Effect of competition on stable carbon isotope ratios of two tussock grass species

Summary Previous studies have shown that plant carbon isotope composition varies when plants experience differences in water and nutrient availability. However, none have addressed the effect of root interactions, including competition for these soil resources, on carbon isotope ratios. We studied the effect of interspecific root interactions on the productivity and carbon isotope ratios of two Great Basin tussock grass species (Agropyron desertorum and Pseudoroegneria spicata). We compared grasses grown in mixture with sagebrush (Artemisia tridentara) to grasses in similar mixtures but where root interactions with sagebrush were limited by fiberglass partitions. During both years of the study, tussocks growing in competition with sagebrush produced tissue with more negative ¹³C values than grasses experiencing limited root interaction with sagebrush. The magnitude of this difference (0.5 to 0.9%) is similar to that found in other studies when soil fertility and moisture availability were altered.     

Ophiostomatoid fungi including two new fungal species associated with pine root-feeding beetles in northern Spain

Many bark beetles live in a symbiosis with ophiostomatoid fungi but very little is known regarding these fungi in Spain. In this study, we considered the fungi associated with nine bark beetle species and one weevil infesting two native tree species (Pinus sylvestris and Pinus nigra) and one non-native (Pinus radiata) in Cantabria (Northern Spain). This included examination of 239 bark beetles or their galleries. Isolations yielded a total of 110 cultures that included 11 fungal species (five species of Leptographium sensu lato including Leptographium absconditum sp. nov., five species of Ophiostoma sensu lato including Ophiostoma cantabriense sp. nov, and one species of Graphilbum). The most commonly encountered fungal associates of the bark beetles were Grosmannia olivacea, Leptographium procerum, and Ophiostoma canum. The aggressiveness of the collected fungal species was evaluated using inoculations on two-year-old P. radiata seedlings. Leptographium wingfieldii, Leptographium guttulatum, and Ophiostoma ips were the only species capable of causing significant lesions.     

Trophic relationships of two species of grebe on a prairie lake based on stable isotope analysis

Loch Leven, U.K., contains brown trout (Salmo trutta), eel (Anguilla anguilla), minnow (Phoxinus phoxinus), perch (Perca fluviatilis), pike (Esox lucius) and three-spined stickleback (Gasterosteus aculeatus), with brook lamprey (Lampetra planeri) and stone loach (Barbatula barbatula) also present in its tributaries. Arctic charr (Salvelinus alpinus), Atlantic salmon (Salmo salar) and flounder (Platichthys flesus) are now extinct. The brown trout population has supported a world-renowned recreational fishery for over a century, although a decline in fishery performance led to extensive stocking between 1983 and 2006, including with non-native rainbow trout (Oncorhynchus mykiss). This review combines historical information with contemporary gill-net and hydroacoustic surveys. In 2008, brown trout, perch and three-spined sticklebacks were abundant, but pike and stone loach were rare. The obstruction of migratory routes was probably responsible for the loss of Atlantic salmon and flounder, while a lowering of water level likely caused the extinction of Arctic charr and contributed to a reduction in pike abundance. Perch abundance has fluctuated markedly, being influenced by disease and eutrophication, although a reduction in nutrients and associated recovery of macrophytes are likely to have benefitted this species. Although the brown trout population has undoubtedly shown a long-term decline, individuals are currently in excellent condition.     

Revisiting the fate of buds: size and position drive bud mortality and bursting in two coexisting Mediterranean Quercus species with contrasting leaf habit

Understanding the relationships between bud size and position and bud fate through time is crucial for identifying and subsequently modeling the mechanisms underlying tree architecture. However, there is a lack of information on how bud size drives crown architectural patterns in coexisting tree species. We studied bud demography in two coexisting Mediterranean oak species with contrasting leaf habit (Quercus ilex, evergreen; Q. faginea, deciduous). The main objective was to analyse the effect of bud size on the fate of buds with different positions along the shoot (apical, leaf axillary and scale-cataphyll axillary buds). The number, length and position of all buds and stems were recorded in marked branches during 4 years. Study species presented different strategies in bud production and lifespan. The evergreen species showed greater mortality rate than the deciduous one, which produced larger buds. Bud size and position were highly related since apical buds where longer than axillary ones and bud length declined basipetally along the stem. Apical buds had also higher chances of bursting than axillary ones. Within positions, longer buds presented a higher probability of bursting than shorter ones, although no absolute size threshold was found below which bud bursting was impaired. In Q. ilex, four-year-old buds were still viable and able to burst, whereas in Q. faginea practically all buds burst in their first year or died soon after. Such different bud longevities may indicate contrasting strategies in primary growth between both species. Q. ilex is able to accumulate viable buds for several ages, whereas Q. faginea seems to rely on the production of large current-year buds with high bursting probability under favourable environmental conditions.     

