bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identifying the demographic determinants of population growth rate: a case study of red‐billed choughs Pyrrhocorax pyrrhocorax
Authors: Reid J. M. , Bignal E. M. , Bignal S. , McCracken D. I. , Monaghan P. 
Published: June 2004

Summary

Identifying which age‐specific demographic rates underlie variation in a population's growth rate (λ) is an important step towards understanding the population's dynamics. Using data from a 20‐year study of marked individuals, we describe patterns of demographic variation and covariation in the Scottish red‐billed chough population (Pyrrhocorax pyrrhocorax), and investigate which demographic rates have the greatest projected and realized influence on λ.
Survival, the probability of breeding and breeding success varied with age in this population. Data were sufficient to estimate year‐specific probabilities of first‐year, second‐year and adult (all ages over 2) survival and mean breeding success. A population trajectory modelled using these parameter estimates closely matched census data, suggesting that estimates and simplifying assumptions were sufficient to accurately describe important demographic processes.
Elasticity analyses based on stage‐classes for which year‐specific survival was estimable suggested that λ was more elastic to variation in adult survival than first‐ or second‐year survival or breeding success. These ranks were consistent across all 15 years for which λ could be estimated directly, although the elasticity of adult survival declined with population growth.
Survival and breeding success were positively correlated across years. λ remained most sensitive to adult survival when this demographic covariation was incorporated into elasticity analyses.
However, elasticities calculated from a fully age‐structured model suggested that λ was more elastic to variation in first‐ and second‐year survival than to survival at any individual older age class. These ranks were robust to realistic demographic variation, but sensitive to postulated patterns of demographic covariation. We emphasize that covariation should be measured and incorporated into elasticity analyses, and that estimated elasticities must be interpreted in the context of the way in which stage‐classes are defined.
Of the demographic rates in which we quantified between‐year variation, first‐year survival varied most, followed by second‐year survival, breeding success and adult survival. These rates consequently contributed more equally to variation in λ than elasticities predicted. Overall, variation in λ was caused primarily by variation in survival rather than breeding success, and variation in prebreeding survival accounted for 56% of the total variation in λ.
Microplankton dynamics in a perennially ice‐covered Antarctic lake – Lake Hoare
Authors: Roberts Emily C. , Priscu John C. , Laybourn‐Parry Johanna 
Published: June 2004

Summary1. Temporal and spatial variation in planktonic abundance, biomass and composition were determined in Lake Hoare (McMurdo Dry Valleys, Antarctica) over two summer seasons (1996–97 and 1997–98).2. Phototrophic nanoflagellates (PNAN) dominated planktonic biomass, with a mean monthly biomass ranging between 27.3 and 40.4 μg C L−1. The deep chlorophyll maximum was mainly composed of cryptophytes (>87% of total PNAN biomass) and varied in depth between 6 and 12 m.3. Maximum bacterial concentration was 11.8 × 105 cells mL−1. Bacterial abundance showed relatively little temporal variation, with the exception of a drop in numbers that occurred in late November of both years studied.4. Ciliates were the most successful heterotrophic protozoan group, with a mean monthly biomass (1.2–3.2 μg C L−1) being typically at least double that of heterotrophic nanoflagellate (HNAN) biomass (0.1–0.7 μg C L−1).5. Microbial processes within this lake appear to be dominated by bottom up control. The relative importance of allochthonous inputs into the lake (from the ice‐cover and stream flow) and autochthonous recycling (by microzooplankton regeneration) are considered.6. Results from a horizontal transect indicate that the permanence of the main sample hole may have enhanced planktonic biomass over a relatively small spatial scale.
Growth and population size of crayfish in headwater streams: individual‐ and higher‐level consequences of acidification
Authors: Seiler Steven M. , Turner Andrew M. 
Published: June 2004

