Showing papers by "University of Guelph published in 1988"

Causes and consequences of migration by large herbivores

Abstract: Many populations of large herbivores migrate seasonally between discrete home ranges. Current evidence suggests that migration is generally selected for as a means of enhancing access to high quality food and/or reducing the risk of predation. The relative importance of these alternative selection pressures should depend on the demographic circumstances facing a given population. Seasonal migration also has important implications for the structure and dynamics of large herbivore communities. Migrants should tend to be regulated by food availability, while residents should tend to be regulated by predators As a result, migrants should often outnumber residents by a considerable margin - a pattern seen in several tropical and temperate ecosystems. Differences in the mode of regulation could also imply that competition for resources will be weak in purely resident assemblages, but strong in communities dominated by migrants. Continual grazing by resident herbivores can sometimes lead to degeneration of vegetation, while systems supporting migrants are apparently more resilient. This implies that migration can have an important impact on the long-term persistence of plant-herbivore systems, particularly in areas with slow rates of vegetation regeneration.

Numerical competence in animals: Definitional issues, current evidence, and a new research agenda.

Abstract: Numerical competence is one of the many aspects of animal cognition that have enjoyed a resurgence of interest during the past decade. Evidence for numerical abilities in animals has followed a tortuous path to respectability, however, from Clever Hans, the counting horse, to modern experimental studies. Recent surveys of the literaturereveal theoretical as well as definitional confusion arising from inconsistent terminology for numerical processes and procedures. The term “counting” has been applied to situations having little to do with its meaning in the human literature. We propose a consistent vocabulary and theoretical framework for evaluating numerical competence. Relative numerousness judgments, subitizing, counting, and estimation may be the essential processes by which animals perform numerical discriminations. Ordinality, cardinality, and transitivity also play an important role in these processes. Our schema is applied to a variety of recent experimental situations. Some evidence of transfer is essential in demonstrating higher-order ability such as counting or “sense of number.” Those instances of numerical competence in which all viable alternatives to counting (e.g., subitizing) have been precluded, but no evidence of transfer has been demonstrated might be described as “protocounting.” To show that animals are capable of “true” counting future research will have to demonstrate generality across situations.

Fuzzy functional dependencies and lossless join decomposition of fuzzy relational database systems

Abstract: This paper deals with the application of fuzzy logic in a relational database environment with the objective of capturing more meaning of the data It is shown that with suitable interpretations for the fuzzy membership functions, a fuzzy relational data model can be used to represent ambiguities in data values as well as impreciseness in the association among them Relational operators for fuzzy relations have been studied, and applicability of fuzzy logic in capturing integrity constraints has been investigated By introducing a fuzzy resemblance measure EQUAL for comparing domain values, the definition of classical functional dependency has been generalized to fuzzy functional dependency (ffd) The implication problem of ffds has been examined and a set of sound and complete inference axioms has been proposed Next, the problem of lossless join decomposition of fuzzy relations for a given set of fuzzy functional dependencies is investigated It is proved that with a suitable restriction on EQUAL, the design theory of a classical relational database with functional dependencies can be extended to fuzzy relations satisfying fuzzy functional dependencies

A meta‐analytic investigation of the impact of interview format and degree of structure on the validity of the employment interview*

Abstract: A meta-analysis of the employment interview was carried out to investigate the impact of interview format (individual vs. board interviews) and interview structure (unstructured vs. structured) on the validity of interviews. A thorough review of the unpublished and published literature worldwide yielded 150 usable validity coefficients for the meta-analysis. Contrary to the predominantly pessimistic views of previous researchers, the interview was found to be a generally good selection instrument. These findings suggest that the ' received doctrine' of interview invalidity is false. However, interview structure moderated predictive validity coefficients to a considerable extent. In fact, structured interviews produced mean validity coefficients twice as high as unstructured interviews. Although considerable variance in structured interviews remained unaccounted for after adjustment for statistical artifacts, all of the variation in observed validity coefficients for unstructured interviews was accounted for. It was concluded that a number of social psychological processes examined in previous interview research would have little effect in moderating the validity coefficients of the unstructured interview. The results also suggest that higher validity coefficients are associated with more reliable interviews and the use of formal job-analytic information in developing interview questions. Implications for research and practice in personnel psychology are explored.