Vibrio species associated with mortality of sharks held in captivity

Two urease-positiveVibrio spp. were isolated from a brown shark (Carcharhinus plumbeus) that died in captivity at a national aquarium. Morphological, biochemical, and molecular genetic studies revealed one of the isolates to beV. damsela; the other isolate was unique and has been classified asV. carchariae sp. nov. BothV. damsela andV. carchariae were found to be virulent for spiny dogfish (Squalus acanthias), causing death in less than 18 hours after intraperitoneal injection of ca. 4×10⁶ cells.V. damsela was strongly cytotoxic for Y1 adrenal cell monolayers;V. carchariae exhibited weak cytotoxicity for Y1 cells.V. damsela contained cryptic plasmids and both isolates were urease positive.V. carchariae was able to utilize urea as sole source of carbon and nitrogen.     

Photosynthesis, water use efficiency and stable carbon isotope composition are associated with anatomical properties of leaf and xylem in six poplar species

Although fast‐growing Populus species consume a large amount of water for biomass production, there are considerable variations in water use efficiency (WUE) across different poplar species. To compare differences in growth, WUE and anatomical properties of leaf and xylem and to examine the relationship between photosynthesis/WUE and anatomical properties of leaf and xylem, cuttings of six poplar species were grown in a botanical garden. The growth performance, photosynthesis, intrinsic WUE (WUE_i), stable carbon isotope composition (δ¹³C) and anatomical properties of leaf and xylem were analysed in these poplar plants. Significant differences were found in growth, photosynthesis, WUE_i and anatomical properties among the examined species. Populus cathayana was the clone with the fastest growth and the lowest WUE_i/δ¹³C, whereas P. × euramericana had a considerable growth increment and the highest WUE_i/δ¹³C. Among the analysed poplar species, the highest total stomatal density in P. cathayana was correlated with its highest stomatal conductance (g_s) and lowest WUE_i/δ¹³C. Moreover, significant correlations were observed between WUE_i and abaxial stomatal density and stem vessel lumen area. These data suggest that photosynthesis, WUE_i and δ¹³C are associated with leaf and xylem anatomy and there are tradeoffs between growth and WUE_i. It is anticipated that some poplar species, e.g. P. × euramericana, are better candidates for water‐limited regions and others, e.g. P. cathayana, may be better for water‐abundant areas.     

Instar-dependent mortality rates of coexisting Daphnia species in Lake Vechten, The Netherlands

In Lake Vechten, population parameters were determined for twocoexisting Daphnia species, D.hyalina and D.cucullata, fromApril 23 to December 10, 1986. Daphnia hyalina is dominant inspring and D.cucullata in summer and autumn. Size frequencydistributions were converted into instar frequency distributionsby using experimental growth curves and field measurements onnewborn size and the size at first reproduction. A discreteevent computer model was used to calculate the instar mortalityrates. Relative importances of instar mortality rates for thepopulation mortality rate were calculated and discussed. Themortality of the juvenile stages was found to be more importantthan adult mortality during most of the sampling season, despiteegg mortality when egg-bearing females are killed. Only in Septemberand October was the mortality of adult instars more important.Correlation coefficients between differences in the rates ofincrease and differences in mean brood size and instar mortalitiesshow that the former are caused mainly by differences in juvenilemortality, the main factor determining the replacement of D.hyalinaby D.cucullata during early summer.     

