Trophic plasticity among spring vs. cave populations of <Emphasis Type="Italic">Gammarus minus:</Emphasis> examining functional niches using stable isotopes and C/N ratios

In some environments, species may exhibit trophic plasticity, which allows them to extend beyond their assigned functional group. For Gammarus minus, a freshwater amphipod classified as a shredder or detritivore, cave populations have been observed consuming heterotrophs as well as shredding leaves, and therefore may be exhibiting trophic plasticity. To test this possibility, we examined the C and N stable isotope and C/N ratios for cave and spring populations of G. minus. A 15-day feeding experiment using leaves and G. minus from a spring population established that the diet-tissue discrimination factor was 3.2 ‰ for δ¹⁵N. Cave G. minus were 8 ‰ higher in δ¹⁵N relative to cave leaves, indicating they did not derive nitrogen from leaves, whereas field collected spring populations were 2–3 ‰ higher than spring leaves, indicating that they did. Cave G. minus were 2.6 ‰ higher in δ¹⁵N than the cave isopod, Caecidotea holsingeri. Relative to spring populations, Organ Cave G. minus were ¹⁵N enriched by 6 ‰, suggesting they occupied a different trophic level, or incorporated an isotopically distinct N source. While stable isotopes cannot tell what the cave G. minus are eating, the isotopes certainly show that G. minus are not eating leaves and are trophically distinct form the surface populations. Differences in C/N ratios were observed, but reflect the size of the G. minus examined and not feeding group or habitat. The isotope data strongly support the hypothesis that cave populations of G. minus have become generalist or omnivorous by including animal protein in their diet.     

The Impacts of Above- and Belowground Plant Input on Soil Microbiota: Invasive <Emphasis Type="Italic">Spartina alterniflora</Emphasis> Versus Native <Emphasis Type="Italic">Phragmites australis</Emphasis>

Invasive plants affect soil food webs through various resource inputs including shoot litter, root litter and living root input. The net impact of invasive plants on soil biota has been recognized; however, the relative contributions of different resource input pathways have not been quantified. Through a 2 × 2 × 2 factorial field experiment, a pair of invasive and native plant species (Spartina alterniflora vs. Phragmites australis) was compared to determine the relative impacts of their living roots or shoots and root litter on soil microbial and nematode communities. Living root identity affected bacteria-to-fungi PLFA ratios, abundance of total nematodes, plant-feeding nematodes and omnivorous nematodes. Specifically, the plant-feeding nematodes were 627% less abundant when living roots of invasive S. alterniflora were present than those of native P. australis. Likewise, shoot and root biomass (within soil at 0–10 cm depth) of S. alterniflora was, respectively, 300 and 100% greater than those of P. australis. These findings support the enemy release hypothesis of plant invasion. Root litter identity affected other components of soil microbiota (that is, bacterial-feeding nematodes), which were 34% more abundant in the presence of root litter of P. australis than S. alterniflora. Overall, more variation associated with nematode community structure and function was explained by differences in living roots than root or shoot litter for this pair of plant species sharing a common habitat but contrasting invasion degrees. We conclude that belowground resource input is an important mechanism used by invasive plants to affect ecosystem structure and function.     

Gutsy genetics: identification of digested piscine prey items in the stomach contents of sympatric native and introduced warmwater catfishes via DNA barcoding

A major focus of ecology is understanding trophic relationships and energy flows in natural systems, associated food web dynamics and changes in food webs due to introduced species. Predator-prey interactions are often assessed by examining stomach contents. However, partially digested remains may be difficult to accurately identify by traditional visual analysis. Here we evaluate the effectiveness of DNA barcoding to identify digested piscine prey remains in invasive Blue Catfish Ictalurus furcatus, non-native, but established Channel Catfish Ictalurus punctatus and native White Catfish Ameiurus catus from Chesapeake Bay, USA. Stomach contents were examined and piscine prey items were scored as lightly digested, moderately digested or severely digested. A 652 base pair region of the cytochrome c oxidase subunit I (COI-5P) mitochondrial DNA gene was sequenced for each prey item. Edited barcode sequences were compared to locally-caught and validated reference sequences in BOLD (Barcode of Life Database). A large majority of prey items were sufficiently digested to limit morphological identification (9.4 % to species and an additional 12.1 % to family). However, overall barcoding success was high (90.3 %) with little difference among the digestion classifications. Combining morphological and genetic identifications, we classified 91.6 % of fish prey items to species. Twenty-three fish species were identified, including species undergoing active restoration efforts (e.g., Alosa spp.) and commercially important species, e.g., Striped Bass Morone saxatilis, White Perch Morone americana, American Eel Anguilla rostrata and Menhaden Brevoortia tyrannus. We found DNA barcoding highly successful at identifying all but the most heavily degraded prey items and to be an efficient and effective method for obtaining diet information to strengthen the resolution of trophic analyses including diet comparisons among sympatric native and non-native predators.     

