A novel mono- and diacylglycerol lipase highly expressed in Pichia pastoris and its application for food emulsifier preparation

A mono- and diacylglycerol lipase (MDL) was cloned from Penicillium cyclopium and expressed in Pichia pastoris strain GS115. The recombinant enzyme was named Lipase GH1. High cell density fermentation was performed by culture in a 7.5-L fermenter using BSMG medium, in which the phosphate in basal salt medium was replaced by sodium glycerophosphate (Na₂GP). The maximal lipase activity detected was 18,000 U per mL, and total protein content in the fermentation supernatant was 3.94 g per L. The activity of the liquid enzyme remained stable under alkaline conditions at 4 °C for 6 months and was 50% after one year. Lipase GH1 was used for the synthesis of mono- and diacylglycerols (MAGs and DAGs), which are commonly used emulsifiers for industrial applications. A conversion rate of 84% after 24 h of reaction was obtained using glycerol/oleic acid molar ratio 11:1, water content 1.5 wt%, enzyme dosage 80 U per g, and reaction temperature 35 °C. Lipase GH1 was more efficient for the synthesis of MAGs and DAGs than was Lipase G50 (a similar, commercially available lipase derived from Penicillium camemberti) when oleic acid was used as an acyl donor. Lipase GH1 has potential for food emulsifier preparation.     

The brown-world role of insectivores: Frogs reduce plant growth by suppressing detritivores in an alpine meadow

Predators of plant-suppressing herbivores have long been known to indirectly enhance plant biomass, while more recent work has revealed that predators of plant-facilitating detritivores can have the opposite effect on plant biomass. Generalist predators, such as frogs that typically facilitate plant growth in green food webs, may potentially negatively affect plant growth by consuming prey from brown food webs. In a marshy Tibetan alpine meadow, we tested the hypothesis that the locally abundant frog Rana kukunoris could negatively affect plant growth through suppression of dung-decomposing detritivores that promote plant growth by enhancing nutrient recycling. We conducted a factorial experiment (presence/absence of predators × presence/absence of dung) using replicate field enclosures over a growing season. Where dung was present, frogs significantly reduced the number of dung-feeding beetles and dung-feeding flies (including fly eggs and maggots) per dung pat, thereby decreasing dung mass loss and, indirectly, aboveground plant biomass (by 22%) surrounding dung pats. Where dung was absent, frogs did not affect plant biomass. Moreover, the number of dung beetles was positively associated with dung mass loss and soil soluble N concentration (but not total N concentrations), which in turn positively correlated with aboveground plant biomass. These results indicate that a generalist predator species standing in green food webs may play a contrasting role in brown food webs and indicate that a more nuanced appreciation of the functional role of predators in tri-trophic systems is required to accurately predict their cascading effects. Future studies must assess the relative strength of cascading effects mediated through brown and green channels in order to assess the net cascading effects of generalist predators in natural food webs.     

Multiple pathways from three types of sugar receptor sites to metabotropic transduction pathways of the blowfly: study by the whole cell-clamp experiments

Differences in the allometric scaling between gut capacity (with body mass, BM^1.00) and food intake (with BM^0.75) should theoretically result in a scaling of digesta retention time with BM^0.25 and therefore a higher digestive efficiency in larger herbivores. This concept is an important part of the so-called ‘Jarman–Bell principle’ (JBP) that explains niche differentiation along a body size gradient in terms of digestive physiology. Empirical data in herbivorous mammals, however, do not confirm the scaling of retention time, or of digestive efficiency, with body mass. Here, we test these concepts in herbivorous reptiles, adding data of an experiment that measured food intake, digesta retention, digestibility and gut capacity in 23 tortoises (Testudo graeca, T. hermanni , Geochelone nigra, G. sulcata, Dipsochelys dussumieri) across a large BM range (0.5–180 kg) to a literature data collection. While dry matter gut fill scaled to BM^1.07 and dry matter intake to BM^0.76, digesta mean retention time (MRT) scaled to BM^0.17; the scaling exponent was not significantly different from zero for species > 1 kg. Food intake level was a major determinant of MRT across reptiles and mammals. In contrast to dietary fibre level, BM was not a significant contributor to dry matter digestibility in a General Linear Model. Digestibility coefficients in reptiles depended on diet nutrient composition in a similar way as described in mammals. Although food intake is generally lower and digesta retention longer in reptiles than in mammals, digestive functions scale in a similar way in both clades, indicating universal principles in herbivore digestive physiology. The reasons why the theoretically derived JBP has little empirical support remain to be investigated. Until then, the JBP should not be evoked to explain niche differentiation along a body size axis in terms of digestive physiology.     

