Details of production of water-borne chemical risk cues for Experiment 3 and a table with details of experimental cue treatments, sources of risk cues associated with Bythotrephes predation, and the cue effects being tested for with each treatment in Experiment 3.
We report measurements of the thermal conductivity in a magnetic field on single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. Unlike in sintered samples, the zero-field thermal conductivity of these crystals above the superconducting transition temperature shows a marked decrease with increasing temperature, demonstrating the importance of phonon-phonon processes and the high quality of the crystals. We find that the thermal conductivity \ensuremath{\kappa} is very sensitive to the presence of fluxoids which are strong scatterers of phonons. The degradation of \ensuremath{\kappa} is particularly large when the magnetic field H is oriented perpendicular to the Cu-O planes. The anisotropic behavior of \ensuremath{\kappa}(H) is in qualitative agreement with a geometric argument based on the anisotropy of the superconducting coherence length. We detect hysteresis at the level of several percent in the dependence of \ensuremath{\kappa} on the field.
Abstract Defensive traits are hypothesized to benefit prey by reducing predation risk from a focal predator but come at a cost to the fitness of the prey. Variation in the expression of defensive traits is seen among individuals within the same population, and in the same individual in response to changes in the environment (i.e., phenotypically plastic responses). It is the relative magnitude of the cost and benefit of the defensive trait that underlies the defensive trait expression and its consequences to the community. However, whereas the cost has received much attention in ecological research, the benefit is seldom examined. Even in a defensive trait as extensively studied as vigilance, there are few studies of the purported benefit of the behavior, namely that vigilance enhances survival. We examined whether prey vigilance increased survival and quantified that benefit in a natural system, with white‐tailed deer ( Odocoileus virginianus ) experiencing unmanipulated levels of predation risk from Florida panther ( Puma concolor coryi ). Deer that spent more time vigilant (as measured by head position using camera trap data) had a higher probability of survival. Indeed, an individual deer that was vigilant 75% of the time was more than three times as likely to be killed by panthers over the course of a year than a deer that was vigilant 95% of the time. Our results therefore show that within‐population variation in the expression of a defensive trait has profound consequences for the benefit it confers. Our results provide empirical evidence supporting a long‐held but seldom‐tested hypothesis, that vigilance is a behavior that reduces the probability of predation and quantifies the benefit of this defensive trait. Our work furthers an understanding of the net effects of a trait on prey fitness and predator–prey interactions, within‐population variation in traits, and predation risk effects.
We present a framework for explaining variation in predator invasion success and predator impacts on native prey that integrates information about predator–prey naïveté, predator and prey behavioral responses to each other, consumptive and non-consumptive effects of predators on prey, and interacting effects of multiple species interactions. We begin with the 'naïve prey' hypothesis that posits that naïve, native prey that lack evolutionary history with non-native predators suffer heavy predation because they exhibit ineffective antipredator responses to novel predators. Not all naïve prey, however, show ineffective antipredator responses to novel predators. To explain variation in prey response to novel predators, we focus on the interaction between prey use of general versus specific cues and responses, and the functional similarity of non-native and native predators. Effective antipredator responses reduce predation rates (reduce consumptive effects of predators, CEs), but often also carry costs that result in non-consumptive effects (NCEs) of predators. We contrast expected CEs versus NCEs for non-native versus native predators, and discuss how differences in the relative magnitudes of CEs and NCEs might influence invasion dynamics. Going beyond the effects of naïve prey, we discuss how the 'naïve prey', 'enemy release' and 'evolution of increased competitive ability' (EICA) hypotheses are inter-related, and how the importance of all three might be mediated by prey and predator naïveté. These ideas hinge on the notion that non-native predators enjoy a 'novelty advantage' associated with the naïveté of native prey and top predators. However, non-native predators could instead suffer from a novelty disadvantage because they are also naïve to their new prey and potential predators. We hypothesize that patterns of community similarity and evolution might explain the variation in novelty advantage that can underlie variation in invasion outcomes. Finally, we discuss management implications of our framework, including suggestions for managing invasive predators, predator reintroductions and biological control.
Predators can have a large influence on their prey through induced changes in prey phenotype. Such “nonlethal” predator effects have been abundantly demonstrated empirically in both terrestrial and aquatic systems. But the extent to which changes in species traits alter short-term responses such as growth rate or probability of survival is not clear. Here we develop models to examine the nonlethal effects of predators on prey growth. Our analyses illustrate how the nonlethal effects of predators on individual prey growth depend on environmental context; e.g., factors such as focal species density, competitor density, resource dynamics, and the timescale over which the interactions occur. This context dependence arises because of complex interactions of three mechanisms; (1) the direct negative effect of induced reduction in foraging rates, which is opposed by (2) the potential positive effects of reductions in intra- and interspecific competition, and (3) resource responses to reduced foraging. We present new empirical work, and review previous work, on larval-anuran growth that is in general support of model predictions. The framework presented here can serve to facilitate the design and interpretation of experimental results and predict how the nonlethal predator effect on prey growth in natural systems will vary over time and space.
Summary Individuals can show positive correlations in performance (e.g. growth and reproduction) through time beyond the effects of size or age. This ‘performance autocorrelation’ has been attributed previously to traits that differ among individuals or to extrinsic generators of environmental heterogeneity. A model of mobile consumers on a dynamic resource showed that consumer foraging gave rise to resource heterogeneity that in turn generated autocorrelation in growth in consumers. Resource heterogeneity and growth autocorrelation were most pronounced when consumers were poorer foragers, moving locally and with an imperfect ability to identify the highest resource cells. The model predicted that lowered population density enhanced resource heterogeneity and the strength of growth autocorrelation. Consistent with model predictions, an experiment with tidepool limpets demonstrated that autocorrelation in growth changed with population density, with individuals in lower density tidepools showing stronger temporal correlations in growth. Our model and empirical results contrast with those of previous studies with plants, where dominance and suppression increases with increasing density. Our results suggest that growth autocorrelation can occur without invoking size‐dependent advantages, intrinsic trait differences or extrinsic generators of environmental heterogeneity.
Many prey modify behaviour in response to predation risk and this modification frequently leads to a foraging rate reduction. Although this reduction can have a clear direct negative effect on prey growth rate, theory predicts that a net positive effect can occur when the combined reduction in foraging by the entire population leads to a large increase in resource level. Here, I present experimental results that corroborate this counterintuitive prediction: the predation threat of ‘nonlethal’ caged larval dragonflies ( Anax longipes ) caused a net increase in small bullfrog ( Rana catesbeiana ) growth. A behavioural response (i.e. a reduction in activity level and microhabitat usage) was likely to have negatively affected growth, but was offset by a positive effect on growth from a large increase in resource levels (measured using a bioassay). Further, the positive Anax effect was dependent on nutrient level, illustrating the role of the resource response magnitude. Results of this study are discussed in the context of studies in which Anax had the opposite (i.e. negative) effect on tadpole growth. Predator‐induced modifications in prey behaviour can have large negative or positive effects on prey growth, the sign and magnitude of which are dependent on relative species density and resource dynamics.
