Showing papers by "University of Georgia published in 1984"

Differentiating Entrepreneurs from Small Business Owners: A Conceptualization

Abstract: The literature of small business and entrepreneurship is explored. It is established that, although there is an overlap between entrepreneurial firms and small business firms, they are different entities. Using the 1934 work of Schumpeter and recognizing the additions to the field of current writers, a conceptual framework is established for the differentiation of entrepreneurs from small business owners.

Demographic influences on mitochondrial DNA lineage survivorship in animal populations

Abstract: Probability models of branching processes and computer simulations of these models are used to examine stochastic survivorship of female lineages under a variety of demographic scenarios. A parameter II, defined as the probability of survival of two or more independent lineages over G generations, is monitored as a function of founding size of a population, population size at carrying capacity, and the frequency distributions of surviving progeny. Stochastic lineage extinction can be very rapid under certain biologically plausible demographic conditions. For stable-sized populations initiated by n females and/or regulated about carrying capacity k = n, it is highly probable that within about 4n generations all descendants will trace their ancestries to a single founder female. For a given mean family size, increased variance decreases lineage survivorship. In expanding populations, however, lineage extinction is dramatically slowed, and the final k value is a far more important determinant of II than is the size of the population at founding. The results are discussed in the context of recent empirical observations of low mitochondrial DNA (mtDNA) sequence heterogeneity in humans and expected distributions of asexually transmitted traits among sexually reproducing species.

The muscle satellite cell: a review.

Abstract: Since the first reports of satellite cells in 1961, considerable knowledge has accumulated concerning their phylogenetic distribution and their location, morphology, and function. There is no doubt that satellite cells are capable of undergoing mitosis and that they have considerable motility. These cells function as the progenitors of the myofiber nuclei that must be added during normal (postnatal) growth of muscle. In muscle undergoing or attempting to undergo regeneration, the satellite cell functions as a myogenic stem cell to produce myoblasts that line up and fuse within the scaffolding of the remnant basal lamina or migrate into the interstitium to produce neofibers . A number of problems remain to be solved concerning the regulation of satellite cell function. At this time it is equivocable whether or not the presumptive myoblast and the satellite cell are functionally identical and at the same stage of myogenic differentiation. Apparently there is species variation in terms of the ability of myotubes from embryonic myogenic cells and satellite cells to synthesize protein. The mechanism(s) by which a wide variety of stimuli activate satellite cells is not known, nor is the mechanism(s) by which satellite cells become inactive during the latter stages of growth and adulthood known. Mitogenic factors are present in damaged muscle; but the specific characteristics of these factors and their mechanism of activation are also unknown. Hormones are certainly involved in the regulation of proliferation and differentiation of myogenic cells, but whether presumptive myoblasts and satellite cells or their myotubes respond similarly to hormones in culture has not been adequately examined. Greater understanding of these mechanisms will increase the possibility of total muscle recovery from severe injury or disease. Such knowledge would also have particular application to the production of meat animals and to a greater understanding of the growth process in general.

Fate of Photosynthetic Fixed Carbon in Light- and Shade-Adapted Colonies of the Symbiotic Coral Stylophora pistillata

Abstract: The total daily flux of photosynthetically fixed carbon in light- and shade-adapted phenotypes of the symbiotic coral, Stylophora pistillata, was quantified. Light adapted corals fixed four times as much carbon and respired twice as much as shade corals. Specific growth rates of zooxanthellae in situ were estimated from average daily mitotic indices and from ammonium uptake rates (nitrate uptake or nitrate reductase activity could not be demonstrated). Specific growth rates were very low, demonstrating that of the total net carbon fixed daily, only a small fraction (less than 5%) goes into zooxanthellae cell growth. The balance of the net fixed carbon (more than 95%) is translocated to the host. New and conventional methods of measuring total daily translocation were compared. The `growth rate' method, which does not employ $^{14}$C, emerged as superior to the conventional in vitro and in vivo methods. The contribution of translocated carbon to animal maintenance respiration (CZAR) was 143% in light corals and 58% in shade corals. Thus, translocation in the former could supply not only the total daily carbon needed for respiration but also a fraction of the carbon needed for growth. Whereas light-adapted corals released only 6%, shade-adapted corals released almost half of their total fixed carbon as dissolved or particulate organic material. This much higher throughput of organic carbon may possibly benefit the heterotrophic microbial community in shade environments.

