Trait‐dependency of trophic interactions in zooplankton food webs

Abstract

Anthropogenic change in the abundance or identity of dominant top predators may induce reorganizations in whole food webs. Predicting these reorganizations requires identifying the biological rules that govern trophic niches. However, we still lack a detailed understanding of the respective contributions of body size, behaviour (e.g. match between predator hunting mode and prey antipredator strategy), phylogeny and/or ontogeny in determining both the presence and strength of trophic interactions. Here, we address this question by measuring zooplankton numerical response to fish predators in lake enclosures. We compared the fit to zooplankton count data of models grouping zooplankters based either on 1) body sizes, 2) antipredator behaviour, 3) body size combined with antipredator behaviour or on 4) phylogeny combined with ontogeny (i.e. different life stages of copepods). Body size was a better predictor of zooplankton numerical response to fish than antipredator behaviour, but combining body size and behaviour provided even better predictions. Models based on phylogeny combined with ontogeny clearly outperformed those based on other zooplankton grouping rules, except when phylogeny was poorly resolved. Removing ontogenetic information plagued the predictive power of the highly‐resolved (genus‐level) phylogenetic grouping but not of medium‐resolved or poorly‐resolved phylogenetic grouping. Our results support the recent use of phylogeny as a superior surrogate for traits controlling trophic niches, and further highlight the added value of combining phylogeny with ontogenetic traits. Further improvements in our mechanistic understanding of how trophic networks are shaped are bound to uncovering the trophic traits captured by phylogeny and ontogeny, but that currently remain hidden to us.

Comparison of size‐structured and species‐level trophic networks reveals antagonistic effects of temperature on vertical trophic diversity at the population and species level

“…Alternatively, this may be explained by a strong inter‐specific variation in the link between body size and trophic ecology, which would break the body size dependency in trophic level. Indeed, not all interactions in our system are solely size‐dependent and specific to each species in our dataset (Allan and Castillo 2007, Hart and Reynolds 2008), which may prevent mapping size mediated effects of temperature at the population level onto the species level (Vincent et al 2020).…”

Energy transfer efficiency rather than productivity determines trophic cascades

“…2b). This may be explained by the physical and chemical characteristics of D. magna, making them better food sources for predators (Vincent et al 2020). Specifically, the lower motility of D. magna can increase the attack rate of predators (Rall et al 2012), and its high body nutrient concentration can increase the assimilation efficiency (DeMott et al 1998).…”

Vertical distribution patterns of zooplankton across a gradient of fish predation in boreal lakes

“…Zooplankton taxonomy and/or functional traits also play an important role in determining vulnerability to predation (Vincent et al, 2020), and are likely to play a key role in determining vertical distribution patterns. For example, Calanoida and Cyclopoida have good swimming abilities that allow them to flee predators (Drenner et al, 1978) while Holopedium glacialis (Ctenopoda) has a gelatinous capsule (Thorp & Covich, 2009) that reduces post‐encounter mortality (Stenson, 1987).…”