High gene flow and metapopulation dynamics detected for three species in a dryland river system

1. The highly variable hydrology of dryland rivers has important implications for population dynamics in these systems. In western Queensland, fluctuations in sub‐population size are likely to lead to local bottlenecks and extinctions, increasing the need for connectivity and gene flow to maintain population viability. 2. Using microsatellite markers, we explored evidence for this metapopulation structure in two species of freshwater fish (Maquaria ambigua and Tandanus tandanus) and one crustacean (Macrobrachium australiense) in a sub‐catchment of the upper Murray–Darling Basin, Australia. 3. Overall, we found very weak genetic structure for all three species. Two species (M. ambigua and M. australiense) showed some significant genetic structure that did not correlate with geographic distance. However, decomposed pairwise regression analysis revealed evidence for intense genetic drift at the waterhole scale, suggesting that local bottlenecks are driving what little genetic structure does exist for these species. 4. The results identify the local impact of bottlenecks on genetic diversity, but highlight the importance of gene flow in maintaining population viability in these highly variable systems. As the impacts of bottlenecks are likely to be tempered by gene flow, it is suggested that the maintenance of connectivity is of paramount importance in this dryland system.     

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

Reduced N cycling in response to elevated CO2, warming,and drought in a Danish heathland: Synthesizing results of the CLIMAITE project after two years of treatments

Field‐scale experiments simulating realistic future climate scenarios are important tools for investigating the effects of current and future climate changes on ecosystem functioning and biogeochemical cycling. We exposed a seminatural Danish heathland ecosystem to elevated atmospheric carbon dioxide (CO₂), warming, and extended summer drought in all combinations. Here, we report on the short‐term responses of the nitrogen (N) cycle after 2 years of treatments. Elevated CO₂ significantly affected aboveground stoichiometry by increasing the carbon to nitrogen (C/N) ratios in the leaves of both co‐dominant species (Calluna vulgaris and Deschampsia flexuosa), as well as the C/N ratios of Calluna flowers and by reducing the N concentration of Deschampsia litter. Belowground, elevated CO₂ had only minor effects, whereas warming increased N turnover, as indicated by increased rates of microbial NH₄⁺ consumption, gross mineralization, potential nitrification, denitrification and N₂O emissions. Drought reduced belowground gross N mineralization and decreased fauna N mass and fauna N mineralization. Leaching was unaffected by treatments but was significantly higher across all treatments in the second year than in the much drier first year indicating that ecosystem N loss is highly sensitive to changes and variability in amount and timing of precipitation. Interactions between treatments were common and although some synergistic effects were observed, antagonism dominated the interactive responses in treatment combinations, i.e. responses were smaller in combinations than in single treatments. Nonetheless, increased C/N ratios of photosynthetic tissue in response to elevated CO₂, as well as drought‐induced decreases in litter N production and fauna N mineralization prevailed in the full treatment combination. Overall, the simulated future climate scenario therefore lead to reduced N turnover, which could act to reduce the potential growth response of plants to elevated atmospheric CO₂ concentration.     

Phenology of high-arctic butterflies and their floral resources： Species-specific responses to climate change

Current global warming is particularly pronounced in the Arctic and arthropods are expected to respond rapidly to these changes. Long-term studies of individual arthropod species from the Arctic are, however, virtually absent. We examined butterfly specimens collected from yellow pitfall traps over 14 years （1996-2009） at Zackenberg in high-arctic, north-east Greenland. Specimens were previously sorted to the family level. We identified them to the species level and examined long-term species-specific phenological responses to recent summer wanning. Two species were rare in the samples （Polaris fritillary Boloria polaris and Arctic blue Plebejus glandon） and statistical analyses of phenological responses were therefore restricted to the two most abundant species （Arctic fritillary, B. chariclea and Northern clouded yellow Colias hecla）. Our analyses demonstrated a trend towards earlier flight seasons in B. chariclea, but not in C. hecla. The timing of onset, peak and end of the flight season in B. chariclea were closely related to snowmelt, July temperature and their interaction, whereas onset, peak and end of the flight season in C. hecla were only related to timing of snowmelt. The duration of the butterfly flight season was significantly positively related to the temporal overlap with floral resources in both butterfly species. We further demonstrate that yellow pitfall traps are a useful alternative to transect walks for butterfly recording in tundra habitats. More phenological studies of Arctic arthropods should be carded out at the species level and ideally be analysed in context with interacting species to assess how ongoing climate change will affect Arctic biodiversity in the near future [Current Zoology 60 （2）： 243-251, 2014].     

Pair bond and breeding success in Blue Tits Parus caeruleus and Great Tits Parus major

Data from 939 nests of the Blue Tit Parus caeruleus and 1008 nests of the Great Tit P. major from nestboxes provided in superabundance in mixed forest study sites between 1976 and 2001 were analysed to examine the effects of mate retention on breeding success and the relationship between mate fidelity and site fidelity. Most birds retained their former partner (76% in Great Tits and 65% in Blue Tits). The probability of a pair divorcing was affected by male age in Great Tits, divorce being more likely in pairs with first‐year males. Great Tit pairs breeding together for a second season bred earlier, but had no higher breeding success than pairs breeding together for the first time. In Blue Tits laying date and start of incubation tended to be earlier in pairs breeding together for a second season, but hatching and fledging dates were not earlier than in other pairs. Great Tit pairs breeding together for two consecutive seasons bred earlier in the second season than in the first, but breeding success did not differ significantly between years. In both species, breeding performance did not differ between pairs that divorced after a season and pairs that stayed together. Thus breeding success did not determine whether a pair divorced or bred together again. Neither Blue Tits nor Great Tits improved their breeding performance through divorce. Blue Tit females even had fewer fledglings in the year after divorce than in the year before. Mate retention affected breeding site fidelity. Blue Tit females had greater breeding dispersal distances between consecutive years when re‐mating than when breeding again with the same mate. In Great Tits both males and females dispersed more when re‐mating than when retaining the former partner, suggesting that mate retention increased the chance of retaining the breeding site. In both species, breeding dispersal distances did not differ between pairs that divorced and pairs in which one mate disappeared. Because no major advantage of mate retention was evident, we suggest that mate retention evolved under different conditions than those found in study sites with high breeding densities and a superabundance of artificial nesting sites.     

