Local and collective transitions in sparsely-interacting ecological communities

Abstract Interactions in natural communities can be highly heterogeneous, with any given species interacting appreciably with only some of the others, a situation commonly represented by sparse interaction networks. We study the consequences of sparse competitive interactions, in a theoretical model of a community assembled from a species pool. We find that communities can be in a number of different regimes, depending on the interaction strength. When interactions are strong, the network of coexisting species breaks up into small subgraphs, while for weaker interactions these graphs are larger and more complex, eventually encompassing all species. This process is driven by emergence of new allowed subgraphs as interaction strength decreases, leading to sharp changes in diversity and other community properties, and at weaker interactions to two distinct collective transitions: a percolation transition, and a transition between having a unique equilibrium and having multiple alternative equilibria. Understanding community structure is thus made up of two parts: first, finding which subgraphs are allowed at a given interaction strength, and secondly, a discrete problem of matching these structures over the entire community. In a shift from the focus of many previous theories, these different regimes can be traversed by modifying the interaction strength alone, without need for heterogeneity in either interaction strengths or the number of competitors per species.

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Intraspecific variation promotes species coexistence and trait clustering through higher order interactions

10.1101/494757 ◽

2018 ◽

Author(s):

Gaurav Baruah ◽

Robert John

Keyword(s):

Intraspecific Variation ◽

Individual Variation ◽

Species Coexistence ◽

Species Traits ◽

Higher Order ◽

Competitive Interactions ◽

Volterra Model ◽

Trait Divergence ◽

Pairwise Interactions ◽

Coexisting Species

AbstractEcological and evolutionary effects of individual variation on species coexistence remains unclear. Competition models for coexistence have emphasized species-level differences in pairwise interactions, and invoked no role for intraspecific variation. These models show that stronger competitive interactions result in smaller numbers of coexisting species. However, the presence of higher-order interactions (HOIs) among species appears to have a stabilizing influence on communities. How species coexistence is affected in a community where both pairwise and higher-order interactions are pervasive is not known. Furthermore, the effect of individual variation on species coexistence in complex communities with pairwise and HOIs remains untested. Using a Lotka-Volterra model, we explore the effects of intraspecific variation on the patterns of species coexistence in a competitive community dictated by pairwise and HOIs. We found that HOIs greatly stabilize species coexistence across different levels of strength in competition. Notably, high intraspecific variation promoted species coexistence, particularly when competitive interactions were strong. However, species coexistence promoted by higher levels of variation was less robust to environmental perturbation. Additionally, species’ traits tend to cluster together when individual variation in the community increased. We argue that individual variation can promote species coexistence by reducing trait divergence and attenuating the inhibitory effects of dominant species through HOIs

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Vulnerable species interactions are important for the stability of mutualistic networks

10.1101/604868 ◽

2019 ◽

Author(s):

Benno I. Simmons ◽

Hannah S. Wauchope ◽

Tatsuya Amano ◽

Lynn V. Dicks ◽

William J. Sutherland ◽

...

Keyword(s):

Species Interactions ◽

Species Coexistence ◽

Species Interaction ◽

Interaction Networks ◽

Ecological Communities ◽

Ecological Context ◽

Intrinsic Properties ◽

Network Stability ◽

Starting Point ◽

The Stability

AbstractSpecies are central to ecology and conservation. However, it is the interactions between species that generate the functions on which ecosystems and humans depend. Despite the importance of interactions, we lack an understanding of the risk that their loss poses to ecological communities. Here, we quantify risk as a function of the vulnerability (likelihood of loss) and importance (contribution to network stability in terms of species coexistence) of 4330 mutualistic interactions from 41 empirical pollination and seed dispersal networks across six continents. Remarkably, we find that more vulnerable interactions are also more important: the interactions that contribute most to network stability are those that are most likely to be lost. Furthermore, most interactions tend to have more similar vulnerability and importance across networks than expected by chance, suggesting that vulnerability and importance may be intrinsic properties of interactions, rather than only a function of ecological context. These results provide a starting point for prioritising interactions for conservation in species interaction networks and, in areas lacking network data, could allow interaction properties to be inferred from taxonomy alone.

