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

Abstract

The competition-defense tradeoff is a significant source of functional diversity in ecological communities. Here, we present a theoretical framework to describe the competition-defense tradeoff and apply it to a size-based model of a unicellular plankton community. Specifically, we investigate how the emergent community structure depends on the shape of the tradeoff, and on whether the cost of defense is paid for by a lowered resource affinity or by an elevated metabolic rate. The inclusion of defense affects the size distribution and trophic strategies of the emerging community dependent on environmental conditions (eutrophic versus oligotrophic) and leads to increased diversity in size and trophic strategy under eutrophic conditions. Eutrophic conditions allow for better-defended organisms than oligotrophic conditions. In most scenarios, competition-defense tradeoffs dampen trophic cascades in the seasonal cycle simulations, and increase the abundance of mixotrophs. We further demonstrate that it matters how the cost of defense is manifest (decreased affinity versus increased metabolic rate), and that it has a significant effect on the resulting plankton community (overall biomass, size and feeding strategy diversity), particularly when the efficiency of the defense increases in direct proportion to the investment. Our results demonstrate that the structure of the ecosystem crucially depends on details of the defense tradeoff. This finding highlights the importance of a mechanistic understanding of defense tradeoffs, e.g. obtained through experimental measurements of specific defense mechanisms.

Latitudinal Variation in Plankton Traits and Ecosystem Function

“…The model could in principle be extended with traits representing vacuole formation and developing a silica frustule, together with related trade-offs in terms of extra metabolic costs and silica dependence, and benefits from resource acquisition, reduction in predation pressure, and buoyancy regulation (Hansen & Visser, 2019). We expect that these traits would provide more benefit 10.1029/2020GB006564 Global Biogeochemical Cycles than phagotrophy during spring at high latitudes and allow big vacuolated cells covered with silica frustule (diatoms) to dominate during spring in high latitudes (Cadier et al, 2019). Another missing strategy is diazotrophy, that is, N 2 fixation.…”

Diatom defence: Grazer induction and cost of shell‐thickening

“…Predator–prey interactions are key in shaping ecosystem structure and function (Belgrad & Griffen, 2016; Creel, 2018; Lima, 1998). In the oceans, zooplankton predation is believed to be an important mechanism maintaining phytoplankton species diversity by allowing the coexistence of defence‐ and competition‐specialists, as demonstrated both theoretically (Cadier, Andersen, Visser, & Kiørboe, 2019; Ehrlich & Gaedke, 2018; Våge et al., 2018) and experimentally (Leibold, Hall, Smith, & Lytle, 2017; McCauley & Briand, 1979). Indeed, phytoplankton have evolved a large range of defence mechanisms, ranging from morphological to biochemical or behavioural (Pančić & Kiørboe, 2018; van Donk, Ianora, & Vos, 2011).…”

The effect of anthropogenic and environmental factors in coupled human‐natural systems: Evidence from Lake Zürich

“…Fish larvae feed on zooplankton, which migrates vertically in the water column to avoid predation during the day. Plankton, therefore, affects the pelagic food‐web, whose functioning and efficiency determines how much energy and biomass reaches high levels of the trophic chain (Barbier & Loreau, ; Cadier et al, ; Carpenter et al, ). Phytoplankton affects both zooplankton standing biomass due to trophic interactions, and the quality of fish habitat: nonedible phytoplankton biomass is degraded by heterotrophic bacteria causing anoxia in the hypolimnion, which has strong impacts on fish ecology (Vonlanthen et al, ).…”

“…Phytoplankton Richness and Evenness, and Zooplankton Richness are used as proxies for plankton biodiversity. Plankton biodiversity is supposed to influence fish stock biomass through trophic cascade effects, with influences on energy and biomass fluxes in the food‐web and eventually on fish growth and demography (Barbier & Loreau, ; Cadier, Andersen, Visser, & Kiørboe, ; Carpenter, Kitchell, & Hodgson, ). Specifically, plankton biodiversity is expected to influence fish stock biomass, as an ecosystem service, via three mechanisms (Drake, ).…”