Abstract
The extent to which prey traits combine to influence the abundance of predators is still poorly understood, particularly for mixed predators in sympatry and in aquatic ecosystems. In this study, we characterise prey use and distribution in iconic bird (grey wagtails and Eurasian dippers) and fish species (brown trout and Atlantic salmon) to assess whether prey traits could predict populations of these four riverine predators. Specifically, we hypothesised that: 1) prey key traits would predict predator populations more effectively than 2) diversity of prey traits, 3) the taxonomic abundance or richness of prey (known as traditional or mass‐effect types of biodiversity) or 4) the prevailing environmental conditions. Combined predator population sizes were predicted better by a few key traits – specifically those revealing prey habitat use, size and drifting behaviour – than by prey diversity or prey trait diversity or environmental conditions. Our findings demonstrate that the complex relationships between prey assemblages and multiple predator species can be represented mechanistically when the key prey traits that govern encounter and consumption rates are identified. Given their apparent potential to reveal trophic relationships, and to complement more traditional measures of prey abundance, we advocate further development of trait‐based approaches in predator–prey research.
Highlights
Research into factors affecting the distribution and abundance of predators has been a perennial theme in ecology, focussing often on prey availability and, at least in single species systems, on the dynamics of predator–prey interactions (Volterra 1928, Lotka 1932, Lima 2002, Pintar and Resetarits 2017)
We used this database to assess the prey of wagtails, trout, salmon and dippers according to features that influence their availability to the predators, including behaviours and morphology; and features of lifehistory that determine the persistence of prey under various environmental conditions
Based on dietary data collected from the literature and using linear mixed-effect models (LMM), we examined how each of the four key trait prey groups (FG1, FG2, FG3, FG4) contributed to the diet of each of the four predators
Summary
Research into factors affecting the distribution and abundance of predators has been a perennial theme in ecology, focussing often on prey availability and, at least in single species systems, on the dynamics of predator–prey interactions (Volterra 1928, Lotka 1932, Lima 2002, Pintar and Resetarits 2017). Understanding the influence of prey traits on predator populations requires knowledge of 1) the ability of a prey species to persist in a given environment, and 2) their influence over predator populations while they are present in that environment. These traits can be grouped as ‘response traits’ and ‘effect traits’, respectively (Suding et al 2008). Combined with an ecosystem-level view and data on predator–prey abundances, trait-based approaches could yield insights into multispecies trophic relationships that are both realistic and potentially mechanistic (McGill et al 2006, Schmitz 2017). Few studies have used this approach at sufficient scale or with sufficient replication across sites to yield meaningful outcomes
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