Finite-size scaling at first-order phase transitions

Abstract: Using thermodynamic fluctuation theory, we study the finite-size rounding of anomalies occurring at first-order phase transitions of the corresponding infinite system. Explicit expressions for thermodynamic functions are derived both for "symmetric transitions" (such as the jump of the spontaneous magnetization in the Ising model from $+{M}_{\mathrm{sp}}$ to $\ensuremath{-}{M}_{\mathrm{sp}}$ as the field changes from ${0}^{+}$ to ${0}^{\ensuremath{-}}$) as well as for asymmetric cases, but restricting attention to (hyper)cubic system shapes. As an explicit example for the usefulness of these considerations in Monte Carlo simulations where it may be a problem to (i) locate a phase transition and (ii) distinguish first-order from second-order transitions, we present numerical results for the two-dimensional nearest-neighbor Ising ferromagnet in a field, both below the critical temperature ${T}_{c}$ and at ${T}_{c}$. The numerical results are found to be in very good agreement with the phenomenological theory and it is shown that one may extract the magnitudes of jumps occurring at first-order phase transitions in a well-defined and accurate way.

Effects of Essential Oils from Plants on Growth of Food Spoilage Yeasts

Abstract: Thirty-two essential oils from plants were screened for inhibitory effects on 13 food-spoilage and industrial yeasts. Of these, essential oils of allspice, cinnamon, clove, garlic, onion, oregano, savory, and thyme were most inhibitory. Oils were subsequently tested for their effects on biomass production and pseudomycelium formation of eight genera of yeasts. Garlic oil was a potent inhibitor of yeast growth at concentrations as low as 25 ppm. The oils of onion, oregano and thyme were also strongly inhibitory. Essential oils (100 ppm) had no effect on pseudomycelium production by Candida lipolytica. However, all eight essential oils delayed pseudomycelium formation by Hansenula anomala, whereas six oils stimulated pseudomycelium production by Lodderomyces elongisporus. Cinnamon and clove oils were clearly stimulatory to pseudomycelium production by Saccharomyces cerevisiae.

Acquisition of Thermotolerance in Soybean Seedlings : Synthesis and Accumulation of Heat Shock Proteins and their Cellular Localization.

Abstract: When soybean Glycine max var Wayne seedlings are shifted from a normal growth temperature of 28°C up to 40°C (heat shock or HS), there is a dramatic change in protein synthesis. A new set of proteins known as heat shock proteins (HSPs) is produced and normal protein synthesis is greatly reduced. A brief 10-minute exposure to 45°C followed by incubation at 28°C also results in the synthesis of HSPs. Prolonged incubation (e.g. 1-2 hours) at 45°C results in greatly impaired protein synthesis and seedling death. However, a pretreatment at 40°C or a brief (10-minute) pulse treatment at 45°C followed by a 28°C incubation provide protection (thermal tolerance) to a subsequent exposure at 45°C. Maximum thermoprotection is achieved by a 2-hour 40°C pretreatment or after 2 hours at 28°C with a prior 10-minute 45°C exposure. Arsenite treatment (50 micromolar for 3 hours) also induces the synthesis of HSP-like proteins, and also provides thermoprotection to a 45°C HS; thus, there is a strong positive correlation between the accumulation of HSPs and the acquisition of thermal tolerance under a range of conditions. During 40°C HS, some HSPs become localized and stably associated with purified organelle fractions ( e.g. nuclei, mitochondria, and ribosomes) while others do not. A chase at 28°C results in the gradual loss over a 4-hour period of the HSPs from the organelle fractions, but the HSPs remain selectively localized during a 40°C chase period. If the seedlings are subjected to a second HS after a 28°C chase, the HSPs rapidly (complete within 15 minute) relocalize in the organelle fractions. The relative amount of the HSPs which relocalize during a second HS increases with higher temperatures from 40°C to 45°C. Proteins induced by arsenite treatment are not selectively localized with organelle fractions at 28°C but become organelle-associated during a subsequent HS at 40°C.

