Dation Rates Research Articles

New tracer to estimate community predation rates of phagotrophic protists

Predation of eukaryotic microbes on prokaryotes is one of the most important trophic interactions on Earth, representing a major mortality term and shaping morphology and composi- tion of prokaryotic communities. Here we introduce and validate a new tracer to determine pre- dation rates on prokaryotes. Minicells of Escherichia coli marked with a bright green fluorescent protein (GFP) vector have many operational advantages over previously used prey analogs such as fluorescently labeled bacteria. GFP-minicells are similar in size to naturally occurring bacteria from a variety of environments including the oligotrophic open ocean and the deep sea. They are relatively stable against microbial and light degradation, are easy to grow and process, and can be produced inexpensively in large numbers. No chemical alteration of the particle surface due to heat killing and staining is involved. Grazing coefficients were compared between GFP-minicells and other GFP-modified bacteria, as well as 5-(4,6-dichlorotriazinyl)aminofluorescein (DTAF)- stained cells. The grazing coefficients obtained from the removal of GFP-minicells compared favorably with estimates from tracer-independent estimates of grazing in the same experiments. Experiments with GFP-minicells resulted in community grazing coefficients similar to those reported for many different marine environments and those derived using various methods.

Aerobic production of methane from dissolved water-column methylphosphonate and sinking particles in the North Pacific Subtropical Gyre

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 73:93-105 (2014) - DOI: https://doi.org/10.3354/ame01714 FEATURE ARTICLE Aerobic production of methane from dissolved water-column methylphosphonate and sinking particles in the North Pacific Subtropical Gyre Daniela A. del Valle*, David M. Karl Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawaii, 1950 East-West Road, Honolulu, Hawaii 96822, USA *Corresponding author: dadv@hawaii.edu ABSTRACT: Supersaturation of methane in aerobic surface waters is a phenomenon widely observed in the ocean, albeit poorly understood. Recent studies have shown that degradation of methylphosphonate (MPn) can lead to the production of methane under aerobic conditions; however, the importance of this process has not been quantified under natural conditions. Here, we quantified the production of methane from dissolved MPn (d-MPn) in surface waters and observed that this process cannot account for the methane oversaturation observed in the oligotrophic waters of the North Pacific Subtropical Gyre. Degradation rates of d-MPn were, however, stimulated by the addition of low concentrations of nitrate and iron, suggesting regulation of the d-MPn degradation pathway by these nutrients. Degradation of d-MPn associated with sediment trap-collected particles was significantly faster than in the water column, even after normalizing to particulate organic carbon, particulate phosphorus, or heterotrophic bacterial numbers, suggesting that MPn degradation might be localized on sinking particles. We hypothesize that MPn is transformed to methane directly from sinking particles, without transitioning through the dissolved phase. KEY WORDS: Methane · Methylphosphonate · Phosphonates · Phosphorus · Station ALOHA · Oligotrophic Full text in pdf format Information about this Feature Article NextCite this article as: del Valle DA, Karl DM (2014) Aerobic production of methane from dissolved water-column methylphosphonate and sinking particles in the North Pacific Subtropical Gyre. Aquat Microb Ecol 73:93-105. https://doi.org/10.3354/ame01714 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 73, No. 2. Online publication date: October 02, 2014 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2014 Inter-Research.

