Predator‐induced changes in dissolved organic carbon dynamics

The fate of dissolved organic carbon (DOC) is partly determined by its availability to microbial degradation. Organisms at upper trophic levels could influence the bioavailability of DOC via cascading effects on primary producers and bacteria. Here we experimentally tested whether the presence of fish in aquatic food webs can indirectly affect the composition of the DOC pool. We found that fish had strong positive effects on phytoplankton biomass that affected the dynamics of DOC composition. Specifically, fish increased protein‐like, algae‐derived DOC mid‐experiment, concurrent with the strongest fish‐induced increase in phytoplankton biomass. Fish also increased bacterial abundance, altered the community composition and diversity of bacteria, and temporarily increased DOC compounds with fluorescence properties indicative of microbially‐reprocessed organic matter. Overall, our experiment revealed that fish can positively influence the substrate (algae‐produced DOC) and the key players (bacteria) of the microbial carbon pump. Consequently, fish could contribute to carbon sequestration by stimulating both the production of bioavailable DOC and the microbial degradation of bioavailable to persistent DOC. We propose this as a novel mechanism whereby the loss of predators from global ecosystems could alter carbon cycling.     

Predator‐induced phenotypic plasticity in an arid‐adapted tropical tadpole

Adaptive phenotypic plasticity is widespread and involves diverse phenotypes. Key environmental stressors, such as predation risk, can simultaneously induce changes in multiple traits, but the magnitude of response is dependent upon the environmental conditions. Species that utilize temporary ponds are expected to exhibit stronger predator‐induced responses in the form of morphology than behaviour (i.e. reduced activity) to meet the demands of rapid development by maintaining high foraging activity while reducing predation risk via morphologically plastic traits. In a laboratory experiment, I examined the effects of predator chemical cues and conspecific alarm cues on activity, development and morphology on Leptodactylus bufonius tadpoles. This species has terrestrial oviposition and completes the early part of its development outside of ephemeral and temporary ponds in the Gran Chaco ecoregion of South America. Tadpoles in the predator treatments exhibited both behavioural and morphological predator‐induced plastic responses. Tadpoles tended to possess shorter, deeper tails when exposed to predators. The greatest reduction in activity was observed in tadpoles exposed to both predator and conspecific alarm cues, which subsequently resulted in the slowest development. Temporary and ephemeral pond adapted species with terrestrial oviposition may capitalize on a head start in development by being able to afford reduced growth rates via a reduction in activity. This may occur when the constraints imposed by pond hydroperiod (e.g. risk of pond drying) are relaxed when compared with species with aquatic oviposition, which must undergo all stages of development during the pond's hydroperiod. Thus, in addition to the predator and hydroperiod gradients, examining phenotypically plastic responses along a ‘terrestriality gradient’ in a comparative framework would provide insights as to the costs and benefits of increasing terrestriality in anuran reproductive modes to environmental stressors.     

Predator–prey interactions in a grassland food chain vary with temperature and food quality

Because species interactions are often context‐dependent, abiotic factors such as temperature and biotic factors such as food quality may alter species interactions with potential consequences to ecosystem structure and function. For example, altered predator–prey interactions may influence the dynamics of trophic cascades, affecting net primary production. In a three‐year field experiment, we manipulated a plant–grasshopper–spider food chain in mesic tallgrass prairie to investigate the effects of temperature and food quality on grasshopper performance, and to understand the direct and indirect tritrophic interactions that contribute to trophic cascades. Because spiders are active at cooler temperatures than grasshoppers in our system, we hypothesized that predator effects would be strongest in cooled treatments, and weakest in warmed treatments. Grasshopper spider interactions were highly context‐dependent and varied significantly with food quality, temperature treatment and year. Spiders most often reduced grasshopper survival in the cooled and ambient temperature treatments, but had little to no effect on grasshopper survival in the warmed treatments, as hypothesized. In some years, plants compensated for grasshopper herbivory and trophic cascades were not observed despite significant effects of predators on grasshopper survival. However, in the year they were observed, trophic cascades only occurred in cooled treatments where predator effects on grasshoppers were strongest. Predicting ecosystem responses to climate change will require an understanding of how temperature influences species interactions. Our results demonstrate that changes in daily temperature regimes can alter predator–prey interactions among arthropods with consequences for ecosystem processes such as primary production and the relative importance of top–down and bottom–up processes.     