The environmental signals of stable carbon isotope in various tree-ring components of Pinus tabulaeformis

Chinese pine (Pinus tabulaeformis) trees were sampled in the Helan Mountain, northwest China. The stable carbon isotope (δ¹³C) values of whole wood, holocellulose and alpha-cellulose in tree rings over 30 years (1968–1997) were measured to study the δ¹³C response of different tree-ring components to past environmental change. There were obvious differences in the δ¹³C values of the three components. The Pearson correlation coefficient between the δ¹³C of alpha-cellulose and that of holocellulose was 0.547 (ρ < 0.01); between alpha-cellulose and whole wood, the coefficient was −0.126 (ρ > 0.10); between holocellulose and whole wood, the coefficient was −0.056. Correlation function analyses indicated that the δ¹³C content of tree-ring alpha-cellulose correlated strongly with the average temperature from June to August (r = 0.427, ρ < 0.05), more than that of holocellulose (0.324, ρ < 0.10) or total wood (−0.245, ρ > 0.10). Significant correlations were observed between δ¹³C of tree-ring alpha-cellulose and the precipitation from the current year’s February to July (r = −0.514, ρ < 0.01) that were much higher than that of holocellulose (−0.481, ρ < 0.05) or total wood (−0.249, ρ > 0.10). A significant correlation (−0.545, ρ < 0.01) was also found between the ring width and the δ¹³C residual chronologies. These results suggest that more past environmental information is retained in the δ¹³C of tree-ring alpha-cellulose. Thus, the δ¹³C of alpha-cellulose of tree rings is the most suitable among the studied parameters for reconstructing the past climatic conditions during the growing season. The δ¹³C values of other organic compounds in Pinus tabulaeformis xylem were affected by the external environment after carbon was fixed from the atmosphere.     

3种松树林林分改造树种的生长格局

对3 种松林下的黎蒴、白花油茶、竹节树苗木的生长进行了研究.3 种苗木的地径和冠幅生长量以及黎蒴和油茶的树高生长量排序为湿地松林分>有凋落物加勒比松林分>无凋落物加勒比松林分,而竹节树在有凋落物加勒比松林下的树高生长略大于湿地松林,二者显著大于无凋落物加勒比松林.无凋落物的加勒比松林因为去除地表凋落物后减少了养分的输入,土壤有机质和氮含量减少,导致苗木生长下降.总体来看,竹节树的地径和冠幅的生长量最大,黎蒴树高的生长量最大,二者是改造松林的优良树种,而油茶生长慢.     

Crown light environments of saplings of two species of rain forest emergent trees

Summary The crown light environments of saplings of two Costa Rican rain forest tree species were simultaneously compared. The species, Dipteryx panamensis (Pitt.) Record & Mell., a relatively shade-intolerant species, and Lecythis ampla Miers, a shade-tolerant species, have contrasting growth and branching patterns. Quantum sensors were placed throughout the crowns of saplings up to 2.5 m tall and quantum fluxes were recorded with microloggers for seven-day periods. The shade-intolerant species had total quantum flux densities 35% larger than those of the shade-tolerant species, but totals for both species were less than 2% of full sun. More than 90% of the quantum flux densities measured within the crowns of both species were less than 25 mol m^-2s^-1. Lateral light was an important component of daily quantum flux totals; for saplings of both species, the half-hour with the maximum average irradiance for the day frequently occurred in mid-morning or midafternoon. Despite dissimilar crown and leaf display, there was no difference in the overall variability of irradiance within the crowns of the two species. However, quantum fluxes received within the crowns differed substantially in both species. Within-crown locations differed significantly from day to day because of variation in weather conditions. Daily total quantum flux densities and totals expressed as a percent of full sun were significantly correlated with height growth over the previous 12 months.     