Summary1. Environmental stress may have indirect positive effects on population size through modification of food‐web interactions, despite having negative effects on individuals. Here we evaluate the individual‐ and population‐level effects of acidification on crayfish (Cambarus bartonii) in headwater streams of the Allegheny Plateau (PA, U.S.A.) with field experiments and survey data. Median baseflow pH of 24 study reaches in nine streams varied from 4.4 to 7.4, with substantial variation found both among and within streams.2. Two bioassays were conducted to evaluate the relationship between stream pH and crayfish growth rates. Growth rates were always higher in circumneutral reaches than in acidic reaches. Crayfish originating in acidic water grew less when transplanted into neutral water than did crayfish originating in neutral water, providing some evidence for a cost of acclimation to acidity.3. Stream surveys showed that fish were less abundant and crayfish more abundant in acidified streams than in circumneutral streams. Crayfish density was sixfold higher in reaches with the lowest pH relative to circumneutral reaches. Large crayfish made up a higher proportion of crayfish populations at sites with high fish biomass, consistent with the hypothesis that fish predation on small individuals may be limiting crayfish population size at these sites.4. Although individual crayfish suffered lower growth in acidified streams, increased acidity appeared to cause an increase in crayfish population size and shifts in size structure, possibly by relieving predation pressure by fish.
Carp (Cyprinus carpio) as a powerful invader in Australian waterways
Authors: Koehn John D. 
Published: June 2004

Summary1. The invasion of carp (Cyprinus carpio L.) in Australia illustrates how quickly an introduced fish species can spread and dominate fish communities. This species has become the most abundant large freshwater fish in south‐east Australia, now distributed over more than 1 million km2.2. Carp exhibit most of the traits predicted for a successful invasive fish species. In addition, degradation of aquatic environments in south‐east Australia has given them a relative advantage over native species.3. Derivation of relative measures of 13 species‐specific attributes allowed a quantitative comparison between carp and abundant native fish species across five major Australian drainage divisions. In four of six geographical regions analysed, carp differed clearly from native species in their behaviour, resource use and population dynamics.4. Climate matching was used to predict future range expansion of carp in Australia. All Australian surface waters appear to be climatically suitable for carp.5. This assessment strongly reinforces the need for immediate management of carp in Australia to include targeted control of human‐assisted dispersal, such as use of carp as bait by anglers, distribution to new locations by anglers and the use of the ‘Koi’ strain in the aquarium industry.6. Given their historical spread, dispersal mechanisms and ecological requirements, the expansion of carp across most of the remainder of Australia is to be expected.
Relative influence of bioturbation and predation on organic matter processing in river sediments: a microcosm experiment
Authors: Mermillod‐Blondin Florian , Gaudet Jean‐Paul , Gerino Magali , Desrosiers Gaston , Jose Jacques , Châtelliers Michel Creuzé des 
Published: June 2004

Summary1. Our objective was to measure the effects of bioturbation and predation on the physical characteristics and biogeochemical processes in river sediments.2. We investigated the impacts of tubificid worms tested separately and together with an omnivore (Gammarus pulex), which does feed on tubificids, on sediment distribution, water flux, sediment organic carbon, biofilm biomass and microbial activities, and the concentrations of dissolved oxygen, dissolved organic carbon, PO, NO, NO and NH in slow filtration sand–gravel columns. We hypothesised that gammarids, which exploit the top 2–3 cm of the sediment, would modify the impact of worms at the sediment surface.3. In experiments both with and without gammarids, bioturbation by the tubificids modified both the distribution of surface particles in the sediment column and water flux. In addition, microbial aerobic (oxygen consumption) and anaerobic (denitrification and fermentative decomposition of organic matter) processes in the sediment were stimulated in the presence of tubificid worms. However, G. pulex did not affect either the density or bioturbation activity of the tubificid worms.4. Bioturbation by the benthos can be a major process in river habitats, contributing to the retention of organic matter in sediment dynamics. The presence of at least one predator had no effect on bioturbation in sediments. In such systems, physical heterogeneity may be sufficient for tubificids to escape from generalist predators, though more specialised ones might have more effect.
Evidence of coprophagy in freshwater zooplankton
Authors: Pilati Alberto , Wurtsbaugh Wayne. A. , Brindza Nathaniel R. 
Published: June 2004