Anaerobic Biodegradation of the Lignin and Polysaccharide Components of Lignocellulose and Synthetic Lignin by Sediment Microflora

Abstract: Specifically radiolabeled [14C-lignin]lignocelluloses and [14C-polysaccharide]lignocelluloses were prepared from a variety of marine and freshwater wetland plants including a grass, a sedge, a rush, and a hardwood. These [14C]lignocellulose preparations and synthetic [14C]lignin were incubated anaerobically with anoxic sediments collected from a salt marsh, a freshwater marsh, and a mangrove swamp. During long-term incubations lasting up to 300 days, the lignin and polysaccharide components of the lignocelluloses were slowly degraded anaerobically to 14CO2 and 14CH4. Lignocelluloses derived from herbaceous plants were degraded more rapidly than lignocellulose derived from the hardwood. After 294 days, 16.9% of the lignin component and 30.0% of the polysaccharide component of lignocellulose derived from the grass used (Spartina alterniflora) were degraded to gaseous end products. In contrast, after 246 days, only 1.5% of the lignin component and 4.1% of the polysaccharide component of lignocellulose derived from the hardwood used (Rhizophora mangle) were degraded to gaseous end products. Synthetic [14C]lignin was degraded anaerobically faster than the lignin component of the hardwood lignocellulose; after 276 days, 3.7% of the synthetic lignin was degraded to gaseous end products. Contrary to previous reports, these results demonstrate that lignin and lignified plant tissues are biodegradable in the absence of oxygen. Although lignocelluloses are recalcitrant to anaerobic biodegradation, rates of degradation measured in aquatic sediments are significant and have important implications for the biospheric cycling of carbon from these abundant biopolymers.

The nature of nucleotide sequence divergence between barley and maize chloroplast dna

Abstract: Analysis of a 2175-base pair (bp) Sma I- Hin dIII fragment of barley chloroplast DNA revealed that rbcL (the gene for the large subunit of ribulose 1,5-bisphosphate carboxylase) and atpB (the gene for the β subunit of ATPase) are transcribed divergently and are separated by an untranscribed region of 155-166 bp. The rbcL mRNA has a 320-residue untranslated leader region, whereas the atpB mRNA has a 296- to 309-residue leader region. The sequence of these regions, together with the initial 113 bp of the atpB -coding region and the initial 1279 bp of the rbcL -coding region, is compared with the analogous maize chloroplast DNA sequences. Two classes of nucleotide differences are present, substitutions and insertions/deletions. Nucleotide substitutions show a 1.9-fold bias toward transitions in the rbcL -coding region and a 1.5-fold bias toward transitions in the noncoding region. The level of nucleotide substitutions between the barley and maize sequences is about 0.065/bp. Seventy-one percent of the substitutions in the rbcL -coding region are at the third codon position, and 95% of these are synonymous changes. Insertion/deletion events, which are confined to the noncoding regions, are not randomly distributed in these regions and are often associated with short repeated sequences. The extent of change for the noncoding regions (about 0.093 events/bp) is less than the extent of change at the third codon positions in the rbcL -coding region (about 0.135 events/bp), including insertion/delection events. Limited sequence analysis of the analogous DNA from a wild line ( Hordeum spontaneum ) and a primitive Iranian barley ( H. vulgare ) suggested a low rate of chloroplast DNA evolution. Compared to spinach chloroplast DNA, the barley rbcL-atpB untranslated region is extremely diverged, with only the putative rbcL promoters and ribosome-binding site being extensively conserved.

