Intuitive and broadly applicable definitions of niche and fitness differences

Spaak, Jürg W.; Laender, Frederik De

doi:10.1101/482703

Cited by 7 publications

(49 citation statements)

References 58 publications

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“…Here we briefly summarize the mathematical formulations derived for the multispecies and two-species frameworks following recent reviews (Barabás et al 2018;Chesson 2018). We focus exclusively on the canonical formalisms of these two frameworks (Chesson 2018;Spaak and DeLaender 2018).…”

Section: Mathematical Formalismsmentioning

confidence: 99%

On the Consequences of the Interdependence of Stabilizing and Equalizing Mechanisms

Song

Barabás

Saavedra

2019

The American Naturalist

101

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We present an overlooked but important property of modern coexistence theory (MCT), along with two key new results and their consequences. The overlooked property is that stabilizing mechanisms (increasing species' niche differences) and equalizing mechanisms (reducing species' fitness differences) have two distinct sets of meanings within MCT: one in a two-species context and another in a general multispecies context. We demonstrate that the two-species framework is not a special case of the multispecies one, and therefore these two parallel frameworks must be studied independently. Our first result is that, using the two-species framework and mechanistic consumer-resource models, stabilizing and equalizing mechanisms exhibit complex interdependence, such that changing one will simultaneously change the other. Furthermore, the nature and direction of this simultaneous change sensitively depend on model parameters. The second result states that while MCT is often seen as bridging niche and neutral modes of coexistence by building a niche-neutrality continuum, the interdependence between stabilizing and equalizing mechanisms acts to break this continuum under almost any biologically relevant circumstance. We conclude that the complex entanglement of stabilizing and equalizing terms makes their impact on coexistence difficult to understand, but by seeing them as aggregated effects (rather than underlying causes) of coexistence, we may increase our understanding of ecological dynamics.

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Section: Mathematical Formalismsmentioning

confidence: 99%

On the Consequences of the Interdependence of Stabilizing and Equalizing Mechanisms

Song

Barabás

Saavedra

2019

The American Naturalist

101

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“…Our combination of MCT and SA focuses on two-species competition dynamics. While SA can be used for two-species and multispecies communities within the same formalism ), here we focus on two-species dynamics given that the canonical formalism of MCT is explicitly justified for two-competing species (Barabás et al, 2018;Chesson, 2018;Song, Barabás, & Saavedra, 2019;Spaak & DeLaender, 2018). Note that MCT can also be applied to multispecies communities, but the formalism and definitions are different (Barabás et al, 2018;Song et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Disentangling the effects of external perturbations on coexistence and priority effects

et al. 2020

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A major challenge in ecological research is to identify the tolerance of ecological communities to external perturbations. Modern coexistence theory (MCT) has been widely adopted as a framework to investigate the tolerance to perturbations in relative reductions of per capita growth rates, often using metrics that explicitly eliminate the independent role of intrinsic growth rates. More recently, the structural approach (SA) was introduced to investigate the tolerance of communities to perturbations in intrinsic growth rates as a function of the strength of intraspecific and interspecific competition. Because the external perturbations are likely to happen in both intrinsic growth rates and competition strengths, no framework alone can fully disentangle the effects of external perturbations. Here we combine MCT and SA to disentangle the tolerance in coexistence and priority effects of a pair of competing species when subject to perturbations in intrinsic growth rates and competition strengths. Through this combination, we reveal the emergence of a key trade‐off: increasing the tolerance to perturbations in intrinsic growth rates typically decreases the tolerance in competition strengths, and vice versa. Furthermore, this trade‐off is stronger under coexistence than under priority effects. We test this combined framework on competing pairs of 18 California annual plant species. For both coexistence and priority effects, we find that the tolerance to perturbations in intrinsic growth rates is maximized instead of that to perturbations in competition strengths in the studied annual plant communities. Synthesis. Our combined framework of modern coexistence theory and structural approach illustrates that it is possible to disentangle the impact of different external perturbations on the persistence of species. Importantly, our findings show that species interactions may reveal whether communities are dominated either by changes in intrinsic growth rates or by competition strengths. Overall, this combined framework can open a new perspective to understand and predict the response of populations to changing environmental conditions.

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“…For each community at equilibrium we computed the niche and fitness differences (N i and F i ) of the persisting species, using the definition Spaak & De Laender (2020). Technically, Spaak & De Laender (2020) define N i based a species i's growth rate under various conditions, including its invasion growth rate (i.e.…”

Section: Analyses and Simulationsmentioning

confidence: 99%

“…We expect this to correspond to the case where species differ markedly in pigmentation. Spaak & De Laender (2020) define F i as the growth rate of species i in absence of niche differences, scaled by the intrinsic growth rate of species i. In that case, the species with the highest scaled growth rate has the largest fitness difference.…”

Section: Analyses and Simulationsmentioning

confidence: 99%

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

Spaak

DeLaender

2020

Preprint

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Trait 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.

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Intuitive and broadly applicable definitions of niche and fitness differences

Cited by 7 publications

References 58 publications

On the Consequences of the Interdependence of Stabilizing and Equalizing Mechanisms

On the Consequences of the Interdependence of Stabilizing and Equalizing Mechanisms

Disentangling the effects of external perturbations on coexistence and priority effects

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

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