Different competitive potential in two coexisting mouse lemur species in northwestern Madagascar

Interspecific competition has been suggested to influence the biogeographic distribution patterns of species. A high competitive potential could entail species-specific advantages during resource acquisition that could translate into a higher potential for range expansion. We investigated whether differences in the competitive potential of the morphologically similar and partially sympatric gray mouse lemur (Microcebus murinus) and golden-brown mouse lemur (Microcebus ravelobensis) may help to explain differences in their geographic range sizes. We carried out encounter experiments with 14 pairs of captured female mouse lemurs of both species. The experimental dyads were tested in a two-cage arrangement, with individuals being separated from each other outside the experiments. Two days of habituation and four subsequent days of 1-h encounter experiments were conducted, before releasing the animals again in the wild. In general, the M. murinus individuals won significantly more conflicts than their partners. In eight of 14 tested pairs, there was a significant species bias in winning conflicts, and in 87.5% of these dyads, M. murinus was the "dyad winner". A high competitive potential did not depend on body mass. Furthermore, "dyad winners" spent more time feeding (P < 0.05) and were less spatially restricted than "dyad losers". To conclude, our results suggest that the widely distributed M. murinus may indeed have a higher competitive potential than the regional endemic M. ravelobensis, which may, among other possible factors, have enabled this species to expand geographically, despite the presence of other competing congeners.     

Interactions of Hylastes species (Coleoptera: Scolytidae) with Leptographium species associated with loblolly pine decline

Hylastes spp. (Coleoptera: Scolytidae) were evaluated as potential vectors of Leptographium spp. fungi. Bark beetles were trapped from stands ofloblolly pine, Pinus taeda L., exhibiting a range of decline symptoms in central Alabama. Under controlled conditions, field-collected adult Hylastes salebrosus Eichoff (Coleoptera: Scolytidae) and Hylastes tenuis Eichoff (Coleoptera: Scolytidae), which had been surface-sterilized and inoculated with Leptographium terebrantis Barras & Perry and Leptographium serpens (Goid.) Wingfield, transmitted the fungi into 100% of wounded and unwounded loblolly root sections with which they were confined. None of the sterilized and uninoculated beetles transmitted any Leptographium spp. to roots. Significantly more H. salebrosus and H. tenuis brood emerged from roots infected with Leptographium species than from sterile roots, indicating an enhancement of Hylastes reproduction.     

Needle terpene concentrations and emissions of two coexisting subspecies of Scots pine attacked by the pine processionary moth (Thaumetopoea pityocampa)

Mediterranean pine forests are often attacked by caterpillars of Thaumetopoea pityocampa (Lep., Thaumetopoidae), one of the most important defoliators in the Mediterranean region causing large economic losses and ecological effects. The needle terpene concentrations and emissions may play a key role in the defense of pines. We studied two subspecies of Pinus sylvestris, nevadensis (an endemic and relict subspecies) and iberica , with different levels of caterpillar attack in Sierra Nevada mountains (Spain). GC–MS analyses showed large total concentrations of terpenes (6 to 39 mg g^?1 of dry weight) in the needles of both subspecies under field conditions. Concentrations were 25 % higher in “Non-Attacked Trees” (NATs) of the iberica than in the nevadensis subspecies. The branches of NATs had terpene concentrations 20 % higher than those of “Attacked Branches of attacked trees” (ABs). Within attacked trees, the “Non-Attacked Branches” (NABs) also had terpene concentrations 20 % higher than those of ABs. Mainly α-pinene and germacrene D had higher concentrations in NATs and NABs than in ABs. Some terpenes had higher concentrations in NABs than in NATs, indicating possible systemic reactions. In subsp. nevadensis, the percentage of monoterpenes relative to total terpenes was higher in ABs than in other attack states. The rates of emission in nevadensis (standardized to 30 °C) were ca. three times higher in ABs than in NABs and NATs. These results suggest that the lower terpene concentrations and high percentages of monoterpenes in ABs were produced by a combination of emission losses and terpene induction in response to herbivorous attack.     

Significant mortality of eggs and young larvae of two pine processionary moth species due to the entomopathogenic fungus Metarhizium brunneum