Grass,mosses, algae,or leaves? Food preference among shredders from open-canopy streams

Shredder feeding is a vital process in making decomposition products available to biota in streams. To investigate which food sources shredders in open-canopy streams exploit, we conducted a feeding preference experiment with the invertebrate detritivores Limnephilus bipunctatus and Nemoura sp., which are commonly found in open-canopy streams on the Swedish island of Öland in the southern Baltic Sea. Leaves of birch, Swedish whitebeam, and shrubby cinquefoil; dead and fresh grass; water moss; and algae were offered to the shredders in multi- and single treatments. We hypothesized that food with high nutritional value would be preferred. Both taxa preferred leaves of shrubby cinquefoil, a bush common in the riparian zone of Öland streams; additionally Nemoura sp. also chose algae. Dead grass, the most abundant food source in the streams during the whole year, was the least consumed food type. The fresh food types had highest nutritional value, measured as carbon to nitrogen content. Therefore, food quality could not alone explain the preference of shrubby cinquefoil. However, among the detritus type offered, shrubby cinquefoil had the highest nutritional value. Shrubby cinquefoil may constitute one important energy source to these open-canopy stream ecosystems and may be essential in maintaining an abundant shredder community in these streams. Thus, the results of this study indicate that detrital resources are indeed important in open-canopy stream systems.     

Endophytic aquatic hyphomycetes in roots of riparian tree species of two Western Ghat streams

Bubble chamber incubation of surface sterilized segments of root bark and xylem of 10 riparian tree species of the Sampaje (475–500 m asl) and V?Badaga (765–800 m asl) stream reaches of the Western Ghats yielded 20 species of endophytic aquatic hyphomycetes. Anguillospora crassa, A. longissima and Cylindrocarpon sp. were among the top five species in streams. A two-way ANOVA showed significantly higher species richness and counts of conidium in the tree species of Sampaje compared to V?Badaga (p < 0.001), while two variables were not significantly different between bark and xylem. The total number of species recovered was slightly higher in bark than in xylem (14–19 vs. 13–17 spp.) and the average species richness between tissues did not differ significantly except for one tree species (Madhuca neriifolia: p < 0.05). The release of conidia from bark of only three tree species was significantly higher than from xylem (M. neriifolia and Canarium strictum: p < 0.05; Vateria indica: p < 0.01). Sørensen’s similarity index for bark as well as xylem between tree species was higher in Sampaje stream than in V?Badaga stream (0.45–0.78 vs. 0.25–0.61). The diversity of aquatic hyphomycetes in bark and xylem was higher in the trees of Sampaje than V?Badaga (3.1–3.3 vs. 2.7). A cluster analysis of aquatic hyphomycetes in bark and xylem resulted in two groups coinciding with the two streams. The results of this study revealed that assemblage and diversity of endophytic aquatic hyphomycetes in riparian tree roots are high in the mid-altitude Sampaje stream as previously documented for saprotrophic aquatic hyphomycetes.     