Metallic ion binding by Bacillus subtilis; implications for the fossilization of microorganisms

Abstract: The silicification of bacterial cells has been followed in a laboratory simulation by electron microscopy and energy-dispersive X-ray spectroscopy. Structural degradation of the bacteria was not influenced by silica availability, but the remains of degraded cells did promote the precipitation of silica. In contrast, cells reacted with ferric iron before aging remained intact, and structures conforming to the original morphology of the bacteria were preserved by silicification. The binding of metallic ions by microbial cells, in particular the retention of iron, is therefore considered to be an important contributing factor to the fossilization of microorganisms.

Bacterial conjugation between pseudomonads in the rhizosphere of wheat

Abstract: Transfer of plasmid RP4 between introduced pseudomonads was studied in rhizosphere and non-rhizosphere soil of wheat, in soil chambers and in culture tubes. In both experiments, the presence of growing wheat roots stimulated the occurrence of plasmid transfers in the soil. The plasmid transfer frequencies in rhizosphere soil in the soil chambers were consistently higher than those in rhizosphere soil in the culture tubes, indicating an influence of the experimental set-up. In the soil chambers, both the survival of introduced donor and recipient strains and the plasmid transfer frequencies decreased drastically at increasing distances from the roots. In addition, plasmid transfer frequencies were influenced by the inoculum densities of both donor and recipient strains; higher frequencies were observed in soil that was initially inoculated with higher cell numbers.

Glyphosate in the environment

Abstract: N-(phosphonomethyl)glycerine (glyphosate) is an extremely effective broad spectrum herbicide. This manuscript reviews glyphosate metabolism in plants and yeasts, its uses in agricultural applications, interactions with soil and water, glyphosate biodegradation, and effects on microbial activities and populations in soil.

Vesicular–arbuscular mycorrhizas and the soil‐disturbance‐induced reduction of nutrient absorption in maize

Abstract: summary In previously reported studies, maize seedlings absorbed more phosphorus (P) from soil in a long-term zero-till system than from the same soil after disturbance. This partly resulted from greater vesicular-arbuscular (VA) mycorrhizal infection in the undisturbed soil. In the study reported herein, a growth room experiment was conducted to determine how long a soil must remain undisturbed before subsequent disturbance will reduce P absorption. Starting with disturbed soil, maize was grown for 3-week cycles. At the conclusion of each growth cycle, half of the pots were disturbed and replanted whereas the other half was replanted without disturbing. Over the three growth cycles, major increases in mycorrhizal infection in the plants in the undisturbed soil were observed concurrently with the increases in nutrient absorption. A significant increase in P absorption occurred in the first growth cycle on undisturbed soil and greater increases occurred after the second and third. At 21 d in the third growth cycle, plants grown in the undisturbed soil had almost twice the dry weight of plants grown in the disturbed and had higher concentrations of N, P, Mg, Cu and Zn in the shoots. Absorption of P between 14 and 21 d of the third growth cycle in the undisturbed soil was 10 times larger than that in the disturbed soil. Absorption of N, Mg, Cu and Zn was more than three times larger. In the third growth cycle, concentrations of N, P, Mg and Zn in the shoot and intensity of VA mycorrhizal infection were greater in the undisturbed soil as early as 14 d after planting. There was a concurrent and rapid increase in VA mycorrhizal infection and P absorption by maize over three growth cycles when an initially disturbed soil was left undisturbed. This rapid concurrent development, particularly starting from an initially disturbed soil, provides good evidence that soil disturbance reduces VA mycorrhizal infection and hence P absorption by maize.