Summary1. Vertical transport of nutrients in sedimenting faecal material is greatly reduced by coprophageous organisms. Unfortunately, nearly all work on faecal production, sedimentation and coprophagy has dealt with copepods in marine ecosystems. Here, we report the first evidence of coprophagy in freshwater zooplankton from oligotrophic and eutrophic lakes. We used 14C‐labelled algae and faecal material to estimate the rates of algal clearance and coprophagy.2. Measured feeding rates per individual on faecal material were similar (Daphnia pulex, D. rosea, Leptodiaptomus tyrelli) or even higher (D. lumholtzi) than filtering rates on phytoplankton. This finding does not necessarily implicate active selection of faeces over algae because: (i) we did not use the same food concentrations for faeces and algae, and (ii) grazers of slightly different sizes were used in each test.3. Weight‐specific clearance rates of L. tyrelli and Holopedium gibberum on faecal matter (0.084–0.089 mL μg−1 h−1) were higher than in the daphniids (0.026 mL μg−1 h−1).4. The data indicate that coprophagy in freshwater ecosystems is an important mechanism of nutrient recycling, and this process should be taken into account when studying nutrient fluxes within lakes and reservoirs.
Retention and supply of zebra mussel larvae in a large river system: importance of an upstream lake
Authors: Stoeckel J. A. , Rehmann C. R. , Schneider D. W. , Padilla D. K. 
Published: June 2004

Summary1. Persistence of zebra mussel populations in river systems probably depends upon the presence of upriver sites capable of hosting self‐recruiting adult populations that act as sources of larvae. In this paper we examine the importance of Lake Pepin, a natural riverine lake in the Upper Mississippi River, as an upriver source of larvae to the downstream populations of zebra mussels.2. Field studies and modelling suggest that Lake Pepin plays a major role in maintaining zebra mussel populations in the Upper Mississippi River. Long water residence times in Lake Pepin allow for self‐recruitment under the right hydraulic conditions. Larval abundance was low to absent upstream of the lake but increased dramatically downriver in all 3 years of the study. Travel time estimates in the Upper Mississippi River show that newly fertilised larvae drifting out of Lake Pepin can contribute substantially to the major downstream peak in larval abundance. In contrast, backwater and other off‐channel sites are unlikely to drive main‐channel abundance patterns. Larval abundances in off‐channel sites were less than or equal to those in the main channel.3. A key factor in assessing the importance of Lake Pepin as a source population was the abundance of early stage, unshelled larvae. Studies that consider only abundances of older shelled stages (visible by cross polarised lighting) may yield misleading results. Results of this study suggest that efforts to control zebra mussels in the Upper Mississippi River should focus on controlling adult populations within Lake Pepin and reducing or eliminating larvae exiting the lake.
Summer use of a small stream by fish and crayfish and exchanges with adjacent lentic macrohabitats
Authors: Cossette Claudia , Rodríguez Marco A. 
Published: June 2004

Summary1. Movements between a stream reach and two adjacent lentic macrohabitats, a beaver pond and a lake, were followed for the Appalachian crayfish and two fish species, brook charr and brown bullhead, over an 85‐d period from early June to late August, and were analysed in relation to water level, maximum water temperature, photoperiod length, lunar luminosity, and age, by use of time‐series regressions.2. Brook charr showed strong net immigration to the stream reach for underyearling (age class 0+) fish but net emigration for 1+ fish. Both immigration and emigration were positively related to water level and temperature; migratory responses to temperature were age‐specific.3. Brown bullhead used the stream primarily as a corridor for downstream migration from the beaver pond to the lake. As with brook charr, water level and temperature had a positive effect on movement and responses were stronger in younger individuals.4. Crayfish emigrated from the stream during the summer. Movements were positively related to increases in water level and temperature, with responses of 1+ crayfish much stronger than those of older individuals.5. The results indicate that the stream tributary played different roles for brook charr (nursery), brown bullhead (dispersal corridor) and Appalachian crayfish (early summer refuge), and suggest that variation in water level or temperature resulting from climatic change or local anthropogenic activities might modify connectivity between macrohabitats, particularly for younger individuals.
Flow extremes and benthic organic matter shape the metabolism of a headwater Mediterranean stream
Authors: Acuña Vicenç , Giorgi Adonis , Muñoz Isabel , Uehlinger Urs , Sabater Sergi 
Published: June 2004