Impacts of the invader giant reed (<Emphasis Type="Italic">Arundo donax</Emphasis>) on riparian habitats and ground arthropod communities

Riparian areas have experienced long-term anthropogenic impacts including the effects of plant introductions. In this study, 27 plots were surveyed across three Mediterranean rivers in north-eastern Spain to explore the effects of the invader giant reed (Arundo donax) on riparian habitat features and the diversity, trophic structure, body size, and abundances of epigeal and hypogeal arthropods in riparian areas. Using pitfall traps and Berlese funnels, this study detected a significant increase in collembola abundance and a decrease in the abundance, body size and diversity of macro-arthropods at order and family levels in invaded plots compared to native stands. Invaded and un-invaded areas also differed in the taxonomical structure of arthropod assemblies but not in trophic guild proportions. However, the fact that arthropods were smaller in A. donax soils, together with the absence of particular taxa within each trophic guild or even an entire trophic group (parasitoids), suggests that food-web alterations in invaded areas cannot be discarded. Habitat features also differed between invaded and un-invaded areas with the poorest herbaceous understory and the largest leaf litter deposition and soil carbon stock observed in A. donax plots. The type of vegetation in riparian areas followed by the total native plant species richness were identified as major causal factors to changes in the abundance, diversity and composition of macro-arthropods. However, our analyses also showed that some alterations related to A. donax invasion were inconsistent across rivers, suggesting that A. donax effects may be context dependent. In conclusion, this study highlights an impoverishment of native flora and arthropod fauna in A. donax soils, and suggests major changes in riparian food webs if A. donax displaces native riparian vegetation.     

Non-native liana, <Emphasis Type="Italic">Euonymus fortunei</Emphasis>, associated with increased soil nutrients,unique bacterial communities,and faster decomposition rate

Invasive plants have wide-ranging impacts on native systems including reducing native plant richness and altering soil chemistry, microbes, and nutrient cycling. Increasingly, these effects are found to linger long after removal of the invader. We examined how soil chemistry, bacterial communities, and litter decomposition varied with cover of Euonymus fortunei, an invasive evergreen liana, in two central Kentucky deciduous forests. In one forest, E. fortunei invaded in the late 1990s but invasion remained patchy and we paired invaded and uninvaded plots to examine the associations between E. fortunei cover and our response variables. In the second forest, E. fortunei had completely invaded the forest by 2005; areas where it had been selectively removed by 2010 were paired with an adjacent invaded plot. Where E. fortunei had patchily invaded, E. fortunei patches had up to 3.5× nitrogen, 2.7× carbon, and 1.9× more labile glomalin in soils than uninvaded plots, whereas there were no differences in soil characteristics between invaded and removal plots. In the patchily invaded forest, bacterial community composition varied among invaded and non-invaded plots, whereas bacterial communities did not vary among invaded and removal plots. Finally, E. fortunei leaf litter decomposed faster (k = 4.91 year^?1) than the native liana (k = 3.77 year^?1), Vitis vulpina; decomposition of both E. fortunei and V. vulpina was faster in invaded (k = 7.10 year^?1) than removal plots (k = 4.77 year^?1). Our findings suggest that E. fortunei invasion increases the rate of leaf litter decomposition via high-quality litter, alters the decomposition environment, and shifts in the soil biotic communities associated with a dense mat of wintercreeper. Land managers with limited resources should target the densest mats for the greatest restoration potential and remove wintercreeper patches before they establish dense mats.     

Continued feeding on <Emphasis Type="Italic">Diporeia</Emphasis> by deepwater sculpin in Lake Huron

Monitoring changes in diets of fish is essential to understanding how food web dynamics respond to changes in native prey abundances. In the Great Lakes, Diporeia, a benthic macroinvertebrate and primary food of native benthivores, declined following the introduction of invasive Dreissena mussels and these changes were reflected in fish diets. We examined the diets of deepwater sculpin Myoxocephalus thompsonii collected in bottom trawls during 2010–2014 in the main basin of Lake Huron, and compared these results to an earlier diet study (2003–2005) to assess if their diets have continued to change after a prolonged period of Dreissena mussel invasion and declined Diporeia densities. Diporeia, Mysis, Bythotrephes, and Chironomidae were consumed regularly and other diet items included ostracods, copepods, sphaerid clams, and fish eggs. The prey-specific index of relative importance calculated for each prey group indicated that Mysis importance increased at shallow (≤55 m) and mid (64–73 m) depths, while Diporeia importance increased offshore (≥82 m). The average number of Diporeia consumed per fish increased by 10.0% and Mysis decreased by 7.5%, while the frequency of occurrence of Diporeia and Mysis remained comparable between time periods. The weight of adult deepwater sculpin (80 mm and 100 mm TL bins) increased between time periods; however, the change in weight was only significant for the 80 mm TL group (p?<?0.01). Given the historical importance of Diporeia in the Great Lakes, the examination of deepwater sculpin diets provides unique insight into the trophic dynamics of the benthic community in Lake Huron.     