Predator‐induced selection on urchin activity level depends on urchin body size

Temporally consistent individual differences in behavior impact many ecological processes. We simultaneously examined the effects of individual variation in prey activity level, covering behavior, and body size on prey survival with predators using an urchin–lobster system. Specifically, we tested the hypothesis that slow‐moving purple sea urchins (Strongylocentrotus purpuratus) and urchins who deploy extensive substrate (pebbles and stones) covering behavior will out‐survive active urchins that deploy little to no covering behavior when pitted against a predator, the California spiny lobster (Panulirus interruptus). We evaluated this hypothesis by first confirming whether individual urchins exhibit temporally consistent differences in activity level and covering behavior, which they did. Next, we placed groups of four urchins in mesocosms with single lobster and monitored urchin survival for 108 hr. High activity level was negatively associated with survival, whereas urchin size and covering behavior independently did not influence survival. The negative effect of urchin activity level on urchin survival was strong for smaller urchins and weaker for large urchins. Taken together, these results suggest that purple urchin activity level and size jointly determine their susceptibility to predation by lobsters. This is potentially of great interest, because predation by recovering lobster populations could alter the stability of kelp forests by culling specific phenotypes, like foraging phenotypes, from urchin populations.     

Predator‐induced morphological defences as by‐products of prey behaviour: a review and prospectus

Predator‐induced morphological defences (PIMDs) are ubiquitous. Many PIMDs may be mediated by prey behaviour rather than directly cued by predators. A survey of 92 studies indicated 40 that quantified prey behaviour, all of which document positive associations between defence production and activity reduction. Thus, PIMDs are associated with changes in prey activity, which could have caused the morphological change. We propose two possible mechanisms: 1) decreased activity reduces feeding rate, resulting in lower growth and morphological change; and 2) activity reduction conserves energy, which is reallocated for growth, subsequently changing morphology. Resource availability also causes similar morphological change to predator presence, suggesting confounding effects of resources and predators with current methodology. Future studies should estimate food ingestion, assimilation efficiency, and growth rate in the presence and absence of predators, crossing predator presence with resource levels. Not all PIMDs will be behaviourally‐mediated, but consideration of causal linkages between prey behaviour and PIMDs is warranted.     

Variation in context‐dependent foraging behavior across pollinators

Pollinator foraging behavior has direct consequences for plant reproduction and has been implicated in driving floral trait evolution. Exploring the degree to which pollinators exhibit flexibility in foraging behavior will add to a mechanistic understanding of how pollinators can impose selection on plant traits. Although plants have evolved suites of floral traits to attract pollinators, flower color is a particularly important aspect of the floral display. Some pollinators show strong innate color preference, but many pollinators display flexibility in preference due to learning associations between rewards and color, or due to variable perception of color in different environments or plant communities. This study examines the flexibility in flower color preference of two groups of native butterfly pollinators under natural field conditions. We find that pipevine swallowtails (Battus philenor) and skippers (family Hesperiidae), the predominate pollinators of the two native Texas Phlox species, Phlox cuspidata and Phlox drummondii, display distinct patterns of color preferences across different contexts. Pipevine swallowtails exhibit highly flexible color preferences and likely utilize other floral traits to make foraging decisions. In contrast, skippers have consistent color preferences and likely use flower color as a primary cue for foraging. As a result of this variation in color preference flexibility, the two pollinator groups impose concordant selection on flower color in some contexts but discordant selection in other contexts. This variability could have profound implications for how flower traits respond to pollinator‐mediated selection. Our findings suggest that studying dynamics of behavior in natural field conditions is important for understanding plant–pollinator interactions.     

Optimal diving behaviour for foraging in relation to body size

Overall, large animals dive longer and deeper than small animals; however, after the difference in body size is taken into account, smaller divers often tend to make relatively longer dives. Neither physiological nor theoretical explanations have been provided for this paradox. This paper develops an optimal foraging diving model to demonstrate the effect of body size on diving behaviour, and discusses optimal diving behaviour in relation to body size. The general features of the results are: (1) smaller divers should rely more heavily on anaerobic respiration, (2) larger divers should not always make longer dives than smaller divers, and (3) an optimal body size exists for each diving depth. These results explain the relatively greater diving ability observed in smaller divers, and suggest that if the vertical distribution of prey in the water column is patchy, there is opportunity for a population of diving animals to occupy habitat niches related to body size.     

