A reassessment of the mating system characteristics of the army ant Eciton burchellii

In a recent study, Denny et al. (2004a) showed that queens of the army ant, Eciton burchellii, mate with multiple males and presented estimates suggesting that they mate with more males than queens of any other ant species so far investigated. They also inferred that data were consistent with queens being inseminated repeatedly throughout their life, which would be exceptional among the social Hymenoptera and contradictory to predictions from kin selection theory. In the present study, we reanalyze these data using new software and supplement them with similar microsatellite data from other colonies of the same species. Mating frequencies in E. burchellii are indeed very high (mean observed and effective queen-mating frequencies of 12.9 each) but considerably lower than the previous estimates. We show that the number of patrilines represented in the first worker offspring of a young queen is lower than in older queens but suggest that this may be due to initial sperm clumping in the queen’s sperm storage organ, rather than to repeated inseminations. Moreover, we found no evidence for repeated mating by genotyping sequential worker generations produced by a single old queen, showing that she did not obtain new inseminations despite ample opportunities for mating.     

Modelling soil phosphorus decline: Expectations of Water Framework Directive policies

Depletion of plant-available soil phosphorus (P) from excessive to agronomically optimum levels is a measure being implemented in Ireland to reduce the risk of diffuse P transfer from land to water. Within the Nitrates and Water Framework Directive regulations the policy tool is designed to help achieve good status by 2015 in water bodies at risk from eutrophication. To guide expectation, this study used soil plot data from eight common soil associations to develop a model of Soil Test P (STP) (Morgan's extract) decline following periods of zero P amendment. This was used to predict the time required to move from excessive (Index 4) to the upper boundary of the optimum (Index 3) soil P concentration range. The relative P balance (P balance : Total soil P) best described an exponential decline (R² = 63%) of STP according to a backwards step-wise regression of a range of soil parameters. Using annual field P balance scenarios (?30 kg P ha^?1, ?15 kg P ha^?1, ?7 kg P ha^?1), average time to the optimum soil P boundary condition was estimated from a range of realistic Total P and STP starting points. For worst case scenarios of high Total P and STP starting points, average time to the boundary was estimated at 7–15 years depending on the field P balance. However, uncertainty analysis of the regression parameter showed that variation can be from 3 to >20 years. Combined with variation in how soil P source changes translate to resulting P delivery to water bodies, water policy regulators are advised to note this inherent uncertainty from P source to receptor with regard to expectations of Water Framework Directive water quality targets and deadlines.     

Assessing trophic position from nitrogen isotope ratios: effective calibration against spatially varying baselines

Nitrogen isotope signatures (δ¹⁵N) provide powerful measures of the trophic positions of individuals, populations and communities. Obtaining reliable consumer δ¹⁵N values depends upon controlling for spatial variation in plant δ¹⁵N values, which form the trophic ‘baseline’. However, recent studies make differing assumptions about the scale over which plant δ¹⁵N values vary, and approaches to baseline control differ markedly. We examined spatial variation in the δ¹⁵N values of plants and ants sampled from eight 150-m transects in both unlogged and logged rainforests. We then investigated whether ant δ¹⁵N values were related to variation in plant δ¹⁵N values following baseline correction of ant values at two spatial scales: (1) using ‘local’ means of plants collected from the same transect and (2) using ‘global’ means of plants collected from all transects within each forest type. Plant δ¹⁵N baselines varied by the equivalent of one trophic level within each forest type. Correcting ant δ¹⁵N values using global plant means resulted in consumer values that were strongly positively related to the transect baseline, whereas local corrections yielded reliable estimates of consumer trophic positions that were largely independent of transect baselines. These results were consistent at the community level and when three trophically distinct ant subfamilies and eight abundant ant species were considered separately. Our results suggest that assuming baselines do not vary can produce misleading estimates of consumer trophic positions. We therefore emphasise the importance of clearly defining and applying baseline corrections at a scale that accounts for spatial variation in plant δ¹⁵N values.     

耕作和混合农业体系未来植物养分利用的前景和挑战

在不污染环境的情况下生产足量的健康食品对未来世界农业是一个严重挑战.瑞典"21世纪的食物"研究计划已经研究了可持续耕作体系的经济的、环境的以及社会的各个方面,本文列举了瑞典"21世纪的食物"研究计划以及其它相关的国际研究计划中注重改善养分利用效率的一些研究,特别是氮和磷.它表明有许多可持续性解决养分利用效率的方法,有些很复杂,但有些就很简单.政府政策包括津贴、研究和技术以及公众对耕作方式的认可,所有这些都与制定这些解决方法结合在一起.需要知识转让的参与式途径,这样科学家、政策决策者、农场主、顾问以及消费者们可以交流信息,一起构建可持续的耕作体系.     

