Can biomass distribution across trophic levels predict trophic cascades?

Abstract

The biomass distribution across trophic levels (biomass pyramid) and cascading responses to perturbations (trophic cascades) are archetypal representatives of the interconnected set of static and dynamical properties of food chains. A vast literature has explored their respective ecological drivers, sometimes generating correlations between them. Here we instead reveal a fundamental connection: both pyramids and cascades reflect the dynamical sensitivity of the food chain to changes in species intrinsic rates. We deduce a direct relationship between cascades and pyramids, modulated by what we call trophic dissipation – a synthetic concept that encodes the contribution of top‐down propagation of consumer losses in the biomass pyramid. Predictable across‐ecosystem patterns emerge when systems are in similar regimes of trophic dissipation. Data from 31 aquatic mesocosm experiments demonstrate how our approach can reveal the causal mechanisms linking trophic cascades and biomass distributions, thus providing a road map to deduce reliable predictions from empirical patterns.

Primary production in subsidized green-brown food webs

“…Estimations for how much production is lost to self-regulation are basically non-existent. It has been suggested that self-regulation and predation coefficients are roughly proportional for predators (Polis et al, 1989;Galiana et al, 2021). Assuming self-regulation and predation coefficients as equal (r C = q C ), renders self-regulation fractions of ρ CC = 1.0 for the aquatic and ρ CC = 0.067 for the terrestrial ecosystem (see calculation in the Parameter derivation subsection).…”

“…Subsidies provided from below, by influx of nutrients or direct provision to primary producers, propagates up to consumer species, increasing the overall biomass and altering the shape of biomass distribution in the food web (Hines et al, 2006). Predator subsidies lead to pressure on the herbivores they consume, and can lead to trophic cascades where primary producers are released from herbivory pressure due to predation (Leroux and Loreau, 2008;Newsome et al, 2015;Galiana et al, 2021). Hence, subsidies can cause positive albeit indirect effects on primary production via trophic interactions, but outcomes of such combined horizontal and vertical effects of subsidies in green-brown food webs are poorly explored.…”

Primary productivity in subsidized green-brown food webs

“…Estimations for how much production is lost to self-regulation are virtually nonexistent. It has been suggested that for predators, self-regulation and predation coefficients are roughly proportional (Polis et al, 1989;Galiana et al, 2021). Assuming self-regulation and predation coefficients as equal (r C = q C ), renders self-regulation fractions of ρ CC = 1.0 for the aquatic and ρ CC = 0.067 for the terrestrial ecosystem (see calculation in the Parameter derivation subsection).…”

“…Subsidization from below, by influx of nutrients or direct subsidization of primary producers, propagates up to consumer species, increasing the overall biomass and the shape of biomass distribution in the food web (Hines et al, 2006). Input of predators leads to pressure on the herbivores they consume, and can lead to trophic cascades where primary producers are released from herbivory pressure due to predation (Leroux & Loreau, 2008;Newsome et al, 2015;Galiana et al, 2021). Hence, subsidies can cause positive albeit indirect effects on primary production via trophic interactions, but outcomes of such combined horizontal and vertical effects of subsidies in green-brown food webs are poorly explored .…”

Energy transfer efficiency rather than productivity determines trophic cascades

“…For instance, food webs often involve many less edible plants (Oksanen & Oksanen 2000) or anti-predative herbivores (Degerman et al 2018), which can significantly hamper vertical energy flow to apex predators (Stiboret al 2004). Inefficiency in energy transfer can significantly influence the biomass distribution of food webs (de Ruiter et al1995;McCauley et al 2018;Barbier & Loreau 2019) and thereby alter the strength of trophic cascades (Heath et al 2014;Galiana et al 2021). In particular, too low energy transfer may decouple biomass production at higher trophic levels from primary production, violating assumptions underlying the productivity hypothesis (Brett & Goldman 1997;Davis et al2010).…”