scholarly journals Omnivory does not preclude strong trophic cascades

2018 ◽  
Author(s):  
Ashkaan K. Fahimipour ◽  
David A. Levin ◽  
Kurt E. Anderson
Keyword(s):  
Empirical Evidence ◽  
Parameter Space ◽  
Growth Rates ◽  
Trophic Cascades ◽  
Empirical Support ◽  
Foraging Strategy ◽  
Foraging Strategies ◽  
Primary Producers ◽  
High Productivity ◽  
Per Capita

AbstractOmnivory has been cited as an explanation for why trophic cascades are weak in many ecosystems, but empirical support for this prediction is equivocal. Compared to predators that feed only on herbivores, top omnivores — species that feed on both herbivores and primary producers — have been observed generating cascades ranging from strong, to moderate, null, and negative. To gain intuition about the sensitivity of cascades to omnivory, we analyzed models describing systems with top omnivores that display either fixed or flexible diets, two foraging strategies that are supported by empirical observations. We identified regions of parameter space wherein omnivores following a fixed foraging strategy, with herbivores and producers comprising a constant proportion of the diet, non-intuitively generate stronger cascades than predators that are otherwise demographically identical: (i) high productivity relative to herbivore mortality, and (ii) small discrepancies in producer versus herbivore reward create conditions in which cascades are stronger with moderate omnivory. In contrast, flexible omnivores that attempt to optimize per capita growth rates during search never induce cascades that are stronger than the case of predators. Although we focus on simple models, the consistency of these general patterns together with prior empirical evidence suggests that omnivores should not be uniformly ruled out as agents of strong trophic cascades.

The Reproduction Vector of the Russian Economy: 1999-2007

2008 ◽  
pp. 94-109 ◽  
Author(s):  
D. Sorokin
Keyword(s):  
Economic Policy ◽  
Human Capital ◽  
Growth Rates ◽  
Developed Countries ◽  
Gdp Per Capita ◽  
Real Sector ◽  
Russian Economy ◽  
Per Capita ◽  
The Developed Countries

The problem of the Russian economy’s growth rates is considered in the article in the context of Russia’s backwardness regarding GDP per capita in comparison with the developed countries. The author stresses the urgency of modernization of the real sector of the economy and the recovery of the country’s human capital. For reaching these goals short- or mid-term programs are not sufficient. Economic policy needs a long-term (15-20 years) strategy, otherwise Russia will be condemned to economic inertia and multiplying structural disproportions.

scholarly journals European Regional Inequalities: The Other Face of Development

2017 ◽  
Vol 9 (4) ◽  
pp. 163
Author(s):  
Celeste Perrucchini ◽  
Hiroshi Ito
Keyword(s):  
European Union ◽  
Empirical Evidence ◽  
Capita Income ◽  
Relevant Literature ◽  
Point Of View ◽  
The European Union ◽  
Per Capita Income ◽  
Member States ◽  
Eu Member States ◽  
Per Capita

Empirical evidence suggests an overall convergence in terms of GDP and per capita income occurring among the European Union (EU) Member States. Nevertheless, economic inequalities have been increasing at the regional level within European Union countries. Through the review of relevant literature, this study analyzes the increasing inequalities from an economical point of view, focusing on Italy and the UK as examples. First, a general overlook of the empirical evidence of the GDP and per capita income at national and sub-national levels will be presented. Second, an explanation of the possible causes of the results will be proposed through the use of economical and sociological theories. The findings of this research might uncover the relative inefficacy of EU Cohesion policies and point towards the necessity for deeper and more thoughtful measures to continue the convergence of Member States while preserving internal equilibria. This paper ends with discussions for the future directions of the EU.

scholarly journals Examining GDP Growth and Its Volatility: An Episodic Approach

Entropy ◽  
2021 ◽  
Vol 23 (7) ◽  
pp. 890
Author(s):  
Jakub Bartak ◽  
Łukasz Jabłoński ◽  
Agnieszka Jastrzębska
Keyword(s):  
Economic Growth ◽  
Genetic Algorithm ◽  
Time Series ◽  
Human Capital ◽  
Growth Rates ◽  
Structural Breaks ◽  
Negative Relationship ◽  
Gdp Per Capita ◽  
Gdp Growth ◽  
Per Capita

