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Mean Growth Rate (mean + growth_rate)
Selected AbstractsChanges in yellow perch (Perca flavescens) growth associated with the establishment of a walleye (Stizostedion vitreum) population in Canadarago Lake, New York (USA)ECOLOGY OF FRESHWATER FISH, Issue 1 2001M. H. Olson Abstract , Piscivorous fish can affect prey growth in two ways: directly by reducing prey density and indirectly by inducing predator-avoidance behaviors. We investigated these two pathways in yellow perch (Perca flavescens) growth responses to walleye (Stizostedion vitreum) stocking in Canadarago Lake, New York (USA) using a 25-year time series. Before walleye stocking, yellow perch growth rate was low and independent of body size. As walleye abundance increased, yellow perch growth increased and became size-dependent. The switch to size-dependent growth occurred in 1 year, indicating a rapid behavioral response to predators. Mean growth rate increased more gradually and was linearly related to walleye density, indicating a slower numerical effect of walleye on yellow perch densities. Although the net effect was an increase in perch growth, small perch growth initially decreased as walleye became established. Therefore, the combination of numerical and behavioral effects produced a complex pattern of size-dependent changes in growth of yellow perch. [source] Patterns of growth of juvenile pink abalone Haliotis corrugata fed re-hydrated natural feeds at a laboratory and a hatcheryAQUACULTURE NUTRITION, Issue 3 2009E. SERVIERE-ZARAGOZA Abstract The feasibility of obtaining a similar growth response from juvenile pink abalone Haliotis corrugata at a research laboratory and a hatchery, when using natural feeds was evaluated. Four macroalgae, Egregia menziesii, Eisenia arborea, Macrocystis pyrifera, Gracilaria sp., and the surfgrass Phyllospadix torreyi were used as feeds. Response patterns of abalone were very similar at both facilities in terms of final length, weight, and survival, varying from 13.0 to 15.50 mm, 0.31 to 0.52 g, and 60.0% to 78.6%, respectively. Better growth was obtained when E. menziesii, M. pyrifera, and Gracilaria sp. were offered. Poor results were obtained with surfgrass. The feed conversion ratio was determined at the laboratory and did not vary significantly, ranging from 42.3 to 199.0; although a significant inverse correlation was observed with growth rate. Growth in length and weight and survival rates varied within 1.6,20.2 ,m day,1, 0.123,1.664 mgday,1, 0.4,0.64%day,1, respectively. Mean growth rate in length (14.7,m day,1) and weight (1.18 mg day,1) at the hatchery were significantly higher than that obtained at the laboratory (9.4 ,m day,1 and 0.77 mg day,1), which is most likely a consequence of more suitable water temperature at the hatchery. Mean survival rate was significantly higher at the laboratory (53.1%day,1) than at the hatchery (46.1%day,1). [source] Productivity and economic growth in Kenyan agriculture, 1964,1996AGRICULTURAL ECONOMICS, Issue 1 2002Anders Gerdin Abstract This paper analyses the patterns of productivity and economic growth in the aggregated Kenyan agriculture between 1964 and 1996. In the 1964,1973 period, the average output growth exceeded 4% but stagnated to an average of 1.2% during 1988,1996. Over the whole period, capital was the most important contributor to output growth. Mean growth rates of intermediate inputs subsequently decreased and were negative in 1988,1996. Labour was the least significant source of growth. The mean total factor productivity growth was less than 0.4% and decreased over time. The contribution of productivity growth to output growth increased from 10.2% in 1964,1973 to 26.8% in 1988,1996. [source] When does parameter drift decrease the uncertainty in extinction risk estimates?ECOLOGY LETTERS, Issue 12 2003Stephen P. Ellner Abstract Halley (2003) proposed that parameter drift decreases the uncertainty in long-range extinction risk estimates, because drift mitigates the extreme sensitivity of estimated risk to estimated mean growth rate. However, parameter drift has a second, opposing effect: it increases the uncertainty in parameter estimates from a given data set. When both effects are taken into account, parameter drift can increase, sometimes substantially, the uncertainty in risk estimates. The net effect depends sensitively on the type of drift and on which model parameters must be estimated from observational data on the population at risk. In general, unless many parameters are estimated from independent data, parameter drift increases the uncertainty in extinction risk. These findings suggest that more mechanistic PVA models, using long-term data on key environmental variables and experiments to quantify their demographic impacts, offer the best prospects for escaping the high data requirements when extinction risk is estimated from observational data. [source] A TADPOLE-INDUCED POLYPHENISM IN THE SALAMANDER HYNOBIUS RETARDATUSEVOLUTION, Issue 10 2002Hirofumi Michimae Abstract., Larvae of the salamander Hynobius retardatus have two distinct morphs: normal and broad-headed, cannibal morphs. We performed three experiments to differentiate among the following hypotheses: The broad-headed morph is induced to allow: (1) feeding on nutritious conspecifics; (2) exclusion of strong competitors for food or space; or (3) feeding on large, tough prey when smaller prey items are unavailable. When newly hatched larvae were reared with a heterospecific, Rana pirica (an anuran amphibian) tadpoles, the broad-headed morph was induced more frequently compared with those reared with conspecifics. The phenotype expressed depended on the size of the tadpoles: The broad-headed morph occurred more frequently with small and the normal morph with large tadpoles. Metamorphosis occurred sooner in larvae fed conspecifics compared with those fed heterospecific tadpoles, and the mean growth rate of larvae fed conspecifics was significantly faster than that of those fed tadpoles, suggesting that the heterospecific tadpoles were less nutritive than the conspecifics. These results do not support the hypotheses that the broad-headed morph evolved for consuming conspecifics because of their better balance of nutrients or for excluding strong competitors for food or space. We tentatively conclude that the morph evolved to eat large, tough prey, including both conspecifics and heterospecific tadpoles. Because H. retardatus usually spawns very early in the spring in small ponds partially covered with ice and snow, newly hatched larvae may starve