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Interaction capacity underpins community diversity

10.1101/2020.04.08.032524 ◽

2020 ◽

Cited By ~ 3

Author(s):

Masayuki Ushio

Keyword(s):

Interspecific Interactions ◽

Experimental Studies ◽

Interaction Strength ◽

Single Species ◽

Species Interaction ◽

Community Diversity ◽

Ecological Communities ◽

Total Dna ◽

Mathematical Equations ◽

The Mean

AbstractHow patterns in community diversity emerge is a long-standing question in ecology. Theories and experimental studies suggested that community diversity and interspecific interactions are interdependent. However, evidence from multitaxonomic, high-diversity ecological communities is lacking because of practical challenges in characterizing speciose communities and their interactions. Here, I analyzed time-varying causal interaction networks that were reconstructed using 1197 species, DNA-based ecological time series taken from experimental rice plots and empirical dynamic modeling, and show that species interaction capacity, namely, the sum of interaction strength that a single species gives and receives, underpins community diversity. As community diversity increases, the number of interactions increases exponentially but the mean species interaction capacity of a community becomes saturated, weakening interaction among species. These patterns are explicitly modeled with simple mathematical equations, based on which I propose the “interaction capacity hypothesis”, namely, that species interaction capacity and network connectance are proximate drivers of community diversity. Furthermore, I show that total DNA concentrations and temperature influence species interaction capacity and connectance nonlinearly, explaining a large proportion of diversity patterns observed in various systems. The interaction capacity hypothesis enables mechanistic explanations of community diversity, and how species interaction capacity is determined is a key question in ecology.

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LifeWebs: A (global) database of bipartite ecological interaction networks

Biodiversity Information Science and Standards ◽

10.3897/biss.5.75626 ◽

2021 ◽

Vol 5 ◽

Author(s):

Philip Butterill ◽

Leonardo Jorge ◽

Shuang Xing ◽

Tom Fayle

Keyword(s):

Interaction Network ◽

Community Level ◽

Interaction Networks ◽

Sampling Effort ◽

Ecological Communities ◽

Bipartite Networks ◽

Data Types ◽

User Friendliness ◽

Global Database ◽

Machine Readable

The structure and dynamics of ecological interactions are nowadays recognized as a crucial challenge to comprehend the assembly, functioning and maintenance of ecological communities, their processes and the services they provide. Nevertheless, while standards and databases for information on species occurrences, traits and phylogenies have been established, interaction networks have lagged behind on the development of these standards. Here, we discuss the challenges and our experiences in developing a global database of bipartite interaction networks. LifeWebs*1 is an effort to compile community-level interaction networks from both published and unpublished sources. We focus on bipartite networks that comprise one specific type of interaction between two groups of species (e.g., plants and herbivores, hosts and parasites, mammals and their microbiota), which are usually presented in a co-occurrence matrix format. However, with LifeWebs, we attempt to go beyond simple matrices by integrating relevant metadata from the studies, especially sampling effort, explicit species information (traits and taxonomy/phylogeny), and environmental/geographic information on the communities. Specifically, we explore 1) the unique aspects of community-level interaction networks when compared to data on single inter-specific interactions, occurrence data, and other biodiversity data and how to integrate these different data types. 2) The trade-off between user friendliness in data input/output vs. machine-readable formats, especially important when data contributors need to provide large amounts of data usually compiled in a non-machine-readable format. 3) How to have a single framework that is general enough to include disparate interaction types while retaining all the meaningful information. We envision LifeWebs to be in a good position to test a general standard for interaction network data, with a large variety of already compiled networks that encompass different types of interactions. We provide a framework for integration with other types of data, and formalization of the data necessary to represent networks into established biodiversity standards.

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Tractable models of ecological assembly

10.1101/2020.09.02.279943 ◽

2020 ◽

Author(s):

Carlos A. Serván ◽

Stefano Allesina

Keyword(s):

Complex Dynamics ◽

Point Of View ◽

Priority Effects ◽

Stable Configuration ◽

Theoretical Point ◽

Ecological Communities ◽

Top Down ◽

Bottom Up ◽

Coexisting Species ◽

And Control

AbstractEcological assembly, the way natural communities form under ecological time-scales, is a fundamental and yet poorly understood process. Recent theoretical and empirical approaches to assembly consider systems in which a group of species is introduced in a new environment, and dynamics prune the system down to a sub-community of coexisting species. This “top-down” assembly approach contrasts with the well-studied “bottom-up”, or sequential, assembly, in which species from a pool enter the system one at a time, giving rise to priority effects and complex dynamics. Here we determine under which conditions the two approaches are equivalent, i.e., lead asymptotically to the same exact set of coexisting species. To achieve this result, we represent the assembly process as a network in which nodes are sub-communities and edges stand for invasions shifting the composition of the ecological community from a stable configuration to another. This abstraction makes it easy to determine which states the community can occupy, as well as highlight the potential for priority effects or cyclic species composition. We discuss how the equivalence between bottom-up and top-down assembly can advance our understanding of this challenging process from an empirical and theoretical point of view, informing the study of ecological restoration and the design and control of ecological communities.