Primary Production and Photoadaptation in Light- and Shade-Adapted Colonies of the Symbiotic Coral, Stylophora pistillata

Abstract: Photoadaptation by photosynthetic organisms to lowered light intensities occurs in part through changes in pigment concentrations and in characteristics of the photosynthetic response curve. We have characterized photoadaptive responses of light- and shade-adapted colonies of the reef coral Stylophora pistillata , which possesses symbiotic algae (zooxanthellae) and grows naturally under a variety of light intensities in the highly cavernous reefs of the Red Sea. Shade-adapted corals have significantly more chlorophyll per individual zooxanthella cell than light-adapted corals (2.98 compared to 12.97 pg chlorophyll a per cell), but not a significantly different number of cells per unit area (1.00 × 10 6 cells per square centimetre), with the result that the mass of chlorophyll per unit area is greater for shade-adapted corals than for light-adapted corals. Tissue nitrogen content per unit area is significantly lower ( p p > 0.05) in shade forms. These biomass characteristics are concomitant with a variety of func­tional responses to natural light intensities. Rate of photosynthesis at saturating light intensities is the same per unit area in both forms (20.2 µgO 2 cm -2 h -1 for shade specimens; 18.8 for light specimens); but it is significantly different when measured by amount of chlorophyll (1.6 µg O 2 (chl a ) -1 h -1 for shade specimens compared with 5.0 for light specimens). The initial slope of the P: I curve, α , is significantly higher for shade specimens by area (0.21 for shade corals compared with 0.12 for light corals), but significantly lower for shade specimens by amount of chlorophyll a (0.01 for specimens from shade compared to 0.04 for specimens growing in the light). I k (the point at which maximum production begins) is significantly lower for shade specimens (138 µmol m -2 s -1 for shade compared to 273 for light), and likewise I c (the compensation point at which net coral photosynthesis = 0) is also significantly less for shade specimens (30 µmol m -2 s -1 for shade compared to 141 for light). The average nocturnal respiration rate is significantly higher for specimens growing in the light (13.9 µg O 2 cm -2 h -1 for light specimens compared to 7.6 for shade specimens). Corals in intense sunlight respire at almost twice the rate of shade corals, probably in response to their higher total gross production. Owing to higher production rates and lower respiration rates, integrated P c (gross)/ R c (24 h) ratios are greater for shade-adapted specimens either in direct sunlight (1.76 P/R for shade specimens in the light compared to 1.10 for light specimens in the light), or in the shade (0.43 for shade specimens in the cave compared to 0.10 for light specimen in the cave). By using previously defined equations and biomass assumptions, it can be shown that light-adapted Stylophora pistillata can acquire all of their basal metabolic carbon through photosynthesis and translocation, but that shade-adapted Stylophora colonies growing in shade acquire slightly less than half. These results also show that if there were no photoadaptive response, shade-adapted specimens would acquire less than 4 % of their carbon from photosynthesis

Videogames, Television Violence, and Aggression in Teenagers

Abstract: VioLit summary: OBJECTIVE: The aim of this paper by Dominick was to examine the effects of videogames and television violence upon levels of self-esteem and aggression in adolescents. The study examined both the stimulation theory of viewing violence, which suggests that viewing such scenes could increase the probability of commission of actual violence, and catharsis theory, suggesting that viewing violence reduces levels of aggression by purging the viewer of aggressive feelings. METHODOLOGY: The author employed a quasi-experimental cross-sectional design with a non-probability sample of tenth and eleventh grade adolescents at three high schools in northeast Georgia. Of the 292 children who agreed to participate, 250 survey questionnaires that could be used in the study were returned. Measures included total amount of time spent per week playing videogames at arcades, and the total amount of money spent per week in these activities. Viewing of television violence was measured by how often each subject watched each of 24 programs, 16 of which were rated as above average in violence by the National Coalition on Television Violence. General television viewing was measured by number of hours spent watching television on an average day, as well as the amount of time spent watching on the day before the survey. School performance was measured with average grades received by the subject, and a measure of socio-economic status (SES) was obtained via use of the Occupational Prestige Scale. Aggression was measured with three types of question. The first involved hypothetical responses to various hypothetical situations, ranging from backing out of the situation to fighting. The second consisted of six items that dealt with interpersonal relations with others and manifest physical aggression, and attitudes to fighting. The third measure of aggression was an index of aggressive delinquency, according to the frequency with which the subject engaged in three violent acts - fighting with several people, hurting someone for revenge and fighting with another student. Self-esteem was measured with four items based upon a scale developed by Rosenberg, with subjects agreeing or disagreeing with statements about self-worth. Analysis was conducted both for the overall sample and separately for boys and for girls, and included correlations, examination of frequencies, ANOVA and Chi-Square. FINDINGS/DISCUSSION: The author found that 24% of the girls and 18% of the boys did not play videogames, with average time playing being less than an hour for girls and an hour and a half for boys. Girls spent an average of $1.50 each week on videogames, with only 6% playing alone, whilst boys spent just over $2.00, with 21% attending the arcade by themselves. 36% of the girls' families owned home systems, with 55% of the boys' families having videogames at home - a variable that was negatively related to school performance for boys. Boys viewed more television violence than did girls, although this finding was only weakly significant (p AUTHOR'S RECOMMENDATIONS: The author recommended future research be conducted using subjects from various age groups in different settings with more accurate and thorough measures of aggression. EVALUATION: This study represents an interesting examination of the relationships among videogame playing, television viewing and aggression. However, the use of a sample from one location with subjects of the same age group might have resulted in either an overestimation or an underestimation of the true effects of violent media upon aggressive behavior. The use of self-report data might have led to inaccurate findings, and the measures of aggression might not have covered all types of aggressive tendencies. Internal validity, therefore, might not be of the highest order. However, the study provides a good basis for further research. (CSPV Abstract - Copyright © 1992-2007 by the Center for the Study and Prevention of Violence, Institute of Behavioral Science, Regents of the University of Colorado) KW - Georgia KW - Grade 10 KW - Grade 11 KW - Senior High School Student KW - Late Adolescence KW - Early Adolescence KW - Exposure to Violence KW - Video Game Violence KW - Aggression Causes KW - Juvenile Aggression KW - Media Violence Effects KW - Television Viewing KW - Television Violence KW - Juvenile Self-Esteem