from the lack of proper food owing to extremely low water temperatures. Thus, the broad-headed morph of H. retardatus may represent a cold-habitat adaptation to overcome the severe circumstance when the only food items available are relatively large conspecifics or heterospecific tadpoles. [source] Effects of size, competition and altitude on tree growthJOURNAL OF ECOLOGY, Issue 5 2007DAVID A. COOMES Summary 1,Understanding the factors influencing tree growth is central to forest ecology because of the significance of growth to forest structure and biomass. One of the simplest, yet most controversial growth models, proposed by Enquist and colleagues, predicts that stem-diameter growth scales as the one-third power of stem diameter. Recent analyses of large-scale data sets have challenged the generality of this theory and highlighted the influence of resource competition on the scaling of growth with size. 2Here we explore the factors regulating the diameter growth of 3334 trees of mountain beech (Nothofagus solandri var. cliffortioides) growing in natural single-species forests in New Zealand. Maximum-likelihood modelling was used to quantify the influences of tree size, altitude, the basal area of taller neighbours (BL) and the basal area of all neighbours (BT) on growth. Our interpretation of the models assumed that taller neighbours compete for light whereas all neighbours compete for nutrients. 3The regression analyses indicate that competition for light has a strong influence on the growth of small trees, whereas competition for nutrients affects trees of all sizes. These findings are consistent with experimental manipulation studies showing that competition for light and nutrients inhibits the growth of small mountain beech trees, and fertilizer application studies showing that nitrogen limits the growth of large trees. 4Tree growth declined with altitude. The regression analyses suggest that the intensity of light competition also declines with altitude, when trees with similar BT and BL values were compared along the gradient. These results are consistent with observations that trees become stunted and have more open canopies at high altitudes. 5Our study is the first to build the effects of competition and environment into Enquist's model of tree growth. We show that competitive interactions alter the scaling of mean growth rate with size, whereas altitude does not influence the scaling of potential growth rate with size. [source] Risk factors for post-weaning mortality of Merino sheep in south-eastern AustraliaAUSTRALIAN VETERINARY JOURNAL, Issue 8 2009AJD Campbell Objective To measure associations between body weight, growth rate, sex, time of shearing and post-weaning mortality of Merino sheep. Design Uni- and multivariable survival analyses of sheep mortality during the first year after weaning, using records (n = 3657) from two field experiments conducted in Western Victoria from 1996 to 2003. Results Overall mortality was 14.3% (range 4.5,26.8%) and mean maximum mortality rate was 29 deaths/1000 weaners/month. Increased mortality risk was associated with decreases in fleece-free body weight and mean weaner growth rate, particularly at low weights and growth rates. Weaners in the lightest weaning weight quintile had a hazard ratio of 3.5, compared with the middle quintile. The hazard ratio for a 2-kg decrease in weaning weight was 1.2 to 1.7 for weaners lighter than 22 kg. The hazard ratio for a reduction in mean weaner growth rate in the first 5 months after weaning of 0.25 kg/month was 1.1 to 6.8 if mean growth rate was less than 1 kg/month, but did not differ significantly from 1 at greater growth rates. The hazard ratio for wether weaners was approximately 1.5 compared with ewe weaners. The hazard ratio for weaners shorn between December and May, compared with unshorn weaners, was 1.2 to 3.5, with the greatest risk difference associated with shearing in March (45 deaths/1000 weaners/month). Conclusion Improving the body weight and mean growth rate of weaner sheep is likely to reduce post-weaning mortality. Lightweight weaners in a flock should be managed separately from the main portion after weaning. In southern Australia, not shearing spring-born Merino weaners between December and May may assist in reducing overall post-weaning mortality. [source] Reference data for evaluating the growth of common riverine fishes in the UKJOURNAL OF APPLIED ICHTHYOLOGY, Issue 5 2007J. R. Britton Summary Comparative assessments of population mean growth rates in length remain important aspects of stock assessment in river fisheries. To facilitate these assessments, for 15 fish species encountered in UK rivers reference data are provided on their expected lengths at age, maximum theoretical lengths (L,), growth coefficient (K) and instantaneous mortality rate (Z). These data are also transferable to fish populations outside of the UK that experience a similar growth season (approximately April to October, mean water temperatures 12,22°C). Considerable plasticity was observed in the growth of all species examined, with length at age values revealing growth rates from very slow to very fast. Populations considered fast growing against reference data were coincident with a relatively low ultimate length, a high growth coefficient and a high instantaneous mortality rate, suggesting a trade-off exists between growth rate, ultimate length and life span. [source] Temperature adaptation in a geographically widespread zooplankter, Daphnia magnaJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2000Mitchell Evidence for temperature adaptation in Daphnia magna was inferred from variation in the shape of temperature reaction norms for somatic growth rate, a fitness-related trait. Ex-ephippial clones from eight populations across Europe were grown under standardized conditions after preacclimation at five temperatures (17,29 °C). Significant variation for grand mean growth rates occurred both within populations (among clones) and between populations. Genetic variation for reaction norm shape was found within populations, with temperature-dependent trade-offs in clone relative fitness. However, the population average responses to temperature were similar, following approximately parallel reaction norms. The among-population variation is not evidence for temperature adaptation. Lack of temperature adaptation at the population level may be a feature of intermittent populations where environmentally terminated diapause can entrain the planktonic stage of the life-history within a similar range of temperatures. [source] | |||||||||||||