In this paper, we study economic growth and its volatility from an episodic perspective. We first demonstrate the ability of the genetic algorithm to detect shifts in the volatility and levels of a given time series. Having shown that it works well, we then use it to detect structural breaks that segment the GDP per capita time series into episodes characterized by different means and volatility of growth rates. We further investigate whether a volatile economy is likely to grow more slowly and analyze the determinants of high/low growth with high/low volatility patterns. The main results indicate a negative relationship between volatility and growth. Moreover, the results suggest that international trade simultaneously promotes growth and increases volatility, human capital promotes growth and stability, and financial development reduces volatility and negatively correlates with growth.

scholarly journals Be different to be better: the effect of personality on optimal foraging with incomplete knowledge

2021 ◽  
Author(s):  
Poppy M. Jeffries ◽  
Samantha C. Patrick ◽  
Jonathan R. Potts
Keyword(s):  
Optimal Foraging ◽  
Optimal Foraging Theory ◽  
Foraging Strategy ◽  
Foraging Strategies ◽  
Partial Knowledge ◽  
Marginal Value ◽  
Animal Populations ◽  
Plausible Mechanism ◽  
Insight Into ◽  
Modelling Approach

AbstractMany animal populations include a diversity of personalities, and these personalities are often linked to foraging strategy. However, it is not always clear why populations should evolve to have this diversity. Indeed, optimal foraging theory typically seeks out a single optimal strategy for individuals in a population. So why do we, in fact, see a variety of strategies existing in a single population? Here, we aim to provide insight into this conundrum by modelling the particular case of foraging seabirds, that forage on patchy prey. These seabirds have only partial knowledge of their environment: they do not know exactly where the next patch will emerge, but they may have some understanding of which locations are more likely to lead to patch emergence than others. Many existing optimal foraging studies assume either complete knowledge (e.g. Marginal Value Theorem) or no knowledge (e.g. Lévy Flight Hypothesis), but here we construct a new modelling approach which incorporates partial knowledge. In our model, different foraging strategies are favoured by different birds along the bold-shy personality continuum, so we can assess the optimality of a personality type. We show that it is optimal to be shy (resp. bold) when living in a population of bold (resp. shy) birds. This observation gives a plausible mechanism behind the emergence of diverse personalities. We also show that environmental degradation is likely to favour shyer birds and cause a decrease in diversity of personality over time.

Effects of turbidity on prey consumption and growth in brook trout and implications for bioenergetics modeling

2001 ◽  
Vol 58 (2) ◽  
pp. 386-393 ◽  
Author(s):  
John A Sweka ◽  
Kyle J Hartman
Keyword(s):  
Growth Rates ◽  
Brook Trout ◽  
Specific Growth ◽  
Abiotic Factors ◽  
Foraging Strategies ◽  
Turbid Water ◽  
Daily Consumption ◽  
Consumption Rates ◽  
The Difference ◽  
Specific Growth Rates

Brook trout (Salvelinus fontinalis) were held in an artificial stream to observe the influence of turbidity on mean daily consumption and specific growth rates. Treatment turbidity levels ranged from clear (<3.0 nephelometric turbidity units (NTU)) to very turbid water (> 40 NTU). Observed mean daily specific consumption rates were standardized to the mean weight of all brook trout tested. Turbidity had no significant effect on mean daily consumption, but specific growth rates decreased significantly as turbidity increased. Brook trout in turbid water became more active and switched foraging strategies from drift feeding to active searching. This switch was energetically costly and resulted in lower specific growth rates in turbid water as compared with clear water. Bioenergetics simulations were run to compare observed growth with that predicted by the model. Observed growth values fell below those predicted by the model and the difference increased as turbidity increased. Abiotic factors, such as turbidity, which bring about changes in the activity rates of fish, can have implications for the accuracy of predicted growth by bioenergetics models.

scholarly journals Diving deep into trouble: the role of foraging strategy and morphology in adapting to a changing environment

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Monique Ladds ◽  
David Rosen ◽  
Carling Gerlinsky ◽  
David Slip ◽  
Robert Harcourt
Keyword(s):  
Foraging Strategy ◽  
Central Place ◽  
Dive Duration ◽  
Foraging Strategies ◽  
Body Morphology ◽  
Sea Lions ◽  
Fur Seals ◽  
Adequate Food ◽  
Physiological Capacity ◽  
Total Body Oxygen

