| 1. |
- 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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| 2. |
- Jacob, Ute, et al.
(författare)
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The Role of Body Size in Complex Food Webs : A Cold Case
- 2011
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Ingår i: Advances in Ecological Research. - : Elsevier. - 0065-2504 .- 2163-582X. ; 45, s. 181-223
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Tidskriftsartikel (refereegranskat)abstract
- Human-induced habitat destruction, overexploitation, introduction of alien species and climate change are causing species to go extinct at unprecedented rates, from local to global scales. There are growing concerns that these kinds of disturbances alter important functions of ecosystems. Our current understanding is that key parameters of a community (e.g. its functional diversity, species composition, and presence/absence of vulnerable species) reflect an ecological network’s ability to resist or rebound from change in response to pressures and disturbances, such as species loss. If the food web structure is relatively simple, we can analyse the roles of different species interactions in determining how environmental impacts translate into species loss. However, when ecosystems harbour species-rich communities, as is the case in most natural systems, then the complex network of ecological interactions makes it a far more challenging task to perceive how species’ functional roles influence the consequences of species loss. One approach to deal with such complexity is to focus on the functional traits of species in order to identify their respective roles: for instance, large species seem to be more susceptible to extinction than smaller species. Here, we introduce and analyse the marine food web from the high Antarctic Weddell Sea Shelf to illustrate the role of species traits in relation to network robustness of this complex food web. Our approach was threefold: firstly, we applied a new classification system to all species, grouping them by traits other than body size; secondly, we tested the relationship between body size and food web parameters within and across these groups and finally, we calculated food web robustness. We addressed questions regarding (i) patterns of species functional/trophic roles, (ii) relationships between species functional roles and body size and (iii) the role of species body size in terms of network robustness. Our results show that when analyzing relationships between trophic structure, body size and network structure, the diversity of predatory species types needs to be considered in future studies.
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| 3. |
- O'Gorman, Eoin J., et al.
(författare)
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Interaction strength, food web topology and the relative importance of species in food webs.
- 2010
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Ingår i: Journal of Animal Ecology. - : Wiley-Blackwell Publishing Ltd.. - 0021-8790 .- 1365-2656. ; 79:3, s. 682-692
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Tidskriftsartikel (refereegranskat)abstract
- 1. We established complex marine communities, consisting of over 100 species, in large subtidal experimental mesocosms. We measured the strength of direct interactions and the net strength of direct and indirect interactions between the species in those communities, using a combination of theoretical and empirical approaches.2. Theoretical predictions of interaction strength were derived from the interaction coefficient matrix, which was parameterised using allometric predator–prey relationships. Empirical estimates of interaction strength were quantified using the ln-ratio, which measures the change in biomass density of species A in the presence and absence of species B.3. We observed that highly connected species tend to have weak direct effects and net effects in our experimental food webs, whether we calculate interaction strength theoretically or empirically.4. We found a significant correlation between our theoretical predictions and empirical estimates of direct effects and net effects. The net effects correlation was much stronger, indicating that our experimental communities were dominated by a mixture of direct and indirect effects.5. Re-calculation of the theoretical predictions of net effects after randomising predator and prey body masses did not affect the negative relationship with connectance.6. These results suggest that food web topology, which in this system is constrained by body mass, is overwhelmingly important for the magnitude of direct and indirect interactions and hence species importance in the face of biodiversity declines.
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| 4. |
- 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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