Patterns of Invertebrate Distribution and Abundance in the Intertidal Salt Marsh: Causes and Questions

Abstract: The intertidal marsh community comprises both benthic and natant faunal components. The benthic components are primarily small invertebrates residing within or on the soft sediments of the vegetated marsh surface. The natant components include larger, fully aquatic organisms (e.g., fish and shrimp) that inhabit the shallow waters adjacent to the marsh at low tide but interact with the benthic components of the community when the marsh is tidally inundated. In this structurally complex and often expansive intertidal environment, patterns of invertebrate distribution and abundance are not apparent to the casual observer. Benthic core samples taken along an intertidal marsh transect on Sapelo Island, Georgia, USA show that many of the inconspicuous infaunal organisms, which numerically dominate the macrofaunal elements of this soft-substrate community, exhibit zonal distribution patterns along a tidal gradient. Patterns of invertebrate distribution in the intertidal salt marsh are often attributed to the activities of aquatic predators. The results of most predator exclusion experiments have left little doubt that predation/disturbance can be an important determinant of invertebrate abundance in soft-substrate communities; but a growing number of experiments, in both freshwater and marine environments, have produced results that apparently conflict with this, general tenet. Dismissed by some as “failed” experiments, these investigations have exposed our lack of knowledge about the effects of specific predators and the importance of complex interactions which involve more than two trophic levels. Although the importance of predation has been stressed in many recent experimental investigations, there are many other factors that, alone or in combination, may also influence the structure of salt marsh invertebrate assemblages. Included among these are: (1) various density-dependent processes (e.g., adult-larval interactions, agonistic behavior, interspecific competition), (2) selective larval settlement or mortality, (3) the influence of physical factors expressed through habitat preferences, and (4) unpredictable or cyclic physical disturbances. Many questions concerning the spatial and temporal patterns of invertebrate distribution and abundance in the salt marsh are unresolved and remain as challenges to our understanding of soft-substrate community dynamics.