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Structured environments fundamentally alter dynamics and stability of ecological communities

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1811887116 ◽

2018 ◽

Vol 116 (2) ◽

pp. 379-388 ◽

Cited By ~ 19

Author(s):

Nick Vallespir Lowery ◽

Tristan Ursell

Keyword(s):

Microbial Communities ◽

Community Dynamics ◽

Physical Structure ◽

Specific Pattern ◽

Ecological Communities ◽

Population Fluctuations ◽

Structural Anisotropy ◽

Chemical Gradients ◽

Environmental Structure ◽

Natural Communities

The dynamics and stability of ecological communities are intimately linked with the specific interactions—like cooperation or predation—between constituent species. In microbial communities, like those found in soils or the mammalian gut, physical anisotropies produced by fluid flow and chemical gradients impact community structure and ecological dynamics, even in structurally isotropic environments. Although natural communities existing in physically unstructured environments are rare, the role of environmental structure in determining community dynamics and stability remains poorly studied. To address this gap, we used modified Lotka−Volterra simulations of competitive microbial communities to characterize the effects of surface structure on community dynamics. We find that environmental structure has profound effects on communities, in a manner dependent on the specific pattern of interactions between community members. For two mutually competing species, eventual extinction of one competitor is effectively guaranteed in isotropic environments. However, addition of environmental structure enables long-term coexistence of both species via local “pinning” of competition interfaces, even when one species has a significant competitive advantage. In contrast, while three species competing in an intransitive loop (as in a game of rock−paper−scissors) coexist stably in isotropic environments, structural anisotropy disrupts the spatial patterns on which coexistence depends, causing chaotic population fluctuations and subsequent extinction cascades. These results indicate that the stability of microbial communities strongly depends on the structural environment in which they reside. Therefore, a more complete ecological understanding, including effective manipulation and interventions in natural communities of interest, must account for the physical structure of the environment.

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Modularity in ecological networks between frugivorous birds and congeneric plant species

Journal of Tropical Ecology ◽

10.1017/s0266467416000444 ◽

2016 ◽

Vol 32 (6) ◽

pp. 526-535 ◽

Cited By ~ 4

Author(s):

Adriano M. Silva ◽

Pietro K. Maruyama ◽

Luís Pedro M. Paniago ◽

Celine Melo

Keyword(s):

Plant Species ◽

Interaction Strength ◽

Species Interaction ◽

Interaction Networks ◽

Similar Species ◽

Bird Abundance ◽

Frugivorous Birds ◽

Dietary Specialization ◽

Connectivity Indices ◽

Binary Information

Abstract:Ecological and evolutionary factors influence the presence of modules in species interaction networks, and these modules usually cluster functional similar species. But whether closely related species form modules is still unknown. We tested whether the interaction networks formed by frugivorous birds and Miconia plants are modular and evaluated how modules were divided. To do so, we gathered from the literature data concerning four networks of Miconia and their frugivorous birds (three from Brazilian savanna and one from a rain forest in Panama). We quantified modularity using binary and weighted algorithms and also tested the relationship between bird traits (body mass, dietary specialization, migratory behaviour and phylogeny) in relation to within- and among-module connectivity indices (c and z values). If considering only binary information, networks did not present distinct modular structure. Nevertheless, by including interaction strength, modules can be detected in all four Miconia-bird networks. None of the bird traits, however, was related with the connectivity indices. The possible fluctuation of frugivorous bird abundance coupled with the asynchronic fruiting period of Miconia might favour the formation of temporal modules comprising birds and plant species with phenological overlap, ensuring seed dispersal and facilitating the coexistence in sympatry. Bird traits had little effect on the role that each species plays within the modular network, probably because the frugivorous assemblages were dominated by small-bodied and opportunistic species.