Boreal peat properties link to plant functional traits of ecosystem engineers

Aims

Warming has the potential to alter plant litter mass loss and nutrient release during decomposition. However, a great deal of uncertainty remains concerning how other factors such as litter species or substrate quality might modify the effects of increased temperature on decomposition. Meanwhile, the temperature sensitivity of plant litter decay in tropical and subtropical forest ecosystems remains poorly resolved.

Methods

This study was designed to assess the effects of experimental warming on litter decomposition and nutrient release of two contrasting tree species (Schima superba and Machilus breviflora) by translocating model forest ecosystems from the high-elevation sites to the lower-elevation sites in subtropical China. Translocating model mountain evergreen broad-leaved forest (MEBF) to the altitude of 300 m and 30 m increased the average monthly soil temperature at 5 cm depth by 0.88 and 1.84 °C, respectively during the experimental period. Translocating model coniferous and broad-leaved mixed forest (CBMF) to the altitude of 30 m increased the average monthly soil temperature at 5 cm depth by 0.85 °C.

Results

We found that experimental warming accelerated litter decomposition in both model forest types, and the promoting efficiency was greater when the temperature increased. The litter with high quality (Schima superba) had stronger response to warming than low quality litter (Machilus breviflora). Warming accelerated Na, K, Mg, P, N and Ca release from Schima superba litter, but only simulated Ca release from Machilus breviflora litter. Overall, litter decomposition was controlled by the order: soil temperature > litter quality > soil moisture > litter incubation forest type under experimental warming in the subtropical China.

Conclusion

We conclude that leaf litter decomposition was facilitated by experimental warming in subtropical China. Litter species might modify the effects of increased temperature on litter decomposition; however, forest type has no effect on litter decomposition.

     

Comparison of trophic function between the globally invasive crayfishes <Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> and <Emphasis Type="Italic">Procambarus clarkii</Emphasis>

Impacts of invasive species may manifest most strongly if these organisms are highly distinct functionally from the native species they often replace. Yet, should we expect functional differences between native and invasive species of generalist organisms like freshwater crayfish? Some existing evidence has pointed to native and invasive crayfish species as ecologically equivalent. We contribute to this literature by comparing the trophic niches of the globally invasive crayfishes Pacifastacus leniusculus and Procambarus clarkii, by applying carbon and nitrogen stable isotope analyses to replicated allopatric (alone) and sympatric (together) lake populations in western Washington State, USA, where P. clarkii has been recently introduced and P. leniusculus is presumed native. Our study corrected for potential inherent differences in lake food webs as a consequence of lake abiotic or biotic characteristics using random effects in linear mixed effects models. We found that although overall trophic niche size or area of these species was not significantly different, P. leniusculus was significantly higher in trophic position than P. clarkii when also accounting for the effects of body size, sex, and lakes as random effects. This pattern of increased trophic position of P. leniusculus over P. clarkii was conserved over time in one sympatric lake for which we had data over multiple years. Cumulatively, our findings point to trophic differences between the globally cosmopolitan crayfishes P. leniusculus and P. clarkii, particularly when accounting for the ways that ecosystem context can affect food web structure of communities and the trophic resources available to these consumers.     

