The robustness of keystone indices in food webs

Summary1. Network analysis, a branch of discrete mathematics that quantifies the structure of links between a set of nodes, is emerging as a powerful methodology to approach complex ecological interactions. 2. There has been a rapidly increasing body of research targeting the topological description of trophic interactions. Here we categorize studies applying a topological approach to empirical trophic networks, with the aim of identifying recent trends and deficiencies in this approach to analyse trophic interactions.3. There were biases in the taxonomic groups addressed and in the methodological approaches used for data collection and analyses. Studies on antagonistic interactions were generally focused on a single kind of bipartite interaction, and most studies compared network attributes across time, ecosystems or treatments. 4. We encourage a broader use of both interlinked and unipartite networks that would allow for describing indirect effects of trophic interactions, as well as time series of networks across seasons and phenological states of organisms. We also noted shortages of studies identifying interaction structures across levels of organization, on the correspondence between network structure and function, and particularly of studies on the behaviour of trophic networks in the face of environmental perturbations, which could provide guidance for preserving ecological interactions.

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“…Few studies in our data base analysed the relationships between indices (e.g. Scotti, Podani & Jordán ; Fedor & Vasas ; Fortuna et al . ).…”

Section: Discussionmentioning

confidence: 99%

“…Few studies in our data base analysed the relationships between indices (e.g. Scotti, Podani & Jord an 2007;Fedor & Vasas 2009;Fortuna et al 2010). Moreover, studies relating network indices to node performance (assessed as processes rates, for example productivity, fitness, population dynamics) or to ecosystem services (e.g.…”

Section: Discussionmentioning

confidence: 99%

A categorization of recent network approaches to analyse trophic interactions

2013

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“…In addition, we could investigate the robustness of the proposed KS index to uncertainty and possible model construction errors. Structural indices for binary food webs, such as the mixed-trophic impact, were demonstrated to be robust to uncertainty (Fedor and Vasas 2009), so that the equivalent functional indices for weighted food webs, used in our approach, may be assumed to be robust as well. Yet, the development of a measure of robustness for functional indices of keystoneness, similar to the one applied to structural indices, would constitute interesting questions for future studies.…”

Section: Perspectives For Future Directions In Keystoneness Analysesmentioning

confidence: 99%

Keystone species: toward an operational concept for marine biodiversity conservation

Valls

Coll

Christensen

2015

Ecological Monographs

133

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Abstract. Various definitions and indices have been proposed in the literature to identify keystone species. In this study, we intended to make the concept of keystone species operational for marine biodiversity conservation. We used an exclusive definition of keystone species, based on the original concept of keystone predator, and derived a new functional index of keystoneness (KS) from an ecosystem-modeling approach. First, several KS indices were formulated, by combining measures of the mixed-trophic impact (MTI) and biomass of species. Then, a meta-analysis was performed, based on 101 published Ecopath food-web models, selected with a scoring method, and representative of the variety of marine ecosystems worldwide. The indices were applied to the models, and two statistical methods were compared to select the most promising KS index. Rank correlation tests were performed to assess the balance between the contribution of the impact and biomass components to the different KS indices. In addition, a classification tree was implemented, based on ecosystemspecific thresholds applied to the latter species traits, and used to confirm the identified keystone species. The selected index obtained the highest number of models with positive results from both the rank correlation tests and the classification tree. We also demonstrated the limitations of existing KS indices previously applied in the literature. Species were ranked according to their estimates of keystoneness with the selected KS index, so that potential keystone species were quantitatively identified in the 101 modeled food webs. The standardized modeling approach allowed for a comparison of the identified keystone species across models: cartilaginous fishes and toothed whales obtained the highest occurrences. Finally, the selected KS index was applied to the well-known case study of Prince William Sound (Alaska, USA). Potentially significant anthropogenic (fishing) impacts on keystone species were also considered and discussed. The operational methodology presented is directly applicable to marine food webs, and may be adapted to other (freshwater or terrestrial) systems.

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“…Of the many network indices that have been derived to identify keystone species , Fedor and Vasas 2009, Ortiz et al 2013, only a relatively small number take the direction of interactions into account (e.g., keystoneness index, mixed trophic impact) and even the value of some of these (e.g., number of dominated nodes) may be limited by their sensitivity to errors in food web structure (Fedor and Vasas 2009). In applying indices such as the (relatively robust) keystoneness index to the four-member motifs in Fig.…”

Section: Keystone Speciesmentioning

confidence: 99%

Relating food web structure to resilience, keystone status and uncertainty in ecological responses

et al. 2014

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Abstract. Food webs often include substructures that occur in much higher numbers than would be expected in random networks. These are referred to in the literature as network motifs. Here we explore how feedbacks within the most common food web motifs influence their responses to external factors such as environmental change or harvesting of species. We have used qualitative modelling approaches to demonstrate that simple three-and four-member motifs that include a closed feedback loop can exhibit a diverse range of qualitative responses, some of which are non-intuitive. The same outcomes are demonstrated to be emergent behaviors of larger food webs represented in complex ecosystem models. The sensitivity of ecological responses to small differences in food web motifs underlines the broader importance of structural uncertainty in ecological models. It is also argued that the resilience of species and their keystone status may be strongly influenced by their ecological role within particular motifs. Examples are provided from fisheries off southeastern Australian, where the slow recovery rates of some species have not previously been explained.

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The robustness of keystone indices in food webs

Cited by 27 publications

References 24 publications

A categorization of recent network approaches to analyse trophic interactions

A categorization of recent network approaches to analyse trophic interactions

Keystone species: toward an operational concept for marine biodiversity conservation

Relating food web structure to resilience, keystone status and uncertainty in ecological responses

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