Associations between fish assemblages and environmental factors for Mediterranean-type rivers during summer

The structure of summer fish assemblages was examined along longitudinal gradients in 31 Mediterranean-type rivers of the middle Guadiana basin (south-west Iberian Peninsula), using data from 157 sites including small streams to deep rivers. An ordination analysis, based on 16 variables, was applied to species presence, using principal component and canonical correspondence analysis. The results for the habitat data were compared with those for the biological data using a Mantel analysis, and the agreement was highly significant. Spatial structure was considered by partitioning the total variability among the environmental and geographical variables. The fish assemblages showed longitudinal zoning during the summer, with species distributed over gradients of habitat size (depth), water quality (current and physico-chemical variables), and cover (substratum and vegetation), according to their adult size and life history. The size of the habitat that remained available in summer had the greatest biological effect, being the most important factor explaining fish species distribution and assemblage structure during this stressing season. Strictly spatial variation was low, but there was still a high residual variation. Habitat associations and life-history strategies are discussed for native and exotic species.     

Short delay in timing of emergence determines establishment success in Pinus sylvestris across microhabitats

BACKGROUND AND AIMS: The date of emergence may have far-reaching implications for seedling performance. Seedlings emerging early in the growing season often have a greater rate of survival or grow better if early emergence provides advantages with respect to an environmental cue. As a result, the benefits of early emergence may be lost if the environmental stress creating the differences among cohorts disappears. The experimental manipulation under field conditions of the factors that constitute the main sources of stress for seedling establishment is thus a straightforward method to evaluate the impact of date of emergence on seedling establishment under realistic conditions. METHODS: Two field experiments were performed to analyse the effect of emergence date on survival and first-year growth of Scots pine seedlings in natural mountain forests in south-east Spain. Two main environmental factors that determine seedling success in these mountains were considered: (1) microhabitat type (monitoring the effect of date of emergence in the three most common microhabitats where seedlings recruit); (2) summer drought (monitored by an irrigation treatment with control and watered sampling points). KEY RESULTS: Overall, early emergence resulted in a higher probability of survival and better growth in the two experiments and across microhabitats. However, the reduction in summer drought did not diminish the differences observed among cohorts: all cohorts increased their survival and growth, but early cohorts still had a clear advantage. CONCLUSIONS: Date of emergence determines establishment success of Pinus sylvestris seedlings, even if cohorts are separated by only a few days, irrespective of the intensity of summer drought. The experimental design, covering a gradient of light intensity and soil moisture that simulates conditions of the regeneration niche of Scots pine across its geographical range, allows the results to be extrapolated to other areas of the species. Date of emergence is thus likely to have a large impact on the demography of Scots pine across its geographical range.     

河北夏蝗大发生与气象条件的关系

利用合成分析和秩相关系数2种方法,分析了河北2种生态类型蝗区中夏蝗LocustamigratoriaL.发生程度与气象条件的关系,以确定影响夏蝗大发生的关键气象因子。结果表明:2个类型蝗区大发生年以前一年5月至当年夏蝗出土以前的气温偏高、降水偏少为主;前一年6月下旬、7月上旬、8月上旬、8月中旬气温、6月上旬降水、当年3月下旬降水、4月下旬气温为沿海蝗区关键影响因子,前一年7月上旬和8月下旬气温、5月中旬降水及当年2月中、下旬气温、4月下旬和5月上旬气温为洼淀蝗区的关键影响因子。     

Infection of Barley by <Emphasis Type="Italic">Ramularia</Emphasis> <Emphasis Type="Italic">collo-cygni</Emphasis>: Scanning Electron Microscopic Investigations

Ramularia collo-cygni causes leaf spots on barley (Hordeum vulgare), a disease of growing economical importance. Scanning electron microscopy was used to study the life cycle of the fungus on barley during the vegetation period and in winter. The infectious stage started with conidium germination on the surface and the penetration into the leaf via the stomatal pore where the hyphae grew within the cells that became necrotic. The conidiophores emerged through the stomatal pore. On older leaves, however, they frequently emerged apart from it and the results suggested a pushing apart of adjacent cell walls of the epidermal cells. An assessment of the amount of conidium formation of one heavily infested barley plant resulted in 4.05 × 10⁶ conidia per plant. For the first time, conidiophores, conidium production and germination of conidia were also observed in winter on barley and on maize leaves.     

Elevational range and timing of breeding in the birds of Ladakh: the effects of body mass, status and diet

We studied the effects of body mass, status (resident or migratory) and diet on the breeding elevation range and timing of reproduction of the birds in the Trans-Himalayan region of Ladakh, northwestern India. Most of breeding birds of Ladakh are Palearctic or breed at high elevations in the mountains. There is a small proportion of Oriental species, and no bird is endemic to this region. We found that heavier birds tended to start their egg-laying earlier than lighter ones. Since body mass is related to the length of incubation and nesting periods, it would appear that one result of this phenomenon is that the time of peak demand for food for most birds coincides with peak food abundance in summer. Status affected the elevation of the breeding range, with resident birds tending to breed at higher elevations than summer visitors. Residents and summer breeders also differed significantly in their diet composition, with the former feeding mainly on plants and seeds, and the latter feeding on molluscs, insects and worms.     

