Simple models combining competition, defence and resource availability have broad implications in pelagic microbial food webs

Abstract

In food webs, interactions between competition and defence control the partitioning of limiting resources. As a result, simple models of these interactions contain links between biogeochemistry, diversity, food web structure and ecosystem function. Working at hierarchical levels, these mechanisms also produce self-similarity and therefore suggest how complexity can be generated from repeated application of simple underlying principles. Reviewing theoretical and experimental literature relevant to the marine photic zone, we argue that there is a wide spectrum of phenomena, including single cell activity of prokaryotes, microbial biodiversity at different levels of resolution, ecosystem functioning, regional biogeochemical features and evolution at different timescales; that all can be understood as variations over a common principle, summarised in what has been termed the 'Killing-the-Winner' (KtW) motif. Considering food webs as assemblages of such motifs may thus allow for a more integrated approach to aquatic microbial ecology.

Competition–defense tradeoff increases the diversity of microbial plankton communities and dampens trophic cascades

“…in eutrophic conditions, eutrophic conditions allow the existence of better defended organisms (Våge et al 2014(Våge et al , 2018, and co-existence is (slightly) more pronounced when the costs are in terms of reduced affinities rather than reduced growth (Ehrlich and 2018). In addition to the increase in diversity along the competition-defense dimension as explored by the simpler models, we here also find changes in diversity in sizes as well as in trophic strategies (i.e.…”

“…they are harnessed only in the presence of predation risk. Such phenotypic defense plasticity may have major impact on predator-prey interactions (van Someren Gréve et al 2019), populations dynamics (Kishida et al 2010), community structure (Miner et al 2005) and ecosystem function (Schmitz and Suttle 2001), and the effects may depend on whether the defense response is immediate (e.g. behavior) or delayed (e.g.…”

“…Size distribution, trophic strategies, defense strategies and food web structure are all emergent properties of the model, not prescribed. The plankton community we explore is therefore more realistic and complex than the simple food webs examined by Våge et al (2014Våge et al ( , 2018 and Ehrlich and Gaedke (2018) (Fig. 1c), but its structure is governed by simple rules and few parameters.…”

An empirical model of carbon flow through marine viruses and microzooplankton grazers

“…Our ecosystem model considers phytoplankton, viruses and microzooplankton each as homogeneous biomass pools, and disregards group‐, species‐ and strain‐specific interactions that may fundamentally influence ecosystem structure and function (Thingstad, ; Le Quere et al ., ; Follows et al ., ; Friedrichs et al ., ; Våge et al ., , ; Thingstad et al ., ; Weitz et al ., ). Viral infection and grazing rates are treated with Holling I encounter terms, overlooking the potential for grazing rate to saturate with prey density, consistent with the Holling II functional response (Holling, ).…”

“…Viruses and microzooplankton grazers are major sources of phytoplankton mortality throughout the world's oceans (Fuhrman, 1999;Calbet and Landry, 2004;Evans and Brussaard, 2012;Mojica et al, 2016;Våge et al, 2018). However, quantification of impacts of these ecological interactions and the resulting fate of carbon remains challenging Weitz and Wilhelm, 2012;Brum et al, 2015;Breitbart et al, 2018).…”