scholarly journals Fitness differences, not niche differences, limit species richness

2019 ◽  
Author(s):  
Jurg W. Spaak ◽  
Camille Carpentier ◽  
Frederik De Laender
Keyword(s):  
Species Richness ◽  
Simple Model ◽  
Empirical Data ◽  
Higher Order ◽  
Coexistence Theory ◽  
Niche Differences ◽  
Species Pairs ◽  
Analytical Proof ◽  
Average Fitness

A key question in ecology is what limits species richness. Coexistence theory presents the persistence of species amidst heterospecifics as a balance between niche differences and fitness differences that favour and hamper coexistence, respectively. With most applications focusing on species pairs, we know little about how niche and fitness differences respond to species richness, i.e. what constraints richness most. We present analytical proof that, in absence of higher-order interactions, the average fitness difference increases with richness, while the average niche difference stays constant. Analysis of a simple model with higher-order interactions, extensive simulations that relaxed all assumptions, and analyses of empirical data, confirmed these results. Our work thus shows that fitness differences, not niche difference, limit species richness. Our results contribute to the expansion of coexistence theory towards multi-species communities.

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.

scholarly journals Unimodal effects of pigment richness on niche and fitness differences explain species richness and ecosystem function in light-limited phytoplankton communities

2020 ◽  
Author(s):  
Jurg Werner Spaak ◽  
Frederik De Laender
Keyword(s):  
Species Richness ◽  
Ecosystem Function ◽  
Necessary Condition ◽  
Limiting Similarity ◽  
Long Term Effects ◽  
Coexistence Theory ◽  
Trait Diversity ◽  
Niche Differences ◽  
Phytoplankton Communities ◽  
And Function

AbstractTrait diversity is traditionally seen as promoting species richness and ecosystem function. Species with dissimilar traits would partition available resources, increasing niche differences, facilitating coexistence and increasing ecosystem function. Here we first show, using theory and simulations for light-limited phytoplankton, that combing photosynthetic pigments is indeed a necessary condition for coexistence and stimulates ecosystem function. However, pigment richness does mostly not permit the coexistence of more than two species, and increases productivity at most 60% compared to single-pigment communities. Surprisingly, combining all nine pigments known to date leads to a 2.5% probability that four species would coexist, illustrating that the coexistence of a high number of species along a continuous niche axis is constrained by limiting similarity. We explain these constraints by unimodal effects of pigment richness on niche and fitness differences, which jointly limit the positive effect of pigment on species richness. Empirical data and additional simulations suggest that pigment richness effects can be stronger during transient dynamics but inevitably weaken with time, i.e. pigment richness effects on species richness and function are likely short-lived. Our results highlight the need to apply coexistence theory to understand the long-term effects of trait diversity on biodiversity and ecosystem function.Statement of authorshipJ.W.S. and F.dL. developed the ideas and wrote the manuscript. J.W.S developed the mathematics and the python code to conduct the study. J.W.S conducted the literature review.

A Simple Model of Separation Logic for Higher-Order Store

2008 ◽  
pp. 348-360 ◽  
Author(s):  
Lars Birkedal ◽  
Bernhard Reus ◽  
Jan Schwinghammer ◽  
Hongseok Yang
Keyword(s):  
Simple Model ◽  
Higher Order ◽  
Separation Logic

scholarly journals Lexical landscapes as largein silicodata for examining advanced properties of fitness landscapes

2019 ◽  
Author(s):  
Victor A. Meszaros ◽  
Miles D. Miller-Dickson ◽  
C. Brandon Ogbunugafor
Keyword(s):  
Evolutionary Theory ◽  
Empirical Data ◽  
In Silico ◽  
Evolutionary Biology ◽  
Fitness Landscape ◽  
Evolutionary Genetics ◽  
Higher Order ◽  
Fitness Landscapes ◽  
Adaptive Landscape ◽  
Data Sets