Gut passage times in Gammarus pulex (Crustacea,Amphipoda) and aspects of summer feeding in a stony stream

Gut passage times in Gammarus pulex (Crustacea, Amphipoda) were calculated by counting and measuring voided faecal pellets. Following feeding on elm leaves conditioned in a stream, or summer fine detritus from the same source, calculated gut passage times were usually short, about 2 h or less at 15 °C. Using harder oak and beech leaves, not previously conditioned in the stream, apparent gut passage times were much longer, 8–48 h, but since intermittent feeding occurred these figures are not comparable to the others.In connection with summer feeding of the animal in the stream, the microbiological status of the fine detritus there was studied. It contained fungal hyphae, which were mostly empty, viable fungal spores of terrestrial derivation, and bacteria, all largely carried on fragments of vascular plant tissues. In experiments, such fungal spores (of Aureobasidium pullulans and of Mucor sp.), incorporated into fine detritus, were not digested by the animal. The bacterium Bacillus cereus was present in the fine detritus and when the latter was consumed it survived passage through the gut of the animal. Using B. cereus as a proportion marker it was concluded that other unicellular bacteria in the fine detritus were not digested either. In other experiments, not immediately related to the summer season, nutrient extraction by the animal from hyphae of the fungus Nectria lugdunensis was examined; it probably occurs through sub-microscopic pores connecting the cells. This mode of extraction may apply when the animal consumes vascular plant tissues.     

Variation in onset of summer dormancy and flowering capacity along an aridity gradient in Poa bulbosa L., a geophytic perennial grass

Variation in the onset of summer dormancy and flowering capacity of 16 populations of Poa bulbosa, collected along a steep north-south aridity gradient in Israel (810-110 mm rain year(-1)), was studied under controlled conditions in a phytotron (16 h daylength, 22/16 degrees C day/night) and under natural conditions in a garden experiment in a net-house. Plant age at the onset of dormancy varied markedly amongst populations (7-16 weeks under controlled conditions) and was positively correlated with mean annual precipitation at the site of origin of the population, i.e. dormancy was earlier as aridity increased. Flowering capacity in the different populations was negatively correlated with rainfall in the original habitat and, consequently, also with the age at onset of dormancy, i.e. the lower the mean annual precipitation, the earlier the onset of dormancy and the higher the proportion of flowering plants and panicles per plant. Differences in xeromorphic leaf traits were also observed among populations from locations differing in aridity. Plants from the more arid sites (110-310 mm year(-1)) generally had greyish and curved leaves, whereas plants from more humid sites (500-810 mm year(-1)) tended to have green and straight leaves. Thus, plants with curved and/or greyish leaves generally had a higher flowering capacity and entered dormancy earlier than plants with straight and/or green leaves. The significance of the association among these traits for the adaptation of P. bulbosa to increasing aridity is discussed.     

Genetic and behavioural estimates of reproductive skew in male fallow deer

Populations of fallow deer, in general, have low genetic diversity. Nevertheless, we screened 39 microsatellite loci and identified 20 that were polymorphic and suitable to determine paternity of fallow deer. To date, paternity has been studied for 87, 110 and 152 fallow deer fawns born between 2000 and 2002. Our results confirm the existence of a strong polygynous mating system in our population and confirm that the number of copulations performed by males is globally a good estimator of their reproductive success: males which performed the largest proportion of matings fathered the largest proportion of fawns. Nevertheless, we report some differences between the two measurements of the males' reproductive success: measures of copulatory success underestimated the variance of the males' reproductive success. On average, males whose copulatory score exceeded their paternity had mated with a higher proportion of younger females. Young females may be more likely to lose the conceptus, or their offspring may suffer high postnatal mortality.     

A resampling approach for evaluating effects of pasture abandonment on subalpine plant species diversity

Abstract. The decline of species‐rich semi‐natural calcareous grasslands is a major conservation problem throughout Europe. Maintenance of traditional animal husbandry is often recommended as an important management strategy. However, results that underpin such management recommendations were derived predominantly from lowland studies and may not be easily applicable to high mountain areas. In this study we analyse the importance of traditional low‐intensity summer farming (cattle grazing) for vascular plant species diversity of a subalpine region in the northern calcareous Alps in Austria by resampling from an existing dataset on its vegetation. Results indicate a significant long term decline of plant species diversity following abandonment at the landscape scale. In contrast, within‐community effects of pasture abandonment on plant species diversity are equivocal and strongly depend on the plant community. We suppose these differences to be due to diet preferences of cattle as well as to the differential importance of competition for structuring the respective communities. From our results we infer that the main mechanism by which pasture abandonment affects vascular plant species diversity, at least during the first ca. 100 yr documented here, are not local‐scale competitive exclusion processes within persisting communities. Instead, post‐abandonment successional community displacements that cause a landscape scale homogenization of the vegetation cover seem to be primarily responsible for a decline of species diversity. We conclude, that successful management of vascular plant species diversity in subalpine regions of the Northeastern Calcareous Alps will depend on the maintenance of large scale pasture systems with a spatially variable disturbance regime.     

Experimental tests of copying and mate choice in fallow deer (Dama dama)

In fallow deer (Dama dama), as well as in other lek-breedingungulates, receptive females arriving at leks commonly joinmales that are defending large harems. This tendency enhancesdifferences in harem size and mating success between males.It could occur because females independendy move to the samemales, because females are attracted to males with females,or because females are attracted to each other. Using controlledexperiments with estrous female fallow deer, we show that, althoughfemales are more attracted to males with harems than to thosewithout, they are as frequently attracted to groups of femaleswithout a male as to female groups with males. We conclude thatfemale fallow deer joining leks are attracted to each otherand copy each other's movements. As yet, there is no firm evidencein fallow deer or in other lek-breeding ungulates that femalescopy each other's choice of mating partners. Key words: Damadama, fallow deer, lek breeding, mate choice, copying behavior.[Behav Ecol 4: 191–193 (1993)]