Above‐ and belowground emergent macrophyte production and turnover in a coastal marsh ecosystem, Georgia1

Abstract: Seasonal patterns of aboveground plant mass and the depth distribution of live roots, rhizomes, and dead belowground organic matter were measured for Spartina alterniflora and Spartina cynosuroides in Georgia tidal marshes. Peak live aboveground biomass was 1.6 x higher for S. cynosuroides than for S. alterniflora. Live biomass was 2.4 x more belowground thanaboveground for S. cynosuroides and 1.7 x for S. alterniflora. Rhizomes made up 76 and 87% of live belowground biomass during the year. Mirrored patterns of biomass accumulation and loss in above- and belowground tissues during the year suggest the importance of seasonal storage and redistribution of organic matter. Belowground production was measured with a technique that partially accounts for midseason decomposition. Total plant production was estimated to be 7,620 g dry mass~m+.yr-’ for S. alterniJlora and 7,708 for S. cynosuroides. Belowground production was roughly 1.6 x aboveground production. Turnover rates for belowground live material were 1.42.yr’ for S. cynosuroides and 3.22.yr-’ for S. alterniflora. The fate of root and rhizome material, including the extent to which such material enters the estuarine or nearshore food webs, is not clear.

Crossover scaling and critical behavior at the «surface-bulk» multicritical point

Abstract: With use of a novel Monte Carlo method suited for the study of surface phenomena, the authors have investigated a three-dimensional Ising model with modified surface exchange. The results verify the scaling behavior of the magnetization profile and confirm and extend renormalization-group predictions. The surface-layer magnetization exponent is ${\ensuremath{\beta}}_{1}=0.78\ifmmode\pm\else\textpm\fi{}0.02$ except at the "special" (multicritical) transition where ${{\ensuremath{\beta}}_{1}}^{m}=0.175\ifmmode\pm\else\textpm\fi{}0.025$ and the crossover exponent is $\ensuremath{\phi}=0.56\ifmmode\pm\else\textpm\fi{}0.04$.

The Transition to Professional Management: Mission Impossible?:

Abstract: This article presents a conceptual model of the transition process when changing from entrepreneurial management to functional management. It may provide a tool for predicting the success or failure of such a change.

Problems in the Identification of Species of Eimeria

Abstract: The paper is concerned with the principles upon which coccidia of the genus Eimeria may be characterized. Reference strains for comparative purposes usually are not available and the limitations of morphological data for speciation are discussed. The value of other parameters are considered such as host and site specificity, pathogenicity, immunological specificity, pre-patent period, sporulation time, enzyme variation, and DNA buoyant density. The weight afforded to each of these parameters for specific identification may vary according to the parasite and host studied. Determinations of physiological and behavioral characteristics that are now becoming available should be included in species definitions wherever possible.

Are attention deficit disorders with and without hyperactivity similar or dissimilar disorders

Abstract: From a population of 625 children in grades 2–5, 10 children were identified as those with attention deficit disorder with hyperactivity (ADD/H) and 20 children were identified as those with attention deficit disorder without hyperactivity (ADD/WO). When compared with matched normal control children on a battery of teacher ratings, peer ratings, and self-report measures, markedly different patterns of characteristics were found for the two ADD groups. ADD/H children exhibited aggressive conduct disorders, bizarre behavior, were guiltless, very unpopular, and performed poorly in school. In contrast, ADD/WO children were found to be anxious, shy, socially withdrawn, moderately unpopular, and poor in sports and school performance. Both groups exhibited depression and poor self-concepts, but differed in the specific areas of low self-esteem. These different patterns suggest that ADD/ H and ADD/WO are dissimilar syndromes and perhaps should not be considered to be subtypes of the same disorder.

Influence of flower color polymorphism on genetic transmission in a natural population of the common morning glory, ipomoea purpurea

Abstract: The processes of genetic transmission are fundamental to evolutionary change. Because mating forms the link between generations an essential aspect ofgenetic transmission is the mating process. In animals the choice of mates is often mediated by behavior, with such criteria as courtship displays, position in a dominance hierarchy, or specific morphological features playing an important role. In plants, mating struture is in part controlled by the vectors utilized in transferring pollen from anther to stigma. These vectors may be simply wind or gravity, or they may be insects or other animals manipulated into performing pollination duty by a plant's floral characteristics. The behavioral characteristics of insect pollinators are thought to have a profound influence on the mating process. For instance, insect pollinators may exhibit consistent preferences when presented with a choice of flower color or morphology (Waser and Price, 1981, 1983). The concept ofan insect pollinator exhibiting flower constancy is very old, having been described by investigators in botany, agriculture and insect behavior (e.g., Grant, 1950). When choices are made among flower color types or morphological types in a polymorphic population, a system ofassortative mating is often imposed on the population. In the study of pollination biology it has been generally assumed that the transmission of genes is consistent with the observed

