Reinterpreting the relationship between number of species and number of links connects community structure and stability

Carpentier, Camille; Barabás, György; Spaak, Jürg W.; Laender, Frederik De

doi:10.1038/s41559-021-01468-2

Cited by 29 publications

(37 citation statements)

References 62 publications

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“…Understanding why these methods differ and when they correspond, i.e. when dimensionality is reducible, is a major objective in stability research (Arnoldi et al 2018, Radchuk et al 2019, Carpentier et al 2021, Clark et al 2021). We argue that similar efforts are needed in modern coexistence theory, if we want to gain synthetic understanding across published results adopting a variety of methods.…”

Section: Discussionmentioning

confidence: 99%

Different measures of niche and fitness differences tell different tales

Spaak

Letten

et al. 2022

Oikos

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In modern coexistence theory, species coexistence can either arise via strong niche differences or weak fitness differences. Having a common currency for interpreting these mechanisms is essential for synthesizing knowledge across different studies and systems. However, several methods for quantifying niche and fitness differences exist, with little guidance on how and why these methods differ. Here, we first organize the available methods into three groups and review their differences from a conceptual point of view. Next, we apply four methods to quantify niche and fitness differences to one simulated and one empirical data set. We show that these methods do not only differ quantitatively, but affect how we interpret coexistence. Specifically, the different methods disagree on how resource supply rates (simulated data) or plant traits (empirical data) affect niche and fitness differences. We argue for a better theoretical understanding of what connects and sets apart different methods and more precise empirical measurements to foster appropriate method selection in coexistence theory.

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Section: Discussionmentioning

confidence: 99%

Different measures of niche and fitness differences tell different tales

Spaak

Letten

et al. 2022

Oikos

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“…Additionally, we have mostly assumed that species richness is independent of other factors such as the average interaction strength, connectance or correlation (Cohen & Briand, 1984; Kokkoris et al, 2002). It is well established that the number of links scales nonlinearly with species richness, causing connectance to decrease with species richness (Carpentier et al, 2021; Cohen & Briand, 1984; Martinez, 1992). However, this will not affect our findings, as the sums in the Equations and only run over species with which the focal species

i

interacts.…”

Section: Discussionmentioning

confidence: 99%

“…Several metrics exist to summarise this diversity of interaction types and study their implications for community dynamics (Fontaine et al, 2011). (2) Two‐species communities are always fully connected (Carpentier et al, 2021) and correlations between interspecific interactions (Barabás et al, 2016) become irrelevant since there is only a single pair of interspecific interactions. In contrast, in an

n

‐species community, there may be anywhere from

n ‐ 1

\frac{n}{2} false(n ‐ 1 false)

connections, and the interspecific effects of species j on species i can be positively or negatively correlated with the effects i has on j (Barabás et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Species richness increases fitness differences, but does not affect niche differences

2021

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A key question in ecology is what limits species richness. Modern coexistence theory presents the persistence of species as a balance between niche differences and fitness differences that favour and hamper coexistence, respectively. With most applications focusing on species pairs, however, we know little about if and how this balance changes with species richness. Here, we apply recently developed definitions of niche and fitness differences, based on invasion analysis, to multispecies communities. We present the first mathematical proof that, for invariant average interaction strengths, the average fitness difference among species increases with richness, while the average niche difference stays constant. Extensive simulations with more complex models and analyses of empirical data confirmed these mathematical results. Combined, our work suggests that, as species accumulate in ecosystems, ever‐increasing fitness differences will at some point exceed constant niche differences, limiting species richness. Our results contribute to a better understanding of coexistence multispecies communities.

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“…Therefore, understanding how the disruption of species interactions affects community stability is fundamental to coping with anthropogenic effects. The vast research on the link between structure and stability has focused on monotrophic networks (e.g., food webs) [3, 4]. Nevertheless, in natural communities, species are often involved in multitrophic interactions.…”

Section: Introductionmentioning

confidence: 99%

Invasive species modulate the structure and stability of a multilayer mutualistic network

Vitali

Ruiz-Suarez

Vázquez

et al. 2022

Preprint

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Species interactions are the backbone of the structure and dynamics of communities. The extensive research into the link between structure and stability has been primarily theoretical and focused on monotrophic networks. Therefore, how the disruption of multitrophic interactions alters communities' response to perturbations in nature remains an open question. Here, we explored how non-native ungulates affect pollination-seed dispersal multilayer networks in Patagonia, Argentina. Ungulates disrupt a hummingbird-mistletoe-marsupial keystone interaction, which alters community composition. We calculated interlayer connectivity, modularity, and species' roles in connecting modules for intact vs. invaded networks. To link structural changes to stability, we quantified network tolerance to a single random species removal (disturbance propagation) and sequential species removal (robustness) using a stochastic coextinction model. Non-native ungulates reduced the connectivity between pollination and seed dispersal and produced fewer modules with a skewed size distribution. Moreover, species shifted their structural role, primarily from connectors to peripherals, thereby fragmenting the network by reducing the "bridges" among modules. These structural changes altered the dynamics of cascading effects in the community, increasing disturbance propagation and reducing network robustness. Our results highlight the importance of understanding the mechanisms that alter the structure and subsequent stability of multitrophic communities in nature.

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Reinterpreting the relationship between number of species and number of links connects community structure and stability

Cited by 29 publications

References 62 publications

Different measures of niche and fitness differences tell different tales

Different measures of niche and fitness differences tell different tales

Species richness increases fitness differences, but does not affect niche differences

Invasive species modulate the structure and stability of a multilayer mutualistic network

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