Balancing the response to predation—the effects of shoal size,predation risk and habituation on behaviour of juvenile perch

Group size, predation risk and habituation are key drivers of behaviour and evolution in gregarious prey animals. However, the extent to which they interact in shaping behaviour is only partially understood. We analyzed their combined effects on boldness and vigilance behaviour in juvenile perch (Perca fluviatilis) by observing individuals in groups of one, two, three and five faced with four different levels of predation risk in a repeated measures design. The perch showed an asymptotic increase in boldness with increasing group size and the highest per capita vigilance in groups of two. With increasing predation risk, individuals reduced boldness and intensified vigilance. The interaction between group size and predation risk influenced vigilance but not boldness. In this context, individuals in groups of two elevated their vigilance compared to individuals in larger groups only when at higher risk of predation. Further, as only group size, they significantly reduced vigilance at the highest level of risk. With increasing habituation, solitary individuals became considerably bolder. Also, predation risk affected boldness only in the more habituated situation. Hence, repeated measures may be essential to correctly interpret certain relationships in behaviour. Our results suggest that perch may adjust boldness behaviour to group size and predation risk independently. This is rather unexpected since in theory, natural selection would strongly favour an interactive adjustment. Finally, vigilance might be particularly effective in groups of two due to the intense monitoring and detailed response to changing levels of risk.     

Hunted hunters? Effect of group size on predation risk and growth in the Australian subsocial crab spider Diaea ergandros

A reduced predation risk is considered to be a major adaptive advantage of sociality. While most studies are concerned with non-predatory prey species, group-living predators are likely to face similar threats from higher-order predators. We studied the relationship between group size and predation risk in the subsocial crab spider Diaea ergandros by testing predictions from theoretical models including attack abatement as well as the formation of protective retreats. In a field survey, we found predatory clubionid spiders in 35 % of the D. ergandros nests and as predicted, nest size did not correlate with predator presence. In a subsequent laboratory experiment, we observed survival probability, nest construction activity and feeding behaviour including weight development between groups of different sizes as well as in the absence or presence of a predator. Large groups had an advantage in terms of survival and growth compared to smaller groups or single individuals. They also built significantly larger nests than smaller groups, supporting the idea of protective retreat formation being an adaptive benefit to group living. Even though clubionids did attack D. ergandros, they did not significantly affect overall mortality of D. ergandros. The feeding experiment showed that spiders fed on a larger proportion of flies in the presence of a predator. However, these groups gained significantly less weight compared to the control groups, indicating that the potential predators not only act as predators but also as food competitors, constituting a twofold cost for D. ergandros.     

Are monoalgal diets inferior to plurialgal diets to maximize cultivation of the calanoid copepod Temora stylifera?

Temora stylifera adult copepods were fed with four different monoalgal diets and six combinations of the same cultures for 15 days. Fecundity, hatching success, number of cannibalized embryos, fecal pellet production, adult mortality and naupliar recruitment were compared, in order to find the best diet for this species. Phytoplankton species tested were Prorocentrum minimum (PRO); Isochrysis galbana (ISO); Tetraselmis suecica (TETRA) and Rhodomonas baltica (RHO) which were supplied alone or in different combinations and at various concentrations ranging from a minimum of 1 mg C L⁻¹ day⁻¹ to a maximum of 66 mg C L⁻¹ day⁻¹. Of the ten diets tested, ISO was the worst and was unable to sustain egg production and adult survival possibly because adults were unable to ingest this alga due to its small size. TETRA was also a poor food since it negatively impacted egg production and adult survival, as well as egg hatching success, possibly due to the lack of essential compounds necessary for optimal embryogenesis. RHO and PRO were the best foods inducing highest egg production, hatching success and naupliar recruitment. Even if mean egg production rates were similar to those obtained with some mixed diets, carbon intake concentrations with mixed diets were from 3 to 33 and from 6.6 to 66 times higher than with RHO and PRO given alone, respectively. Mixed diets of ISO and PRO, especially when supplied at higher concentrations (66 mg C L⁻¹ day⁻¹), had a negative effect on egg hatching success and adult survival, with a corresponding reduction in naupliar recruitment. On the other hand, mixed diets of TETRA and PRO promoted high naupliar recruitment but values were similar to PRO offered alone. Our results indicate that a good monoalgal diet such as RHO and PRO can be as effective as a mixed diet to sustain the mass cultivation of T. stylifera.     

Size-based predation by kookaburras (Dacelo novaeguineae) on lizards (Eulamprus tympanum: Scincidae): what determines prey vulnerability?

Lizards and birds are both popular ”model organisms” in behavioural ecology, but the interactions between them have attracted little study. Given the putative importance of birds as predators of diurnal lizards, it is of considerable interest to know which traits (of lizards as well as birds) influence the outcome of a predatory attempt. We studied predation by giant terrestrial kingfishers (kookaburras, Dacelo novaeguineae: Alcedinidae) on heliothermic diurnal lizards (highland water skinks, Eulamprus tympanum: Scincidae), with particular reference to the role of prey (lizard) size. Our approach was twofold: to gather direct evidence (sizes of lizards consumed in the field, compared to those available) and indirect evidence (size-related shifts in lizard behaviour). We quantified the size structure of a natural population of skinks (determined by an extensive mark-recapture program), and compared it to the sizes of wild lizards taken by kookaburras (determined by analysis of prey remains left at the birds’ nests). Kookaburras showed size-based predation: they preyed mainly on small and medium-sized rather than large lizards in the field. However, the mechanism producing this bias remains elusive. It is not due to any distinctive behavioural attributes (locomotor ability, activity level, habitat usage) of the lizards of the size class disproportionately taken by the kookaburras. The greater vulnerability of subadult lizards may reflect subtle ontogenetic shifts in ecological and behavioural traits, but our data suggest that great caution is needed in inferring patterns of vulnerability to predation from indirect measures based on either the prey or the predator alone. Instead, we need direct observations on the interaction between the two. Received: 30 May 2000 / Revised: 29 July 2000 / Accepted: 26 August 2000     