Host–parasite nestedness: A result of co-evolving trait-values

Nestedness is an intriguing feature of ecological networks, where those species found in species-depauperate communities are subsets of those found in communities with greater species richness. For bipartite interaction networks, a “community” of species may be thought of as all those pollinating a particular plant, or infecting a particular host, for example. While there is much clear evidence for nestedness in mutualistic webs, host–parasite webs have proven more contentious. There have been a number of suggested causes for nestedness, including an association between the abundance of individuals and the resulting number of species interactions, and the matching of phenotypic traits between species. Questions remain as to the relative importance of these driving factors, especially as host–parasite and mutualistic webs contain completely different interaction types.We propose a model motivated by both of the above factors, considering a trade-off in resources that a species faces in optimizing its transmission or defense. We construct a multi-species model in which both hosts and parasites have limited resources with which to attack or defend themselves from each other. We analyze the evolution of the manner in which they use these resources using adaptive dynamics, to arrive at a final species interaction matrix, which we then test for nestedness. A general model with m hosts and n microparasite species is described here, but results are given for m = n = 5, chosen to be a large enough system for patterns to be identified, but not so large that computational time becomes prohibitive.Our results demonstrate that this co-evolution leads to an unusual amount of nestedness when the trade-offs in transmission for parasites are concave, and an unusual amount of anti-nestedness when they are convex. This enables us to predict the circumstances under which we would expect to observe nestedness in real networks.     

The age of monumental olive trees (Olea europaea) in northeastern Spain

Trees can reach ages that in some cases amount to thousands of years. In the Mediterranean region, olive trees (Olea europaea) have traditionally been considered a particularly long-lived species. The main objective of this study was to assess the age of large olive trees considered to be millenarian and classified as monumental trees in northeastern Spain. We extracted cores of 14 individuals and obtained 8 sections of trees which had already been cut in the area where the largest olive trees in the northeastern Iberian Peninsula are found. The age of the sampled olive trees was assessed by counting the number of annual growth rings. Tree rings did not cross-date well, neither within nor between individuals, but boundaries between likely annual rings were clearly distinct. We found a linear relationship between DBH and tree age (in years) (Age = 2.11 × diameter(cm) + 88.93, R² = 0.80), which was used to estimate the age of unsampled olive trees. The maximum estimated age (627 ± 110 years) is among the greatest ages reported for olive trees around the world (700 years) and among the oldest trees in Mediterranean ecosystems.     

Mononuclear arene ruthenium complexes containing 5,6-diphenyl-3-(pyridine-2-yl)-1,2,4-triazine as chelating ligand: Synthesis and molecular structure

The mononuclear cations of the general formula [(η⁶-arene)RuCl(pdpt)]⁺ (pdpt = 5,6-diphenyl-3-(pyridine-2-yl)-1,2,4-triazine; arene = C₆H₆ (1); C₆H₅Me (2); p-PrⁱC₆H₄Me (3); C₆Me₆ (4)) have been synthesised from 5,6-diphenyl-3-(pyridine-2-yl)-1,2,4-triazine (pdpt) and the corresponding chloro complexes [(η⁶-C₆H₆)Ru(μ-Cl)Cl]₂, [(η⁶-C₆H₅Me)Ru(μ-Cl)Cl]₂, [(η⁶p-PrⁱC₆H₄Me)Ru(μ-Cl)Cl]₂ and [(η⁶-C₆Me₆)Ru(μ-Cl)Cl]₂, respectively. The X-ray crystal structure analyses of [1][PF₆] · (C₆H₆)_2.5 and [2][PF₆] · (CH₃CN)₂ reveal a typical piano-stool geometry around the metal centre and in the crystal packing a complexed networks of intermolecular interactions.     