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Shared ancestry influences community stability by altering competitive interactions: evidence from a laboratory microcosm experiment using freshwater green algae

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2013.1548 ◽

2013 ◽

Vol 280 (1768) ◽

pp. 20131548 ◽

Cited By ~ 12

Author(s):

Patrick A. Venail ◽

Markos A. Alexandrou ◽

Todd H. Oakley ◽

Bradley J. Cardinale

Keyword(s):

Related Species ◽

Temporal Stability ◽

Biodiversity Loss ◽

Competitive Interactions ◽

Ecological Communities ◽

Freshwater Microalgae ◽

Community Biomass ◽

Shared Ancestry ◽

The Stability ◽

The Impact

The impact of biodiversity on the stability of ecological communities has been debated among biologists for more than a century. Recently summarized empirical evidence suggests that biodiversity tends to enhance the temporal stability of community-level properties such as biomass; however, the underlying mechanisms driving this relationship remain poorly understood. Here, we report the results of a microcosm study in which we used simplified systems of freshwater microalgae to explore how the phylogenetic relatedness of species influences the temporal stability of community biomass by altering the nature of their competitive interactions. We show that combinations of two species that are more evolutionarily divergent tend to have lower temporal stability of biomass. In part, this is due to negative ‘selection effects’ in which bicultures composed of distantly related species are more likely to contain strong competitors that achieve low biomass. In addition, bicultures of distantly related species had on average weaker competitive interactions, which reduced compensatory dynamics and decreased the stability of community biomass. Our results demonstrate that evolutionary history plays a key role in controlling the mechanisms, which give rise to diversity–stability relationships. As such, patterns of shared ancestry may help us predict the ecosystem-level consequences of biodiversity loss.

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Effect of Localization on the Stability of Mutualistic Ecological Networks

10.1101/023275 ◽

2015 ◽

Author(s):

Samir Suweis ◽

Jacopo Grilli ◽

Jayanth Banavar ◽

Stefano Allesina ◽

Amos Maritan

Keyword(s):

Species Abundance ◽

Interaction Network ◽

Species Interaction ◽

Interaction Networks ◽

Ecological Communities ◽

Weighted Degree ◽

Perturbation Propagation ◽

The Stability ◽

The Impact ◽

The Relationship

The relationships between the core-periphery architecture of the species interaction network and the mechanisms ensuring the stability in mutualistic ecological communities are still unclear. In particular, most studies have focused their attention on asymptotic resilience or persistence, neglecting how perturbations propagate through the system. Here we develop a theoretical framework to evaluate the relationship between architecture of the interaction networks and the impact of perturbations by studying localization, a measure describing the ability of the perturbation to propagate through the network. We show that mutualistic ecological communities are localized, and localization reduces perturbation propagation and attenuates its impact on species abundance. Localization depends on the topology of the interaction networks, and it positively correlates with the variance of the weighted degree distribution, a signature of the network topological hetereogenity. Our results provide a different perspective on the interplay between the architecture of interaction networks in mutualistic communities and their stability.

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Experimental removal reveals only weak interspecific competition between two coexisting lizards

Canadian Journal of Zoology ◽

10.1139/cjz-2017-0279 ◽

2018 ◽

Vol 96 (8) ◽

pp. 888-896 ◽

Cited By ~ 1

Author(s):

James E. Paterson ◽

Stacey L. Weiss ◽

Gabriel Blouin-Demers

Keyword(s):

Habitat Selection ◽

Interspecific Competition ◽

Habitat Type ◽

Microhabitat Use ◽

Ecological Communities ◽

Urosaurus Ornatus ◽

Tree Lizards ◽

Coexisting Species ◽

Resource Levels ◽

Sceloporus Virgatus

Competition for resources is an important mechanism that shapes ecological communities. Interspecific competition can affect habitat selection, fitness, and abundance in animals. We used a removal experiment and mark–recapture to test the hypothesis that competition with the larger and more abundant Striped Plateau Lizard (Sceloporus virgatus H.M. Smith, 1938) limits habitat selection, fitness, and abundance in Ornate Tree Lizards (Urosaurus ornatus (Baird in Baird and Girard, 1852)). Ornate Tree Lizards in the plots where Striped Plateau Lizards were removed switched between habitat types more frequently and moved farther than Ornate Tree Lizards in control plots. However, there were no significant changes in the relative densities of Ornate Tree Lizards in each habitat type or in microhabitat use. We also found no changes in growth rates, survival, or abundance of Ornate Tree Lizards in response to the removal of Striped Plateau Lizards. Our results suggest that interspecific competition was not strong enough to limit habitat use or abundance of Ornate Tree Lizards. Perhaps interspecific competition is weak between coexisting species when resource levels are not severely depleted. Therefore, it is important to consider environmental conditions when assessing the importance of interspecific competition.

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