Abstract
Predation, predation risk, and resource quality affect suites of prey traits that collectively impact individual fitness, population dynamics, and community structure. However, studies of multi‐trophic level effects generally focus on a single prey trait, failing to capture trade‐offs among suites of covarying traits that govern population responses and emergent community patterns. We used structural equation models (SEM) to summarize the non‐lethal and lethal effects of crayfish, Procambarus fallax, and phosphorus (P) addition, which affected prey food quality (periphyton), on the interactive effects of behavioral, morphological, developmental, and reproductive traits of snails, Planorbella duryi. Univariate and multivariate analyses suggested trade‐offs between production (growth, reproduction) and defense (foraging behavior, shell shape) traits of snails in response to non‐lethal crayfish and P addition, but few lethal effects. SEM revealed that non‐lethal crayfish effects indirectly limited per capita offspring standing stock by increasing refuge use, slowing individual growth, and inducing snails to produce thicker, compressed shells. The negative effects of non‐lethal crayfish on snails were strongest with P addition; snails increased allocation to shell defense rather than growth or reproduction. However, compared to ambient conditions, P addition with non‐lethal crayfish still yielded greater per capita offspring standing stock by speeding individual snail growth enabling them to produce more offspring that also grew faster. Increased refuge use in response to non‐lethal crayfish led to a non‐lethal trophic cascade that altered the spatial distribution of periphyton. Independent of crayfish effects, snails stimulated periphyton growth through nutrient regeneration. These findings illustrate the importance of studying suites of traits that reveal costs associated with inducing different traits and how expressing those traits impacts population and community level processes.
Highlights
Developmental and behavioral systems are integrated to yield suites of covarying traits that respond through trait plasticity to biotic and abiotic environmental cues
We propose that ignoring phenotypic trade-offs among suites of prey traits diminish the ability to predict prey population growth and community structure along nutrient and predator density gradients
Tanks were filled to 30 cm with well water on 30 May 2007; the day, we used a 2000-ml graduated cylinder modified with drain holes to add a 900-ml aliquot of fresh benthic periphyton to each tank collected from a nearby marsh and sorted to remove large mat-dwelling invertebrates and macrophyte stems
Summary
Developmental and behavioral systems are integrated to yield suites of covarying traits that respond through trait plasticity to biotic and abiotic environmental cues. Tollrian and Harvell 1999, Murdoch et al 2003, Werner and Peacor 2003, Preisser et al 2009) Both lethal and non-lethal impacts of predators cascade to resources eaten by prey producing indirect effects (e.g., trophic cascades) across trophic links (Turner and Mittelbach 1990, Schmitz et al 2000, Werner and Peacor 2003, Wojdak and Luttbeg 2005). Most of this work has focused on individual traits in consumers rather than the suites of prey traits that characterize plastic responses to environmental cues in these interaction webs (but see: Bronmark et al 2012, Hoverman and Relyea 2012). Because traits may be negatively correlated leading to trade-offs, consideration of single traits in isolation may fail to reveal the constraints or synergies of environmental drivers on primary consumers that determine indirect effects within a food web
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