Associations between anuran tadpoles and salinity in a landscape mosaic of wetlands impacted by secondary salinisation

1. The secondary salinisation of wetlands is a global problem that poses a great threat to most freshwater biodiversity, including amphibians. We examined tadpole diversity in relation to wetland conductivity (our proxy for salinity) in wetlands in south‐eastern Australia to better understand (i) how salinity and amphibian diversity interact and (ii) the threat posed by secondary salinisation. 2. Six tadpole species were trapped in 56 wetlands that reflected a typical salinity gradient for the study region. We developed Bayesian models to examine the relationships between conductivity and both the probability of species occupancy and expected number of species with the imperfect detection probability of species accounted for in the models. 3. The probability of occupancy for all species and expected species number was negatively associated with wetland conductivity. Our results predict that conductivity should not limit tadpole presence below about 3000 μS cm⁻¹ at 25 °C (approximately 6% seawater) in the region, but will largely exclude amphibian larvae beyond about 6000 μS cm⁻¹ at 25 °C (approximately 12% seawater). 4. We also detected subtle among‐species differences in salinity tolerance. The results reported here show that tadpoles in the study region are likely to be negatively affected by projected future increases in salinisation.     

Relationship Between Photosynthate Supply and Endosperm Development in Maize

Maize (Zea mays L., cultivar Pioneer 3925) plants were givenshaded, thinned and control light treatments during 10 d or20 d periods surrounding pollination. Glucose, sucrose, starch,and dry matter (DM) contents were measured at intervals in compositesamples of pericarp/nucellus (PN), and in endosperms taken fromdeveloping kernels. Total kernel DM per ear at maturity washigher in the thinned treatment than control and shaded treatmentsdue to higher kernel set in apical regions of ears. In PNs at11 d after pollination (DAP), DM and sucrose contents were slightlygreater in thinned than control and shaded plants. Glucose contentswere substantially greater than controls in PNs of thinned plantsand were less than controls in shaded plants. In endospermsfrom apical kernels at 8 to 12 DAP (during cell division), DM,glucose and sucrose contents were substantially less in shadedthan control and thinned plants. Sucrose contents were greaterin endosperms of thinned than control plants. Sugar contentsin endosperms from basal kernels were nearly the same in thethree light treatments. At 12 DAP, apical and basal endospermsin shaded plants had fewer nuclei than those of the other lighttreatments. The light treatments appeared to effect apical kernelgrowth by influencing the extent of cell division. Zea mays L, maize, light treatment, endosperm, cell division, glucose, sucrose, starch     

The frequency distribution of bird body weights: aquatic and terrestrial species

The frequency distribution of the log-transformed body-weights of the world's bird species is right-skewed. The reasons for this skew are unknown. Aquatic bird species are on average heavier and have a less skewed distribution of weights than would be expected if they were a random sample from the overall weight distribution. Conversely, terrestrial species on average weigh less, and their weight distribution is more skewed. This is partly a phylogenetic effect; species of aquatic and terrestrial birds belong to different families. These differences suggest factors which may be important determinants of the overall weight distribution of birds.     

Ten years of elevated atmospheric carbon dioxide alters soil nitrogen transformations in a sheep‐grazed pasture

The increasing concentration of atmospheric carbon dioxide (CO₂) is expected to lead to enhanced competition between plants and microorganisms for the available nitrogen (N) in soil. Here, we present novel results from a ¹⁵N tracing study conducted with a sheep‐grazed pasture soil that had been under 10 years of CO₂ enrichment. Our study aimed to investigate changes in process‐specific gross N transformations in a soil previously exposed to an elevated atmospheric CO₂ (eCO₂) concentration and to examine indicators for the occurrence of progressive nitrogen limitation (PNL). Our results show that the mineralization–immobilization turnover (MIT) was enhanced under eCO₂, which was driven by the mineralization of recalcitrant organic N. The retention of N in the grassland was enhanced by increased dissimilatory NO₃^? reduction to NH₄⁺ (DNRA) and decreased NH₄⁺ oxidation. Our results indicate that heterotrophic processes become more important under eCO₂. We conclude that higher MIT of recalcitrant organic N and enhanced N retention are mechanisms that may alleviate PNL in grazed temperate grassland.     

