The ectoparasitization of Coleophora alticolella (Lepidoptera) in relation to its aititudinal distribution

Abstract. 1. The parasitization of the larvae of Coleophora alticolella . feeding on Juncus squarrosus , was investigated at a series of altitudes from 15 to 520m above sea-level in northern England during 1977 and 1978.
2. Six species of primary parasitoid and one hyperparasitoid were reared from this host. Five of the primary parasitoids were ectophagous; only two specimens of the endoparasitoid, Gonotypus melanostoma , were reared.
3. All of the parasitoid species were recorded at 15 m but fewer at sites of higher altitude. Only one species, Scambus brevicomis , was recorded above 305 m, and none above 395 m. The hyperparasitoid, Tetrastichus endemus, was present only at 15 m.
4. Percentage parasitization was highest at 15 m; it was reduced from 51% to only 2% between 215 and 305 m in 1978. There was an increase in host density over this altitudinal range.
5. Three species, Scambus brevicomis. Elachertus olivaceus and Euderus viridis , accounted for most of the parasitization, but their relative proportions vaned at different altitudes.
6. The sex-ratios of the parasitoids reared from Coleophora alticolella ranged from 3.2% females for Scambus brevicomis , which is considered to also use larger hosts, to 99.4% females for Elachertus olivaceus , which develops by thelytokous parthenogenesis.
7. Euderus viridis and Scambus brevicomis started to attack the Coleophora alticolella larvae at a later date at 245 m than at 15 m, but attack by Elachertus olivacats was not delayed at the higher site.     

Variability in the distribution and abundance of stream salmonids, and the associated use of habitat models

The effective management of salmonid fisheries requires that the factors influencing variation in the abundance of stream populations are understood. The use of habitat models to explain the spatial component of population variance offers potential for management, but has not previously been set in the context of long term variation in population abundance because of the lack of suitable data sets. This paper examines contributions of spatial and temporal factors lo fish density variance using a 10-year data set from five tributaries of the River Conwy, North Wales. Recently developed habitat models were applied to the data to test their ability to explain nominal spatial variance. Spatial variance accounted for between 21 and 62% of the overall variance of salmonid abundance, and habitat models explained up to 95% of the spatial variance component. Synchrony in population variation amongst sites within and between tributaries is described, and some of the factors that may influence this are discussed.     

Summer drought exposure,stand structure,and soil properties jointly control the growth of European beech along a steep precipitation gradient in northern Germany

Increasing exposure to climate warming-related drought and heat threatens forest vitality in many regions on earth, with the trees' vulnerability likely depending on local climatic aridity, recent climate trends, edaphic conditions, and the drought acclimatization and adaptation of populations. Studies exploring tree species' vulnerability to climate change often have a local focus or model the species' entire distribution range, which hampers the separation of climatic and edaphic drivers of drought and heat vulnerability. We compared recent radial growth trends and the sensitivity of growth to drought and heat in central populations of a widespread and naturally dominant tree species in Europe, European beech (Fagus sylvatica), at 30 forest sites across a steep precipitation gradient (500–850 mm year⁻¹) of short length to assess the species' adaptive potential. Size-standardized basal area increment remained more constant during the period of accelerated warming since the early 1980s in populations with >360 mm growing season precipitation (April–September), while growth trends were negative at sites with <360 mm. Climatic drought in June appeared as the most influential climatic factor affecting radial growth, with a stronger effect at drier sites. A decadal decrease in the climatic water balance of the summer was identified as the most important factor leading to growth decline, which is amplified by higher stem densities. Inter-annual growth variability has increased since the early 1980s, and variability is generally higher at drier and sandier sites. Similarly, within-population growth synchrony is higher at sandier sites and has increased with a decrease in the June climatic water balance. Our results caution against predicting the drought vulnerability of trees solely from climate projections, as soil properties emerged as an important modulating factor. We conclude that beech is facing recent growth decline at drier sites in the centre of its distribution range, driven by climate change-related climate aridification.     

Rainfall and flowering synchrony in a tropical shrub: Variable selection on the flowering time ofErythroxylum havanense

Summary We tested the adaptive significance of flowering synchrony by means of a quantitative analysis of selection and by flowering induction experiments with the deciduous shrubErythroxylum havanense. Temporal schedules of flower and fruit production were determined for a local population (in three sites) in a Mexican seasonal forest for 2 years (1987–1988). The consequences of natural variation in flowering time (flowering initiation day) on maternal reproductive success (fecundity) were evaluated. We observed high levels of inter- and intraindividual flowering synchrony in 1987, but not in 1988 and this contrast was related to differences in rainfall patterns between the two years. A significant proportion (15.4%) of the phenotypic variation in flowering initiation day was accounted for by environmental variance. The expression of phenotypic variance of flowering time and, consequently, the opportunity for selection to act, are controlled by annual variation in rainfall. Despite the between-year difference in flowering synchrony, we detected a relatively intense directional selection on flowering initiation day in both years, but selection coefficients were of opposite sign (standardized directional gradients were –0.326 and 0.333 for 1987 and 1988, respectively). For both years there was a significant relationship between individual relative fitness and the number of neighbouring flowering plants in a given day, suggesting positive frequency-dependent selection.     