Food web's backbones and energy delivery in ecosystems

A food web can be seen as a collection of pathways distributing energy to the ecological community. Because of thermodynamical as well as ecological constraints, some pathways are more important than others, as they carry a much larger share of the energy flow. Such pathways, composed of ‘strong’ links, might be hidden in the tangled network of trophic interactions. Due to thermodynamic efficiency, leading to considerable loss at every passage, we expect these important pathways to be short – i.e. of minimal length. Minimum length spanning trees, which are trees formed by the minimum number of links to keep food webs connected, have been indicated as main energy routes. To test this hypothesis, we analyzed 30 well‐resolved, weighted empirical food webs. From each food web, we extracted the minimum length spanning tree (MLST), and compared it to the maximum weight spanning tree (MWST) – a tree composed of connections of maximum strength. To have a robust comparison, we also computed the minimum weight spanning tree (MinWST), composed of the links of minimal strength. Finally, we extracted from each web 1000 random weighted spanning trees (RWSTs) to serve as a null model. We contrasted the different tree structures, and found that MWSTs are significantly shorter than random trees and MinWSTs, but always longer than MLSTs. In addition, MinWSTs are significantly longer than what expected from random trees. Our results show that in food webs, the bulk of energy travels along pathways that tend to be short, although they never coincide with the minimum length spanning trees.     

Diversity and spatial clustering of shade trees affect cacao yield and pathogen pressure in Costa Rican agroforests

The importance of the spatial organisation of individuals in explaining species coexistence within a community is widely recognised. However, few analyses of spatial structure have been performed on tropical agroforests.The main objective of this study was to highlight the links between spatial organisation of shade trees on the one hand, and shade tree species richness and cacao yield on the other, using data from 29 cacao agroforests in Costa Rica.A method of spatial statistics, Ripley's K-function, was used to analyse the spatial organisation of shade and cacao trees in the study plots. For each stand, the X and Y coordinates of ≥2.5-m-tall trees were recorded. In each plot we also assessed shade tree species richness and cacao yield (with total number of pods = number of pods damaged by frosty pod rot + number of healthy pods).Three types of stands were identified: the first was characterised by significant clustering of shade trees, the highest shade tree species richness (S = 6), and the highest number of damaged pods (139 pods ha^?1 year^?1). The second type was characterised by random spatial organisation of shade trees. The third type showed a trend towards regular organisation. Species richness of shade trees did not differ significantly between the last two types (S = 4 for both), nor did the number of damaged pods (56 pods ha^?1 year^?1 and 67 pods ha^?1 year^?1 respectively).Although the trends were not statistically significant for all the variables in our data set, the clustered spatial structure appears to favour a synergy between environmental (tree species richness), and provisioning (cacao production) services.     

Influence of climatic conditions and industrial emissions on spruce tree-ring Pb isotopes analyzed at ppb concentrations in the Athabasca oil sands region