Climate-related trends in Australian vegetation cover as inferred from satellite observations, 1981–2006

Using Advanced Very High Resolution Radiometer data spanning 1981–2006 and calibrated for long‐term analyses of vegetation dynamics, we examine whether vegetation cover has increased across Australia and whether there has been a differential response of vegetation functional types in response to changes in climatic growing conditions. Trends in vegetation cover are interpreted within Budyko's energy – water limitation framework. Results from an Australia‐wide analysis indicate that vegetation cover (as described by the fraction of Photosynthetically Active Radiation absorbed by vegetation; fPAR) has increased, on average, by 0.0007 per year – an increase of ∼8% over the 26 years. The majority of this change is due to a 0.0010 per year increase in persistent fPAR (representing nondeciduous perennial vegetation types; up 21%). In contrast, recurrent fPAR (representing deciduous, annual and ephemeral vegetation types) decreased, on average, by 0.0003 per year (down 7%), the trends of which are highly seasonal. Over the same period, Australian average annual precipitation increased by 1.3 mm yr⁻² (up 7%). A site‐based analysis using 90 long‐term meteorological stations with minimal localized land‐cover changes showed that energy‐limited sites where total fPAR increased generally experienced decreases in precipitation, and water‐limited sites that experienced decreases in cover were almost always associated with decreases in precipitation. Interestingly, where vegetation cover increased at water‐limited sites, precipitation trends were variable indicating that this is not the only factor driving vegetation response. As Australia is a generally highly water‐limited environment, these findings indicate that the effective availability of water to plants has increased on average over the study period. Results also show that persistent vegetation types have benefited more than recurrent types from recent changes in growing conditions. Regardless of what has been driving these changes, the overall response of vegetation over the past 2–3 decades has resulted in an observable greening of the driest inhabited continent on Earth.     

The role of species traits in the establishment success of exotic birds

There is now abundant evidence that propagule pressure, a composite measure of the number of individuals released into the nonnative location that varies between introduction events, is the most consistent predictor of success in the establishment of exotic species. However, the reasons why we expect propagule pressure to be important – because larger propagules ameliorate the effects of demographic, environmental or genetic stochasticity, or of Allee effects – also predict an influence of species traits on success. Here, we use a quantitative meta-analytical approach to assess the effect of three categories of species-level traits in the successful establishment of nonnative bird species: traits relating to population growth rates, traits that predispose species to Allee effects, and traits that enable a species to cope with novel environments. Traits that predispose species to Allee effects tend to decrease introduction success, whereas traits that enable a species to cope with novel environments tend to increase success. The breadth of habitats a species uses has the strongest mean effect of all variables analysed here. Mean effects for traits relating to population growth rates conflict in sign: in general, success is greater for species with large body mass whereas clutch size is not consistently related to establishment success. These results suggest a likely influence of some species-level traits on exotic bird establishment success, especially traits that enable a species to cope with novel environments. We suggest that considering such traits in terms of the small-population paradigm from conservation biology may be a productive avenue for future research.     

Birds in the diet of the Eurasian badger Meles meles: a review and meta-analysis

1. We reviewed 110 published studies of badger diet or badger predation of birds. The studies covered most of the Eurasian badger's range, from Ireland east to Japan and from Sweden south to southern Spain. 2. Bird remains were recorded in 2038 cases out of a total 36699 samples of badger faeces and stomachs. The overall percentage frequency of occurrence of bird remains in badger faeces and stomachs was 5.55% for all studies combined, and 7.97% for UK studies. The remains of 45 bird species from 11 orders were recorded. 3. The percentage frequency of occurrence of birds in badger diet increased significantly with latitude. There was no significant relationship between the occurrence of birds in badger diet and season. 4. While the prevalence of birds in the diet of badgers is generally low, the studies reviewed here provide insufficient evidence to assess whether badger predation has an impact on bird populations at a national scale, and experimental approaches to this problem are required.