DOI: 10.25338/b8d909
title: The effects of predation-risk on prey stoichiometry: A meta-analysis

description: A decade ago, the General Stress Paradigm (GSP) aimed to develop a
 predictive framework linking predator effects to ecosystem function. The
 GSP was based on the notion that animals, across taxa, exhibit similar
 physiological responses to predation risk that divert resources from
 growth and reproduction [which require N-rich biomolecules (i.e.,
 protein)] to emergency functions [which require C-rich biomolecules (e.g.,
 carbohydrates)]. The GSP predicts that stressed prey should have a greater
 dietary demand for C-rich resources, a higher body C:N ratio, and elevated
 N excretion. Now, ten years later, we aim to revisit the GSP— using
 quantitative meta-analysis to test the original predictions of the GSP and
 how 1) predator hunting mode, 2) multiple stressors, and 3) prey dietary
 shifts affect prey stoichiometric responses to predation-risk. Our dataset
 was consistent with previous work showing that predation-risk increases
 prey glucocorticoid levels and metabolic rates and decreases prey growth
 rates. We found that predation-risk tended to decrease the fat,
 carbohydrate, and protein content of prey bodies; increased the C:P and
 N:P of prey bodies; but had no effect on the C, N, P or C:N content of
 prey bodies. Additionally, we found no effect of predation risk on the N
 content of prey excretions. Prey responses to predation risk were
 unaffected by multiple stressors or the prey’s ability to shift their
 diet, but predator hunting mode did affect the nature of prey
 stoichiometric responses. Specifically, ambush predators decreased prey
 macronutrient content and suppressed prey growth; while active predators
 had no effect on prey macronutrient content and a smaller effect on prey
 growth than ambush predators.  The significant effects of
 predation risk were supported by robust fail-safe numbers, despite the
 high between comparison heterogeneity that was found in all analyses. Our
 findings highlight the need to expand the GSP framework to include more
 diverse taxa and ecosystems as well as other types of inducible defenses;
 while also considering predator traits and the mismatch between
 macronutrient content and prey stoichiometry.
description: We
 surveyed the literature using Web of Science and the following search
 terms, "predat* AND prey stoichiometry OR prey physiological stress
 OR prey nutritional geometry OR prey general stress paradigm OR prey
 physiological plasticity." The search was conducted on 10 June 2019.
 We used the preferred reporting practices outlined by PRISMA to structure
 our overall literature search (Moher et al. 2009). Our search identified
 435 potential manuscripts. For each potential manuscript, we read the
 abstract and determined if the study measured prey stoichiometric
 responses to predation-risk (including conspecific alarm cues). This screening yielded 51 manuscripts
 that we read in full to determine if they were eligible for inclusion in
 our quantitative meta-analysis (see Fig. 1). Studies were deemed eligible if they
 induced one or more measurement of prey stoichiometry (i.e., macronutrient
 or elemental composition) in the presence and absence of
 predation-risk. We targeted studies that measured the effects of
 predation-risk on: (i) the macronutrient composition, (ii) the elemental
 composition, and (iii) the elemental ratios of a prey’s body and waste
 materials. After reading 51 manuscripts in full, we had to exclude 24
 manuscripts because they either failed to address our objectives or were
 missing data (e.g., sample size, Fig. 1). From the 27 included
 manuscripts, we also
 extracted data on the effects of predation-risk on prey growth, foraging,
 assimilation efficiency, metabolic rate, RNA: DNA, and CORT concentrations
 when possible. We
 extracted these additional metrics because previous meta-analyses on
 predator effects have generated robust predictions for how predation-risk
 should affect these prey traits (see Preisser et al. 2005, Preisser and
 Bolnick 2008). Thus, by comparing the findings from our dataset to these
 pre-existing conclusions (based on larger datasets) we hoped to gain
 insight into how studies in our small dataset compare to the larger body
 of literature on predator-risk effects.
description: NA in predator hunting mode means study used conspecific cuses
 rather than direct predator cues. Unknown in predator hunting mode means
 we were unable to classify the predator's hunting mode based in the
 information provided in the study or from outside resources.