Conflicting effects of predator cue and ocean acidification on the mussel Mytilus coruscus byssus production

Understanding the impact of ocean acidification and warming on communities and ecosystems is a researcher priority. This can only be achieved through a combination of experimental and field approaches that would allow developing a mechanistic understanding of impacts across level of biological organizations. Surprisingly, most published studies are still focusing on single species responses with little consideration for interspecific interactions. In this study, the impacts of a 3 days exposure to three parameters (temperature, pH, and presence/absence of the predator cue of the crab Charybdis japonica) and their interactions on an ecologically important endpoint were evaluated: the byssus production of the mussel Mytilus coruscus. Tested temperatures (25°C and 30°C) were within the present range of natural variability whereas pH (8.1, 7.7, and 7.4) covered present as well as near-future natural variability. As expected, the presence of the crab cue induced an antipredator response in Mytilus coruscus (significant 10% increase in byssus secretion rate, 22% increase in frequency of shed byssus, and 30% longer byssus). Decreased pH but not temperature had a significant negative impact on the same endpoints (up to a 17% decrease in byssus secretion rate, 40% decrease in frequency of shed byssus, and 10% shorter byssus at pH 7.3 as compared with pH 8.1) with no significant interactions between the three tested parameters. In this study, it has been hypothesized that pH and predator cue have different modes of action and lead to conflicting functional responses (escape response versus stronger attachment). Functional consequences for ecosystem dynamics still need to be investigated.

Interactive effects of ocean acidification and rising sea temperatures alter predation rate and predator selectivity in reef fish communities

Ocean warming and acidification are serious threats to marine life. While each stressor alone has been studied in detail, their combined effects on the outcome of ecological interactions are poorly understood. We measured predation rates and predator selectivity of two closely related species of damselfish exposed to a predatory dottyback. We found temperature and CO2 interacted synergistically on overall predation rate, but antagonistically on predator selectivity. Notably, elevated CO2 or temperature alone reversed predator selectivity, but the interaction between the two stressors cancelled selectivity. Routine metabolic rates of the two prey showed strong species differences in tolerance to CO2 and not temperature, but these differences did not correlate with recorded mortality. This highlights the difficulty of linking species-level physiological tolerance to resulting ecological outcomes. This study is the first to document both synergistic and antagonistic effects of elevated CO2 and temperature on a crucial ecological process like predator-prey dynamics.

Food availability and predation risk, rather than intrinsic attributes are the main factors shaping the reproductive decisions of a long-lived predator

Funded by Natural Research Limited Natural Environment Research Council studentship. Grant Numbers: NE/J500148/1, NE/F021402/1

Predator-induced stress makes the pesticide carbaryl more deadly to gray treefrog tadpoles (Hyla versicolor)

Global declines in amphibians likely have multiple causes, including widespread pesticide use. Our knowledge of pesticide effects on amphibians is largely limited to short-term (4-d) toxicity tests conducted under highly artificial conditions to determine lethal concentrations (LC50). We found that if we used slightly longer exposure times (10–16 d), low concentrations of the pesticide carbaryl (3–4% of LC504-d) killed 10–60% of gray treefrog (Hyla versicolor) tadpoles. If predatory cues also were present, the pesticide became 2–4 times more lethal, killing 60–98% of tadpoles. Thus, under more realistic conditions of increased exposure times and predatory stress, current application rates for carbaryl can potentially devastate gray treefrog populations. Further, because predator-induced stress is ubiquitous in animals and carbaryl's mode of action is common to many pesticides, these negative impacts may be widespread in nature.

The contribution of trait-mediated indirect effects to the net effects of a predator

Many prey modify traits in response to predation risk and this modification of traits can influence the prey's resource acquisition rate. A predator thus can have a “nonlethal” impact on prey that can lead to indirect effects on other community members. Such indirect interactions are termed trait-mediated indirect interactions because they arise from a predator's influence on prey traits, rather than prey density. Because such nonlethal predator effects are immediate, can influence the entire prey population, and can occur over the entire prey lifetime, we argue that nonlethal predator effects are likely to contribute strongly to the net indirect effects of predators (i.e., nonlethal effects may be comparable in magnitude to those resulting from killing prey). This prediction was supported by an experiment in which the indirect effects of a larval dragonfly (Anax sp.) predator on large bullfrog tadpoles (Rana catesbeiana), through nonlethal effects on competing small bullfrog tadpoles, were large relative to indirect effects caused by density reduction of the small tadpoles (the lethal effect). Treatments in which lethal and nonlethal effects of Anax were manipulated independently indicated that this result was robust for a large range of different combinations of lethal and nonlethal effects. Because many, if not most, prey modify traits in response to predators, our results suggest that the magnitude of interaction coefficients between two species may often be dynamically related to changes in other community members, and that many indirect effects previously attributed to the lethal effects of predators may instead be due to shifts in traits of surviving prey.

