Distributed Modeling Approach Research Articles

Revealing areas of high nature conservation importance in a seasonally dry tropical forest in Brazil: Combination of modelled plant diversity hot spots and threat patterns

The Caatinga biome has been identified as one of the important wilderness areas on earth. However, less than 1% of the region is under strictly legal protection although Seasonally Dry Tropical Forests (SDTFs) are globally highly endangered. There is an urgent need to increase the understanding of diversity pattern and threaten status of Caatinga plant species to preserve the unique biodiversity and protect endangered species. Species distribution modelling (SDM) can support strategic decisions in nature conservation for poorly researched tropical regions. This study provides the first highly representative, spatially explicit overview of plant diversity and threat status for the entire Caatinga, a semi-arid area in Northeast Brazil. For this purpose, we developed (a) a stacked species distribution modelling (S-SDM) approach to predict quantitatively floristic species richness and patterns of threatened plant species and (b) a combined approach of diversity hot spots and hubs of threatened species to derive conservation importance units (CIU) to contribute to improved nature reserve management. We applied the modelling technique MaxEnt to establish predictive distribution models with 22 uncorrelated predictors including climate, topography, solar radiation and soil information at a high spatial resolution of 30 arc-seconds (approx. 1km). Spatial patterns of species richness and threat status were derived by stacking 1062 plant species and 27 endangered species, respectively. These outputs were compared to two levels of protected areas (Brazilian and international standards) and intensive human land use patterns to define a set of recommendations for conservation management. Our complementary S-SDM approach showed that our predicted CIUs covered an area of 24% across the entire biome, whereas only 7% of the Caatinga is currently protected based on the Brazilian standards. We found that apart from an excellent overlap of 38% between CIUs and the current protected areas, a substantial proportion of CIUs (89%) was predicted outside the existing reserve network. Moreover, our findings enable targeted surveys to be done in order to enhance conservation efforts and ensure the efficient use of available resources in this poorly studied tropical region. Future upcoming local and regional studies could focus on a multi-taxonomic approach including e.g. insects, reptiles or mammals as a holistic perspective towards biodiversity conservation.

Selecting umbrella species for conservation: A test of habitat models and niche overlap for beach-nesting birds

Umbrella species are rarely selected systematically from a range of candidate species. On sandy beaches, birds that nest on the upper beach or in dunes are threatened globally and hence are prime candidates for conservation intervention and putative umbrella species status. Here we use a maximum-likelihood, multi-species distribution modeling approach to select an appropriate conservation umbrella from a group of candidate species occupying similar habitats. We identify overlap in spatial extent and niche characteristics among four beach-nesting bird species of conservation concern, American oystercatchers (Haematopus palliatus), black skimmers (Rynchops niger), least terns (Sterna antillarum) and piping plovers (Charadrius melodus), across their entire breeding range in New Jersey, USA. We quantify the benefit and efficiency of using each species as a candidate umbrella on the remaining group. Piping plover nesting habitat encompassed 86% of the least tern habitat but only 15% and 13% of the black skimmer and American oystercatcher habitat, respectively. However, plovers co-occur with all three species across 66% of their total nesting habitat extent (~649ha), suggesting their value as an umbrella at the local scale. American oystercatcher nesting habitat covers 100%, 99% and 47% of piping plover, least tern and black skimmer habitat, making this species more appropriate conservation umbrellas at a regional scale. Our results demonstrate that the choice of umbrella species requires explicit consideration of spatial scale and an understanding of the habitat attributes that an umbrella species represents and to which extent it encompasses other species of conservation interest. Notwithstanding the attractiveness of the umbrella species concept, local conservation interventions especially for breeding individuals in small populations may still be needed.

Do forests represent a long-term source of contaminated particulate matter in the Fukushima Prefecture?