Bioassays were conducted to determine the susceptibility of egg masses and young larvae of two pine processionary moth species, Thaumetopoea pityocampa and Thaumetopoea wilkinsoni, to two strains (ARSEF4556, V275) of the entomopathogenic fungus Metarhizium brunneum. Mortality of treated eggs by both strains ranged from 96% to 99% but not all of this was caused by M. brunneum since control groups also experienced egg mortality due to saprophytic fungi. Still, larvae hatched in the laboratory from eggs treated with M. brunneum were all killed by this fungus, acquiring M. brunneum conidia, whereas larval mortality was 0% in the control groups. Young larvae of both pine processionary moth species were also highly susceptible to ARSEF4556 and V275 with larval mortality ranging between 94% and 100%, 8 days post-inoculation, with the vast majority of larvae being killed within the first 2–4 days. Larval mortality was dose dependent. Results were consistent across the two pine processionary moth species, showing that the pathogenicity of M. brunneum to both eggs and young larvae might be promising for biological control of these insect pests. The study also showed that non-target parasitoids of pine processionary moth eggs were also susceptible to M. brunneum. Further work is required to understand and reduce the M. brunneum effect on non-target insects.     

The effects of ozone and acid mist on Scots pine saplings

Summary It has been suggested that the forest decline (Neuartige Waldschäden) seen recently in parts of West Germany is due to the direct effects of ozone combined with acid mists, rather than soil-mediated effects of acid deposition. It has been proposed that ozone (a) makes the needles of affected conifers more susceptible to leaching by acid mist and (b) damages the photosynthetic apparatus, giving rise to diminished carbohydrate reserves which reduce the ability of affected trees to replace the leached nutrients. This nutrient deficiency (especially of Ca and Mg) is a characteristic symptom of the Waldschäden, which progresses through growth decline, needle loss, and eventually death. Parts of this hypothesis were tested in a preliminary experiment in which 3-year old Pinus sylvestris (Scots pine) saplings were exposed to 4 different O₃ levels, with and without acid mist (pH 3) treatment, for 56 days between July and September, 1983 in outdoor solardome fumigation chambers. The visual symptoms observed at >100 g m^-3 were more characteristic of the chlorotic mottle seen on O₃-affected trees in the USA than the general chlorosis of affected stands in Germany. O₃ at mean concentrations of >200 g m^-3 for 56 days reduced the fine root biomass and accelerated the senescence of older needles, in keeping with field effects observed in Germany. However, these O₃ levels increased, rather than decreased, the concentrations of most elements in the needles. Acid mist had no effect on needle concentrations, and there was no O₃-acid mist interaction. O₃ up to 300 g m^-3 also had no effect on the amount of ions leached from the needles, whereas acid mist increased the leaching of some ions, and again there was no interaction. The only nutritional effect of O₃ was to reduce the foliar uptake of NO _- ³ from the acid mist solution. An aphid infection part way through the experiment caused a large increase in leaching, particularly of K, and affected the intermediate O₃ and watersprayed plants most. Caution is needed in extrapolating these results to the field, as the experiments were of short duration on young trees with fully-formed needles, growing in a soil better supplied with nutrients than field soils. Nevertheless, these preliminary results do not support the hypothesis of an O₃-mediated increase in foliar leaching as the major cause of forest decline nor were the symptoms of O₃-injury on Scots pine comparable with those reported in the field.     

Growth and mortality in two Pleistocene bathyal micromorphic bivalves

Size-frequency and growth-ring data have been used to calculate mortality and growth patterns in two micromorphic bivalve species from pelagic mud of Lower-Middle Pleistocene age on Rhodes (Greece). Phaseolus ovatus Sequenza, a lametilid deposit-feeder, showed increasing mortality and a slow-fast-slow growth pattern accompanied by an abrupt change of shape in the fast-growing interval. This in turn is coincident with a minimum in the size-frequency distribution. The bimodality occurring in all distributions is interpreted as a recurrent population character, probably a non-annual reproduction cycle, while height and spacing of the modes, which differ among the distributions, are environmentally controlled. Kelliella miliaris (Philippi), a vesicomyid suspension-feeder, showed a near-constant mortality and a logarithmic growth rate. The difference in mortality between the two species is related to grain-size of the sediment and to stability of the food source. Growth pattern, mortality, food sources, reproduction.     

