| 1. |
- Barabas, György, et al.
(författare)
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Self-regulation and the stability of large ecological networks
- 2017
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Ingår i: NATURE ECOLOGY and EVOLUTION. - : NATURE PUBLISHING GROUP. - 2397-334X. ; 1:12, s. 1870-
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Tidskriftsartikel (refereegranskat)abstract
- The stability of complex ecological networks depends both on the interactions between species and the direct effects of the species on themselves. These self-effects are known as self-regulation when an increase in a species abundance decreases its per-capita growth rate. Sources of self-regulation include intraspecific interference, cannibalism, time-scale separation between consumers and their resources, spatial heterogeneity and nonlinear functional responses coupling predators with their prey. The influence of self-regulation on network stability is understudied and in addition, the empirical estimation of self-effects poses a formidable challenge. Here, we show that empirical food web structures cannot be stabilized unless the majority of species exhibit substantially strong self-regulation. We also derive an analytical formula predicting the effect of self-regulation on network stability with high accuracy and show that even for random networks, as well as networks with a cascade structure, stability requires negative self-effects for a large proportion of species. These results suggest that the aforementioned potential mechanisms of self-regulation are probably more important in contributing to the stability of observed ecological networks than was previously thought.
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| 2. |
- Dee, Laura E., et al.
(författare)
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Operationalizing Network Theory for Ecosystem Service Assessments
- 2017
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Ingår i: Trends in Ecology & Evolution. - : ELSEVIER SCIENCE LONDON. - 0169-5347 .- 1872-8383. ; 32:2, s. 118-130
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Forskningsöversikt (refereegranskat)abstract
- Managing ecosystems to provide ecosystem services in the face of global change is a pressing challenge for policy and science. Predicting how alternative management actions and changing future conditions will alter services is complicated by interactions among components in ecological and socioeconomic systems. Failure to understand those interactions can lead to detrimental outcomes from management decisions. Network theory that integrates ecological and socioeconomic systems may provide a path to meeting this challenge. While network theory offers promising approaches to examine ecosystem services, few studies have identified how to operationalize networks for managing and assessing diverse ecosystem services. We propose a framework for how to use networks to assess how drivers and management actions will directly and indirectly alter ecosystem services.
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| 3. |
- Eklöf, Anna, 1976-, et al.
(författare)
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Networks, Ecological
- 2012. - 1
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Ingår i: Encyclopedia of Theoretical Ecology. - : University of California Press. - 9780520269651 - 9780520951785 ; , s. 470-478
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Bokkapitel (refereegranskat)
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| 4. |
- Eklöf, Anna, 1976-, et al.
(författare)
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Relevance of evolutionary history for food web structure
- 2012
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society Publishing. - 0962-8452 .- 1471-2954. ; 279:1733, s. 1588-1596
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Tidskriftsartikel (refereegranskat)abstract
- Explaining the structure of ecosystems is one of the great challenges of ecology. Simple models for foodweb structure aim at disentangling the complexity of ecological interaction networks and detect the main forces that are responsible for their shape. Trophic interactions are influenced by species traits, which in turn are largely determined by evolutionary history. Closely related species are more likely to share similar traits, such as body size, feeding mode and habitat preference than distant ones. Here, we present a theoretical framework for analysing whether evolutionary history—represented by taxonomic classification—provides valuable information on food web structure. In doing so, we measure which taxonomic ranks better explain species interactions. Our analysis is based on partitioning of the species into taxonomic units. For each partition, we compute the likelihood that a probabilistic model for food web structurere produces the data using this information. We find that taxonomic partitions produce significantly higher likelihoods than expected at random. Marginal likelihoods (Bayes factors) are used to perform model selection among taxonomic ranks. We show that food webs are best explained by the coarser taxonomic ranks (kingdom to class). Our methods provide a way to explicitly include evolutionary history in models for food web structure.
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| 5. |
- Eklöf, Anna, 1976-, et al.
(författare)
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Secondary extinctions in food webs : a Bayesian network approach
- 2013
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Ingår i: Methods in Ecology and Evolution. - : Wiley-Blackwell. - 2041-210X. ; 4:8, s. 760-770
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Tidskriftsartikel (refereegranskat)abstract
- Ecological communities are composed of populations connected in tangled networks of ecological interactions. Therefore, the extinction of a species can reverberate through the network and cause other (possibly distantly connected) species to go extinct as well. The study of these secondary extinctions is a fertile area of research in ecological network theory.However, to facilitate practical applications, several improvements to the current analytical approaches are needed. In particular, we need to consider that (i) species have different ‘a priori’ probabilities of extinction, (ii) disturbances can simultaneously affect several species, and (iii) extinction risk of consumers likely grows with resource loss. All these points can be included in dynamical models, which are, however, difficult to parameterize.Here we advance the study of secondary extinctions with Bayesian networks. We show how this approach can account for different extinction responses using binary – where each resource has the same importance – and quantitative data – where resources are weighted by their importance. We simulate ecological networks using a popular dynamical model (the Allometric Trophic Network model) and use it to test our method.We find that the Bayesian network model captures the majority of the secondary extinctions produced by the dynamical model and that consumers’ responses to species loss are best modelled using a nonlinear sigmoid function. We also show that an approach based exclusively on food web structure loses power when species at higher trophic levels are preferentially lost. Because the loss of apex predators is unfortunately widespread, the results highlight a serious limitation of studies on network robustness.