Earthworm communities in conventional wheat monocropping and low-input wheat-clover intercropping systems

A comparative study was conducted on earthworm communities in a conventional winter wheat monocropping system and a low‐input intercropping system in which successive crops of winter wheat were direct‐drilled into a permanent white clover sward. Earthworm abundance, biomass and species composition under the two cropping systems in the second and third years of successive cropping were assessed each spring and autumn in farm‐scale field plots at four sites using formalin and electrical extraction methods. The wheat‐clover cropping system supported larger earthworm communities (overall mean abundance 548 individuals m^?2, 137 g biomass m^?2) than conventional wheat monocropping (194 individuals m‐2, 36 g biomass m‐2). Between one and five more earthworm species were recorded in the wheat‐clover system than in the wheat system at three out of the four study sites. Wheat–clover cropping especially favoured species belonging to the epigeic and epigeic/anecic ecological groups such as Lumbricus castaneus, L. festivus, L. rubellus, juvenile Lumbricus and Satchellius mammalis. Earthworm communities in the wheat‐clover cropping system were comparable in size and species composition to communities normally found in perennial grassland‐type habitats such as pastures and grass‐legume leys.     

Field responses of stink bugs to the natural and synthetic pheromone of the Neotropical brown stink bug, Euschistus heros (Heteroptera: Pentatomidae)

Abstract.The synthetic racemic mixture of methyl 2,6,10‐trimethyltridecanoate, a component of the male produced pheromone of Euschistus heros (F.) (Heteroptera, Pentatomidae), was attractive to pentatomid species in a field test, using homemade pheromone trap designs. The pentatomid Piezodorus guildinii was caught in high numbers in field traps, during two field experiments, indicating a consistent response of this species to the E. heros pheromone. A correlation was found between the range of insects caught in the pheromone‐baited traps and a random sampling method. The synthetic stereoisomeric mixture of methyl 2,6,10‐trimethyldodecanoate, a minor component of E. heros pheromone, was also field tested and caught no pentatomids. Egg parasitoids were caught in traps baited with E. heros pheromone, indicating that this pheromone can be exploited as a kairomone. A synchrony in the periodicity of trap catch, between the egg parasitoids and their host, was also recorded.     

Linking evolution and development: Synchrotron Radiation X‐ray tomographic microscopy of planktic foraminifers

Abstract: Making the link between evolutionary processes and development in extinct organisms is usually hampered by the lack of preservation of ontogenetic stages in the fossil record. Planktic foraminifers, which grow by adding chambers, are an ideal target organism for such studies as their test incorporates all prior developmental stages. Previously, studies of development in these organisms were limited by the small size of their early chambers. Here, we describe the application of synchrotron radiation X‐ray tomographic microscopy (SRXTM) to document the ontogenetic history of the foraminifers Globigerinoides sacculifer and Globorotalia menardii. Our SRXTM scans permit resolution at submicrometre scale, thereby displaying additional internal structures such as pores, dissolution patterns and complexity of the wall growth. Our methods provide a powerful tool to pick apart the developmental history of these microfossils and subsequently assist in inferring phylogenetic relationships and evolutionary processes.     

Hydrological and biogeochemical controls on the timing and magnitude of nitrous oxide flux across an agricultural landscape

Anticipated increases in precipitation intensity due to climate change may affect hydrological controls on soil N₂O fluxes, resulting in a feedback between climate change and soil greenhouse gas emissions. We evaluated soil hydrologic controls on N₂O emissions during experimental water table fluctuations in large, intact soil columns amended with 100 kg ha^?1 KNO₃‐N. Soil columns were collected from three landscape positions that vary in hydrological and biogeochemical properties (N= 12 columns). We flooded columns from bottom to surface to simulate water table fluctuations that are typical for this site, and expected to increase given future climate change scenarios. After the soil was saturated to the surface, we allowed the columns to drain freely while monitoring volumetric soil water content, matric potential and N₂O emissions over 96 h. Across all landscape positions and replicate soil columns, there was a positive linear relationship between total soil N and the log of cumulative N₂O emissions (r²= 0.47; P= 0.013). Within individual soil columns, N₂O flux was a Gaussian function of water‐filled pore space (WFPS) during drainage (mean r²= 0.90). However, instantaneous maximum N₂O flux rates did not occur at a consistent WFPS, ranging from 63% to 98% WFPS across landscape positions and replicate soil columns. In contrast, instantaneous maximum N₂O flux rates occurred within a narrow range (?1.88 to ?4.48 kPa) of soil matric potential that approximated field capacity. The relatively consistent relationship between maximum N₂O flux rates and matric potential indicates that water filled pore size is an important factor affecting soil N₂O fluxes. These data demonstrate that matric potential is the strongest predictor of the timing of N₂O fluxes across soils that differ in texture, structure and bulk density.