Complexity and structural properties of food webs in the Barents Sea

Abstract

A food web topology describes the diversity of species and their trophic interactions, i.e. who eats whom, and structural analysis of food web topologies can provide insight into ecosystem structure and function. It appears simple, at first sight, to list all species and their trophic interactions. However, the very large number of species at low trophic levels and the impossibility to monitor all trophic interactions in the ocean makes it impossible to construct complete food web topologies. In practice, food web topologies are simplified by aggregating species into groups termed trophospecies. It is not clear though, how much simplified versions of food webs retain the structural properties of more detailed networks. Using the most comprehensive Barents Sea food web to date, we investigate the performance of methods to construct simplified food webs using three approaches: taxonomic, structural and regular clustering. We then evaluate how topological properties vary with the level of network simplification. Results show that alteration of food web structural properties due to aggregation are highly sensitive to the methodology used for grouping species and trophic links. In the specific case of the Barents Sea, we show that it is possible to preserve key structural properties of the original complex food web in simplified versions when using taxonomic or structural clustering combined with intermediate 25% linkage for trophic aggregation.

The role of marine mammals in the Barents Sea foodweb

“…This measure is not symmetrical as two species usually have different diet breadth and takes into account only a part of a species' direct neighbours (here the prey species). 2) The Jaccard index is a measure of structural equivalence and is defined as the ratio of shared prey and predators over the total number of prey and predators for both species (Lai et al, 2012;Olivier and Planque, 2017). This index considers all the direct neighbours (prey and predators).…”

“…Food web analyses are useful tools to address ecological role in ecosystems based on a species' links to prey and predators and on its position in the ecological network (Luczovich et al, 2003;Dunne, 2009;Jordán, 2009;Lai et al, 2012). Food webs provide a description of species interactions, ecosystem structure and functioning (Dunne et al, 2002a;Ings et al, 2008;Olivier and Planque, 2017) and determine how perturbations propagate and energy flows from basal to top species (Rooney et al, 2006). Trophic interactions are considered to be one of the main regulators of ecosystem dynamics (Link, 2002;Allesina and Pascual, 2008), and the food web structure can help evaluate ecosystem vulnerability.…”

Exploring the temporal variability of a food web using long‐term biomonitoring data

“…The information required to assess changes in food webs over time has often been available only for smaller networks (such as the Skipwith pond food web, Warren 1989; the Elm flux or the Arctic tundra food webs, Schoenly and Cohen 1991), or more aggregated groups of species (North Sea Ecopath food web, Mackinson and Daskalov 2007), although aggregation is known to alter food web structure and to make comparability across studies questionable (Allesina and Bondavalli 2003, Pinnegar et al 2005, Olivier and Planque 2017. recording the occurrence of all species and all of their interactions at each time step.…”

“…recording the occurrence of all species and all of their interactions at each time step. The information required to assess changes in food webs over time has often been available only for smaller networks (such as the Skipwith pond food web, Warren 1989; the Elm flux or the Arctic tundra food webs, Schoenly and Cohen 1991), or more aggregated groups of species (North Sea Ecopath food web, Mackinson and Daskalov 2007), although aggregation is known to alter food web structure and to make comparability across studies questionable (Allesina and Bondavalli 2003, Pinnegar et al 2005, Olivier and Planque 2017. Poorly and/or unevenly resolved dynamical food webs have also been used to investigate stability and food web dynamics (McCann 2000, Heath 2005), as well as management scenarios (Christensen and Pauly 1992, Ulanowicz 2004, Mackinson and Daskalov 2007.…”

Untitled

“…Functional groups for ecosystem models typical have been established using expert knowledge of the system and its inhabitants (Baretta et al, 1995;Olivier and Planque, 2017), while groups representing functional diversity have been created using trait or diet data and statistical classification methods (Petchey and Gaston, 2002). Diet data are commonly used to create functional groups of fishes in marine ecosystems, because diet can demonstrate resource partitioning between species, which is a key indicator of interspecific competition (Colloca et al, 2010;Sala and Ballesteros, 1997).…”