This study investigates Pb isotope ratios at low concentrations (parts per billion; ppb) in tree rings and soils in the Northern Athabasca Oil Sands Region (NAOSR), western Canada, to evaluate if: (1) climatic conditions influence on tree-ring Pb assimilation; and (2) such low Pb content allows inferring the regional Pb depositional history.Our results reflect the influence of winter snow cover and the importance of minimum temperature and precipitation in spring and summer on the bioavailability of Pb and its passive assimilation by trees in sub-arctic semi-humid climatic conditions. Winter conditions can influence the state of root systems that subsequently impacts the following growth period, while spring and summer conditions likely control microbial processes and water source, and may thus impact Pb assimilation by trees. Thus, the results of tree-ring Pb concentrations show interesting correlation with cumulated snow from November of the previous year to February (ρ = 0.53; P < 0.01; n = 36). Likewise, the ²⁰⁶Pb/²⁰⁷Pb ratios inversely correlate with minimum temperature from April to September (ρ = −0.67; P < 0.01; n = 40) and precipitation from May to August (ρ = −0.42; P < 0.01; n = 36). The isotopic results also suggest that the effects of climatic variations are superimposed by regional industrial Pb deposition: Western North American Aerosols (WNAA) and fugitive dust from the oil sands mining operations appear to be the most likely sources.Importantly, this study suggests that even at low Pb concentrations, tree-ring Pb isotopes are modulated by climatic conditions and potential input of regional and long-range transport of airborne Pb. These interpretations open the possibility of using Pb isotopes as an environmental tool for inferring the pollution history in remote regions, and improving our understanding of its natural cycle through the forest environment.     

Seasonal occurrence and distribution of myxomycetes on different types of leaf litter in a warm temperate forest of western Japan

The seasonal occurrence and distribution of myxomycetes on different types of newly defoliated leaf litter were examined in a secondary forest in a warm temperate region of western Japan. The two types of leaf litter (deciduous trees, Prunus verecunda and Quercus variabilis, and evergreen trees, Q. glauca and Cinnamomum camphora) were incubated in trays on the forest floor. A total of 45 myxomycete species were recorded from 3021 collected samples that occurred at the July peak during the warmest and humidest season from April to November. The occurrence of species was significantly related to the changes in mean temperature and minimum temperature on both leaf types under humid conditions. Myxomycete assemblages were divided into three seasonal phases. Most of the species occurred in June–September, while a few species demonstrated characteristic distributions; i.e., Didymium melanospermum appeared in April– May and Diderma umbilicatum appeared in October– November. The respective leaf types supported the reproduction of myxomycetes with high species richness and diversity, with 34 species and H’ = 2.59 on deciduous trees and similarly 30 species and H’ = 2.49 on evergreen trees. Several species, however, exhibited a preference for either the deciduous tree or evergreen tree leaves. Thus, a mixed forest that defoliates during different two seasons yields a greater species diversity of myxomycete assemblage.     

Gambierdiscus (Dinophyceae) species diversity in the Flower Garden Banks National Marine Sanctuary,Northern Gulf of Mexico,USA

Globally, ciguatera fish poisoning (CFP) is the principal cause of non-bacterial illness associated with seafood consumption. The toxins (ciguatoxins) responsible for CFP are produced by dinoflagellates in the genus Gambierdiscus, which are endemic to tropical and sub-tropical areas. Ciguatoxins are lipophilic and bioaccumulate in marine food webs, typically reaching their highest concentrations in fish. Following a CFP event in 2008, the U.S. Food and Drug Administration (USFDA) issued a ciguatera toxin alert that included fish harvested in the northern Gulf of Mexico in and near the Flower Garden Banks National Marine Sanctuary (FGBNMS). The East Flower Garden Bank (EFGB) and West Flower Garden Bank (WFGB) are characterized by thriving coral communities that support Gambierdiscus growth. This study was undertaken specifically to document the diversity of Gambierdiscus species present in the sanctuary that may be sources of ciguatoxins entering the food web. Samples collected from the FGBNMS over a three year period were screened using species-specific polymerase chain reaction assays. A diverse assemblage of Gambierdiscus species was distributed to depths of >45 m, a new depth record for Gambierdiscus. Gambierdiscus belizeanus, Gambierdiscus caribaeus, Gambierdiscus carolinianus, Gambierdiscus carpenteri and Gambierdiscus ribotype 2 were all found on both East and West FGB with Gambierdiscus ruetzleri also recorded from the WFGB. The most common species was G. carolinianus, originally identified from samples collected between 35 and 40 m off the coast of NC, USA. Our findings are consistent with recent physiological studies showing that some Gambierdiscus species can grow year round at the temperatures and salinities at the FGBNMS and at light levels as low as 10 μmol photons m⁻² s⁻¹. Such irradiances are estimated to occur in the FGBNMS at depths of ∼70–80 m. The consistent recovery of Gambierdiscus species from deep sampling sites in areas known to produce ciguatoxic fish signals a substantial change in our concept of suitable habitats for Gambierdiscus to include depths greater than 50 m.     