Diversity of culturable bacterial communities in the intestinal tracts of goldfish (<Emphasis Type="Italic">Carassius auratus</Emphasis>) and their ability to produce <Emphasis Type="Italic">N</Emphasis>-acyl homoserine lactone

Intestinal bacteria isolated from goldfish (Carassius auratus) were identified based on 16 ribosomal RNA (rRNA) gene sequences and screened for their ability to produce N-acyl homoserine lactone (AHL), an autoinducer of the quorum sensing (QS) system. The 230 aerobes/facultative anaerobes that were isolated comprised members of the genera Aeromonas (184 isolates), Citrobacter (11), Enterobacter (2), Shewanella (28), Vagococcus (1), and Vibrio (4). Among these genera, the two most abundant species were Aeromonas veronii (163 isolates) and Shewanella xiamenensis (27). In addition, 142 obligate anaerobes consisting of Cetobacterium somerae (139 isolates), Clostridium frigidicarnis (2), and Cetobacterium sp. (1) were also isolated. One hundred seventy isolates (74.2%) belonging to the genera Aeromonas, Citrobacter, Enterobacter, Shewanella, and Vibrio produced AHL, while 155 (67.7%) and 91 (39.7%) isolates possessed the luxR and luxI gene homologs, respectively. None of the obligate anaerobes produced AHL or possessed luxRI homologs. Total viable counts ranged from 1.2 × 10⁷ to 2.2 × 10⁹ CFU/g, which were accounted for 0.8 to 15.2% of direct counts. Aeromonas veronii, S. xiamenensis, and C. somerae were detected from five goldfish at densities ranging from 4.0 × 10⁶ to 1.7 × 10⁹ CFU/g, indicating that these bacteria are dominant components of the culturable gut flora in goldfish. In addition, members of the genera Aeromonas and Shewanella appeared to communicate with each other by using the QS system to some extent when the concentration of AHL reaches a certain threshold. It is therefore suggested that bacteria with the ability to disrupt AHL secretion in intestinal environments are potential candidates for probionts for preventing opportunistic infections in freshwater fish such as goldfish.     

Concentrations of trace elements in sea urchins and macroalgae commonly present in <Emphasis Type="Italic">Sargassum</Emphasis> beds: implications for trophic transfer

The aim of the study was to evaluate the dynamic of cadmium, lead, copper, zinc, and iron among lower trophic levels, sea urchins and macroalgae. Diets and isotopic values were used in combination to explore trophic positions and potential transference of metals from primary producers to consumers. Concentrations of trace elements were measured in two species of sea urchin (Tripneustes depressus and Eucidaris thouarsii) and nine macroalgae that are usually used as food in four Sargassum beds, one of which is close to a phosphorite mine. Specimens were collected when Sargassum fronds were at their greatest (winter) and lowest (summer) abundance. Highest concentrations of Cd, and Cu in both urchin species were recorded in winter at the site near the phosphorite mine. Concentrations of Pb in T. depressus were below the detectable limit, whereas E. thouarsii, which in addition to a high concentration of Pb, had high amounts of Cu and Zn. Gut content analysis, indicates that the diet of both sea urchins at the four sites and two collection dates is mainly macroalgae. The δ ¹⁵N isotopic values in sea urchins in a typical Sargassum bed were in good agreement with a diet dominated by macroalgae, with T. depressus having herbivorous habits and E. thouarsii having omnivorous habits in this environment. We found macroalgae important in the dynamics of metals in food webs, potentially contributing to transferring Cd, Cu, and Zn to key invertebrate species, such as sea urchins, indicating connectivity of food webs and ecological structuring of marine environments.     

Herbivore functional traits and macroinvertebrate food webs have different responses to leaf chemical compounds of two macrophyte species in a tropical lake’s littoral zone

This research addressed the question of whether invertebrate food web structure varied between a native and an invasive macrophyte leaf species in the littoral zone of a tropical reservoir. We compared macroinvertebrate herbivore functional trait diversity composition with food web structure on the two macrophyte leaves, the invasive white ginger lily (Hedichium coronarium—Zingiberaceae) and the native pickerelweed (Pontederia cordata—Pontederiaceae). We predicted that the herbivore macroinvertebrate trait indices would decrease with macrophyte leaf species due to a lower resource quality with the flow-on effects in the food web structure. We calculated the number of functionally singular species (sing.sp) and herbivore functional trait richness (FRic) indices. For the macroinvertebrate food webs, we calculated the total number of trophic links (L), link density (L/S), connectance (C) and predator–prey ratios using a predator–prey matrix. We analysed the relationship between chemical traits of the macrophyte species’ leaves herbivore traits and food web indices using multivariate regression and Pearson’s correlation. Hedichium coronarium leaves had higher biomass and higher nitrogen content than the native P. cordata, which had higher phosphorus and carbohydrate content. Pontederia cordata leaves were associated with specialist macroinvertebrate species which primarily feed on biofilms (e.g. Ulmeritrus and Scirtidae) and plant leaves (e.g. Beardius). Food webs on P. cordata had lower numbers of trophic links (L), links per species (L/S) and predator–prey ratios. Connectance, which represents food web complexity, was similar between macroinvertebrate assemblages on the two leaf types. Our study suggests that chemical compounds of macrophyte leaves quality may have potential flow-on effects on food web structure.     

