Coupled changes in traits and biomasses cascading through a tritrophic plankton food web

Abstract

Trait-based approaches have broadened our understanding of how the composition of ecological communities responds to environmental drivers. This research has mainly focussed on abiotic factors and competition determining the community trait distribution, while effects of trophic interactions on trait dynamics, if considered at all, have been studied for two trophic levels at maximum. However, natural food webs are typically at least tritrophic. This enables indirect interactions of traits and biomasses among multiple trophic levels leading to underexplored effects on food web dynamics. Here, we demonstrate the occurrence of mutual trait adjustment among three trophic levels in a natural plankton food web (Lake Constance) and in a corresponding mathematical model. We found highly recurrent seasonal biomass and trait dynamics, where herbivorous zooplankton increased its size, and thus its ability to counter phytoplankton defense, before phytoplankton defense actually increased. This is contrary to predictions from bitrophic systems where counter-defense of the consumer is a reaction to prey defense. In contrast, counter-defense of carnivores by size adjustment followed the defense of herbivores as expected. By combining observations and model simulations, we show how the reversed trait dynamics at the two lower trophic levels result from a "trophic biomass-trait cascade" driven by the carnivores. Trait adjustment between two trophic levels can therefore be altered by biomass or trait changes of adjacent trophic levels. Hence, analyses of only pairwise trait adjustment can be misleading in natural food webs, while multitrophic trait-based approaches capture indirect biomass-trait interactions among multiple trophic levels.

Top predators govern multitrophic diversity effects in tritrophic food webs

“…In this study, we want to advance our understanding of how functional diversity affects ecosystem functioning in model communities by including a diverse third trophic level. Although it has often been highlighted how important the effects of the third trophic level on ecosystem functions are (Bruno and O'Connor 2005, Duffy et al 2007, Abdala‐Roberts et al 2019, Daam et al 2019, Ehrlich and Gaedke 2020), relatively few studies have attempted to take these effects into account explicitly. Ceulemans et al (2019) showed that functional diversity increases the biomass production, temporal stability, and biomass transfer efficiency to higher trophic levels of a tritrophic food web, when diversity is increased simultaneously at all three trophic levels.…”

Toward trait‐based food webs: Universal traits and trait matching in planktonic predator–prey and host–parasite relationships

“…The different feeding strategies such as passive (filter) or active (ambush) feeding can also be included to better characterize the trophic interaction (Wirtz 2012). The ingested prey is then converted to zooplankton biomass with a certain biomass conversion efficiency which can be different for different prey but often assumed the same (Ehrlich and Gaedke 2020).…”

“…As with most predator–prey interactions, the interaction between a phytoplankter and a zooplankter includes several processes, including prey encounter, selection, capture, ingestion and digestion (Flynn and Mitra 2016) and each of these processes are influenced by the interacting traits of both predator and prey. There are numerous modeling studies describing phytoplankton–zooplankton interactions that range in their generality and complexity (Banas 2011; Ehrlich and Gaedke 2020; Serra‐Pompei et al 2020). We provide a very brief overview here but the detailed descriptions of the different models can be found elsewhere (Tirok and Gaedke 2010; Serra‐Pompei et al 2020).…”

“…Some of the models of predator–prey interactions specifically focus on how traits change as a result of such interactions (Tirok and Gaedke 2010; Banas 2011; Ehrlich and Gaedke 2020). In a strict sense, those are “trait‐based” models, in contrast to models that simply incorporate traits (most models) (Klausmeier et al 2020).…”

Top predators govern multitrophic diversity effects in tritrophic food webs

“…In this study, we want to advance our understanding of how functional diversity affects ecosystem functioning in model communities by including a diverse third trophic level. While it has often been highlighted how important the effects of the third trophic level on ecosystem functions are (Bruno and O’Connor, 2005; Duffy et al, 2007; Daam et al, 2019; Abdala-Roberts et al, 2019; Ehrlich and Gaedke, 2020), relatively few studies have attempted to explicitly take these effects into account. Ceulemans et al (2019) showed that functional diversity increases the biomass production, temporal stability, and biomass transfer efficiency to higher trophic levels of a tritrophic food web, when diversity is increased simultaneously at all three trophic levels.…”