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted in radiocesium fallout contaminating coastal catchments of the Fukushima Prefecture. As the decontamination effort progresses, the potential downstream migration of radiocesium contaminated particulate matter from forests, which cover over 65% of the most contaminated region, requires investigation. Carbon and nitrogen elemental concentrations and stable isotope ratios are thus used to model the relative contributions of forest, cultivated and subsoil sources to deposited particulate matter in three contaminated coastal catchments. Samples were taken from the main identified sources: cultivated (n = 28), forest (n = 46), and subsoils (n = 25). Deposited particulate matter (n = 82) was sampled during four fieldwork campaigns from November 2012 to November 2014. A distribution modelling approach quantified relative source contributions with multiple combinations of element parameters (carbon only, nitrogen only, and four parameters) for two particle size fractions (<63 μm and <2 mm). Although there was significant particle size enrichment for the particulate matter parameters, these differences only resulted in a 6% (SD 3%) mean difference in relative source contributions. Further, the three different modelling approaches only resulted in a 4% (SD 3%) difference between relative source contributions. For each particulate matter sample, six models (i.e. <63 μm and <2 mm from the three modelling approaches) were used to incorporate a broader definition of potential uncertainty into model results. Forest sources were modelled to contribute 17% (SD 10%) of particulate matter indicating they present a long term potential source of radiocesium contaminated material in fallout impacted catchments. Subsoils contributed 45% (SD 26%) of particulate matter and cultivated sources contributed 38% (SD 19%). The reservoir of radiocesium in forested landscapes in the Fukushima region represents a potential long-term source of particulate contaminated matter that will require diligent management for the foreseeable future.

Modelling food web structure using an end-to-end approach in the coastal ecosystem of the Gulf of Gabes (Tunisia)

Given the ecological importance and high socio-economic value of the fishery of the Gulf of Gabes, an end-to-end model was applied to its continental shelf ecosystem to characterize the structure of the food web in the 2000s. This approach consisted in forcing a high trophic level model (OSMOSE) with an existing biogeochemical model (Eco3M-MED) representing the seasonal dynamics of the low trophic levels. The two models were linked through trophic interactions to represent the ecosystem dynamics from primary producers to top predators. In this study, we developed the multispecies, individual-based model OSMOSE in the Gulf of Gabes (OSMOSE-GoG). This model aims to capture the main processes that influence species life cycle and simulate the functioning of the ecosystem according to opportunistic predation process based on size selection and spatio-temporal co-occurrence between a predator and its prey. The spatial distribution of the eleven modelled species was derived from a Multi-Scale Species Distribution Modelling approach. We calibrated OSMOSE-GoG model with available data of biomass and fishing yield, using an optimization method based on evolutionary algorithms which is suitable for complex and stochastic models. Finally, OSMOSE-GoG was validated against independent data sets at different hierarchical levels: the individual (diet composition), population (mean size of commercial catch) and community levels (mean trophic level) following the Pattern-Oriented Modelling approach. The model outputs were overall consistent with the diet compositions and mean trophic levels derived from the ECOPATH model of the Gulf of Gabes (ECOPATH-GoG) and the observations of mean size of catches. The OSMOSE-GoG can be considered as a baseline model to investigate ecosystem responses to environmental changes and fishing management measures in the Gulf of Gabes.

Spatio‐temporal variability of water and energy fluxes – a case study for a mesoscale catchment in pre‐alpine environment

AbstractWater and energy fluxes at and between the land surface, the subsurface and the atmosphere are inextricably linked over all spatio‐temporal scales. Our research focuses on the joint analysis of both water and energy fluxes in a pre‐alpine catchment (55 km2) in southern Germany, which is part of the Terrestrial Environmental Observatories (TERENO). We use a novel three‐dimensional, physically based and distributed modelling approach to reproduce both observed streamflow as an integral measure for water fluxes and heat flux and soil temperature measurements at an observation location over a period of 2 years. While heat fluxes are often used for comparison of the simulations of one‐dimensional land surface models, they are rarely used for additional validation of physically based and distributed hydrological modelling approaches. The spatio‐temporal variability of the water and energy balance components and their partitioning for dominant land use types of the study region are investigated. The model shows good performance for simulating daily streamflow (Nash–Sutcliffe efficiency &gt; 0.75). Albeit only streamflow measurements are used for calibration, the simulations of hourly heat fluxes and soil temperatures at the observation site also show a good performance, particularly during summer. A limitation of the model is the simulation of temperature‐driven heat fluxes during winter, when the soil is covered by snow. An analysis of the simulated spatial fields reveals heat flux patterns that reflect the distribution of the land use and soil types of the catchment. The water and energy partitioning is characterized by a strong seasonal cycle and shows clear differences between the selected land use types. Copyright © 2016 The Authors Hydrological Processes Published by John Wiley &amp; Sons Ltd.

