scholarly journals An Empiricist’s Guide to Modern Coexistence Theory for Competitive Communities

2019 ◽  
Author(s):  
Casey M. Godwin ◽  
Feng-Hsun Chang ◽  
Bradley Cardinale
Keyword(s):  
Species Coexistence ◽  
Empirical Studies ◽  
Empirical Work ◽  
Relative Fitness ◽  
Empirical Methods ◽  
Coexistence Theory ◽  
Niche Differences ◽  
Rate Versus ◽  
Resource Requirements ◽  
Competitive Hierarchies

AbstractWhile most ecological theories have historically invoked niche differences as the primary mechanism allowing species coexistence, we now know that species coexistence in competitive communities actually depends on the balance of two opposing forces: niche differences (ND) that determine how species limit their own growth rate versus that of their competitor, and relative fitness differences (RFD) that establish competitive hierarchies among species. Several different empirical methods have been proposed for measuring ND and RFD in order to make predictions about coexistence of species, yet it remains unclear which method(s) are appropriate for a given empirical study and whether or not those methods actually yield the same information. Here we summarize and compare five different empirical methods, with the aim of providing a practical guide for empiricists who want to predict coexistence among species. These include two phenomenological methods that estimate ND and RFD based on observing competitive interactions among species; two mechanistic methods that estimate ND and RFD based solely on information about species’ resource requirements; and a fifth method that does not yield ND and RFD but describes the impacts of those forces within communities. Based on the specific requirements, limitations, and assumptions of each approach, we offer a series of decision steps that can be used to determine which method(s) are best for a given study system. In particular, we show there are important tradeoffs between mechanistic methods, which require detailed understanding of species niches and physiology but are more tractable experimentally, and phenomenological methods which do not require this detailed information but can be impractical for some study designs. Importantly, we show that although each method can be used to estimate ND and RFD, the methods do not always yield the same values. Therefore we caution against future syntheses that compile these estimates from different empirical studies. Finally, we highlight several areas where modern coexistence theory could benefit from additional empirical work.

scholarly journals An experimental manipulation of species’ phenologies overturns competitive hierarchies

2019 ◽  
Author(s):  
Christopher Blackford ◽  
Rachel M. Germain ◽  
Benjamin Gilbert
Keyword(s):  
Head Start ◽  
Species Coexistence ◽  
Experimental Manipulation ◽  
Grass Species ◽  
Relative Timing ◽  
Niche Differences ◽  
Competitive Hierarchies ◽  
Germination Timing ◽  
Phenological Event

AbstractEcological theory produces opposing predictions about whether differences in the timing of life history transitions, or ‘phenology’, promote or limit coexistence. Phenological separation is predicted to create temporal niche differences, increasing coexistence, yet phenological separation may competitively favour one species, increasing fitness differences and hindering coexistence. We experimentally manipulated relative germination timing, a critical phenological event, of two annual grass species,Vulpia microstachysandV. octoflora, to test these contrasting predictions. We parameterized a competition model to estimate within-season niche differences, fitness differences, and coexistence, and to estimate coexistence when among-year fluctuations of germination timing occur. Increasing germination separation caused parallel changes in niche and fitness differences, with the net effect of weakening within-year coexistence. Both species experienced a competitive advantage by germinating earlier, strongly enough to allow the generally inferior competitor to exclude the other with at least a four day head start. The overall consequence of germination separation was to limit coexistence within a given year, although among-year variation in relative timing of germination was sufficient to support long-term coexistence. Our results clarify how phenological differences structure competitive interactions, and highlight the need to quantify among-year variation in these differences to better understand species coexistence.

scholarly journals Different methods for niche and fitness differences computation offer contrasting explanations of species coexistence

2021 ◽  
Author(s):  
Juerg W Spaak ◽  
Po-Ju Ke ◽  
Andrew W Letten ◽  
Frederik De Laender
Keyword(s):  
Empirical Data ◽  
Species Coexistence ◽  
Plant Traits ◽  
Simulated Data ◽  
Data Sets ◽  
Phylogenetic Distance ◽  
Simultaneous Application ◽  
Coexistence Theory ◽  
Niche Differences ◽  
Better Than