An Intertemporal Model of Industrial Exit

Abstract: A finite horizon model of industrial exit is developed. After an initial lag, most exits are by young firms. The duration of the lag is positively related to sunk entry costs, but not due to the fallacy of sunk costs. The conception of entry differs from previous research; as a result, not all entrants are identical; and firm size affects the rate of learning. On average, larger new firms last longer. Entrepreneurs in declining firms act more lazily as the firm declines. A number of empirical observations about declining firms are organized by the model.

The initiation of particle movement by wind

Abstract: When air blows across the surface of dry, loose sand, a critical shear velocity (fluid threshold, ut), must be achieved to initiate motion. However, since most natural sediments consist of a range of grain sizes, fluid threshold for any sediment cannot be defined by a finite value but should be viewed as a threshold range which is a function of the size, shape, sorting and packing of the surface sediment. In order to investigate the initiation of particle movement by wind a series of wind-tunnel tests was carried out on a range of pre-screened fluvial sands and commercially available glass beads with differing mean sizes and sorting characteristics. A sensitive laser-monitoring system was used in conjunction with a high speed counter to detect initial grain motion and to count individual grain movements. Test results indicate that when velocity is slowly increased over the sediment surface the smaller or more exposed grains are first entrained by the fluid drag and lift forces either in surface creep (rolling) or in saltation (bouncing or hopping downwind). As velocity continues to rise, larger or less exposed grains may also be moved by fluid drag. On striking the surface saltating grains impart momentum to stationary grains. This impact may result in the rebound of the original grain as well as the ejection of one or more stationary grains into the air stream at shear velocities lower than that required to entrain a stationary particle by direct fluid pressure. As a result, there is a cascade effect with a few grains of varying size initially moving over a range of shear velocities (the fluid threshold range) and setting in motion a rapidly increasing number of grains. Results of the tests showed that the progression from fluid to dynamic threshold, based on grain movement, can be characterized by a power function, the coefficients of which are directly related to the mean size and sorting characteristics of the sediment.

The bacterial surface: general considerations towards design and function

Abstract: The shape of bacteria is determined by the wall which surrounds the protoplast. This enveloping structure resides in diverse chemical and organizational forms and is of fundamental importance for several aspects of cellular life and growth. This article discusses these general aspects and serves as an introduction to the journal issue and to the more specific papers which follow in the section.

The annual cycle of heterotrophic planktonic ciliates in the waters surrounding the Isles of Shoals, Gulf of Maine: an assessment of their trophic role

Abstract: Ciliates in the waters surrounding the Isles of Shoals, Gulf of Maine were collected from May 1985 to August 1986 in sampling bottles, fixed in Bouin's solution, and quantitatively protargol stained. Cell abundance and biomass were separated into four size classes. Large species were prevalent in the spring while smaller species dominated in the summer. Ciliate abundance ranged from 0.35 to 6×106 m-3 annually while biomass ranged from 2.7 to 240 J m-3. Production, estimated using a multiple regression equation which incorporated ambient temperature and cell volume, ranged from 2.5 to 105 J m-3d-1. A model was constructed to determine the relative importance of ciliates in the planktonic food web. Blooms could provide a brief but significant transfer of energy to upper trophic levels. However, at best, ciliates may contribute 12% to the copepod ration and 3% of their available food.