Quantifying sediment sources in a lowland agricultural catchment pond using 137Cs activities and radiogenic 87Sr/86Sr ratios

Soil erosion often supplies high sediment loads to rivers, degrading water quality and contributing to the siltation of reservoirs and lowland river channels. These impacts are exacerbated in agricultural catchments where modifications in land management and agricultural practices were shown to accelerate sediment supply. In this study, sediment sources were identified with a novel tracing approach combining cesium (137Cs) and strontium isotopes (87Sr/86Sr) in the Louroux pond, at the outlet of a lowland cultivated catchment (24km2, Loire River basin, France) representative of drained agricultural areas of Northwestern Europe.Surface soil (n=36) and subsurface channel bank (n=17) samples were collected to characterize potential sources. Deposited sediment (n=41) was sampled across the entire surface of the pond to examine spatial variation in sediment deposits. In addition, a 1.10m sediment core was sampled in the middle of the pond to reconstruct source variations throughout time. 137Cs was used to discriminate between surface and subsurface sources, whereas 87Sr/86Sr ratios discriminated between lithological sources. A distribution modeling approach quantified the relative contribution of these sources to the sampled sediment.Results indicate that surface sources contributed to the majority of pond (μ 82%, σ 1%) and core (μ 88%, σ 2%) sediment with elevated subsurface contributions modeled near specific sites close to the banks of the Louroux pond. Contributions of the lithological sources were well mixed in surface sediment across the pond (i.e., carbonate sediment contribution, μ 48%, σ 1% and non-carbonate sediment contribution, μ 52%, σ 3%) although there were significant variations of these source contributions modeled for the sediment core between 1955 and 2013. These fluctuations reflect both the progressive implementation of land consolidation schemes in the catchment and the eutrophication of the pond.This original sediment fingerprinting study demonstrates the potential of combining radionuclide and strontium isotopic geochemistry measurements to quantify sediment sources in cultivated catchments.

Predicting the distributions of predator (snow leopard) and prey (blue sheep) under climate change in the Himalaya.

Future climate change is likely to affect distributions of species, disrupt biotic interactions, and cause spatial incongruity of predator–prey habitats. Understanding the impacts of future climate change on species distribution will help in the formulation of conservation policies to reduce the risks of future biodiversity losses. Using a species distribution modeling approach by MaxEnt, we modeled current and future distributions of snow leopard (Panthera uncia) and its common prey, blue sheep (Pseudois nayaur), and observed the changes in niche overlap in the Nepal Himalaya. Annual mean temperature is the major climatic factor responsible for the snow leopard and blue sheep distributions in the energy‐deficient environments of high altitudes. Currently, about 15.32% and 15.93% area of the Nepal Himalaya are suitable for snow leopard and blue sheep habitats, respectively. The bioclimatic models show that the current suitable habitats of both snow leopard and blue sheep will be reduced under future climate change. The predicted suitable habitat of the snow leopard is decreased when blue sheep habitats is incorporated in the model. Our climate‐only model shows that only 11.64% (17,190 km2) area of Nepal is suitable for the snow leopard under current climate and the suitable habitat reduces to 5,435 km2 (reduced by 24.02%) after incorporating the predicted distribution of blue sheep. The predicted distribution of snow leopard reduces by 14.57% in 2030 and by 21.57% in 2050 when the predicted distribution of blue sheep is included as compared to 1.98% reduction in 2030 and 3.80% reduction in 2050 based on the climate‐only model. It is predicted that future climate may alter the predator–prey spatial interaction inducing a lower degree of overlap and a higher degree of mismatch between snow leopard and blue sheep niches. This suggests increased energetic costs of finding preferred prey for snow leopards – a species already facing energetic constraints due to the limited dietary resources in its alpine habitat. Our findings provide valuable information for extension of protected areas in future.

Semantic latent dirichlet allocation for automatic topic extraction

With the inception and uncontrollable growth of digital documents, Automatic Topic Extraction is found to be an active research topic. In order to handle the processing of documents, variety of algorithms was presented in literature for topic extraction using distribution Modeling and classification approaches. Among different modeling methods of topic extraction, Latent Dirichlet Allocation (LDA) is one of the important algorithms for Topic Identification. Even though LDA is popular technique for topic identification, it turns to difficulty in determining the model parameters and also, suffers with finding the degree of similarity and semantic handling. In order to handle these challenges, a new method is proposed for automatic topic extraction. Accordingly, this method called, Semantic Latent Dirichlet Allocation (SLDA) is proposed by extending LDA in a semantic way. A new mathematical computation is included where the model parameters are estimated using new membership degree in Semantic Latent Dirichlet Process along with semantic similarity measure. The experimentation is carried out with two different databases and it observed that SLDA outperformed by showing better when compared with existing LDA in Jaccord Coefficient.