Seedling regeneration of <I>Quercus liaotungensis</I> in Liupan Mountains, China

Aims Quercus liaotungensis forest, which occurs on shaded, semi-shaded and semi-sunny slopes at an elevation of 1 700-2 300 m, is the main natural secondary forest and zonal climax community in China's Liupan Moun- tains. It is essential for forest management to better understand the natural regeneration processes and limiting factors in the restoration of degraded Q. liaotungensis shrubs and secondary Q. liaotungensis forest. Our objec- tives are to (a) investigate the important ecological processes associated with recruitment and seedling regenera- tion (seed production, seed bank composition, seed storage and seed/cotyledon predation) and (b) analyze poten- tial bottlenecks limiting seedling regeneration. Methods We surveyed the seed production of Q. liaotungensis shrubs and soil seed bank composition of secon- dary Q. liaotungensis forest in Daliang Mountain and Qiuqianjia forest region of Liupan Mountains, respectively. We also investigated the effects of moist sand and natural air-dry storage on seed life-span and the effects of coty- ledon predation (by excluding animals) on seedling establishment. Important findings The percentage of viable seeds of Q. liaotungensis shrubs was 27.51%, and the rate of seed predation/removal (41.51%) was significantly higher than that of other seed types (P < 0.01). The rate of germina- tion and insect infection in soil seed bank of secondary Q. liaotungensis forest was 35.16% and 38.29%, respec- tively, while only 13.65% of seeds were viable in the soil seed bank. Seed predators played an important role in influencing the density of the soil seed bank by removing and hoarding seeds. Storage in moist sand for 60 d re- sulted in germination of 96.67% of Q. liaotungensis seeds, and both short-term moist sand and air-dry storage led to accelerated germination timing and enhanced germination percentage and germination index. However, with the extension of the storage period, germination was delayed and germination percentage, germination index and vigor index were decreased. Survival rates of seedlings treated by predator elimination caged seedlings were 80% and 83% in forest gap and under canopy, respectively, while only 25% and 31% of survival rate, respectively, were found for uncaged seedlings, indicating the important role of cotyledons in seedling establishment. The pre- dation rate of cotyledons in forest gaps (85.00%) was higher than that under canopy (71.00%). Although the

Predation behaviour of Cancer irroratus and Carcinus maenas during conspecific and heterospecific challenges

We investigated the predation behaviour of rock crab Cancer irroratus and green crab Carcinus maenas in laboratory experiments in autumn 2006 and spring 2007 during various conspe- cific and heterospecific challenges. The number of prey eaten by a focal crab during a given chal- lenge was recorded for both crab species using competition treatments (solitary crab, 2 conspecifics or 2 heterospecifics) crossed with 2 different prey densities (4 or 30 mussels) and 3 different temper- atures (5, 12 or 20°C). To validate laboratory results, complementary field experiments were carried out in aquaculture leases in Prince Edward Island, Canada, in 2007, during which crab stomach con- tents from identical competition treatments were studied and mussel socks were surveyed monthly for crab abundance. In the laboratory, predation rates of both crab species generally increased with temperature and mussel density, and were not affected by the presence of a heterospecific regardless of the season. During autumn 2006, the Temperature × Mussel density interaction influenced the pre- dation rate of rock crab while only temperature affected the predation rate of green crab. During spring 2007, the predation rate of green crab varied again according to temperature whereas the pre- dation rate of rock crab was affected by the Temperature × Mussel density × Competition interaction. In the field, blue mussels Mytilus edulis were the most abundant food item observed in stomach con- tents. The competition treatments did not affect the stomach contents. Both crab species displayed different abundance patterns and seemed to avoid each other on mussel socks. Overall, our results suggest that the 2 crab species can potentially coexist.

A new route to prepare nanocomposites based on polyvinyl chloride and MgAl layered double hydroxide intercalated with laurylether phosphate

The MgAl layered double hydroxide (LDH) with laurylether phosphate was prepared using reconstruction method. Delamilation of the LDH with laurylether phosphate (LDH-PK) in tetrahydrofuran was characterized by AFM (atomic force microscopy), indicating that a large part of the LDH was delaminated into single, double and multi layers. The delaminated LDH-PK suspension was then used with polyvinyl chloride (PVC) to prepare a series of high-LDH-load- ing nanocomposites. Both the XRD (X-ray diffraction) patterns and TEM (transmission electron microscopy) photographs of the as-prepared PVC/LDH nanocomposites indicated that the LDH nanolayers dispersed uniformly in the PVC matrix. With differential scanning calorimetry (DSC) the glass transition temperatures of PVC phases in the PVC/LDH nanocom- posites were measured and a slightly lower value than that of pristine PVC has been observed. Thermogravimetric analysis results show that the presence of LDH enhanced the dehydrochlorination temperature (Tmax1), reduced the maximum degra- dation rate (Rmax1) and the 5% weight loss temperature, and promoted the char formation of PVC. However, the thermal degradation temperature (Tmax2) and thermal degradation rate (Rmax2) of the dehydrochlorinated PVC were slightly affected by the presence of LDH. The apparent activation energies were calculated by the method of Flynn-Wall-Ozawa in nitrogen at four different heating rates, showing that the nanofiller increased the apparent activation energies by 10-26 kJ/mol when compared with pristine PVC, probably implying that the LDH nanolayers improve the stability of chlorine atom on the PVC chains.