Energy and nutrient dynamics of predator and prey arthropod populations in a grassland eco-system

Based upon a dissertation by R. I. Van Hook to the Graduate Council of Clemson University in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

Predator control - why and how,

Mode of access: Internet.

A study of predator control on Valcour Island.

Pittman-Robertson project 1-R, Supplement 1.

Predator species identification from saliva at kill sites with limited remains

Thesis (Master's)--University of Washington, 2016-06

Predator-mediated phenotypic plasticity in tadpoles of the striped marsh frog, Limnodynastes peronii

We tested the phenotypic responses of larval striped marsh frogs (Limnodynastes peronii) to the odonate nymph predator, Aeshna brevistyla. When reared in the presence of dragonfly nymphs feeding upon conspecifics of L. peronii larvae the tadpoles showed a strong change in morphology. Morphological changes included an increase in total tail height, but also an unexpected marked change in head-body shape. In addition, we examined how tadpole development, as well as mass and length at metamorphosis, was affected by exposure to dragonfly nymphs. Larval development of L. peronii was strongly influenced by exposure to the predatory behaviour of dragonfly nymphs. Predator-induced tadpoles had significantly slower developmental rates than control larvae. Although metamorphs of non-exposed L. peronii were approximately 33% lighter than predator-exposed metamorphs and possessed lower jump distances, after adjusting for mass there was no difference in jump distance. The newly described morphological response may assist in more accurately relating morphological plasticity to fitness.

Predator-specific changes in the morphology and swimming performance of larval Rana lessonae

1. We investigated the morphological responses of larval Rana lessonae to the presence of two predators with substantially different prey-detection and capture techniques; larval dragonflies (Aeshna cyanea) and the Pumpkinseed Sunfish (Lepomis gibossus). 2. We also examined the functional implications of any predator-induced morphological variation on their swimming ability by assessing performance during the initial stages of a startle response. 3. We found the morphological responses of larval R. lessonae were dependent on the specific predator present. Tadpoles raised in the presence of dragonfly larvae preying upon conspecific tadpoles developed total tail heights 5.4% deeper and tail muscles 4.7% shallower than tadpoles raised in a non-predator environment, while tadpoles raised with sunfish possessed tails 2% shallower and tail muscles 2.5% higher than non-predator-exposed tadpoles. 4. Predator-induced morphological variation also significantly influenced swimming performance. Tadpoles raised with sunfish possessed swimming speeds 9.5 and 14.6% higher than non- and dragonfly predator groups, respectively. 5. Thus, the expression of these alternative predator-morphs leads to a functional trade-off in performance between the different environments.

Predator-induced phenotypic plasticity in tadpoles: extension or innovation?

Phenotypic plasticity, the ability of a trait to change as a function of the environment, is central to many ideas in evolutionary biology. A special case of phenotypic plasticity observed in many organisms is mediated by their natural predators. Here, we used a predator-prey system of dragonfly larvae and tadpoles to determine if predator-mediated phenotypic plasticity provides a novel way of surviving in the presence of predators (an innovation) or if it represents a simple extension of the way noninduced tadpoles survive predation. Tadpoles of Limnodynastes peronii were raised in the presence and absence of predation, which then entered a survival experiment. Induced morphological traits, primarily tail height and tail muscle height, were found to be under selection, indicating that predator-mediated phenotypic plasticity may be adaptive. Although predator-induced animals survived better, the multivariate linear selection gradients were similar between the two tadpole groups, suggesting that predator-mediated phenotypic plasticity is an extension of existing survival strategies. In addition, nonlinear selection gradients indicated a cost of predator-induced plasticity that may limit the ability of phenotypic plasticity to enhance survival in the presence of predators.