Improving essential fish habitat designation to support sustainable ecosystem-based fisheries management

A major limitation to fully integrated ecosystem based fishery management approaches is a lack of information on the spatial distribution of marine species and the environmental conditions shaping these distributions. This is particularly problematic for deep-water species that are hard to sample and are data poor. The past decade has seen the rapid development of a suite of advanced species distribution, or ecological niche, modelling approaches developed specifically to support efficient and targeted management. However, model performance can vary significantly and the appropriateness of which methods are best for a given application remains questionable. Species distribution models were developed for three commercially valuable Hawaiian deep-water eteline snappers: Etelis coruscans (Onaga), Etelis carbunculus (Ehu) and Pristipomoides filamentosus (Opakapaka). Distributional data for these species was relatively sparse. To identify the best method, model performance and distributional accuracy was assessed and compared using three approaches: Generalised Additive Models (GAM), Boosted Regression Trees (BRT) and Maximum Entropy (MaxEnt). Independent spatial validation data found MaxEnt consistently provided better model performance with ‘good’ model predictions (AUC =>0.8). Each species was influenced by a unique combination of environmental conditions, with depth, terrain (slope) and substrate (low lying unconsolidated sediments), being the three most important in shaping their distributions. Sustainable fisheries management, marine spatial planning and environmental decision support systems rely on an understanding species distribution patterns and habitat linkages. This study demonstrates that predictive species distribution modelling approaches can be used to accurately model and map sparse species distribution data across marine landscapes. The approach used herein was found to be an accurate tool to delineate species distributions and associated habitat linkages, account for species-specific differences and support sustainable ecosystem-based management.

Application of deterministic distributed hydrological model for large catchment: a case study at Vu Gia Thu Bon catchment, Vietnam

In order to create a tool to help hydrologists and authorities to have good understanding about occurrences in stream flow regime together with its variation in the future under the impact of climate change in the Vu Gia Thu Bon catchment, a deterministic distributed hydrological model has been developed and constructed. This model covers the major processes in the hydrologic cycle including rainfall, evapotranspiration, overland flow, unsaturated flow, groundwater flow, channel flow, and their interactions. The model is calibrated and validated against the daily data recorded at seven stations during 1991–2000 and 2001–2010, respectively. The quality of results is demonstrated by Nash–Sutcliffe and correlation coefficients that reach 0.82 and 0.92, respectively, in discharge comparison. With water levels, the obtained coefficients are lower but the quality of results still remains high; Nash–Sutcliffe and correlation coefficients reach 0.77 and 0.89, respectively, in the upstream part of the catchment. This analysis demonstrates the performance of the deterministic distributed modeling approach in simulating hydrological processes one more time; it also confirms the usefulness of this model with ungauged catchments or large catchments. Additionally, this analysis proves the role of multi-calibration in increasing the accuracy of hydrological models for large catchments.

Understanding habitat selection of the Vulnerable wild yak Bos mutus on the Tibetan Plateau

AbstractWe tested a series of hypotheses on drivers of habitat selection by the Vulnerable wild yak Bos mutus, combining distribution-wide sighting data with species distribution modelling approaches. The results indicate that climatic conditions are of paramount importance in shaping the wild yak's distribution on the Tibetan Plateau. Habitat selection patterns were seasonal, with yaks appearing to select areas closer to villages during the vegetation-growing season. Unexpectedly, our index of forage quantity had a limited effect in determining the distribution of the species. Overall, our results suggest that expected changes in climate for this region could have a significant impact on habitat availability for wild yaks, and we call for more attention to be focused on the unique wildlife in this ecosystem.

Will climate change increase the risk of plant invasions into mountains?