Ecology and evolution of Devonian trees in New York,USA

The first trees in New York were Middle Devonian (earliest Givetian) cladoxyls (?Duisbergia and Wattieza), with shallow-rooted manoxylic trunks. Cladoxyl trees in New York thus postdate their latest Emsian evolution in Spitzbergen. Progymnosperm trees (?Svalbardia and Callixylon–Archaeopteris) appeared in New York later (mid-Givetian) than progymnosperm trees from Spitzbergen (early Givetian). Associated paleosols are evidence that Wattieza formed intertidal to estuarine mangal and Callixylon formed dry riparian woodland. Also from paleosols comes evidence that Wattieza and Callixylon required about 350 mm more mean annual precipitation than plants of equivalent stature today, that Wattieza tolerated mean annual temperature 7 °C less than current limits of mangal (20 °C), and Callixylon could tolerate temperatures 14 °C less than modern mangal. Devonian mangal and riparian woodland spread into New York from wetter regions elsewhere during transient paleoclimatic spikes of very high CO₂ (3923 ± 238 ppmv), and subhumid (mean annual precipitation 730 ± 147 mm) conditions, which were more likely extrinsic atmospheric perturbations rather than consequences of tree evolution. For most of the Middle Devonian CO₂ was lower (2263 ± 238 ppmv), and paleoclimate in New York was semiarid (mean annual precipitation 484 ± 147 mm). Such transient perturbations and immigration events may explain the 40 million year gap between the late Emsian (400 Ma) evolution of trees and Famennian (360 Ma) CO₂ drawdown and expansion of ice caps.     

Horizontal transmission of the Picea glauca foliar endophyte Phialocephala scopiformis CBS 120377

We have studied the presence of the foliar endophtye of Picea glauca (white spruce) Phialocephala scopiformis CBS 120377 and its affect on the growth of Choristoneura fumiferana (spruce budworm). Here we examine the transmission of this fungus from 50 trees planted in a test field site to 250 P. glauca seedlings planted under the emerging canopies. After 3 y, the endophyte spread to 40 % of these trees (now 20–30 cm) with an average rugulosin (an anti-insect toxin) concentration of 1 μg g^?1. All woody plants within 2 m of the test trees were collected. These were all shown to be negative for P. scopiformis except for some spruce seedlings that arose from seeds (natural generation). This is positive evidence for the horizontal transmission of P. scopiformis and its apparent specificity to P. glauca under field conditions.     

Use of response surface methodology for the optimization of the lipase-catalyzed synthesis of mannosyl myristate in pure ionic liquid

The purpose of the present study is to find the conditions allowing to reach the highest 24 h-yield (24 h-η) for the synthesis of mannosyl myristate catalyzed by the immobilized lipase B from Candida antarctica (Novozym^® 435) in the ionic liquid (IL) [Bmpyrr][TFO] (1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate). A full factorial design (FFD) was used in order to study the influence of three variables (temperature, mannose/vinyl myristate ratio and total substrate quantity) on the 24 h-η. This design led to a model based on a second order polynomial response function. The resulting predicted contour plots have shown that the highest 24 h-η should be obtained with high temperatures, low sugar/vinyl ester molar ratio and intermediate total substrate quantities (mmol). The model has been successfully verified and experimentally confirmed at the optimal conditions of 80 °C, substrate molar ratio of 1/10 and total substrate quantity of 0.26 mmol leading to the highest predicted 24 h-η of 72.2%.     