Comparative analysis of physical stress responses in soybean seedlings using cloned heat shock CDNAs

Abstract: Soybean seedlings were subjected to a wide range of physical (abiotic) or environmental stresses. Cloned cDNAs to heat shock (hs)-induced mRNAs were used to assess whether these diverse stresses induced the accumulation of poly(A)RNAs in common with those induced by hs. Northern blot hybridization analyses indicated that a wide range of stress agents lead to the accumulation of detectable levels of several of the hs-induced poly(A)RNAs; the relative concentration of those RNAs ‘induced’ by the wide range of stress agents (e.g. water stress, salt stress, anaerobiosis, high concentrations of hormones, etc.), was generally in the order of 100-fold lower than that induced by hs. There are two notable exceptions to that pattern of response to the stress agents. First, arsenite treatment resulted in accumulation of the ‘hs poly(A)RNAs’ to levels similar to those induced by hs. Cadmium also induced a somewhat normal spectrum of the ‘hs poly(A)RNAs’, but generally lower levels accumulated than in hs- and arsenite0treated tissues. Second, one set of poly(A)RNAs which are present at low and variable levels in control (non-stressed tissue) tissue, and which are increased some 5- to 10-fold by hs, increased in relative concentration in response to a wide range of the stress agents similarly to the response to hs. The physiological significance of the accumulation of this set of poly(A)RNAs (which translate into four electrophoretically different 27 kd proteins) is not known, but they certainly seem to serve as a monitor (or barometer) of physiological stress conditions. Cadmium treatment results in the accumulation of those same poly(A)RNAs and an additional band of higher molecular weight poly(A)RNA homologous to the same hs cDNA clone (clone pCE 54). Ethylene seems to have no obvious causal relationship to the hs response, even though hs-treated seedlings display some symptoms similar to those exhibited by ethylene-treated seedlings.

Predator and population density control of homing behavior in the Caribbean echinoid Diadema antillarum

Abstract: The frequency of homing behavior (percent returns to the same crevice) of Diadema antillarum Philippi varied from 30 to 84% among areas. Frequency of homing was positively correlated with predator abundance and negatively the protective quality of crevices and more readily vacates low quality crevices than more protective ones when a simulated predation attempt occurs. Previously grazed portions of the foraging range of homing individuals do not appear to be regrazed on successive nights and an avoidance of such areas is suggested. This predator-mediated behavior pattern and its effects on coral reef communities may be a tropical analog to predator-sea urchin-algal relationships in temperate marine communities.

A simulation analysis of continental shelf food webs

Abstract: Energy flow through continental shelf food webs was examined using a simulation model. The model structure expands the two traditional marine food chains of phytoplankton-zooplankton-pelagic fish and benthos-demersal fish into a complex web which includes detritus, dissolved organic matter (DOM), bacteria, protozoa, and mucus net feeders. Simulation of energy flux for different shelf systems using the expanded web revealed that heterotrophic microorganisms and their predators account for a significant component of the energy flux in the continental shelf ecosystem. Contrary to previous models, where all phytoplankton were considered to be grazed by zooplankton, our simulation results indicate that only slightly more than 50% of the annual net primary production is grazed. A substantial quantity of the phytoplankton production directly becomes detritus. Bacteria mineralize detritus and DOM produced by phytoplankton and other components of the food web, converting these to biomass with high efficiency. Consequently, the model predicts that planktonic bacterial production is equivalent to zooplankton production. Exclusion of the bacteria requires the assumption that all DOM is either exported from the system or consumed by another component of the food web. Neither of these assumptions can be supported by present knowledge of the dynamics of DOM in the sea. Model simulations were also employed to test the hypothesis that production exceeds consumption on continental shelves, resulting in exports of 50% of the annual primary production. Simulations of shelves with high rates of primary production resulted in a particulate export of 27% and realistic estimates of secondary production. Results of other simulations suggest that shelves with lower primary production cannot export production and still maintain the macrobenthos and their predators. General properties about continental shelves can also be inferred from the model. From simulations of shelves of differing primary production, nanoplankton are predicted to account for a greater proportion of the primary production in nutrient limited systems. Benthic production appears to be related to both the quantity of primary production and the sinking rates of the phytoplankton. The model indicates that zooplankton fecal inputs to the shelf benthos are only a small portion of the total detrital flux, leading to the prediction that fecal pellets are of little significance in determining benthic production. Finally, the model generates production efficiencies that are highly variable depending on the type of system and kind of populations involved. We argue that the assumed ecological efficiency of 10% should be abandoned for continental shelves and other ecosystems.