Mountain ecosystems have been less adversely affected by invasions of non-native plants than most other ecosystems, partially because most invasive plants in the lowlands are limited by climate and cannot grow under harsher high-elevation conditions. However, with ongoing climate change, invasive species may rapidly move upwards and threaten mid-, and then high-elevation mountain ecosystems. We evaluated this threat by modeling the current and future habitat suitability for 48 invasive plant species in Switzerland and New South Wales, Australia. Both regions had contrasting climate interactions with elevation, resulting in possible different responses of species distributions to climate change. Using a species distribution modeling approach that combines data from two spatial scales, we built high-resolution species distribution models (≤ 250 m) that account for the global climatic niche of species and also finer variables depicting local climate and disturbances. We found that different environmental drivers limit the elevation range of invasive species in each of the two regions, leading to region-specific species responses to climate change. The optimal suitability for plant invaders is predicted to markedly shift from the lowland to the montane or subalpine zone in Switzerland, whereas the upward shift is far less pronounced in New South Wales where montane and subalpine elevations are already suitable. The results suggest that species most likely to invade high elevations in Switzerland will be cold-tolerant, whereas species with an affinity to moist soils are most likely to invade higher elevations in Australia. Other plant traits were only marginally associated with elevation limits. These results demonstrate that a more systematic consideration of future distributions of invasive species is required in conservation plans of not yet invaded mountainous ecosystems.

Fine-scale distribution of treeline trees and the nurse plant facilitation on the eastern Tibetan Plateau

Above-average climate warming occurred during the 20th century in high altitude regions, and alpine treelines are believed to be an early indicator to respond to these warming-related changes. However, empirical investigations on treeline dynamics showed diverse results. The main objectives of this study are: (1) to investigate if treeline position shifted and if tree recruitment changed along with climate warming, and (2) to test if adult trees have “nursing effect” on tree establishment at treelines. We investigated two Balfour spruce (Picea balfouriana Rehd. et Wils.) treelines in Chang Niang (CNT) and Dang Dui (DDT), Dingqing county, Changdu prefecture, eastern Tibet. At each treeline site, three replicate plots with a size 30m×50m were established. The coordinates of each tree within the plots were recorded and the age of each tree was identified by dendrochronological method. The changes in treeline position and tree recruitment were examined from spatially fine-scale distribution of trees and their age structure. The spatial patterns of individual trees were analyzed to infer the neighborhood effects. Results indicate that plots CNT2, CNT3, DDT1 and DDT2 showed stable treeline position during the last century, whereas plots CNT1 and DDT3 showed treeline advancing movement. Tree recruitments in all the six plots were enhanced during the 20th century, with two peaks occurring in the 1890–1910s and the 1950–1990s. Seedlings and saplings showed a general clustered distribution in all the six plots. The diverse pattern of treeline movement and episodic regeneration suggest that the treeline activity is not merely a result of climate change. “Nursing effects” from adult trees may play an important role in shaping the treeline activities on the eastern Tibetan Plateau. Our findings reveal diverse patterns in treeline dynamics at a local scale and highlight the importance of incorporating biotic interactions into species distribution modeling approaches.

Cryptic diversity and population structure at small scales: the freshwater snailAncylus(Planorbidae, Pulmonata) in the Montseny mountain range

Anthropogenic impacts like intensified land use and climate change are severe threats to freshwater biodiversity and effective biodiversity monitoring is therefore one of the most urgent tasks. This is, however, often hampered by the lack of knowledge regarding the number and ecology of species. Molecular tools have shown many freshwater taxa to comprise morphologically cryptic species, which often occur in sympatry on a small geographic scale. Here, we studied the freshwater snail Ancylus fluviatilis (Muller, 1774) species complex in the Iberian Montseny Mountains. We hypothesized that (1) several species of A. fluviatilis sensu lato occur in the Montseny and (2) the different species seldom co-occur in syntopy due to different ecological demands or interspecific competition. We barcoded 180 specimens from 36 sites in the Montseny for the cytochrome c oxidase subunit I (COI) barcoding gene and molecularly identified two Ancylus species. These species seldom occurred in syntopy and a species distribution modelling approach showed differing bioclimatic preferences of the species. One species occurs mainly in cooler, higher altitude streams while the second species occurs in lower-altitude areas with higher temperatures. Tests of population structure showed that both species possibly do not disperse well in the study area and that populations within species might be adapted to certain bioclimatic conditions in different regions of the Montseny. Our results highlight the need to incorporate molecular techniques into routine monitoring programmes.