Summary1. Single‐station diel oxygen curves were used to monitor the oxygen metabolism of an intermittent, forested third‐order stream (Fuirosos) in the Mediterranean area, over a period of 22 months. Ecosystem respiration (ER) and gross primary production (GPP) were estimated and related to organic matter inputs and photosynthetically active radiation (PAR) in order to understand the effect of the riparian forest on stream metabolism.2. Annual ER was 1690 g O2 m−2 year−1 and annual GPP was 275 g O2 m−2 year−1. Fuirosos was therefore a heterotrophic stream, with P : R ratios averaging 0.16.3. GPP rates were relatively low, ranging from 0.05 to 1.9 g O2 m−2 day−1. The maximum values of GPP occurred during a few weeks in spring, and ended when the riparian canopy was fully closed. The phenology of the riparian vegetation was an important determinant of light availability, and consequently, of GPP.4. On a daily scale, light and temperature were the most important factors governing the shape of photosynthesis–irradiance (P–I) curves. Several patterns could be generalised in the P–I relationships. Hysteresis‐type curves were characteristic of late autumn and winter. Light saturation responses (that occurred at irradiances higher than 90 μE m−2 s−1) were characteristic of early spring. Linear responses occurred during late spring, summer and early autumn when there was no evidence of light saturation.5. Rates of ER were high when compared with analogous streams, ranging from 0.4 to 32 g O2 m−2 day−1. ER was highest in autumn 2001, when organic matter accumulations on the streambed were extremely high. By contrast, the higher discharge in autumn 2002 prevented these accumulations and caused lower ER. The Mediterranean climate, and in its effect the hydrological regime, were mainly responsible for the temporal variation in benthic organic matter, and consequently of ER.
Silencing of ribosomal protein L3 genes in N. tabacum reveals coordinate expression and significant alterations in plant growth, development and ribosome biogenesis
Authors: Popescu Sorina C. , Tumer Nilgun E. 
Published: June 2004

SummaryThe expression of ribosomal protein genes is coordinately regulated in bacteria, yeast, and vertebrates, so that equimolar amounts of ribosomal proteins accumulate for assembly into ribosomes. To understand how expression of ribosomal protein genes is regulated in plants, we altered expression of the large subunit ribosomal protein L3 (RPL3) genes in Nicotiana tabacum using post‐transcriptional gene silencing (PTGS). L3 is encoded by two genes, RPL3A and RPL3B, with 80.2% amino acid sequence identity in tobacco. Two types of ‘hairpin’ RNA (hpRNA) vectors carrying the RPL3A or RPL3B sequences in both sense and antisense orientation were generated in order to alter the expression level of both RPL3 genes. Tobacco plants transformed with a vector containing a 5′‐terminal fragment of RPL3A gene displayed decreased RPL3A mRNA levels and a marked increase in the abundance of RPL3B mRNA. These results indicated that expression of the RPL3 genes is coordinately regulated in tobacco. The transgenic plants that contained higher levels of RPL3B mRNA exhibited leaf overgrowth and mottling. Epidermal cells of these plants were increased in number and decreased in size. The precursor rRNA (pre‐rRNA) and the mature rRNAs accumulated in these plants, suggesting that ribosome biogenesis is upregulated. Tobacco plants transformed with an hpRNA vector harboring the full‐length RPL3B cDNA exhibited efficient silencing of both RPL3A and RPL3B genes, reduced L3 levels, and an abnormal phenotype characterized by a delay in development, stunting, and inhibition of lateral root growth. L3 deficiency led to a reduction in cell number and an increase in cell size, suggesting that L3 positively regulates cell division. Decreasing RPL3 gene expression resulted in a decrease in accumulation of the pre‐rRNA, establishing a prominent role for L3 in ribosome biogenesis in plants.
Phosphatidic acid accumulation is an early response in theCf‐4/Avr4interaction
Authors: De Jong Camiel F. , Laxalt Ana M. , Bargmann Bastiaan O. R. , De Wit Pierre J. G. M. , Joosten Matthieu H. A. J. , Munnik Teun 
Published: June 2004

