized by a similar hierarchy of impacts of the master factors. Analyses prove that vegetation units are either independent of each other (they are the reflection of a geomorphological structure, of climatic differences or of human influences), or organized into more or less complex phytoecological systems in which the mosaic of plant associations is governed by the activity of plant interactions. Some examples from salt ponds and sand dune systems explain these conclusions.     

The behaviour of Dutch fresh water ecologists in response to environmental concern

Due to the rise of environmental concern ecologists have been asked for advice more frequently since the late 1960s. This article discusses how the changing relationship between ecologists and society has affected the behaviour of one particular group of ecologists, namely Dutch fresh water ecologists, by focussing on their behaviour towards job market control and public interest activities. The analysis has been based on interviews with 65 Dutch fresh water ecologists together with an analysis of their publications.In contrast with American ecologists, Dutch fresh water ecologists have made little effort to control their job market by formal arrangements such as formulating a code of ethics and certification procedures. Secondly, Dutch fresh water ecologists generally conceive of their own role in contributing to the solution of environmental problems in relation to that of the environmentalists by doing good research and reliable advisory work. Although a significant number of researchers also address lay publics by writing popular articles and/or holding lectures, only a minority actively participates in environmental politics.     

Environmental effects on zein chromatograms of maize inbred lines revealed by reversed-phase high-performance liquid chromatography

Summary Alcohol soluble seed storage proteins (zeins and alcohol soluble glutelins) of maize (Zea mays L.) were separated by reversed-phase high-performance liquid chromatography (RP-HPLC). The objectives were to assess the reproducibility of chromatographic profiles using seed of inbred lines that had been produced in different locations and years. Reproducible differences between sources were seen but these were restricted to proteins that contributed 2% or less to an inbred profile. The majority of variation (93% for peak percent area; 99.8% for elution time) was between inbreds. RP-HPLC can therefore provide distinctive phenotypic profiles that are largely characteristic of genotype. Such qualitative and quantitative data will be valuable for studies of taxonomy, evolution, genetics, and germplasm identification.     

Increased straying by adult steelhead trout,Salmo gairdneri,following the 1980 eruption of Mount St. Helens

Synopsis This paper describes the magnitude and geographic dispersion of adult steelhead trout, Salmo gairdneri, diverted from Columbia River tributaries which were impacted by the 1980 volcanic eruption of Mount St. Helens. Compelling circumstantial evidence suggests that for 1–3 yr after the eruption, large numbers of adult steelhead migrating toward affected tributaries entered two non-affected tributaries flowing into the Columbia River upstream of natal streams. Streams downstream of affected tributaries did not appear to receive substantial numbers of displaced fish. I estimated that the percentage of non-natal steelhead migrating into the lower portions of the nearest upstream river increased from 16% pre-eruption to 45% post-eruption. Winter-run steelhead strays probably originated from both the Cowlitz and Toutle rivers, whereas summer-run strays originated predominantly from the Toutle River. Increased natural production in tributaries resulting from the infusion of large numbers of strays was of insufficient magnitude to be detected by the methods of this study.     

Nuclear and atomic analytical techniques in environmental studies in South America

The use of nuclear analytical techniques for environmental studies in South America is selectively reviewed since the time of earlier works of Lattes with cosmic rays until the recent applications of the PIXE (particle-induced X-ray emission) technique to study air pollution problems in large cities, such as São Paulo and Rio de Janeiro. The studies on natural radioactivity and fallout from nuclear weapons in South America are briefly examined.

     

大田玉米、高粱、芝麻、豇豆叶片水势、蒸腾速率、气孔阻力对环境因素的反应

本文研究了田间生长的玉米、高梁、芝麻、豇豆在不同土壤供水条件下,叶水势、气孔阻力、蒸腾速率日变化及其与环境因素的关系。结果表明,四种作物气孔开闭与光强密切相关:夜间气孔关闭,rs高;白天气孔开放,rs低。ψ_(WL)、TR与环境因素(气温、RH、ψ_(WV)、光强等)密切相关,它们之间的相关系数(在0.05和0.01水平)显著。四种作物ψ_(WL)日节奏为“正弦曲线”状,13:00—15:00小时ψ_(WL)最低,黎明前最高。中午ψ_(WV)和土壤含水量愈低。ψ_(ML)愈低。四种作物TR在早晨逐斩增高,13:00—15:00小时最强;傍晚前又降低;夜间TR最低。干旱植株ψ_(WL)、TR低于灌水植株,而rs高于灌水植株。     

Small-scale environmental heterogeneity and the analysis of species distributions along gradients

Abstract. The observed distribution of a species along an environmental gradient is strongly affected by environmental variability within a quadrat. Because a quadrat does not represent a point along an environmental gradient, but rather a range of conditions, it is likely to contain species not typically associated with the mean conditions in the quadrat. Systematic relationships exist between a species' true distribution, the observed distribution as a function of mean quadrat environment, and the frequency distribution of the environment within that quadrat. The observed species habitat breadth increases and the observed maximum abundance decreases as within-quadrat environmental heterogeneity increases. If species distributions or beta diversities are to be compared among species or coenoclines, they should be correctedforintra-quadratheterogeneity.Wederive simple corrections for environmental heterogeneity. The distributions of hardwood forest understory species along a soil acidity gradient in the North Carolina piedmont are presented as an example.