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| 6. |
- Eklöf, Anna, et al.
(författare)
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The dimensionality of ecological networks
- 2013
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Ingår i: Ecology Letters. - : Blackwell Publishing. - 1461-023X .- 1461-0248. ; 16:5, s. 577-583
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Tidskriftsartikel (refereegranskat)abstract
- How many dimensions (trait-axes) are required to predict whether two species interact? This unansweredquestion originated with the idea of ecological niches, and yet bears relevance today for understanding whatdetermines network structure. Here, we analyse a set of 200 ecological networks, including food webs,antagonistic and mutualistic networks, and find that the number of dimensions needed to completelyexplain all interactions is small ( < 10), with model selection favouring less than five. Using 18 high-qualitywebs including several species traits, we identify which traits contribute the most to explaining networkstructure. We show that accounting for a few traits dramatically improves our understanding of the structureof ecological networks. Matching traits for resources and consumers, for example, fruit size and billgape, are the most successful combinations. These results link ecologically important species attributes tolarge-scale community structure.
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| 7. |
- Grilli, Jacopo, et al.
(författare)
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Correction: Feasibility and coexistence of large ecological communities (vol 8, pg 14389, 2017)
- 2018
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 9
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Nature Communications 8: Article number: 14389; Published: 24 February 2017; Updated: 13 July 2018 The original HTML version of this Article had an incorrect article number of ‘0’; it should have been ‘14389’. This has now been corrected in the HTML version of the Article. The PDF version was correct from the time of publication.
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| 8. |
- Grilli, Jacopo, et al.
(författare)
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Feasibility and coexistence of large ecological communities
- 2017
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The role of species interactions in controlling the interplay between the stability of ecosystems and their biodiversity is still not well understood. The ability of ecological communities to recover after small perturbations of the species abundances (local asymptotic stability) has been well studied, whereas the likelihood of a community to persist when the conditions change (structural stability) has received much less attention. Our goal is to understand the effects of diversity, interaction strengths and ecological network structure on the volume of parameter space leading to feasible equilibria. We develop a geometrical framework to study the range of conditions necessary for feasible coexistence. We show that feasibility is determined by few quantities describing the interactions, yielding a nontrivial complexity-feasibility relationship. Analysing more than 100 empirical networks, we show that the range of coexistence conditions in mutualistic systems can be analytically predicted. Finally, we characterize the geometric shape of the feasibility domain, thereby identifying the direction of perturbations that are more likely to cause extinctions.
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| 9. |
- Grilli, Jacopo, et al.
(författare)
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Higher-order interactions stabilize dynamics in competitive network models
- 2017
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 548:7666, s. 210-
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Tidskriftsartikel (refereegranskat)abstract
- Ecologists have long sought a way to explain how the remarkable biodiversity observed in nature is maintained. On the one hand, simple models of interacting competitors cannot produce the stable persistence of very large ecological communities(1-5). On the other hand, neutral models(6-9), in which species do not interact and diversity is maintained by immigration and speciation, yield unrealistically small fluctuations in population abundance(10), and a strong positive correlation between a species' abundance and its age(11), contrary to empirical evidence. Models allowing for the robust persistence of large communities of interacting competitors are lacking. Here we show that very diverse communities could persist thanks to the stabilizing role of higher-order interactions(12,13), in which the presence of a species influences the interaction between other species. Although higher-order interactions have been studied for decades(14-16), their role in shaping ecological communities is still unclear(5). The inclusion of higher-order interactions in competitive network models stabilizes dynamics, making species coexistence robust to the perturbation of both population abundance and parameter values. We show that higher-order interactions have strong effects in models of closed ecological communities, as well as of open communities in which new species are constantly introduced. In our framework, higher-order interactions are completely defined by pairwise interactions, facilitating empirical parameterization and validation of our models.
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| 10. |
- Zook, Alexander E, et al.
(författare)
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Food webs : ordering species according to body size yields high degree of intervality
- 2011
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Ingår i: Journal of Theoretical Biology. - : Elsevier. - 0022-5193 .- 1095-8541. ; 271:1, s. 106-113
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Tidskriftsartikel (refereegranskat)abstract
- Food webs, the networks describing "who eats whom" in an ecosystem, are nearly interval, i.e. there is a way to order the species so that almost all the resources of each consumer are adjacent in the ordering. This feature has important consequences, as it means that the structure of food webs can be described using a single (or few) species' traits. Moreover, exploiting the quasi-intervality found in empirical webs can help build better models for food web structure. Here we investigate which species trait is a good proxy for ordering the species to produce quasi-interval orderings. We find that body size produces a significant degree of intervality in almost all food webs analyzed, although it does not match the maximum intervality for the networks. There is also a great variability between webs. Other orderings based on trophic levels produce a lower level of intervality. Finally, we extend the concept of intervality from predator-centered (in which resources are in intervals) to prey-centered (in which consumers are in intervals). In this case as well we find that body size yields a significant, but not maximal, level of intervality. These results show that body size is an important, although not perfect, trait that shapes species interactions in food webs. This has important implications for the formulation of simple models used to construct realistic representations of food webs.
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