In silicoapproaches have served a central role in the development of evolutionary theory for generations. This especially applies to the concept of the fitness landscape, one of the most important abstractions in evolutionary genetics, and one which has benefited from the presence of large empirical data sets only in the last decade or so. In this study, we propose a method that allows us to generate enormous data sets that walk the line betweenin silicoand empirical: word usage frequencies as catalogued by the Google ngram corpora. These data can be codified or analogized in terms of a multidimensional empirical fitness landscape towards the examination of advanced concepts—adaptive landscape by environment interactions, clonal competition, higher-order epistasis and countless others. We argue that the greaterLexical Landscapesapproach can serve as a platform that offers an astronomical number of fitness landscapes for exploration (at least) or theoretical formalism (potentially) in evolutionary biology.

scholarly journals Multitrophic higher-order interactions modulate species persistence

2021 ◽  
Author(s):  
Lisa Buche ◽  
Ignasi Bartomeus ◽  
Oscar Godoy
Keyword(s):  
Plant Species ◽  
Network Structure ◽  
Higher Order ◽  
Species Persistence ◽  
Pairwise Interactions ◽  
Species Pairs ◽  
Diverse Communities ◽  
Plant Persistence ◽  
Per Capita ◽  
Plant Pollinator

There is growing recognition that interactions between species pairs are modified in a multispecies context by the density of a third species. However, how these higher-order interactions (HOIs) affect species persistence remains poorly understood. To explore the effect of HOIs steaming from multiple trophic layers on plant persistence, we experimentally built a mutualistic system containing three plants and three pollinators species with two contrasting network structures. For both structures, we first estimated the statistically supported HOIs on plant species, in addition to the pairwise interactions among plants and plant-pollinators. Following a structuralist approach, we then assessed the effects of the supported HOIs on the persistence probability of each of the three competing plant species and their combinations. HOIs produced substantial effects on the strength and sign of per capita interactions between plant species to such an extent that predictions of species persistence differ from a non-HOIs scenario. Changes in network structure due to removing a plant-pollinator link further modulated the species persistence probabilities by reorganizing per capita interaction strengths of both pairwise interactions and HOIs. Our study provides empirical evidence of the joint importance of HOIs and network structure for determining the probability of species to persist within diverse communities.

Species coexistence

2020 ◽  
pp. 5-27 ◽  
Author(s):  
Peter Chesson
Keyword(s):  
Community Ecology ◽  
Species Coexistence ◽  
Neutral Theory ◽  
Niche Overlap ◽  
Shared Environment ◽  
Similar Species ◽  
Average Performance ◽  
Niche Differences ◽  
Ecological Drift ◽  
Average Fitness

In most places on Earth, many similar species are found coexisting. This key observation is often explained in terms of ecological differences in how species interact with their shared environment, that is, in terms of their niche differences. Niche differences can to lead to stable coexistence in contrast to the ecological drift predicted by the neutral theory of community ecology. Coexistence becomes stabilized as density feedback within species is strengthened relative to density feedback between species. Coexistence is reflective of two distinct niche comparisons, niche overlap, and species relative average fitness. In general, low niche overlap (dissimilarity in use of the environment) and similar average fitnesses (similar average performance) favor coexistence. For a unified theory of species coexistence, it is shown how the Lotka–Volterra competition model can reflect and quantify several types of niche comparison, including comparisons of resource use, susceptibility to natural enemies, and temporal variation in activity.

Niche difference determines coexistence and similar underlying processes in four ecological groups

2021 ◽  
Author(s):  
Lisa Buche ◽  
Juerg W Spaak ◽  
Javier Jarillo Diaz ◽  
Frederik de Laender
Keyword(s):  
Species Interactions ◽  
Species Coexistence ◽  
Ecological Groups ◽  
Annual Plants ◽  
Perennial Plant ◽  
Niche Differences ◽  
Species Pairs ◽  
Community Types ◽  
Underlying Processes ◽  
Important Objective

Understanding how species interactions affect community composition is an important objective in ecology. Yet, the multitude of methods to study coexistence has hampered cross-community comparisons. Here, we standardized niche and fitness differences across 1018 species pairs to compare the processes driving composition and outcomes, among four community types (annual plant, perennial plant, phytoplankton, and bacteria/yeast). First, we show that niche differences are more important drivers of coexistence than fitness differences. Second, in all community types negative frequency dependence is the most frequent process. Finally, the outcome of species interactions differs among community types. Coexistence was the most frequent outcome for perennial plants and phytoplankton, while competitive exclusion was the most prevalent outcome in annual plants and bacteria/yeasts. Overall, our results show that niche and fitness differences can be used as a common currency that allow cross community comparisons to understand species coexistence.

