Annual methane uptake by temperate semiarid steppes as regulated by stocking rates,aboveground plant biomass and topsoil air permeability

Overgrazing‐induced degradation of temperate semiarid steppes may affect the soil sink for atmospheric methane (CH₄). However, previous studies have primarily focused on the growing season and on single grazing patterns. Thus, the response of annual CH₄ uptake by steppes compared with various grazing practices is uncertain. In this study, we investigated the effects of grazing on the annual CH₄ uptake by two typical Eurasian semiarid steppes (the Stipa grandis steppe and the Leymus chinensis steppe) located in Inner Mongolia, China. The CH₄ fluxes were measured year‐round using static chambers and gas chromatography at 12 field sites that differed primarily in grazing intensities. Our results indicated that steppe soils were CH₄ sinks throughout the year. The annual CH₄ uptake correlated with stocking rates, whereas the seasonality of CH₄ uptake was primarily dominated by temperature. The annual CH₄ uptake at all sites averaged 3.7±0.7 kg C ha^?1 yr^?1 (range: 2.3–4.5), where approximately 35% (range: 23–40%) occurred during the nongrowing season. Light‐to‐moderate grazing (stocking rate≤1 sheep ha^?1 yr^?1) did not significantly change the annual CH₄ uptake compared with ungrazed steppes, but heavy grazing reduced annual CH₄ uptake significantly (by 24–31%, P<0.05). These findings imply that easing the pressure of heavily grazed steppes (e.g. moving to light or moderate stocking rates) would help restore steppe soil sinks for atmospheric CH₄. The empirical equations based on the significant relationships between annual CH₄ uptake and stocking rates, aboveground plant biomass and topsoil air permeability (P<0.01) could provide simple approaches for the estimation of regional CH₄ uptake by temperate semiarid steppes.     

Delayed setting of the photoperiodic response in recombinant clones of the aphid species Sitobion avenae

1. To explore the possible causes of apparent changes in reproductive mode from obligate to cyclical parthenogenesis over time in recombinant clones of the aphid Sitobion avenae Fabricius, all F1 progenies from various crosses were tested for several consecutive years for sexual morph production, after several weeks' exposure to a short photoperiod. 2. Variable proportions of the F1 progenies from selfing and outcrossing holocyclic clones did not produce mating females when induction was attempted in the year of hatching, but only after further induction, the following year or after. This ‘delayed setting of the photoperiodic response’ (DSPR) was much stronger in recombinants from crosses involving only clones from oceanic regions than in those involving one clone from a region with a continental climate. 3. F1 progenies resulting from crosses between one holocyclic and one intermediate clone did not show DSPR. It appeared again in the F2. 4. DSPR preferentially affected the latest hatched clones in a given progeny. 5. This phenomenon is neither an experimental artefact nor as a result of clone contamination. It appears to be because of a genetically controlled quantitative trait affecting the length of the ‘interval timer’, and may represent an adaptation of holocyclic aphid clones from oceanic regions to unpredictable winter climates.     

Chick provisioning rates and growth in Blacklbrowed Albatross Diomedea melanophris and Grey-headed Albatross D. chrysostoma at Bird Island, South Georgia

We compared the parental division of labour and the pattern and rate of parental provisioning by two sympatric species of albatross of similar mass and breeding timetable but differing in diet and in the duration of chick‐rearing. Using electronic weighing platforms inside artificial nests, we recorded chick mass of Black‐browed Albatross and Grey‐headed Albatross at Bird Island, South Georgia every 10 minutes for both species in 1993 and 1994 and for each species in two other years between 1990 and 1996. The chick mass data (nearly one million weighings) were used to calculate meal mass (over 5000 meals) and intervals between meals. Adult birds were fitted with radio‐transmitters which allowed each meal to be allocated to the appropriate parent. The combination of meal mass and foraging trip duration were used to calculate provisioning rates for chicks and individual adults. Overall, Black‐browed Albatrosses delivered significantly lighter meals (569 g) than Grey‐headed Albatrosses (616 g) but more frequently (every 2.07 days and 2.50 days respectively). Thus combining foraging trip data for both parents, Black‐browed Albatross chicks received a meal every 1.22 days compared with 1.26 days for Greyheaded Albatross. These rates did not differ significantly. The contribution of each sex of each species in chick provisioning fluctuated between years, being similar in some years or biased towards males in others. Chicks of both species that failed to fledge received smaller, less frequent meals than successful chicks. In 1990 and 1994, Black‐browed Albatross chick provisioning rates were lower than in 1992 and 1993. In 1990, both meal mass and trip duration were affected, but only in 1994 was trip duration longer. Greyheaded Albatross chick provisioning rate was lower in 1994 than in other years but trip duration was longer. In each species, significant changes in meal mass and trip duration occurred within the chick‐rearing period. Chick provisioning rates invariably declined before chicks attained their peak mass. For both species, chick growth rates and peak and fledging mass, but not fledging age, were affected by differences in provisioning rate.     