In modern coexistence theory, species coexistence can either arise via stabilizing mechanisms that increase niche differences or equalizing mechanisms that reduce fitness differences.Having a common currency for interpreting these mechanisms is essential for synthesizing knowledge across different studies and systems.Several methods for quantifying niche and fitness differences exist, but it remains unknown to what extent these methods agree on the reasons why species coexist. Here, we apply four common methods to quantify niche and fitness differences to one simulated and two empirical data sets. We ask if different methods result in different insights into what drives species coexistence. We find that different methods disagree on the effects of resource supply rates (simulated data), and of plant traits or phylogenetic distance (empirical data), on niche and fitness differences. More specifically, these methods often do not agree better than expected by chance. We argue for (1) a better understanding of what connects and sets apart different methods, and (2) the simultaneous application of multiple methods to enhance a more complete insight into why species coexist.

What is—or, for that Matter, isn’t—‘Experimental’ Semantics?

2018 ◽  
Author(s):  
Pauline Jacobson
Keyword(s):  
Natural Language ◽  
Large Scale ◽  
Empirical Work ◽  
Thought Experiments ◽  
Natural Language Semantics ◽  
Empirical Methods ◽  
Language Semantics ◽  
Experimental Semantics

This chapter examines the currently fashionable notion of ‘experimental semantics’, and argues that most work in natural language semantics has always been experimental. The oft-cited dichotomy between ‘theoretical’ (or ‘armchair’) and ‘experimental’ is bogus and should be dropped form the discourse. The same holds for dichotomies like ‘intuition-based’ (or ‘thought experiments’) vs. ‘empirical’ work (and ‘real experiments’). The so-called new ‘empirical’ methods are often nothing more than collecting the large-scale ‘intuitions’ or, doing multiple thought experiments. Of course the use of multiple subjects could well allow for a better experiment than the more traditional single or few subject methodologies. But whether or not this is the case depends entirely on the question at hand. In fact, the chapter considers several multiple-subject studies and shows that the particular methodology in those cases does not necessarily provide important insights, and the chapter argues that some its claimed benefits are incorrect.

Assessing Medical Evidence

2018 ◽  
Author(s):  
Jacob Stegenga
Keyword(s):  
Quality Assessment ◽  
Randomized Trials ◽  
Empirical Studies ◽  
Allocation Concealment ◽  
Assessment Tools ◽  
Medical Evidence ◽  
Empirical Methods ◽  
First Order ◽  
First Order Methods

Medical scientists employ ‘quality assessment tools’ to assess evidence from medical research, especially from randomized trials. These tools are designed to take into account methodological details of studies, including randomization, subject allocation concealment, and other features of studies deemed relevant to minimizing bias. There are dozens of such tools available. They differ widely from each other, and empirical studies show that they have low inter-rater reliability and low inter-tool reliability. This is an instance of a more general problem called here the underdetermination of evidential significance. Disagreements about the quality of evidence can be due to different—but in principle equally good—weightings of the methodological features that constitute quality assessment tools. Thus, the malleability of empirical research in medicine is deep: in addition to the malleability of first-order empirical methods, such as randomized trials, there is malleability in the tools used to evaluate first-order methods.

Media portrayals of older employees: a success story?