Combining multiple fallout radionuclides (137Cs, 7Be, 210Pbxs) to investigate temporal sediment source dynamics in tropical, ephemeral riverine systems

Land use change and the associated acceleration of soil erosion have increased sediment supply to rivers worldwide. To effectively manage sediment loads, it is important to understand sediment dynamics. Fallout radionuclides (i.e. Be-7, excess Pb-210, Cs-137) separately provide spatial and temporal sediment source information. However, their combined application has been limited by an assumption that subsurface sources do not receive Be-7 fallout. Here, we examine this assumption and investigate the utility of combining these radionuclides to simultaneously model spatial and temporal sediment source dynamics. Soil and subsurface material were sampled to characterize potential sediment sources in a 12-km(2) catchment in northern Laos. This included material that was directly sampled from surface and subsurface sources (n = 65) and also in situ sediment source samples that were collected in ephemeral flow on hillslopes (n = 19). Suspended sediment (n = 16) was sampled at two monitoring stations. A distribution modelling approach quantified the relative contributions of surface and subsurface sources, as well as the proportion of material labelled with Be-7. The results from these two end-member models were compared to a four end-member model examining contributions from recently eroded surface, recently eroded subsurface, re-suspended surface and re-suspended subsurface sources. Approximately 80 % of sediment was modelled to be supplied by sources labelled with Be-7. Subsurface sources were modelled to contribute similar to 75 % of sediment. Accordingly, there was similar to 55 % more sediment modelled from subsurface sources than expected if subsurface sources were sheltered from Be-7 fallout. Differences between subsoil and Be-7-labelled source contributions modelled by the two and four end-member models were, with one exception (0.3 %), within the range of model uncertainty, further supporting the existence of re-suspended subsurface sources. At an upstream sampling location (S4), surface sources contributed the majority of sediment (55 %) whereas subsurface sources dominated the supply of sediment downstream (S10-74 %). Importantly, re-suspended subsurface sources, labelled with Be-7, were a significant sediment source at the catchment outlet (S10-60 %) during the investigated event. This study demonstrates the utility of combining multiple radionuclides when investigating spatial and temporal sediment source dynamics in tropical, ephemeral catchments. In the future, this approach should be tested with larger source datasets during the entire wet season and in larger catchments. This research furthers our understanding of sediment propagation in tropical catchments, contributing to the implementation of efficient soil conservation measures to reduce the deleterious effects of suspended sediment loads.

A discussion of the importance of particle size distribution data for characterizing Athabasca Oil Sands

Abstract Predicting bitumen recovery from the McMurray Formation oil sands is required to optimize resource management and development planning. While there are many parameters that affect the recovery predictions, bitumen grade and fines in the oil sands mining, and permeability in the in situ projects, are the most important geological parameters. In this paper, we discuss how particle size distribution data can aid in the estimation of these and some other parameters and what value it brings in improving our understanding of oil sands quality and recovery. We conclude with a short review of the methods currently available for particle size distribution modeling, while paying special attention to a practical particle size distribution modeling approach based on look-up tables. The proposal is illustrated using Telephone Lake data.

Global climate suitability of citrus huanglongbing and its vector, the Asian citrus psyllid, using two correlative species distribution modeling approaches, with emphasis on the USA

Two approaches to correlative species distri- bution models (MaxEnt and Multi-Model Framework) were used to predict global and local potential distribu- tion of huanglongbing (HLB) caused by Candidatus Liberibacter asiaticus (CLas) and its vector the Asian citrus psyllid (ACP, Diaphorina citri Kuwayama). Long-term climate data were sourced from the Worldclim website. The global distribution of CLas and ACP was gathered from online databases, literature review and communication with specialists. Data on Clas and ACP distribution in the USA were not used in model calibration to allow model validation for inde- pendent locations. Both models successfully predicted Florida and coastal areas in the Gulf Coast states as highly suitable for Clas and ACP. The models also predicted that coastal areas in California were climatologically favorable for ACP and Clas, but less so than in Florida. When current USA presence data were included in the models, the suitable areas for ACP establishmentexpandedtotheCentralValley,CA,while this area remained less conducive for CLas. Climate suitability was primarily related to rainfall and second- arily to temperature. Globally, both models predicted that climates in large areas of Africa, Latin America and North Australia were highly suitable for ACP and CLas, while the climate in the Mediterranean area was moderately suitable for ACP but less suitable for CLas, except for that in southern Portugal and Spain. Clas predictions from our models could be informative for countries like Australia, New Zealand, citrus-producing European countries and much of Africa, where CLas and D. citri have not been reported.

Population genetic structure of Oryza rufipogon and Oryza nivara: implications for the origin of O.nivara.