Male disguised females: costs and benefits of female‐limited dimorphism in a butterfly

1. In polymorphic species, two or more discrete phenotypes co‐occur simultaneously. Sex‐limited polymorphism is a particular case of polymorphism, in which several discrete morphs coexist within one of the two sexes only. Several hypotheses were proposed to explain the existence and the maintenance of sex‐limited polymorphism in insects: (i) the morphs have similar fitness, such as similar survival and expected fecundity, and their frequencies vary randomly (i.e. the null hypothesis); (ii) harassment by males is reduced towards the less common female morph, in this case andromorph females (i.e. the male mimicry and learned mate recognition hypotheses); (iii) morphs differ in predation risk (i.e. the predation hypothesis); or (iv) morphs differ in thermoregulation ability (i.e. the thermoregulation hypothesis). 2. Field observations and experiments were employed to compare the relative support of these hypotheses using dimorphic females of the bog fritillary butterfly. Differences were detected between morphs in survival, fecundity, harassment by males, predation pressure and thermal properties, thereby rejecting the null hypothesis. 3. The lifestyle of both morphs is associated with different costs and benefits, with advantages in daily survival and precocious emergence for the gynomorph females, and advantages in fecundity, predation and male harassment for the andromorph females. Besides, as the bog fritillary butterfly is protandrous (i.e. males emerge before females), the longer development of andromorph females puts them at risk of emerging when all the males are dead. The results raise the question as to which mechanisms control the ontogenetic pathways driving the production of the two morphs (i.e. genetic polymorphism or phenotypic plasticity).     

Effect of Drought on Metabolism and Partitioning of Carbon in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the partitioning of carbonon the third and seventh day from anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. The 9-d drought treatment, imposed just after anthesisduring the period of cell division in the grains, reduced grainyield by 18 per cent in Warigal and 30 per cent in Condor. Netcarbon fixation was up to 60 per cent higher in Warigal thanCondor towards the end of the drought period and this correlatedwith better osmotic adjustment in the flag leaf. Carbon partitioningbetween plant organs responded to water deficit more rapidlythan net carbon fixation. On day 3, carbon allocation to theroots of droughted plants was maintained in Condor and increasedby 14 per cent in Warigal, whereas carbon allocation to theear decreased in both varieties. However the roots did not competewell with the ear when the water deficit became more severe.Warigal accumulated 3 times more stem reserves than Condor underdrought. In the roots, the pattern of carbon allocation betweenrespiration and carbon accumulation changed soon after impositionof drought. Although total root respiration decreased underdrought it became more energy efficient, particularly for Warigal,as less respiration took place via the alternative pathway.On day 3, the larger carbon allocation to the roots and thelower root respiration accounted for the 4-times larger sugaraccumulation in droughted roots of Warigal compared with thoseof Condor. Osmotic adjustment in mature leaves and roots maybe of importance for the maintenance of vital processes andfor recovery after drought. Triticum aestivum L., wheat, drought, carbon, partitioning     

Comparative phylogeography of two sibling species of forest‐dwelling rodent (Praomys rostratus and P. tullbergi) in West Africa: different reactions to past forest fragmentation