Synchronization of drosophila cells in culture

Summary We synchronized Drosophila cell lines (Schneider's line 2 and K_c) by allowing the cells to enter the stationary phase of growth and then diluting them into fresh culture medium. The cells of both cell lines entered S phase, after an 8- to 14-hr delay, in a state of partial synchrony; 60 to 80% of the cell population accumulated in S phase. Measurements of the cell cycle phases of Schneider's line 2 cells (S=14 to 16 hr; G₂=6 to 8 hr; M=0.4 hr) were similar to those of K_c cells. This work was performed under the auspices of the U.S. Energy Research and Development Administration. A.R. was supported by an NIH post-doctoral fellowship, No. CA01060.     

European springtime temperature synchronises ibex horn growth across the eastern Swiss Alps

Direct effects of climate change on animal physiology, and indirect impacts from disruption of seasonal synchrony and breakdown of trophic interactions are particularly severe in Arctic and Alpine ecosystems. Unravelling biotic from abiotic drivers, however, remains challenging because high‐resolution animal population data are often limited in space and time. Here, we show that variation in annual horn growth (an indirect proxy for individual performance) of 8043 male Alpine ibex (Capra ibex) over the past four decades is well synchronised among eight disjunct colonies in the eastern Swiss Alps. Elevated March to May temperatures, causing premature melting of Alpine snowcover, earlier plant phenology and subsequent improvement of ibex food resources, fuelled annual horn growth. These results reveal dependency of local trophic interactions on large‐scale climate dynamics, and provide evidence that declining herbivore performance is not a universal response to global warming even for high‐altitude populations that are also harvested.     

麋鹿幼仔的活动同步性与同性聚群倾向

哺乳动物幼体从出生到性成熟这段时间存在生理和行为上的巨大变化.麋鹿幼仔出生1周内,与成鹿和其它仔鹿呈隔离状态,且藏卧于隐蔽处,母鹿哺乳是引起幼仔活动的主要因素.     

Multiple responses to increasing spring temperatures in the breeding cycle of blue and great tits (Cyanistes caeruleus,Parus major)

Many bird species start laying their eggs earlier in response to increasing spring temperatures, but the causes of variation between and within species have not been fully explained. Moreover, synchronization of the nestling period with the food supply not only depends on first‐egg dates but also on additional reproductive parameters including laying interruptions, incubation time and nestling growth rate. We studied the breeding cycle of two sympatric and closely related species, the blue tit Cyanistes caeruleus and the great tit Parus major in a rich oak‐beech forest, and found that both advanced their mean first‐egg dates by 11–12 days over the last three decades. In addition, the time from first egg to fledging has shortened by 2–3 days, through a decrease in laying interruptions, incubation time (not statistically significant) and nestling development time. This decrease is correlated with a gradual increase of temperatures during laying, suggesting a major effect of the reduction in laying interruptions. In both species, the occurrence of second clutches has strongly decreased over time. As a consequence, the average time of fledging (all broods combined) has advanced by 15.4 and 18.6 days for blue and great tits, respectively, and variance in fledging dates has decreased by 70–75%. Indirect estimates of the food peak suggest that both species have maintained synchronization with the food supply. We found consistent selection for large clutch size, early laying and short nest time (laying to fledging), but no consistent changes in selection over time. Analyses of within‐individual variation show that most of the change can be explained by individual plasticity in laying date, fledging date and nest time. This study highlights the importance of studying all components of the reproductive cycle, including second clutches, in order to assess how natural populations respond to climate change.     

Genetic monogamy in blue-headed vireos and a comparison with a sympatric vireo with extrapair paternity

Based on the breeding synchrony hypothesis, we predicted, intwo congeners that nest in simiilar habitat but differ in nestingsynchrony, that blue-headed vireos (Vireo solitarius) wouldhave fewer extrapair fertilizations (EPFs) thaii red-eyed vireos(V. olivaceus EPFs were rare in blue-headed vireos (1/37 nestlings),but common in red-eyed vireos (11/19 nestlings). We studiedthe behavior of blue-headed vireos to determine what factorscould promote genetic monogamy. We found no evidence that malesmate guarded to prevent extrapair copulations from occurring.Males did not follow fertile mates closely when mates left thenest (14–25% of female departures) and, during the egg-layingperiod, males were often alone on the nest (22.3 mm/h). Femaleblue-headed vireos, but not red-eyed vireos, obtain direct benefitsfrom social mates such as nest building and incubation (49.1%of the total), and they assess male quality long before becomingfertile. Female blue-headed vireos spent more time incubatingwhen their mates had low incubation effort. Furthermore, maleincubation effort was positively correlated with nest survivalduring incubation. We discuss the evolution of genetic monogamyand sex role convergence in blue-headed vireos in relation toasynchronous breeding.