SummaryTheCladosporium fulvum(Cf)‐4gene of tomato confers resistance to the fungusC. fulvum, expressing the corresponding avirulence (Avr)4gene, which codes for an elicitor protein. Little is known about how such mechanisms work, but previous studies have shown that elicitor recognition activates Ca2+signalling and protein kinases, such as mitogen‐activated protein kinase (MAPK) and calcium‐dependent protein kinase (CDPK). Here, we provide evidence that a new signalling component, the lipid second messenger phosphatidic acid (PA), is produced within a few minutes of AVR4/Cf‐4 interaction. Using transgenic tobacco cells expressing the tomatoCf‐4‐resistance gene as a model system, phospholipid signalling pathways were studied by pre‐labelling the cells with32Piand assaying for the formation of lipid signals after challenge with the fungal elicitor AVR4. A dramatic rapid response was an increase in32P‐PA, together with its metabolic product diacylglycerol pyrophosphate (DGPP). AVR4 increased the levels of PA and DGPP in aCf‐4+‐, time‐ and dose‐dependent manner, while the non‐matching elicitor AVR9 did not trigger any response. In general, PA signalling can be triggered by two different pathways: via phospholipase D (PLD), which generates PA directly by hydrolysing structural phospholipids like phosphatidylcholine (PC), or via PLC, which generates diacylglycerol (DAG) that is subsequently phosphorylated to PA by DAG kinase (DGK). To determine the origin of the AVR4‐induced PA formation, a PLD‐specific transphosphatidylation assay and a differential32P‐labelling protocol were used. The results clearly demonstrated that most PA was produced via the phosphorylation of DAG. Neomycin and U73122, inhibitors of PLC activity, inhibited AVR4‐induced PA accumulation, suggesting that the increase in DGK activity was because of increased PLC activity producing DAG. Lastly, evidence is provided that PLC signalling and, in particular, PA production could play a role in triggering responses, such as the AVR4‐induced oxidative burst. For example, PLC inhibitors inhibited the oxidative burst, and when PA was added to cells, an oxidative burst was induced.
Characterization of C‐terminal domains of Arabidopsis heat stress transcription factors (Hsfs) and identification of a new signature combination of plant class A Hsfs with AHA and NES motifs essential for activator function and intracellular localization
Authors: Kotak Sachin , Port Markus , Ganguli Arnab , Bicker Frank , Von Koskull‐Döring Pascal 
Published: June 2004

SummaryHeat stress transcription factors (Hsfs) are the major regulators of the plant heat stress (hs) response. Sequencing of the Arabidopsis genome revealed the existence of 21 open‐reading frames (ORFs) encoding putative Hsfs assigned to classes A–C. Here we present results of a functional genomics approach to the Arabidopsis Hsf family focused on the analysis of their C‐terminal domains (CTDs) harboring conserved modules for their function as transcription factors and their intracellular localization. Using reporter assays in tobacco protoplasts and yeast as well as glutathione‐S‐transferase (GST) pull‐down assays, we demonstrate that short peptide motifs enriched with aromatic and large hydrophobic amino acid (aa) residues embedded in an acidic surrounding (AHA motifs) are essential for transcriptional activity of class A Hsfs. In contrast to this, class B and C Hsfs lack AHA motifs and have no activator function on their own. We also provide evidence for the function of a leucine (Leu)‐rich region centered around a conserved QMGΦL motif at the very C‐terminus as a nuclear export signal (NES) of class A Hsfs. Sequence comparison indicates that the combination of a C‐terminal AHA motif with the consensus sequence FWxxF/L,F/I/L as well as the adjacent NES represents a signature domain for plant class A Hsfs, which allowed to identify more than 60 new Hsfs from the expressed sequence tag (EST) database.