INVESTIGATION OF A THEORY WITH SOLITON-LIKE CONFIGURATIONS

1988 ◽  
Vol 03 (10) ◽  
pp. 2349-2369 ◽  
Author(s):  
A. WIEDEMANN ◽  
H.J.W. MÜLLER-KIRSTEN ◽  
D.H. TCHRAKIAN
Keyword(s):  
Simple Model ◽  
Green's Function ◽  
Schrodinger Equation ◽  
Zero Mode ◽  
Finite Energy ◽  
Higher Order ◽  
Scalar Theory ◽  
Yang Mills ◽  
Field Fluctuations ◽  
Finite Action

Motivated by the study of classical finite-action field configurations of higher order Yang-Mills-Higgs theories, we construct the Lagrangian of a scalar theory in one space and one time dimensions which can serve as a relatively simple model for the investigation of the properties of theories with finite energy or action classical configurations. The condition of stability of the classical configuration, the zero mode and the significance of the latter in connection with constraints which ensure the existence of the Green’s function, are studied in detail. It is then shown how a Schrödinger equation can be established and solved whose eigenfunctionals determine the probability of field fluctuations in the neighborhood of the classical configuration.

scholarly journals A Perception-Based Model of Complementary Afterimages

SAGE Open ◽  
2017 ◽  
Vol 7 (1) ◽  
pp. 215824401668247 ◽  
Author(s):  
Riccardo Manzotti
Keyword(s):  
Simple Model ◽  
Visual System ◽  
Empirical Evidence ◽  
Empirical Data ◽  
Background Color ◽  
Color Stimulus ◽  
Complementary Color

Complementary afterimages are often modeled as illusory Hering opponent hues generated by the visual system as a result of adaptation. Yet, the empirical evidence suggests a different picture—Complementary afterimages are localized RGB filtered perception based on complementary color pairs. The article aims to bring to the fore an ongoing ambiguity about red/green afterimages and then to address all cases of complementary afterimages. A simple model of afterimages based both on empirical data and the available literature is reconsidered and discussed: The afterimage color A depends both on the color stimulus S and on the ensuing background color B as estimated by the relation, A = B – kS.

scholarly journals Plant functional traits and the multidimensional nature of species coexistence

2015 ◽  
Vol 112 (3) ◽  
pp. 797-802 ◽  
Author(s):  
Nathan J. B. Kraft ◽  
Oscar Godoy ◽  
Jonathan M. Levine
Keyword(s):  
Functional Traits ◽  
Community Dynamics ◽  
Species Coexistence ◽  
Plant Functional Traits ◽  
Annual Plants ◽  
Phenotypic Differences ◽  
Niche Differences ◽  
Whole Plant ◽  
Complex Relationships ◽  
Average Fitness

Understanding the processes maintaining species diversity is a central problem in ecology, with implications for the conservation and management of ecosystems. Although biologists often assume that trait differences between competitors promote diversity, empirical evidence connecting functional traits to the niche differences that stabilize species coexistence is rare. Obtaining such evidence is critical because traits also underlie the average fitness differences driving competitive exclusion, and this complicates efforts to infer community dynamics from phenotypic patterns. We coupled field-parameterized mathematical models of competition between 102 pairs of annual plants with detailed sampling of leaf, seed, root, and whole-plant functional traits to relate phenotypic differences to stabilizing niche and average fitness differences. Single functional traits were often well correlated with average fitness differences between species, indicating that competitive dominance was associated with late phenology, deep rooting, and several other traits. In contrast, single functional traits were poorly correlated with the stabilizing niche differences that promote coexistence. Niche differences could only be described by combinations of traits, corresponding to differentiation between species in multiple ecological dimensions. In addition, several traits were associated with both fitness differences and stabilizing niche differences. These complex relationships between phenotypic differences and the dynamics of competing species argue against the simple use of single functional traits to infer community assembly processes but lay the groundwork for a theoretically justified trait-based community ecology.

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