2014 ◽  
Vol 27 (4) ◽  
pp. 583-597 ◽  
Author(s):  
Martine van Selm ◽  
Beatrice I.J.M. Van der Heijden
Keyword(s):  
Mass Media ◽  
Older Workers ◽  
Longitudinal Research ◽  
Empirical Studies ◽  
Empirical Work ◽  
Corporate Communication ◽  
Content Type ◽  
Media Portrayals ◽  
Older Employees ◽  
Age Related

Purpose – The purpose of this paper is to provide an analysis of how portrayals of older employees in mass media messages can help combating stereotypical beliefs on their employability. Design/methodology/approach – The authors conducted a systematic review of empirical studies on mass media portrayals of older employees in order to show what these reveal about the ways in which their employment status, occupation, job type, or work setting is portrayed. The approach builds upon theory on media portrayals, media effects, and stereotypes of older workers’ employability. Findings – This study shows that older employees in media portrayals, when present at all, are relatively often shown in higher-level professional roles, herewith overall, depicting an image that is positive, yet differs from stereotypical beliefs on their employability that are prevalent in working organizations. Research limitations/implications – Further empirical work is needed to more safely conclude on the prevalence of age-related portrayals of work and employment in mass media. In addition, longitudinal research is called for in order to better understand the possible causes for the way in which older employees are portrayed, as well as effects of age-related stereotyping in mass media and corporate communication outlets over time. Practical implications – This research sparks ideas about how new portrayals of older employees in mass media and corporate communication outlets can contribute to novel approaches to managing an aging and multi-generational workforce. Social implications – This study shows how working organizations can make use of the positive and powerful media portrayals of older employees, in order to activate normal and non-ageist behaviors toward them, and herewith, to increase their life-long employability. Originality/value – This study highlights the role of media portrayals of older employees in combating stereotypes about their employability.

scholarly journals Advances in species coexistence theory

2017 ◽  
Vol 25 (4) ◽  
pp. 345-354 ◽  
Author(s):  
Chengjin Chu ◽  
◽  
Youshi Wang ◽  
Yu Liu ◽  
Lin Jiang ◽  
...  
Keyword(s):  
Species Coexistence ◽  
Coexistence Theory

The virtue of narrowing: the fiscal federalism setting

2019 ◽  
pp. 99-128
Author(s):  
Pierre Salmon
Keyword(s):  
Theoretical Analysis ◽  
Fiscal Federalism ◽  
Empirical Studies ◽  
Empirical Work ◽  
Data Sets ◽  
Exact Nature ◽  
Yardstick Competition ◽  
Alternative Approaches ◽  
Short Section

This chapter mainly discusses the empirical work in the domain of local (subcentral) finance involving yardstick competition. It begins with a short section on the systemic novelty introduced by yardstick competition into the theory of fiscal federalism. The central part of the chapter focuses on the empirical arguments developed to probe the presence of yardstick competition and yardstick voting in various data sets. Then, some queries are formulated about the exact nature of what has been established empirically so far. It seems clearly confirmed that some form of yardstick competition or yardstick voting is at work in different settings. That result is important but the findings should not be supposed to validate the game-theoretical analysis or the pure mimicking behavior assumption typically associated with the empirical studies. Alternative approaches are considered toward the end of the chapter.

Gendered caregiving and structural constraints: An empirical ethical study

2020 ◽  
pp. 096973302091251
Author(s):  
Xiang Zou ◽  
Jing-Bao Nie ◽  
Ruth Fitzgerald
Keyword(s):  
Rural China ◽  
Empirical Studies ◽  
Empirical Work ◽  
Family Care ◽  
Aged Care ◽  
Structural Constraints ◽  
Female Labour ◽  
Current Configuration ◽  
Normative Evaluation ◽  
The Impact

Background: The pressing issue of aged care has made gendered caregiving a growing subject of feminist bioethical enquiry. However, the impact of feminism on empirical studies in the area of gendered care in Chinese sociocultural contexts has been less influential. Objectives: To examine female members’ lived experiences of gendered care in rural China and offer proper normative evaluation based on their experiences. Research design: This article adopted an empirical ethical approach that integrates ethnographical investigation and feminist ethical inquiry. Participants and research context: This article focused on three cases of gendered caregiving for sick older members collected from a 6-month fieldwork conducted in a primary hospital in rural China. Ethical consideration: Approval was obtained from the university ethics committee. Findings: The empirical work highlights caregivers’ voices of weiqu (a sense of unfairness) resulting from their constrained choice when being pressured to engage in caregiving, which is associated with a disadvantageous socio-institutional and structural backdrop in current rural China. Informed by the conception of structural injustice, the normative analysis of this article traced various forms of social norms, structural deficiencies and ageing welfare institutions, as they intertwine and transmit into additional care deficiencies against rural families and their female caregivers. Conclusion: This article identified the constraint of gender hierarchy and its intersection with external social structure that exacerbate gendered oppression and exploitation of female labour in rural China. Normatively, this article argues that the current configuration of rural family care, featured by structural impediments and exploration of female labour, is unjust. Some policy recommendations are proposed to empower caregivers and advance care for rural older people.