Behavioural mechanisms underlying functional response of sea stars Asterias vulgaris preying on juvenile sea scallops Placopecten magellanicus

The functional response characterises the relationship between prey density and the consumption rate of individual predators. Typically, it is studied by fitting a model to observations of predation rate at different prey densities. The behavioural mechanisms underlying a functional response are not well understood, and estimates of model parameters seldom conform to observations of behaviour. We have developed a mechanistic approach that directly incorporates behavioural observations into characterisation of the functional response. Laboratory experiments were used to record predation rates and observe foraging behaviour of sea stars Asterias vulgaris preying on juve- nile sea scallops Placopecten magellanicus at different densities. Experiments were conducted in tanks with no sediment and tanks with sediment. Behavioural data from the experiments were used to calculate parameters of functional response models Th (handling time per prey) and a (rate of suc- cessful search). On both substrates, Th remained constant across prey density, while a was density- dependent. An inverse quadratic was used to describe a and was incorporated into a functional response model. Estimates of a were also obtained by fitting the functional response model to the pre- dation rate data using regression analysis. These estimates of a were highly consistent with the esti- mates calculated from behavioural data. On both substrates, sea stars preying on scallops had a Type III sigmoid-shaped functional response; on sediment, predation rate decreased at high prey densities. Sea star ability to capture attacked prey was probably the mechanism underlying the observed responses. In general, behavioural information can lead to better understanding of observed func- tional responses.

Predation on Posidonia australis seeds in seagrass habitats of Rottnest Island, Western Australia: patterns and predators

Seed predation is an important process governing the dynamics of many plant popula- tions. We assessed seed mortality due to predation in the seagrass Posidonia australis by identifying predators and quantifying predation events using underwater video cameras, laboratory and field observations, and field tethering experiments in shallow-water habitats off Rottnest Island, Western Australia in 2003 (2 sites) and 2004 (5 sites). We assessed 4 dominant habitats: within seagrass mead- ows of (1) P. australis, (2) Amphibolis antarctica and (3) Halophila ovalis, and on (4) unvegetated sand. Video analysis and field and laboratory observations showed that at least 6 different crustacean taxa were seed predators — the portunid crabs Nectocarcinus integrifrons and an unidentified portu- nid similar to Thalamita crenata, the majid Naxia aurita, the isopod Cymodoce sp., and the hermit crabs Paguristes purpureantennatus and Calcinus dapsiles — with N. integrifrons and Cymodoce sp. being the principal seed predators. Various species of fishes were observed approaching (but never eating) seeds in the video analysis, and none appeared to be seed predators. In 2003, daily seed pre- dation rates were dramatically higher in A. antarctica beds than in other habitats at Parker Point (mean 63% d -1 compared to means of <20% d -1 for the other habitats), but not at Nancy Cove, the only other site studied in 2003. In 2004, daily seed predation rates were higher in Posidonia australis (40 to 73% d -1 ) and A. antarctica (36 to 85% d -1 ) beds than in H. ovalis (9% d -1 ) beds and unvege- tated sand (3 to 13% d -1 ) at all 5 sites studied. Logistic regression showed an approximately 20-fold increased chance of a predation event occurring within a 24 h period in P. australis and A. antarctica beds compared to unvegetated sand, but no increase in predation in the H. ovalis beds compared to sand. Although predation rates varied among sites and years, patterns among habitats were gener- ally consistent. P. australis and A. antarctica, the 2 seagrass species with structurally complex canopies, had much higher rates of seed predation than the habitats with less structure, i.e. H. ovalis and bare sand, which may provide insufficient refuge for seed predators. These results may have important consequences for plant demographics and genetic structuring of local populations. View- ing seagrass seed dispersal strategies in the context of faunal-dependent predation processes, rather than simply in terms of plant-plant competitive interactions, may provide a better understanding of seagrass spatial distributions and successional dynamics.