The plankton community of Lake Matano: factors regulating plankton composition and relative abundance in an ancient,tropical lake of Indonesia

Recent evidence reveals that food webs within the Malili Lakes, Sulawesi, Indonesia, support community assemblages that are made up primarily of endemic species. It has been suggested that many of the species radiations, as well as the paucity of cosmopolitan species in the lakes, are related to resource limitation. In order to substantiate the possibility that resource limitation is playing such an important role, a study of the phytoplankton and zooplankton communities of Lake Matano was implemented between 2000 and 2004. We determined species diversity, relative abundances, size ranges, and total biomass for the phytoplankton and zooplankton, including the distribution of ovigerous individuals throughout the epilimnion of Lake Matano in three field seasons. The phytoplankton community exhibited very low biomass (<15 μg l^?1) and species richness was depressed. The zooplankton assemblage was also limited in biomass (2.5 mg l^?1) and consisted only of three taxa including the endemic calanoid Eodiaptomus wolterecki var. matanensis, the endemic cyclopoid, Tropocyclops matanensis and the rotifer Horaella brehmi. Zooplankton were very small (<600 μm body length), and spatial habitat partitioning was observed, with Tropocylops being confined to below 80 m, while rotifer and calanoid species were consistently observed above 80 m. Less than 0.1% of the calanoid copepods in each year were egg-bearing, suggesting very low population turnover rates. It was concluded that chemical factors as opposed to physical or biological processes were regulating the observed very low standing crops of phytoplankton which in turn supports a very minimal zooplankton community restricted in both species composition and abundance. As chemical factors are a function of the catchment basin of Lake Matano, it is predicted that resource limitation has long played an important role in shaping the unique endemic assemblages currently observed in the food web of the lake.     

Spatial and temporal litterfall heterogeneity generated by woody species in the Central Monte desert

In arid and semiarid environments, the presence of woody species generates a series of environmental gradients that increase spatial heterogeneity and modify the pattern of distribution of the other species. We postulate that the temporal and spatial variability in litter input generated by woody species is a relevant factor in the generation of edaphic heterogeneity by redistribution of nutrients and the physical effects of litter. The objective of this study was to determine the temporal and spatial variability in the amount of litter input under the canopy of dominant woody plants (Prosopis flexuosa and Larrea divaricata) and in exposed areas at the Ñacuñán Reserve, in the central zone of the Monte desert. Litterfall was collected during 2 years from 30-cm-diameter litter traps distributed at three microsites: under P. flexuosa canopy, under L. divaricata canopy, and in exposed areas. Microhabitats beneath Prosopis showed the highest litter input per m² (between 320 and 527 g/m²), and, consequently, more than 50% of it fell to the soil beneath the canopy of P. flexuosa. Only 10% fell on exposed areas, which exhibited an annual input rate per m² of a lower order of magnitude than the sites under Prosopis. Litterfall presented a peak in summer as a consequence of convective storms, and a second one in autumn due to phenological shedding. Our results suggest that woody species have a central importance in the dynamics of nutrients in arid lands by both the increase of total productivity and litterfall, and the spatial and temporal regulation of litter input.     