Wide interguild relationships among entomopathogenic and free-living nematodes in soil as measured by real time qPCR

Entomopathogenic nematodes (EPNs) are promising biological control agents of soil-dwelling insect pests of many crops. These nematodes are ubiquitous in both natural and agricultural areas. Their efficacy against arthropods is affected directly and indirectly by food webs and edaphic conditions. It has long been suggested that a greater understanding of EPN ecology is needed to achieve consistent biological control by these nematodes and the development of molecular tools is helping to overcome obstacles to the study of cryptic organisms and complex interactions. Here we extend the repertoire of molecular tools to characterize soil food webs by describing primers/probe set to quantify certain free-living, bactivorous nematodes (FLBNs) that interact with EPNs in soil. Three FLBN isolates were recovered from soil baited with insect larvae. Morphological and molecular characterization confirmed their identities as Acrobeloides maximum (RT-1-R15C and RT-2-R25A) and Rhabditis rainai (PT-R14B). Laboratory experiments demonstrated the ability of these FLBNs to interfere with the development of Steinernema diaprepesi, Steinernema riobrave and Heterorhabditis indica parasitizing the weevil Diaprepes abbreviatus (P < 0.001), perhaps due to resource competition. A molecular probe was developed for the strongest competitor, A. maximum. We selected the highly conserved SSU rDNA sequence to design the primers/probe, because these sequences are more abundantly available for free-living nematodes than ITS sequences that can likely provide better taxonomic resolution. Our molecular probe can identify organisms that share ?98% similarity at this locus. The use of this molecular probe to characterize soil communities from samples of nematode DNA collected within a citrus orchard revealed positive correlations (P < 0.01) between Acrobeloides-group nematodes and total numbers of EPNs (S. diaprepesi, H. indica and Heterorhabditis zealandica) as well as a complex of nematophagous fungi comprising Catenaria sp. and Monachrosporium gephyropagum that are natural enemies of EPNs. These relationships can be broadly interpreted as supporting Linford’s hypothesis, i.e., decomposition of organic matter (here, insect cadavers) greatly increases bactivorous nematodes and their natural enemies.     

Assessing the importance of nursery areas of European hake (Merluccius merluccius) using a body condition index

In this study, we analysed the variability of reserve storage in juvenile European hake (Merluccius merluccius) off the western coasts of Italy (Central Mediterranean Sea). Reserve storage was measured by the hepatosomatic index (HSI), in relation to environmental and population covariates. HSI has been proved to be a consistent measure of energy storage in gadoids, thus reflecting quantity and quality of food availability for growth. Generalized Additive Models for Location, Scale and Shape (GAMLSS) were used to model the effect of depth, bottom temperature, bottom currents, fish density and fish body size on HSI of juvenile European hake. The results revealed that reserve storage in the liver appears to be maximized for juveniles living on the shelf break, between 120 and 170 m depth, with bottom temperature and current speed not exceeding 14 °C and 0.04 m s⁻¹ respectively. Furthermore, HSI significantly increased with fish density up to about 6000 individuals per km⁻² and decreased at higher densities indicating that reserve accumulation in the liver might be subject to density-dependent mechanisms (e.g. competition for food) as well. These findings suggest that the use of density as measure of nursery importance need to be further investigated. Finally, we found that HSI increased with fish size up to about 14 cm total length. Based on these results, HSI appears a reasonable index to indirectly measure the quality of habitats where juvenile European hake aggregate after their settlement on the bottom, and to potentially monitor habitat suitability as nursery across the spatial-temporal gradient.     