scholarly journals Power, pork and patronage: Decentralisation and the politicisation of the development budget in Papua New Guinea

1970 ◽  
pp. 7-31 ◽  
Author(s):  
Matthew Allen ◽  
Zahid Hasnain
Keyword(s):  
Political Culture ◽  
Papua New Guinea ◽  
Local Level ◽  
Empirical Studies ◽  
Empirical Work ◽  
New Guinea ◽  
Development Planning ◽  
State Development ◽  
Patronage Politics ◽  
History Of

This paper examines a number of recent empirical studies of local-level decision-making in relation to development planning and, especially, the allocation of state development funds in Papua New Guinea. The discussion is framed by the extensive theoretical and Papua New Guinea literature on patronage politics and political culture, by the recent history of decentralisation reforms, and by the frequently articulated, but largely anecdotal, observations about the functioning of district and local-level governance processes.In contrast to the anecdotal vision of widespread and chronic dysfunctionality, the studies considered here paint a picture of considerable spatial and regional variation. We offer some tentative hypotheses to explain this variation, while flagging the need for more empirical work. We outline how these preliminary findings have informed a program of research that is currently being undertaken at the district and local government levels with a view to gaining a better understanding of the extent and nature of spatial variation in the local-level governance of state development funds in Papua New Guinea.

scholarly journals Vigor in the Face of Fluctuating Rates of Reward: An Experimental Examination

2011 ◽  
Vol 23 (12) ◽  
pp. 3933-3938 ◽  
Author(s):  
Marc Guitart-Masip ◽  
Ulrik R. Beierholm ◽  
Raymond Dolan ◽  
Emrah Duzel ◽  
Peter Dayan
Keyword(s):  
Reinforcement Learning ◽  
Computational Models ◽  
Average Rate ◽  
Empirical Studies ◽  
Empirical Work ◽  
Healthy Human ◽  
Average Return ◽  
The Face ◽  
Cost Of Time ◽  
Human Participants

Two fundamental questions underlie the expression of behavior, namely what to do and how vigorously to do it. The former is the topic of an overwhelming wealth of theoretical and empirical work particularly in the fields of reinforcement learning and decision-making, with various forms of affective prediction error playing key roles. Although vigor concerns motivation, and so is the subject of many empirical studies in diverse fields, it has suffered a dearth of computational models. Recently, Niv et al. [Niv, Y., Daw, N. D., Joel, D., & Dayan, P. Tonic dopamine: Opportunity costs and the control of response vigor. Psychopharmacology (Berlin), 191, 507–520, 2007] suggested that vigor should be controlled by the opportunity cost of time, which is itself determined by the average rate of reward. This coupling of reward rate and vigor can be shown to be optimal under the theory of average return reinforcement learning for a particular class of tasks but may also be a more general, perhaps hard-wired, characteristic of the architecture of control. We, therefore, tested the hypothesis that healthy human participants would adjust their RTs on the basis of the average rate of reward. We measured RTs in an odd-ball discrimination task for rewards whose magnitudes varied slowly but systematically. Linear regression on the subjects' individual RTs using the time varying average rate of reward as the regressor of interest, and including nuisance regressors such as the immediate reward in a round and in the preceding round, showed that a significant fraction of the variance in subjects' RTs could indeed be explained by the rate of experienced reward. This validates one of the key proposals associated with the model, illuminating an apparently mandatory form of coupling that may involve tonic levels of dopamine.

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