A Putative New Growth Factor in Ascitic Fluid from Ovarian Cancer Patients: Identification, Characterization, and Mechanism of Action

Abstract: Ascitic fluid from ovarian cancer patients (n = 16), but not from patients with other cancers or with benign diseases, contains a growth-promoting activity which induces the proliferation of both fresh ovarian cancer cells (n = 5) and the ovarian cancer cell line HEY. The ascitic fluid growth factor(s) appears to signal cells through binding and activation of specific, saturable, high-affinity cell surface receptors. Incubation of fresh or cultured ovarian cancer cells with a partially purified preparation of ascitic fluid stimulates phosphatidylinositol turnover and increases cytosolic-free calcium. Each of these biochemical events has been implicated in the action of growth factors. Purified preparations of previously identified growth factors including epidermal growth factor, transforming growth factor-β, tumor necrosis factor, platelet-derived growth factor, thrombin, insulin, interleukin-1, interleukin-2, vasopressin, angiotensin, α- and γ-interferons, and fibroblast growth factor did not increase cytosolic-free calcium in either fresh ovarian cancer cells or HEY cells. Therefore, ascitic fluid appears to contain one or more previously unidentified growth factors which activate ovarian cancer cells through phosphatidylinositol hydrolysis and resultant changes in cytosolic-free calcium.

Cohort sampling, anaesthesia and stocking‐density effects on plasma cortisol, thyroid hormone, metabolite and ion levels in rainbow trout, Salmo gairdneri Richardson

Abstract: The effect of serial removal of fish from aquaria, anaesthesia and stocking density on plasma cortisol, thyroid hormone, metabolite and ion levels was examined in rainbow trout, Salmo gairdneri, to determine the consequences of normal handling and maintenance procedures on the activity of the pituitary-adrenal and pituitary-thyroid axes in the species. The capture and handling associated with serial removal of fish from an aquarium resulted in a rapid elevation of plasma cortisol concentrations and a slower rise in plasma glucose, Mg2+ and Na+ concentrations; plasma K.+ levels showed a transient fall shortly after commencing the sampling, followed by a significant increase. A lethal concentration of 3-aminobenzoic acid ethyl ester (MS 222) of 125 mgl−1 (but not a sublethal concentration of 62.5 ng 1−1) prevented the capture stressor-associated changes in most of the measured parameters, including plasma cortisol levels, although plasma protein and ion concentrations were elevated in fish sampled after MS 222-anaesthesia. Stocking densities from 1 to 64 fish 80 1−1 aquarium did not appear to effect changes in the measured parameters, except for plasma T3/T4 ratios which decreased with increasing stocking density. The exception was found in fish which were stocked in pairs: one member of each pair had a markedly elevated plasma cortisol level and there was a high incidence of mortality, probably related to aggressive social interaction.

Selection on individual phenotype and best linear unbiased predictor of breeding value in a closed swine herd.

Abstract: Computer simulation of a closed 100-sow and 4-boar swine herd was used to analyze effects of selection method on genetic change, inbreeding and genetic variance over 10 yr for traits with heritabilities (h2) of .10, .30 and .60. Selection of replacement animals was either on individual phenotype or best linear unbiased predictor (BLUP) of breeding value using an animal model. For both methods, culling of existing breeding animals was at random on age and reproductive performance. The effect of additional culling of existing breeding animals when a replacement with better individual phenotype or BLUP of breeding value was available also was evaluated. Genetic gain was greater for selection on BLUP than on individual phenotype, but relative differences narrowed with increasing heritability. At yr 10 the relative advantage of selection on BLUP was 55% for h2 = .10, 25% for h2 = .30 and 10% for h2 = .60. Culling when a replacement with better individual phenotype or BLUP of breeding value was available resulted in considerably increased genetic progress (34% to 57%). The proportional effect of culling on rate of genetic gain was relatively independent of heritability and type of selection. Inbreeding (F) was higher with selection on BLUP (F = .27 to .38 at yr 10) than on individual phenotype (F = .17 to .22 at yr 10). As heritability increased, rate of inbreeding increased for selection on individual phenotype, but rate of inbreeding tended to decrease with increasing heritability for selection on BLUP.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary zinc or copper deficiency on the primary free radical defense system in rats.