Zooplankton abundance in the pelagic region of Lake Kasumigaura (Japan): monthly data since 1980

Microscopic crustaceans (cladocerans and copepods) and rotifers are the principal zooplankton components of the pelagic food webs in lakes. They play important ecological roles, functioning as essential links between primary producers and planktivorous fish. Individuals zooplankton are important nodes of matter flow in pelagic ecosystems. The zooplankton community structure can provide useful indicators of top–down processes, such as the magnitude or strength of planktivorous predators and the extent of zooplankton grazing. Here we report the abundance of zooplankton taxa (crustaceans and rotifers) that were recorded monthly, from January 1980 to September 2015, at two stations on Lake Kasumigaura, a shallow eutrophic lake that is the second largest lake in Japan. The data include information on 12 copepod species (taxa), 20 cladoceran species (taxa), 40 rotifer species (taxa), and the opossum shrimp (Neomysis intermedia). In the 1980s, the plankton of the lake were characterized by cyanobacterial blooms and the co-dominance of Bosmina and Diaphanosoma in the summer. In addition, the two cladoceran genera, Daphnia galeata and Chydorus sphaericus were often prominent. The plankton profile changed dramatically in the middle (1997–2004) of the present long-term monitoring period, when cyanobacteria disappeared and diatoms became dominant even in the summer; concurrently, only the Diaphanosoma cladocerans were evident. However, in the past 10 years, cyanobacterial blooms, the co-dominance of Bosmina and Diaphanosoma, and D. galeata have re-emerged. Zooplankton monitoring forms part of the Lake Kasumigaura Long-Term Environmental Monitoring Program, which has been conducted by the National Institute for Environmental Studies (NIES) since 1977. Data on other planktonic components (phytoplankton and the elements of microbial food webs) noted during monitoring and on primary production were published in Takamura and Nakagawa (Ecol Res 27:839 2012a, Ecol Res 27:837 2012b, Ecol Res 31:287 2016). Lake Kasumigaura is a core site of the Japan Long-term Ecological Research Network, a member of the International Long-term Ecological Research Network. Our quantitative dataset spanning several decades is unique in terms of the work on lakes and the plankton therein, and is freely available. The dataset has been used in ecological and environmental programs, as well as in studies on lake management.     

Potential for exploitative competition,not intraguild predation,between invasive harlequin ladybirds and flowerbugs in urban parks

In aphidophagous insect communities invaded by the harlequin ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae), intraguild predation (IGP) is widely implicated in the displacement of native predators, however, indirect trophic interactions are rarely assessed. Using molecular gut-content analysis, we investigated the relative frequencies of IGP by H. axyridis on the predatory flowerbug Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) and prey overlap for a shared prey, the lime aphid Eucallipterus tiliae L. (Hemiptera: Aphididae), in Tilia × europaea crowns in urban parks. The frequency of IGP by H. axyridis was low: 2.7 % of larvae and 3.4 % of adults tested positive for A. nemoralis DNA. The presence of lime aphid DNA in predators was higher: 56.5 and 47.9 % of H. axyridis larvae and adults, respectively, contained E. tiliae DNA, whereas 60.8 % of adult A. nemoralis tested positive for aphid DNA. Incorporating insect densities revealed that the density of H. axyridis larvae had a strong negative effect on the likelihood of detecting aphid DNA in A. nemoralis. Prey overlap for E. tiliae was widespread in space (2–13 m height in tree crowns) and time (May–October 2011) which suggests that interspecific exploitative competition, mediated by predator life-stage, more so than IGP, is an important indirect trophic interaction between co-occurring H. axyridis and A. nemoralis. Whether exploitative competition equates to displacement of A. nemoralis populations requires further investigation. Our results emphasize the need to incorporate indirect interactions in studies of insect communities following invasion, not least because they potentially affect more species than direct interactions alone.     