The energetic cost of response to blue-green algal filaments by cladocerans1

Abstract: On examine l'effet de l'augmentation de la concentration en filaments d'Anabaena sur le comportement alimentaire et la depense energetique de Daphnia parvula, Ceriodaphnia lacustris et Bosmina longirostris cohabitant. Cet effet a une relation avec la taille de l'animal

Absorption and Utilization of Radiant Energy by Light- and Shade-Adapted Colonies of the Hermatypic Coral Stylophora pistillata

Abstract: The specific absorption coefficient for chlorophyll a (k$\_{\text{c}}$) was measured in zooxanthellae from light- and shade-adapted colonies of the hermatypic coral, Stylophora pistillata from the Red Sea These data, together with measurements of photosynthetic rates and irradiance, were used to compare the quantum yields of photosynthesis in these corals Quantum yields varied from 010 CO$\_{2}$ per quantum at low light to less than 0001 CO$_{2}$ per quantum at maximal irradiances Shade-adapted corals had higher pigment content, which allowed them to have twice as much light harvesting capability as light-adapted corals In all cases, however, the quantum yield of the light-adapted corals was higher by a factor of about 15

Relative contributions of bacteria and fungi to rates of degradation of lignocellulosic detritus in salt-marsh sediments.

Abstract: Specifically radiolabeled [14C-lignin]lignocellulose and [14C-polysaccharide]lignocellulose from the salt-marsh cordgrass Spartina alterniflora were incubated with an intact salt-marsh sediment microbial assemblage, with a mixed (size-fractionated) bacterial assemblage, and with each of three marine fungi, Buergenerula spartinae, Phaeosphaeria typharum, and Leptosphaeria obiones, isolated from decaying S. alterniflora. The bacterial assemblage alone mineralized the lignin and polysaccharide components of S. alterniflora lignocellulose at approximately the same rate as did intact salt-marsh sediment inocula. The polysaccharide component was mineralized twice as fast as the lignin component; after 23 days of incubation, ca. 10% of the lignin component and 20% of the polysaccharide component of S. alterniflora lignocellulose were mineralized. Relative to the total sediment and bacterial inocula, the three species of fungi mediated only very slow mineralization of the lignin and polysaccharide components of S. alterniflora lignocellulose. Experiments with uniformly 14C-labeled S. alterniflora material indicated that the three fungi and the bacterial assemblage were capable of degrading the non-lignocellulosic fraction of S. alterniflora material, but only the bacterial assemblage significantly degraded the lignocellulosic fraction. Our results suggest that bacteria are the predominant degraders of lignocellulosic detritus in salt-marsh sediments.

The effect of seed size and maternal source on individual size in a population of ludwigia leptocarpa (onagraceae)

Abstract: Seed size is normally distributed for many annual species, while mature plant size is frequently positively skewed. A study was conducted to determine the influence of seed size and the role of genetic differences in determining relative seedling size for Ludwigia leptocarpa. Seed size had a significant effect on percentage germination and time of seed germination but no effiect on dry weight or leaf area of seedlings. Seed size and spacing had a significant effiect on seedling dry weight for plants grown under competition, while relative day of emergence had no effect. Familial (genetic) diffierences were found in average seed weight between maternal plants, but not in average number of days to germination, average weight of seeds which germinated, or shoot dry weight. It is concluded that neither seed size alone nor genetic differences between plants are directly responsible for the development of size hierarchies in L>dwigia leptocarpa populations. Large seed size does convey an advantage in growth when plants from seeds of differing initial size interact.