Ecological speciation plays a primary role in driving species divergence and adaptation. Oryza rufipogon and Oryza nivara are two incipient species at the early stage of speciation with distinct differences in morphology, life history traits and habitat preference, and therefore provide a unique model for the study of ecological speciation. However, the population genetic structure of the ancestral O.rufipogon has been controversial despite substantial study, and the origin of the derivative O.nivara remains unclear. Here, based on sequences of 10 nuclear and two chloroplast loci from 26 wild populations across the entire geographic ranges of the two species, we conducted comprehensive analyses using population genetics, phylogeography and species distribution modelling (SDM) approaches. In addition to supporting the two previously reported major subdivisions, we detected four genetically distinct groups within O.rufipogon and found no correlation between the genetic groups and either species identity or geographical regions. The SDM clearly showed substantial change in the distribution range of O.rufipogon in history, demonstrating that the repeated extinction and colonization of local populations due to multiple glacial-interglacial cycles during the Quaternary was most likely the main factor shaping the confounding population genetic structure of O.rufipogon. Moreover, we found significant differences between the two species in climate preferences, suggestive of an important role for climatic factors in the adaptation, persistence and expansion of O.nivara. Finally, based on the genetic pattern and dynamics of the O. nivara populations, we hypothesize that O.nivara might have independently originated multiple times from different O.rufipogon populations.

Testing projected wild bee distributions in agricultural habitats: predictive power depends on species traits and habitat type.

Species distribution models (SDM) are increasingly used to understand the factors that regulate variation in biodiversity patterns and to help plan conservation strategies. However, these models are rarely validated with independently collected data and it is unclear whether SDM performance is maintained across distinct habitats and for species with different functional traits. Highly mobile species, such as bees, can be particularly challenging to model. Here, we use independent sets of occurrence data collected systematically in several agricultural habitats to test how the predictive performance of SDMs for wild bee species depends on species traits, habitat type, and sampling technique. We used a species distribution modeling approach parametrized for the Netherlands, with presence records from 1990 to 2010 for 193 Dutch wild bees. For each species, we built a Maxent model based on 13 climate and landscape variables. We tested the predictive performance of the SDMs with independent datasets collected from orchards and arable fields across the Netherlands from 2010 to 2013, using transect surveys or pan traps. Model predictive performance depended on species traits and habitat type. Occurrence of bee species specialized in habitat and diet was better predicted than generalist bees. Predictions of habitat suitability were also more precise for habitats that are temporally more stable (orchards) than for habitats that suffer regular alterations (arable), particularly for small, solitary bees. As a conservation tool, SDMs are best suited to modeling rarer, specialist species than more generalist and will work best in long-term stable habitats. The variability of complex, short-term habitats is difficult to capture in such models and historical land use generally has low thematic resolution. To improve SDMs' usefulness, models require explanatory variables and collection data that include detailed landscape characteristics, for example, variability of crops and flower availability. Additionally, testing SDMs with field surveys should involve multiple collection techniques.

Quantifying the dominant sources of sediment in a drained lowland agricultural catchment: The application of a thorium-based particle size correction in sediment fingerprinting

Soil erosion is one of the main factors influencing land degradation and water quality at the global scale. Identifying the main sediment sources is therefore essential for the implementation of appropriate soil erosion mitigation measures. Accordingly, caesium-137 (137Cs) concentrations were used to determine the relative contribution of surface and subsurface erosion sources in a lowland drained catchment in France. As 137Cs concentrations are often dependent on particle size, specific surface area (SSA) and novel thorium (Th) based particle size corrections were applied. Surface and subsurface samples were collected to characterize the radionuclide properties of potential sources. Sediment samples were collected during one hydrological year and a sediment core was sampled to represent sediment accumulated over a longer temporal period. Additionally, sediment from tile drains was sampled to determine the radionuclide properties of sediment exported from the drainage network. A distribution modelling approach was used to quantify the relative sediment contributions from surface and subsurface sources. The results highlight a substantial enrichment in fine particles and associated 137Cs concentrations between the sources and the sediment. The application of both correction factors reduced this difference, with the Th correction providing a more accurate comparison of source and sediment samples than the SSA correction. Modelling results clearly indicate the dominance of surface sources during the flood events and in the sediment core. Sediment exported from the drainage network was modelled to originate predominantly from surface sources. This study demonstrates the potential of Th to correct for 137Cs particle size enrichment. More importantly, this research indicates that drainage networks may significantly increase the connectivity of surface sources to stream networks. Managing sediment transferred through drainage networks may reduce the deleterious effects of suspended sediment loads on riverine systems in similar lowland drained agricultural catchments.