Habitat structure and the survival of juvenile scallops Pecten novaezelandiae: comparing predation in habitats with varying complexity

Fishing disturbances that remove epifauna and other elements of benthic habitat struc- ture have a secondary impact on the survival of juvenile Pecten novaezelandiae, the native New Zealand scallop. We investigated habitat structure and scallop predation rates in 4 soft-sediment habitats naturally utilised by P. novaezelandiae over multiple spatial scales. We found that habitats exposed to fishing disturbance had significantly fewer elements of benthic structure and that preda- tion rates were significantly (up to 44%) higher compared to unfished habitats. Habitat complexity primarily differed at the spatial scale of site, which corresponds to the scale of fishing disturbance. Scallop predation was negatively correlated with the number of habitat elements such as sponges, horse mussels and ascidians in the immediate area, and positively correlated with predator density. Another factor that affected juvenile scallop survival was ambient scallop density, with higher pre- dation rates at the site where scallop numbers had been artificially enhanced. Although size-specific predation could not be formally tested in this study, it appeared that the predation rate was higher for larger scallops (mean size of 23 cm) compared to smaller scallops (mean size of 16 cm) in at least one of the sites but this requires further investigation. The results suggest that simplification of benthic systems by bottom-towed fishing activity degrades habitats and subsequently increases the vulnera- bility of juvenile scallops to predation. This may have important consequences for the sustainability of wild and enhanced scallop populations.

Forest Landscape Patterns around Marbled Murrelet Nest Sites in the Oregon Coast Range

We analyzed forest composition and landscape preferences of marbled murrelets (Brachyramphus marmoratus). Using dawn surrreys and tree climbing, we found 41 murrelet nest sites on state and federal lands in the Oregon Coast Range Province in western Oregon between 1990 and 1998. Landscapes in 0.5- and 1.0-km-radius plots at these nest sites were compared to patterns in similar plots around a set of points randomly selected from stands of mature or old- growth trees on public lands in the same province. We found less open-sapling and hardwood forests in the plots at nest sites than at random sites for both plot sizes. Conversely, the pro- portion of pole-young conifer habitat was greater at nest sites than at random sites for both plot sizes. Landscape pattern analysis showed that the amount of edge-perimeter density, nest-patch perimeter, and high-contrast edge of nest patches was lower in the 1.0-km-radius plots at nest sites than at random sites. Our best multivariate logistic regression model indicated that greater amounts of pole-young and mature-old-growth forests, less edge (perimeter density and high- contrast edge at nest patches), and more cohesive nest-patch shape best distinguished murrelet nest sites from random sites. We hypothesize that murrelet nest-site selection at the landscape scale may be the result of an antipredator strategy to reduce predation risks on eggs and juvenile murrelets. Young (simple-structure) conifer stands adjacent to nesting areas may decrease pre- dation rates at murrelet nests. Land managers should consider limiting clearcut harvest units both adjacent to murrelet nest patches and within at least 1 km of murrelet nests, as clearcuts increase high-contrast edge in addition to increasing fragmentation levels.

Biodegradable and Tensile Properties of Cotton/Cellulose Acetate Nonwovens

A possible candidate as an environmentally friendly nonwoven fabric is one that can be formed from the thermal calendering of a cotton/cellulose acetate blend. Our results focus on biodegradable properties of the fibers as well as tensile properties of the fabric. Cotton, which is a comfortable, absorbent, biodegradable fiber, is the base fiber in the nonwovens. Cellulose acetate, which is a thermoplastic, hydrophilic, mod ified cellulosic fiber, is used for the binder fiber. We examine the biodegradability of cellulose acetate, cotton, and these fibers in the blend using an ASTM standard pro cedure in which the amount of CO 2 evolved from the decomposition of cellulose acetate and cotton fibers due to microbial activity is monitored. Increased biodegra dation rates in fiber blends are attributed to the synergistic effects of multi-enzyme systems. Opening, blending, carding, and thermal calendering processes are used to fabricate the nonwovens. Pretreatment with solvent vapors is introduced to modify the softening temperatures of the cellulose acetate and to lower the calendering tem peratures. The success of this procedure is demonstrated in enhanced tensile strength of the nonwoven. In addition, modifying tensile properties with solvent vapor pre treatment shows how enhanced strength can be obtained with lower calendering tem peratures.