Potential risks of systemic imidacloprid to parasitoid natural enemies of a cerambycid attacking Eucalyptus

A community of insect herbivores has established on eucalyptus species in California following their introduction from Australia. A number of the species are under complete or partial biological control. A response to introduction of additional pest species into the complex has been the application of systemic insecticides to infested trees. Natural enemies that have been introduced to control the various pest species feed on the nectar of treated trees, and thus may be affected by these pesticides. In this study, Eucalyptus rudis trees were treated at label rates with the neonicotinoid systemic insecticide imidacloprid and nectar sampled at 5 months post-treatment during the spring bloom. The concentration of imidacloprid and its toxic metabolites in nectar was measured by ELISA at 660 ppb. Adults of the encyrtid egg parasitoid Avetianella longoi that were fed floral nectar collected from treated trees had significantly lower survival and reproductive fitness than adults fed nectar from untreated trees. In feeding bioassays, in which the adults were fed a range of concentrations of imidacloprid in sugar water, the LC₅₀ for A. longoi was 212 ppb imidacloprid. Bioassays were also conducted with the braconid larval parasitoid, Syngaster lepidus. The LC₅₀ for S. lepidus was 288 ppb imidacloprid. The insecticide appears to be concentrating in the nectar at higher levels than reported from other plant species and at concentrations exceeding the LC₅₀ for two important parasitoids. If tree treatments become widespread as a result of continual introductions of new eucalypt herbivores, established biological control programs could be at significant risk.     

Support vector machines to model presence/absence of Alburnus alburnus alborella (Teleostea,Cyprinidae) in North-Western Italy: Comparison with other machine learning techniques

Alburnus alburnus alborella is a fish species native to northern Italy. It has suffered a very sharp decrease in population over the last 20 years due to human impact. Therefore, it was selected for reintroduction projects. In this research project, support vector machines (SVM) were tested as possible tools for building reliable models of presence/absence of the species. A system of 198 sites located along the rivers of Piedmont in North-Western Italy was investigated. At each site, 19 physical-chemical and environmental variables were measured. We verified that performances did not improve after feature selection but, instead, they slightly decreased (from Correctly Classified Instances [CCI] = 84.34 and Cohen's k [k] = 0.69 to CCI = 82.81 and k = 0.66). However, feature selection is crucial in identifying the relevant features for the presence/absence of the species. We then compared SVMs performances with decision trees (DTs) and artificial neural networks (ANNs) built using the same dataset. SVMs outperformed DTs (CCI = 81.39 and k = 0.63) but not ANNs (CCI = 83.03 and k = 0.66), showing that SVMs and ANNs are the best performing models, proving that their application in freshwater management is more promising than traditional and other machine-learning techniques.     

Determination of food sources and trophic position in Malaysian tropical highland streams using carbon and nitrogen stable isotopes

Stable isotope analysis has been extensively used as an effective tool in determination of trophic relationship in ecosystems. In freshwater ecosystem, aquatic invertebrates represent main component of a river food web. This study was carried out to determine potential food sources of freshwater organism together with pattern of trophic position along the river food web. In this study, rivers of Belum-Temengor Forest Complex (BTFC) has been selected as sampling site as it is a pristine area that contains high diversity and abundance of organisms and can be a benchmark for other rivers in Malaysia. Stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were applied to estimate trophic position and food web paradigm. Analysis of stable isotopes based on organic material collected from the study area revealed that the highest δ¹³C value was reported from filamentous algae (? 22.68 ± 0.126⁰/₀₀) and the lowest δ¹³C was in allocthonous leaf packs (? 31.58 ± 0.187⁰/₀₀). Meanwhile the highest δ¹⁵N value was in fish (8.45 ± 0.177⁰/₀₀) and the lowest value of δ¹⁵N was in autochthonous aquatic macrophyte (2.00 ± 1.234⁰/₀₀). Based on the δ¹⁵N results, there are three trophic levels in the study river and it is suggested that the trophic chain begins with organic matter followed by group of insects and ends with fish (organic matter < insects < fish).