Abstract Physiology places constraints on an animal’s ability to forage and those unable to adapt to changing conditions may face increased challenges to reproduce and survive. As the global marine environment continues to change, small, air-breathing, endothermic marine predators such as otariids (fur seals and sea lions) and particularly females, who are constrained by central place foraging during breeding, may experience increased difficulties in successfully obtaining adequate food resources. We explored whether physiological limits of female otariids may be innately related to body morphology (fur seals vs sea lions) and/or dictate foraging strategies (epipelagic vs mesopelagic or benthic). We conducted a systematic review of the increased body of literature since the original reviews of Costa et al. (When does physiology limit the foraging behaviour of freely diving mammals? Int Congr Ser 2004;1275:359–366) and Arnould and Costa (Sea lions in drag, fur seals incognito: insights from the otariid deviants. In Sea Lions of the World Fairbanks. Alaska Sea Grant College Program, Alaska, USA, pp. 309–324, 2006) on behavioural (dive duration and depth) and physiological (total body oxygen stores and diving metabolic rates) parameters. We estimated calculated aerobic dive limit (cADL—estimated duration of aerobic dives) for species and used simulations to predict the proportion of dives that exceeded the cADL. We tested whether body morphology or foraging strategy was the primary predictor of these behavioural and physiological characteristics. We found that the foraging strategy compared to morphology was a better predictor of most parameters, including whether a species was more likely to exceed their cADL during a dive and the ratio of dive time to cADL. This suggests that benthic and mesopelagic divers are more likely to be foraging at their physiological capacity. For species operating near their physiological capacity (regularly exceeding their cADL), the ability to switch strategies is limited as the cost of foraging deeper and longer is disproportionally high, unless it is accompanied by physiological adaptations. It is proposed that some otariids may not have the ability to switch foraging strategies and so be unable adapt to a changing oceanic ecosystem.

scholarly journals Population and biological parameters of selected fish species from the middle Xingu River, Amazon Basin

2015 ◽  
Vol 75 (3 suppl 1) ◽  
pp. 112-124 ◽  
Author(s):  
M. Camargo ◽  
T. Giarrizzo ◽  
VJ. Isaac
Keyword(s):  
Fish Species ◽  
Growth Rates ◽  
Amazon Basin ◽  
High Growth ◽  
Life Cycles ◽  
Biological Parameters ◽  
High Productivity ◽  
Xingu River ◽  
Biological Yield ◽  
Belo Monte

Abstract This study estimates the main biological parameters, including growth rates, asymptotic length, mortality, consumption by biomass, biological yield, and biomass, for the most abundant fish species found on the middle Xingu River, prior to the construction of the Belo Monte Dam. The specimens collected in experimental catches were analysed with empirical equations and length-based FISAT methods. For the 63 fish species studied, high growth rates (K) and high natural mortality (M) were related to early sexual maturation and low longevity. The predominance of species with short life cycles and a reduced number of age classes, determines high rates of stock turnover, which indicates high productivity for fisheries, and a low risk of overfishing.

scholarly journals Productivity and Institutions

2015 ◽  
Vol 11 (2) ◽  
pp. 375
Author(s):  
Gylfi Zoega
Keyword(s):  
19Th Century ◽  
Legal System ◽  
Industrial Revolution ◽  
Lower Cost ◽  
Standard Of Living ◽  
Gdp Per Capita ◽  
Past Century ◽  
High Productivity ◽  
The Past ◽  
Per Capita

Differences in productivity account for differences in output per capita between countries as well as changes in output and the standard of living for each country over long periods of time. During the first industrial revolution, one could already see the emergence of two groups of countries: the high- and the low-GDP per capita countries. The list of countries belonging to the highproductivity group has not changed much over the past century. Differences in institutions separate the two clubs. The high-productivity group is, amongst many other differences, characterized by less corruption, a better legal system, superior enforcement of contracts, a lower cost of starting a business and lower tariffs. Historical output series for Britain going back to the mid-19th century show that productivity has increased greatly and improved the standard of living.

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