Drought can offset potential water use efficiency of forest ecosystems from rising atmospheric CO2

Increasing atmospheric CO₂ is both leading to climate change and providing a potential fertilisation effect on plant growth. However, southern Australia has also experienced a significant decline in rainfall over the last 30 years, resulting in increased vegetative water stress. To better understand the dynamics and responses of Australian forest ecosystems to drought and elevated CO₂, the magnitude and trend in water use efficiency (WUE) of forests, and their response to drought and elevated CO₂ from 1982 to 2014 were analysed, using the best available model estimates constrained by observed fluxes from simulations with fixed and time-varying CO₂. The ratio of gross primary productivity (GPP) to evapotranspiration (ET) (WUEe) was used to identify the ecosystem scale WUE, while the ratio of GPP to transpiration (Tr) (WUEc) was used as a measure of canopy scale WUE. WUE increased significantly in northern Australia (p < 0.001) for woody savannas (WSA), whereas there was a slight decline in the WUE of evergreen broadleaf forests (EBF) in the southeast and southwest of Australia. The lag of WUEc to drought was consistent and relatively short and stable between biomes (≤3 months), but notably varied for WUEe, with a long time-lag (mean of 10 months). The dissimilar responses of WUEe and WUEc to climate change for different geographical areas result from the different proportion of Tr in ET. CO₂ fertilization and a wetter climate enhanced WUE in northern Australia, whereas drought offset the CO₂ fertilization effect in southern Australia.     

Tissue accumulation of aluminium is not a predictor of toxicity in the freshwater snail, Lymnaea stagnalis

The amount of toxic metal accumulated by an organism is often taken as an indicator of potential toxicity. We investigated this relationship in the freshwater snail, Lymnaea stagnalis, exposed to 500 μg l⁻¹ Al over 30 days, either alone or in the presence of phosphate (500 μg l⁻¹ P) or a fulvic acid surrogate (FAS; 10 mg l⁻¹ C). Behavioural activity was assessed and tissue accumulation of Al quantified. Lability of Al within the water column was a good predictor of toxicity. FAS increased both Al lability and behavioural dysfunction, whereas phosphate reduced Al lability, and completely abolished Al-induced behavioural toxicity. Tissue accumulation of Al was not linked to toxicity. Higher levels of Al were accumulated in snails exposed to Al + P, compared to those exposed to Al alone, whereas FAS reduced Al accumulation. These findings demonstrate that the degree of tissue accumulation of a metal can be independent of toxicity.     

Quantifying phosphorus retention and release in rivers and watersheds using extended end-member mixing analysis (E-EMMA)

Extended end-member mixing analysis (E-EMMA) is presented as a novel empirical method for exploring phosphorus (P) retention and release in rivers and watersheds, as an aid to water-quality management. E-EMMA offers a simple and versatile tool that relies solely on routinely measured P concentration and flow data. E-EMMA was applied to two river systems: the Thames (U.K.) and Sandusky River (U.S.), which drain similar watershed areas but have contrasting dominant P sources and hydrology. For both the Thames and Sandusky, P fluxes at the watershed outlets were strongly influenced by processes that retain and cycle P. However, patterns of P retention were markedly different for the two rivers, linked to differences in P sources and speciation, hydrology and land use. On an annual timescale, up to 48% of the P flux was retained for the Sandusky and up to 14% for the Thames. Under ecologically critical low-flow periods, up to 93% of the P flux was retained for the Sandusky and up to 42% for the Thames. In the main River Thames and the Sandusky River, in-stream processes under low flows were capable of regulating the delivery of P and modifying the timing of delivery in a way that may help to reduce ecological impacts to downstream river reaches, by reducing ambient P concentrations at times of greatest river eutrophication risk. The results also suggest that by moving toward cleaner rivers and improved ecosystem health, the efficiency of P retention may actually increase.     

Impacts of Land‐Cover Change on Suspended Sediment Transport in Two Agricultural Watersheds1

Schilling, Keith E., Thomas M. Isenhart, Jason A. Palmer, Calvin F. Wolter, and Jean Spooner, 2011. Impacts of Land‐Cover Change on Suspended Sediment Transport in Two Agricultural Watersheds. Journal of the American Water Resources Association (JAWRA) 47(4):672‐686. DOI: 10.1111/j.1752‐1688.2011.00533.x Abstract: Suspended sediment is a major water quality problem, yet few monitoring studies have been of sufficient scale and duration to assess the effectiveness of land‐use change or conservation practice implementation at a watershed scale. Daily discharge and suspended sediment export from two 5,000‐ha watersheds in central Iowa were monitored over a 10‐year period (water years 1996‐2005). In Walnut Creek watershed, a large portion of land was converted from row crop to native prairie, whereas in Squaw Creek land use remained predominantly row crop agriculture. Suspended sediment loads were similar in both watersheds, exhibiting flashy behavior typical of incised channels. Modeling suggested that expected total soil erosion in Walnut Creek should have been reduced 46% relative to Squaw Creek due to changes in land use, yet measured suspended sediment loads showed no significant differences. Stream mapping indicated that Walnut Creek had three times more eroding streambank lengths than did Squaw Creek suggesting that streambank erosion dominated sediment sources in Walnut Creek and sheet and rill sources dominated sediment sources in Squaw Creek. Our results demonstrate that an accounting of all sources of sediment erosion and delivery is needed to characterize sediment reductions in watershed projects combined with long‐term, intensive monitoring and modeling to account for possible lag times in the manifestation of the benefits of conservation practices on water quality.