Two sibling species of the rodent genus Praomys occur in West African forests: P. tullbergi and P. rostratus. By sampling across their geographical ranges (459 individuals from 77 localities), we test the hypothesis that climatic oscillations during the Quaternary made an impact on the observed pattern of cytochrome b sequence variation. We show that, although these two species have parapatric geographical distributions, their phylogeographical histories are dissimilar, which could be related to their distinct ecological requirements. Since the arid phases of the Pleistocene were characterized by isolated forest patches, and intervening wetter periods by forest expansion, these changes in forest cover may be the common mechanism responsible for the observed phylogeographical patterns in both of these species. For example, in both species, most clades had either allopatric or parapatric geographical distributions; however, genetic diversity was much lower in P. tullbergi than in P. rostratus. The genetic pattern of P. tullbergi fits the refuge hypothesis, indicating that a very small number of populations survived in distinct forest blocks during the arid phases, then expanded again with forest recovery. In contrast, a number of populations of P. rostratus appear to have survived during the dry periods in more fragmented forest habitats, with varying levels of gene flow between these patches depending on climatic conditions and forest extent. In addition, historical variations of the West African hydrographic network could also have contributed to the pattern of genetic differentiation observed in both species.     

Synchrony in population counts predicts butterfly movement frequencies

1. Measuring functional connectivity, the ability of species to move between resource patches, is essential for conservation in fragmented landscapes. However, current methods are highly time consuming and expensive. 2. Population synchrony‐ the correlation in time series of counts between two long‐term population monitoring sites, has been suggested as a possible proxy measure of functional connectivity. To date, population synchrony has been shown to correlate with proxies for movement frequency such as the coverage of suitable habitat types in intervening landscapes, and also least cost distances around hostile land cover types. 3. This provides tentative evidence that synchrony is directly driven by movements of the focal species, but an alternative explanation is that these land cover types affect the movement of interacting species (e.g. natural enemies of the focal species) which can also drive synchronous population dynamics. Therefore, what is needed is a test directly relating population synchrony to movement frequencies of a focal species. 4. Here we use data from a 21 year mark‐release‐recapture study and show that population synchrony does indeed predict movements of a focal butterfly species Boloria eunomia (Esper). 5. There is growing evidence that population synchrony can be a useful conservation tool to measure functional connectivity.     

Proharpoceras Chao: a new ammonoid lineage surviving the end-Permian mass extinction

Based on new, bed-rock controlled material from northwestern Guangxi and Oman, the Early Triassic genus Proharpoceras Chao is shown to be a representative of Otocerataceae. Character analysis excludes a direct link with the Griesbachian Otoceratidae and favours a derivation of Proharpoceras from the late Permian Anderssonoceratidae. The biostratigraphic range of Proharpoceras is restricted to the Smithian and its biogeographic distribution comprises Oman, South China, and Primorye, thus indicating an essentially low palaeolatitudinal distribution. Proharpoceras has no apparent relatives among other Early and Middle Triassic Ceratitida and is thus considered to be the last representative of Otocerataceae. This offshoot of the late Permian Anderssonoceratidae implies that an additional ammonoid lineage survived the end Permian extinction and that it dwindled away for some 2 Myr before going extinct.     

Characterization of polymorphic microsatellite loci in the terrestrial isopod Porcellionides pruinosus

We developed a set of six polymorphic microsatellite loci for the woodlouse, Porcellionides pruinosus. We screened 43 individuals from three French populations and found that locus‐specific allelic diversity ranges from 3 to 17 alleles (mean = 9.8) and observed heterozygosity ranges from 0.51 to 0.89 (mean = 0.77). These are the first microsatellites loci reported from the woodlouse.     

Will European soil-monitoring networks be able to detect changes in topsoil organic carbon content?

Within the United Nations Framework Convention on Climate Change, articles 3.3 and 3.4 stipulate that some voluntary activities leading to an additional carbon (C) sequestration in soils could be accounted as C sinks in national greenhouse gas inventories. These additional C stocks should be verifiable. In this work, we assess the feasibility of verifying the effects of changes in land use or management practice on soil organic carbon (SOC), by comparing minimum detectable changes in SOC concentration for existing European networks suitable for soil monitoring. Among the tested scenarios, the minimum detectable changes differed considerably among the soil-monitoring networks (SMNs). Considerable effort would be necessary for some member states to reach acceptable levels of minimum detectable change for C sequestration accounting. For SOC, a time interval of about 10 years would enable the detection of some simulated large changes in most European countries. In almost all cases, the minimum detectable change in SOC stocks remains greater than annual greenhouse gases emissions. Therefore, it is unlikely that SMNs could be used for annual national C accounting. However, the importance of organic C in soil functions, and as an indicator of soil condition and trends, underlines the importance of establishing effective national SMNs.