Global dataset for carbon and nitrogen stable isotope ratios of lotic periphyton

Carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) have been widely employed in food web analysis. In lotic environments, periphyton is a major primary producer that makes a large contribution to food web production as well as carbon and nitrogen cycling. While the δ¹³C and δ¹⁵N values have many advantages as a natural tracer, the controls over their high spatial and temporal variability in stream periphyton are not well known. Here, we present the global dataset of δ¹³C and δ¹⁵N values of lotic periphyton from 54 published and two unpublished sources, including 978 observations from 148 streams/rivers in 38 regions around the world, from arctic to tropical sites. The 54 published sources were articles recorded during the period of 1994–2016 in 25 academic journals. The two unpublished sources were from the authors’ own data. The dataset showed that δ¹³C and δ¹⁵N values of periphyton ranged from ?47.3 to ?9.3‰ and from ?5.6 to + 22.6‰, respectively. The dataset also includes physicochemical factors (altitude, coordinates, catchment area, width, depth, geology, vegetation, canopy coverage, biome, season, presence of anadromous salmon, temperature, pH, current velocity, and discharge), nutrient data (nitrate and ammonium concentrations), and algal attributes (chlorophyll a concentration, algal species compositions, and carbonates removal) in streams/rivers studied, all of which may help interpret the δ¹³C and δ¹⁵N values of periphyton. The metadata file outlines structure of all the data and with references for data sources, providing a resource for future food web studies in stream and river ecosystems.     

Polar night ecology of a pelagic predator,the chaetognath <Emphasis Type="Italic">Parasagitta elegans</Emphasis>

The annual routines and seasonal ecology of herbivorous zooplankton species are relatively well known due to their tight coupling with their pulsed food source, the primary production. For higher trophic levels of plankton, these seasonal interactions are less well understood. Here, we study the mid-winter feeding of chaetognaths in high-Arctic fjord ecosystems. Chaetognaths are planktivorous predators which comprise high biomass in high-latitude seas. We investigated the common species Parasagitta elegans around the Svalbard archipelago (78–81°N) during the winters of 2012 and 2013. Our samples consisted of individuals (body lengths 9–55 mm) from three fjords, which were examined for gut contents (n = 903), stable isotopes, fatty acid composition, and maturity status (n = 352). About a quarter of the individuals contained gut contents, mainly lipid droplets and chitinous debris, whilst only 4 % contained identifiable prey, chiefly the copepods Calanus spp. and Metridia longa. The δ¹⁵N content of P. elegans, and its average trophic level of 2.9, confirmed its carnivorous position and its fatty acid profile [in particular its high levels of 20:1(n-9) and 22:1(n-11)] confirmed carnivory on Calanus. Observations of undeveloped gonads in many of the larger P. elegans, and the absence of small individuals <10 mm, suggested that reproduction had not started this early in the year. Its average feeding rate across fjords and years was 0.12 prey ind.^?1 day^?1, which is low compared to estimates of spring and summer feeding in high-latitude environments. Our findings suggest reduced feeding activity during winter and that predation by P. elegans had little impact on the mortality of copepods.     

Interactive influences of the marine yabby (<Emphasis Type="Italic">Trypaea australiensis</Emphasis>) and mangrove (<Emphasis Type="Italic">Avicennia marina</Emphasis>) leaf litter on benthic metabolism and nitrogen cycling in sandy estuarine sediment

A previous study has demonstrated that in sandy sediment the marine yabby (Trypaea australiensis) stimulated benthic metabolism, nitrogen regeneration and nitrification, but did not stimulate denitrification, as the intense bioturbation of the yabbies eliminated anoxic microzones amenable to denitrification. It was hypothesised that organic matter additions would alleviate this effect as the buried particles would provide anoxic microniches for denitrifiers. To test this hypothesis a 55-day microcosm (75 cm × 36 cm diameter) experiment, comprising four treatments: sandy sediment (S), sediment + yabbies (S + Y), sediment + A. marina litter (S + OM) and sediment + yabbies + A. marina litter (S + Y + OM), was conducted. Trypaea australiensis significantly stimulated benthic metabolism, nitrogen regeneration, nitrification and nitrate reduction in the presence and the absence of litter additions. In contrast, the effects of litter additions alone were more subtle, developed gradually and were only significant for sediment oxygen demand. However, there was a significant interaction between yabbies and litter with rates of total nitrate reduction and denitrification being significantly greater in the S + Y + OM than all other treatments, presumably due to the decaying buried litter providing anoxic micro-niches suitable to nitrate reduction. In addition, both T. australiensis and litter significantly decreased rates of DNRA and its contribution to nitrate reduction.