Intraguild Predation and Competition Between Larval Dragonflies: Direct and Indirect Effects on Shared Prey

We conducted manipulative field experiments in artificial ponds to quantify the predatory impact of larvae of a migratory dragonfly (Tramea lacerata) on a common resident dragonfly species (Erythemis simplicicollis), and on damselflies as shared prey of the two dragonflies. We found that the combined predatory effects of these two dragonflies on damselflies were not additive. To determine the underlying cause of non—additive predation rates in the field, we conducted a second experiment in laboratory aquaria to isolate the impact of each predator on the consumption rates of the other. Dragonfly consumption rates of damselflies in single—predator treatments were compared to those in the presence of heterospecifics or conspecifics with their menta (mouthparts) surgically modified so that they could not capture prey. In the laboratory experiment, de—mented Tramea reduced the consumption rates of Erythemis to less than half of that observed when Erythemis foraged alone. Erythemis numbers were also reduced by Tramea predation. Erythemis had neither effect on Tramea. Both of the negative effects of Tramea on Erythemis will have indirect positive effects on damselflies. The "behavioral" component (reduced Erythemis foraging rate) should be more important than the "trophic link" (reduced Erythemis numbers) indirect effect. Together these indirect positive effects will allay, but not completely compensate for, the direct negative effects of Tramea predation on damselflies. These results illustrate how an asymmetric potential for intraguild predation can lead to asymmetries in interference competition and to non—additive effects on prey mortality. The addition of removal of predators that interact in this manner to or from communities should have only a small net effect on prey because of compensating direct and indirect effects. This may explain why predator manipulations have often had unpredictable or undetectable effects on freshwater benthic communities.

Reproductive Biology of Shrubsteppe Passerine Birds: Geographical and Temporal Variation in Clutch Size, Brood Size, and Fledging Success

We investigated geographical and temporal variation in clutch size, brood size, and fledging success in three common passerine species in shrubsteppe habitats of the northern Great Basin of western North America. Over a 2-year period we surveyed three vegetationally similar sites spanning a latitudinal gradient of 650 km (the geographical component), one of which we sampled for five consecutive years (the temporal component). Clutch sizes of Sage (Amphispiza belli) and Brewer's (Spizella breweri) sparrows did not differ significantly among sites, but brood sizes and (for Brewer's Sparrow) fledging success did. These geographical differences were associated with site-specific variation in nest-pre- dation rates and were attributed to differences in the abundances of snakes. Nests at a site in central Oregon that lacked snakes suffered virtually no predation during the 2-year geo- graphical sampling, whereas nests in southeastern Washington and northern Nevada suffered significantly higher rates (40% and 93%, respectively). During the 5-year temporal sampling at the central Oregon site, all measured reproductive parameters of Sage and Brewer's sparrows and clutch size in Sage Thrashers (Oreoscoptes montanus) varied significantly. Although the region experienced extremes of precipitation during this period, in Sage Sparrows only brood size was significantly correlated with rainfall during the previous winter. The principal source of variation in Sage Sparrow final repro- ductive success was predation, which peaked during an outbreak of Townsend's ground squirrels (Spermophilus townsendi) in 1979. This ground squirrel irruption appeared to be triggered by a pattern of a drought year followed by two relatively wet years, beginning in winter 1976-1977. Although Brewer's Sparrows also experienced considerable predation pressure in 1979, clutch size, brood size, and fledging success were significantly correlated with winter precipitation. No component of Sage Thrasher reproduction was associated with climatic variation. The relationship between avian reproductive success and precipitation in arid regions is more complex than the traditional view of desert birds responding directly to increased primary and secondary productivity; such relationships are indirectly influenced by the effects of rainfall on predator populations, and are further complicated by time lags (up to 2 years) in predator response.