Predator‐induced morphological defences in two invasive dreissenid mussels: implications for species replacement

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Dynamics of Predator‐Prey Interactions in Continuous Cultures

This paper studies the behavior of a general unstructured kinetic model for continuous bioreactors involving interactions between predator, prey and a limiting substrate. The analysis carried out in this paper shows how closed analytical conditions for arbitrary growth rates can be derived that describe the conditions for the existence of the interacting species in an oscillatory behavior. It is also demonstrated how practical diagrams in terms of operating and kinetic parameters can be constructed that classify the different behavior predicted by the model. Applications of these general results to a number of experimentally validated models have revealed that the saturation model always predicts hard oscillations for a certain range of dilution rates, for any values of model parameters. Bifurcation diagrams in the operating parameter space permitted the delineation of regions of hard oscillations, regions of static coexistence, regions of predator washout and regions of total washout. The analysis of the double saturation model has proven its ability to predict two Hopf points. Hard oscillations are therefore expected within the dilution rates corresponding to the two Hopf points. Practical diagrams were also constructed to delineate the boundaries separating hard oscillations from static coexistence and washout conditions.     

Sex‐specific foraging behavior in response to fishing activities in a threatened seabird

Some seabird species have learnt to efficiently exploit fishing discards from trawling activities. However, a discard ban has been proposed as necessary in Europe to ensure the sustainability of the seas. It is of crucial importance for the management and conservation purposes to study the potential consequences of a discard ban on the foraging ecology of threatened seabirds. We assessed the influence of fishing activities on the feeding habits of 22 male and 15 female Audouin's gulls (Larus audouinii) from the Ebro Delta (Mediterranean Sea) during the breeding period using GPS loggers together with Stable Isotope Analysis (SIA), which provided new insights into their foraging behavior and trophic ecology, respectively. GPS data revealed different sex‐specific foraging patterns between workdays and weekends. Females were highly consistent in that they foraged at sea throughout the week even though discarding stops at weekends. In contrast, males switched from foraging at sea during the week (when discards are produced) to an increased use of rice field habitats at weekends (when fishermen do not work). This sex‐specific foraging behavior could be related to specific nutritional requirements associated with previous egg production, an energetically demanding period for females. However, on a broader time scale integrated by the SIA, both sexes showed a high degree of individual specialization in their trophic ecology. The need to obtain detailed information on the dependence and response of seabirds to fishing activities is crucial in conservation sciences. In this regard, sex‐specific foraging behavior in relation to fisheries has been overlooked, despite the ecological and conservation implications. For instance, this situation may lead to sex differentiation in bycatch mortality in longlines when trawlers do not operate. Moreover, any new fisheries policy will need to be implemented gradually to facilitate the adaptation of a specialized species to a discard ban scenario.     

Use of time‐at‐temperature data to describe dive behavior in five species of sympatric deep‐diving toothed whales

This paper develops and validates a method of using time‐at‐temperature (TAT) histograms from satellite transmitter tags to describe the dive activity patterns and approximate depth distributions of five deep‐diving toothed whale species in the northern Bahamas. TAT histograms represent a bandwidth‐conserving method of recovering a long‐term proxy record of dive activity. However, using temperature to interpret TAT on a scale of approximate depths required the complex estimation of TAT histogram bin boundary depths in a dynamic oceanographic region. Here we evaluated the relative performance of four interpolation methods and a global reanalysis data assimilation model in estimating climatological isotherm depth surfaces within our study area. TAT‐derived approximate time‐at‐depth (TAD) distributions aligned closely with directly observed TAD distributions from a smaller sample of depth‐recording satellite tags deployed on separate individuals of each species. TAT‐derived approximate depth distributions were also consistent with various published accounts for this suite of species. Estimating dive ranges and time budgets are important components of (1) understanding habitat overlap between species, (2) evaluating the potential role of these predators in meso‐ and bathypelagic ecosystems, and (3) assessing vulnerability and exposure to anthropogenic impacts.     

The development of an intermediate‐duration tag to characterize the diving behavior of large whales

The development of high‐resolution archival tag technologies has revolutionized our understanding of diving behavior in marine taxa such as sharks, turtles, and seals during their wide‐ranging movements. However, similar applications for large whales have lagged behind due to the difficulty of keeping tags on the animals for extended periods of time. Here, we present a novel configuration of a transdermally attached biologging device called the Advanced Dive Behavior (ADB) tag. The ADB tag contains sensors that record hydrostatic pressure, three‐axis accelerometers, magnetometers, water temperature, and light level, all sampled at 1 Hz. The ADB tag also collects Fastloc GPS locations and can send dive summary data through Service Argos, while staying attached to a whale for typical periods of 3–7 weeks before releasing for recovery and subsequent data download. ADB tags were deployed on sperm whales (Physeter macrocephalus; N = 46), blue whales (Balaenoptera musculus; N = 8), and fin whales (B. physalus; N = 5) from 2007 to 2015, resulting in attachment durations from 0 to 49.6 days, and recording 31 to 2,539 GPS locations and 27 to 2,918 dives per deployment. Archived dive profiles matched well with published dive shapes of each species from short‐term records. For blue and fin whales, feeding lunges were detected using peaks in accelerometer data and matched corresponding vertical excursions in the depth record. In sperm whales, rapid orientation changes in the accelerometer data, often during the bottom phase of dives, were likely related to prey pursuit, representing a relative measure of foraging effort. Sperm whales were documented repeatedly diving to, and likely foraging along, the seafloor. Data from the temperature sensor described the vertical structure of the water column in all three species, extending from the surface to depths >1,600 m. In addition to providing information needed to construct multiweek time budgets, the ADB tag is well suited to studying the effects of anthropogenic sound on whales by allowing for pre‐ and post‐exposure monitoring of the whale's dive behavior. This tag begins to bridge the gap between existing long‐duration but low‐data throughput tags, and short‐duration, high‐resolution data loggers.     

