Does hydraulic lift exist in shallow-rooted species? A quantitative examination with a half-shrub Gutierrezia sarothrae

Hydraulic lift occurs in some deep-rooted shrub and herbaceous species. In this process, water taken up by deep roots from the moist subsoil is delivered to the drier topsoil where it is later reabsorbed by shallow roots. However, little is known about the existence of hydraulic lift in shallow-rooted xeric species. The objectives of this study were 1) to ascertain whether hydraulic lift exists in Gutierrezia sarothrae (broom snakeweed), a widespread North American desert species with a shallow root system, grown in pot and field conditions and 2) if it does, how much water can be transferred from the subsoil to the 30 cm topsoil during the night. Snakeweed seedlings were transplanted in buried pots allowing the deeper roots to grow into the subsoil 30 cm below the surface. Soil water content inside and outside of the pot was measured seasonally and diurnally with time domain reflectometry technique (TDR). An increase in water content was detected in the pot after the plant was covered for 3 h by an opaque plastic bag during the day, suggesting hydraulic lift from deeper depths and exudation of water into the drier topsoil. Root exudation was also observed on native range sites dominated by snakeweed. Water efflux in the pot was 271 g per plant per night. which was equivalent to 15.3% of the extrapolated, porometer-derived whole-plant daily transpiration. Hydraulic lift observed in Gutierrezia improved water uptake during the day when evaporative demand is high and less water is available in the topsoil. We concluded that hydraulic lift might help snakeweed to alleviate the effect of water stress.     

Phylogenetic island disequilibrium: evidence for ongoing long‐term population dynamics in two Mediterranean butterflies

Aim Our aims were to verify the existence of phylogenetic disequilibrium between butterfly lineages at the subcontinental scale for islands and the nearest mainland and to test the capacity of islands for hosting ancestral populations of butterflies and the significance of such relict populations. Location The western Mediterranean continental area of Europe and North Africa together with several large and small islands (Balearics, Tuscan Archipelago, Aeolian Archipelago, Capri, Sardinia, Sicily, Corsica). Methods Using geometric morphometrics, the shape of male genitalia was analysed in two common butterflies (Pyronia cecilia and Pyronia tithonus), whose spatial heterogeneity in the Mediterranean region has recently been described. Observed patterns in genital shapes were compared with shapes predicted for islands and fossil islands to assess the contribution of historical and current events in accounting for the transition from a refugial model to an equilibrium model. Measurements were taken for 473 specimens in 90 insular and mainland sites. Results The shape of the genitalia of populations of most islands differed substantially from that predicted by the equilibrium hypothesis while closely fitting the refugial hypothesis. The comparison between different models strongly suggests that islands maintain ancestral lineages similar to those living in Spain (P. cecilia) and France (P. tithonus). A high correlation between observed and predicted patterns on islands and fossil islands occurs during the first steps of modelled introgressive hybridization while the following steps exposed a successively lower fit, suggesting that the process from a refugial to an equilibrium situation is highly skewed towards an earlier non‐equilibrium. Main conclusions The observed non‐equilibrium pattern supports the refugial hypothesis, suggesting that an ancestral lineage was originally distributed from Spain to Italy, and also occupied offshore islands. This lineage, replaced in Italy, has persisted on the islands owing to their isolation. A comparison of the distribution patterns for genetic and morphometric markers in several species indicates that the situation highlighted for Pyronia may represent a common biogeographic feature for many Mediterranean butterflies.     

Biological Aspects of Medorippe lanata (Linnaeus, 1767) (Brachyura: Dorippidae) from the Eastern Ligurian Sea (Western Mediterranean)

The aim of the present study is to investigate the demographic structure and to identify some aspects of the biology of an exploited population of Medorippe lanata (Brachyura: Dorippidae) in the eastern Ligurian Sea, western Mediterranean. 1364 specimens (639 males and 725 females) of M. lanata were collected on a monthly basis from January to December 2001, in a wide area of the eastern Ligurian Sea usually exploited by the Viareggio ‘rapido’ trawl fleet. M. lanata represented an important fraction of the discard, both in weight and in number of individuals. Maximum abundance of this species occurred in late summer-early autumn (up to 3369 ind. km⁻² and 50.6 kg km⁻² in August). The overall females:males sex-ratio was 1.13:1, while the monthly sex-ratio did not differ statistically from 1:1 in all months, except in September and October, when females significantly outnumbered males. The sampled population was composed of two cohorts from November to April. Sizes ranged from 10 to 29 mm carapace length (CL) for females and from 9 to 29 mm CL for males. The von Bertalanffy growth curve, computed for both sexes, gave a higher growth rate in males than in females. Recently moulted males and females were observed throughout the year, except in summer, when the highest number of ovigerous females was present. Females with external eggs were collected from March to November, with peaks in August and September. The monthly evolution of the ovarian maturity stages showed no clear temporal trend. At 21 mm CL, 50% of females were ovigerous or showed macroscopically mature ovaries. According to the dimorphism in chelae size, the presence of adult males (post-puberty stage) was observed all year round, from 18 to 29 mm CL, without evident temporal trends.     

Grassland birds and rotational-grazing in the northeast: Breeding ecology,survival and management opportunities

We studied long-term (2002–2009) demographics of bobolinks (Dolichonyx oryzivorus) and savannah sparrows (Passerculus sandwichensis) breeding in rotationally grazed systems in the northeastern United States. Both nest success (6–44% bobolink; 7–48% savannah sparrow) and annual productivity (0.43–2.83 bobolink; 0.70–2.35 savannah sparrow) varied annually. Predation (48%) and trampling by cows (32%) accounted for most failed nests. Annual adult apparent survival ranged from 23% to 85% and showed substantial variation by species and sex. Although grazing resulted in substantial loss of vegetative cover, savannah sparrows responded similarly to predation and grazing-induced nest failure (time to renest, distance moved between nests) and generally remained in the same paddock to renest. Minimum paddock size to accommodate one female within this rotation was 70 m × 70 m (0.49 ha), allowing a female to stay within a paddock and move (approx. 50 m) between nesting attempts. To balance pasturing objectives and birds' needs in paddocks first grazed before 25 June, managers in the Northeast should rest that paddock 42–50 days before the second grazing. © 2011 The Wildlife Society.     

Power and limitation of soil properties as predictors of variation in peak plant biomass in a northern mixed-grass prairie

Soil properties are thought to affect annual plant productivity in rangelands, and thus soil variables that are consistently correlated with plant biomass may be general indicators of rangeland health. Here we measured several soil properties (e.g. aggregate stability, organic carbon, total nitrogen) and tested each as a would-be predictor of local variation in peak aboveground grassland biomass. Individual properties explained a slight (≤10%) amount of variation in plant biomass. Plant biomass was mainly (negatively) associated with two soil properties, subsurface soil carbonate concentration and the stability of soil macroaggregates near the soil surface. Less important predictive variables included: elevation, plant community composition, surface soil organic carbon, and soil carbon:nitrogen. Plot-to-plot variation in plant biomass is seemingly difficult to predict based on soil properties, including popular indicators of soil and rangeland health and even root biomass. While protection of soil is critical to overall rangeland ecosystem function, our findings suggest that the relationship between soil properties and plant biomass in natural grasslands is complex. Thus, there may not be one or even several soil properties that consistently predict appreciable variation in peak grassland biomass, especially variation within an ecosystem independent of precipitation.