Abstract: The effect of dietary Zn or Cu deficiency on the primary free radical defense system was examined in the lungs and livers of 6-wk-old rats. Enzymatic compo nents (Superoxide dismutase, catalase and glutathione peroxidase) and nonenzymatic components (a-tocoph- erol, ascorbate, glutathione and metallothionein) of the pri mary free radical defense system, as well as tissue con centrations of Cu, Zn and Fe, were measured. LiverCuZn- superoxide dismutase and liver catalase activities were sig nificantly lower (P < 0.05), and lung metallothionein and liver ascorbate concentrations were significantly higher (P < 0.05) in Cu-deficient rats than in either pair-fed or ad libitum-fed controls. Zn-deficient rats had a significantly lower (P < 0.05) concentration of livermetallothionein than either control group. Other changes in the enzymatic and nonenzymatic components of the primary free radical de fense system could be attributed to the reduction in feed intake by Zn- or Cu-deficient rats and not to a direct effect of the Zn or Cu deficiency per se. The primary free radical defense system in lung and liver of severely Zn- or Cu- deficient rats was not seriously compromised. J. Nutr. 118:613-621,1988.

Chaotic dynamics in economic time‐series

Abstract: . There has recently been considerable interest in chaotic dynamics in a variety of disciplines. This paper introduces and then surveys some of the associated literature and techniques. Applications to economic theory are discussed but the primary focus is on empirical applicability. In addition to surveying the literature we also provide an example of the use of these techniques in economics. We conclude by highlighting the importance of the techniques for empirical work as well as considering their context in econometric methodology.

Effect of diet on the feeding and casting activity of lumbricus terrestris and l. rubellus in laboratory culture

Abstract: Summary-Earthworm feeding and casting activities are difficult to monitor because of problems associated with assessing subsurface activity in the held. Thus it is difficult to predict the effect of a change in cropping pattern on earthworm activity with its attendant effects on soil structure and nutrient cycling. Therefore, feeding and casting activities of Lumbricus ferresrris L. and L. rubellus Hoff. were monitored in laboratory cultures with each species provided with alfalfa, bromegrass, corn, red clover or no-food diets. Both species produced predominately surface casts under experimental conditions. Food consumption values of L. rubellus ranged from 5 to 52 mg g-’ live worm day-’ and were several times higher than those for L. terresfris (Z-13 mgg-’ live worm day-‘) for all food sources except bromegrass. which both species rejected as food. Cast production was also greater for L. rubehs with values ranging from 80 to 460 mg g-’ live worm day-’ vs 70 to I80 mg g-’ live worm day-’ for L. terresrris. Both species exhibited large weight gains on diets of alfalfa or red clover leaves, slight weight gains when provided with corn leaves, but lost weight when provided with bromegrass leaves or no food. Rejection of bromegrass may have been related to its chemical composition or state of decomposition. Estimates of field food consumption suggested that food supply may limit casting activity of earthworm populations in alfalfa fields, whereas food quality may limit population levels and. thereby, limit casting activity in fields used for corn production.

Induction of xylose reductase and xylitol dehydrogenase activities in Pachysolen tannophilus and Pichia stipitis on mixed sugars

Abstract: The induction of xylose reductase and xylitol dehydrogenase activities on mixed sugars was investigated in the yeasts Pachysolen tannophilus and Pichia stipitis. Enzyme activities induced on d-xylose served as the controls. In both yeasts, d-glucose, d-mannose, and 2-deoxyglucose inhibited enzyme induction by d-xylose to various degrees. Cellobiose, l-arabinose, and d-galactose were not inhibitory. In liquid batch culture, P. tannophilus utilized d-glucose and d-mannose rapidly and preferentially over d-xylose, while d-galactose consumption was poor and lagged behind that of the pentose sugar. In P. stipitis, all three hexoses were used preferentially over d-xylose. The results showed that the repressibility of xylose reductase and xylitol dehydrogenase may limit the potential of yeast fermentation of pentose sugars in hydrolysates of lignocellulosic substrates.