Characterisation of Predator‐Directed Displays in Tephritid Flies

Flies of the family Tephritidae are known to perform a display in front of their salticid spider predators. This display involves extending the wings while the fly moves from side to side. The wings of many of fly species are banded, and in some species, these bands are thought to deter their predators by mimicking the leg patterns of salticids. However, as this display is also seen in non‐mimicking flies, there is some uncertainty over the functional significance of these displays. In this study, we explored the efficacy of displays by the lightly banded but non‐mimicking Mexican fruit fly (Anastrepha ludens) in deterring attacks by the salticids Paraphidippus aurantius and Phidippus bidentatus. We tested the effect of band visibility and the fly's physiological condition on the production of these displays and the probability of attack by salticids. We filmed the interactions of flies and spiders and analysed fly displays in the presence of the salticid. We show that the fly's display deters salticids and promotes the fly's chances of survival and that the presence or absence of bands does not alter the possibility of attack. Flies fed on different quality diets showed similar rates of display. Our results suggest that tephritid flies deter attacks because of their display and not their appearance.     

Predator‐avoidance behaviour in a nocturnal petrel exposed to a novel predator

Many species of bird recognize acoustic and visual cues given by their predators and have complex defence adaptations to reduce predation risk. Recognition of threats posed by specific predators and specialized anti‐predation behaviours are common. In this study we investigated predator recognition and anti‐predation behaviours in a pelagic seabird, Leach's Storm‐petrel Oceanodroma leucorhoa, at a site where predation risk from Great Skuas Stercorarius skua is exceptionally high. Leach's Storm‐petrels breed in burrows and come on land only at night. Counter‐predator adaptations were investigated correlatively in relation to changing natural light levels at night, and experimentally in relation to nocturnal visual and acoustic signals from Great Skuas. Colony attendance by Leach's Storm‐petrels was attuned to changes in light conditions at night and was highest when nights were darkest. This behaviour is likely to reduce predation risk on land; however, specific recognition of Great Skuas and specialized defence behaviours were not found. Leach's Storm‐petrels, in particular apparently non‐breeding individuals, were entirely naïve to the threat posed by Great Skuas and were captured easily in a variety of different ways, on the ground and in the air. Lack of specialized behavioural adaptations in Leach's Storm‐petrels against Great Skuas may be because spatial overlap of breeding distributions of these species appears to be a rare and recent phenomenon.     

Development of novel mass spectrometric methods for identifying HOCl‐induced modifications to proteins

Protein oxidation is thought to contribute to a number of inflammatory diseases, hence the development of sensitive and specific analytical techniques to detect oxidative PTMs (oxPTMs) in biological samples is highly desirable. Precursor ion scanning for fragment ions of oxidized amino acid residues was investigated as a label‐free MS approach to mapping specific oxPTMs in a complex mixture of proteins. Using HOCl‐oxidized lysozyme as a model system, it was found that the immonium ions of oxidized tyrosine and tryptophan formed in MS² analysis could not be used as diagnostic ions, owing to the occurrence of isobaric fragment ions from unmodified peptides. Using a double quadrupole linear ion trap mass spectrometer, precursor ion scanning was combined with detection of MS³ fragment ions from the immonium ions and collisionally‐activated decomposition peptide sequencing to achieve selectivity for the oxPTMs. For chlorotyrosine, the immonium ion at 170.1 m/z fragmented to yield diagnostic ions at 153.1, 134.1, and 125.1 m/z, and the hydroxytyrosine immonium ion at 152.1 m/z gave diagnostic ions at 135.1 and 107.1 m/z. Selective MS³ fragment ions were also identified for 2‐hydroxytryptophan and 5‐hydroxytryptophan. The method was used successfully to map these oxPTMs in a mixture of nine proteins that had been treated with HOCl, thereby demonstrating its potential for application to complex biological samples.