Diurnal variations of needle water isotopic ratios in two pine species

Diurnal fluctuations of leaf water isotope ratios (δ¹⁸O and δD) were measured for Jeffrey (Pinus jeffreyi Balf.) and lodgepole (Pinus contorta Douglas ex Louden) pine. Two trees per species were sampled every few hours on 15–16 October 2005 and 19–20 June 2006. Diurnal gas exchange was measured during the summer sampling. In fall 2005, leaf water δ¹⁸O ranged from 0.7 to 9.0‰, and leaf water δD ranged from −70 to −50‰. In summer 2006, leaf water δ¹⁸O ranged from 7.7 to 20.7‰, and leaf water δD ranged from −61 to −24‰. Diurnal variation of leaf water isotope values typically reached a maximum in early afternoon, began decreasing around midnight, and reached a minimum in mid-morning. Both periods showed a high degree of enrichment relative to source water, with leaf water–source water enrichments ranging up to 37.8‰ for δ¹⁸O, and up to 95‰ for δD. Leaf water enrichment varied by season with summer enrichment being greater than fall enrichment. A steady-state model (i.e., modified Craig–Gordon modeling) for leaf water isotope compositions did not provide a good fit to measured values of leaf water. In summer, a non-steady state model provided a better fit to the measured data than the steady-state model. Our findings demonstrate substantial leaf water enrichment above source water and diurnal variations in the isotopic composition of leaf water, which has application to understanding short-term variability of atmospheric gases (water vapor, CO₂, O₂), climate studies based on the isotopic composition of tree rings, and ecosystem water fluxes.     

Seasonal variation in terrestrial resource subsidies influences trophic niche width and overlap in two aquatic snake species: a stable isotope approach

Quantifying diet is essential for understanding the functional role of species with regard to energy processing, transfer, and storage within ecosystems. Recently, variance structure in the stable isotope composition of consumer tissues has been touted as a robust tool for quantifying trophic niche width, a task that has previously proven difficult due to bias in direct dietary analyses and difficulties in integrating diet composition over time. We used carbon and nitrogen stable isotope analyses to examine trophic niche width of two sympatric aquatic snakes, banded watersnakes Nerodia fasciata and black swamp snakes Seminatrix pygaea inhabiting an isolated wetland where seasonal migrations of amphibian prey cause dramatic shifts in resource availability. Specifically, we characterized snake and prey isotope compositions through time, space, and ontogeny and examined isotope values in relation to prey availability and snake diets assessed by gut content analysis. We determined that prey cluster into functional groups based on similarity of isotopic composition and seasonal availability. Isotope variance structure indicated that the trophic niche width of the banded watersnake was broader (more generalist) than that of the black swamp snake. Banded watersnakes also exhibited seasonal variation in isotope composition, suggesting seasonal diet shifts that track amphibian prey availability. Conversely, black swamp snakes exhibited little seasonal variation but displayed strong ontogenetic shifts in carbon and nitrogen isotope composition that closely paralleled ontogenetic shifts in their primary prey, paedomorphic mole salamanders Ambystoma talpoideum. Although niche dimensions are often treated as static, our results demonstrate that seasonal shifts in niche dimensions can lead to changes in niche overlap between sympatric species. Such short‐term fluctuations in niche overlap can influence competitive interactions and consequently the composition and dynamics of communities and ecosystems.     

Growth, mortality, parasitism, and potential yields of two Priacanthus species in the South China Sea

In the northern part of the South China Sea the 'big-eye', Priacanthus tayenus , spawned once a year in June, had von Bertalanffy growth parameters of k = 0.8 and L ∞= 30 cm, and a mean total annual instantaneous mortality of Z = 2.0, calculated from adjusted catch curves and a mean length equation. The natural mortality rate M = 1.4, fishing mortality rate F = 0.6, and the exploitation rate (E) was 0.27. The maximum potential yield, calculated using Marten's method, was 0.06 kg/recruit when F = 5.4. The fish were heavily parasitised by the protozoan Pleistophora priacanthicola .
A second big-eye, P. macracanthus , spawned twice a year in May-June and September, had growth parameters of κ= 0.7 and L∞= 32, and population parameters of Z = 2.0, . F = 0.7, and E = 0.34. The maximum potential yield was 0.13 kg/recruit when F = 5.8.
A marked reduction in fishing mortality occurred for both species between 1965 and 1966, coinciding with the onset of the Chinese Cultural Revolution. Our estimates of maximum potential yield correspond to fishing mortalities eight times estimated levels, though such heavy exploitation could risk recruitment failure.