Recognising one’s enemies: a functional approach to risk assessment by prey

Little has been done to compare the relative importance of various mechanisms through which prey assess the potential risk from natural enemies. We used predator-naive spider mites (Tetranychus urticae, Tetranychidae) to (1) compare the responses of prey to chemical cues from enemy and non-enemy species and (2) investigate the source of these cues. In the laboratory, we observed the distribution of T. urticae in response to cues from nine mite species, including (1) predators of spider mites, (2) predators/parasites of other animals, and (3) fungivores/pollen-feeders. When given a choice over 24 h, spider mites foraged and oviposited in fewer numbers on leaf discs that were previously exposed to predatory or parasitic mites (including species incapable of attacking spider mites) than on clean leaf discs (unexposed to mites). Interestingly, previous exposure of leaf arenas to fungivores and pollen-feeders had no significant effect on spider mite distribution. We then observed the response of T. urticae to cues from two species of predator that had been reared on a diet of either spider mites or pollen. T. urticae showed stronger avoidance of leaf discs that were previously exposed to spider-mite-fed predators than of discs exposed to pollen-fed predators. Nevertheless, for one predator species (Amblyseius andersoni), T. urticae still preferred to forage and oviposit on clean (unexposed) discs than on discs exposed to pollen-fed predators. Protein-derived metabolic wastes of predatory or parasitic mites may provide a general cue about potential predation risk for T. urticae. However, T. urticae also avoided areas exposed to pollen-fed predators, suggesting there may be other sources of enemy recognition by the spider mites. We discuss the ecological and evolutionary mechanisms that may influence the scope of information through which animals assess predation risk. Received: 11 January 1999 / Received in revised form: 25 October 1999 / Accepted: 20 November 1999     

Vulnerability of newly settled red drum (Sciaenops ocellatus) to predatory fish: is early-life survival enhanced by seagrass meadows?

We conducted predation experiments to evaluate the vulnerability of red drum Sciaenops ocellatus (Linnaeus) larvae and early juveniles to pinfish Lagodon rhomboides (Linnaeus) predators. Experiments were designed to analyze the effects of habitat complexity, prey size, and rearing condition on prey vulnerability. Three structurally different habitats [unvegetated (substrate only), shoal grass Halodule wrightii (Aschers) and turtle grass Thalassia testudinum (Bank ex König)] were simulated in experimental mesocosms. Instantaneous hourly mortality rates (Z?h^?1 predator^?1) for hatchery-reared red drum were significantly higher in the unvegetated habitat (0.189) than in either shoal grass (0.069) or turtle grass (0.046). A similar trend in predation mortality was observed for wild-caught red drum; instantaneous hourly mortality rates were 0.166, 0.047, and 0.021 in unvegetated, shoal grass, and turtle grass habitats, respectively. Mortality rates (adjusted means) for hatchery red drum were higher than for wild individuals in all three habitats; however, the differences were not significant. Predation mortality decreased with increasing prey size (3 to 9% decrease in Z per mm increase in length), suggesting that small red drum (i.e. new settlers) were most vulnerable to predators. We conclude that habitat complexity is critical to the survival of newly settled red drum, and changes in the complexity or areal coverage of natural seagrass meadows may affect early-life survival and possibly recruitment levels.     

Chronic kidney disease of unknown etiology and the effect of multiple-ion interactions

High incidence of chronic kidney disease of unknown etiology (CKDU) prevalent in many countries (e.g., Sri Lanka, equatorial America) is reviewed in the context of recent experimental work and using our understanding of the hydration of ions and proteins. Qualitative considerations based on Hofmeister-type action of these ions, as well as quantitative electrochemical models for the Gibbs free energy change for ionpair formation, are used to explain why (1) fluoride and water hardness due to magnesium ions (but not due to calcium ions) and similarly (2) cadmium ions in the presence of suitable pairing ions can be expected to be more nephrotoxic, while arsenite in the presence of fluoride and hardness may be expected to be less nephrotoxic. No synergy of arsenic with calcium hardness is found. The analysis is applied to a variety of ionic species that may be found in typical water sources to predict their likely combined electrochemical action. These results clarify the origins of chronic kidney disease that has reached epidemic proportions in the North Central Province of Sri Lanka as being most likely due to the joint presence of fluoride and magnesium ions in drinking water. The conclusion is further strengthened by a study of the dietary load of Cd and other toxins in the affected regions and in the healthy regions where the dietary toxin loads and lifestyles are similar, and found to be safe especially when the mitigating effects of micronutrient ionic forms of Zn, Se, as well as corrections for bioavailability are taken into account. The resulting etiological picture is consistent with the views of most workers in the field who have suspected that fluoride and other ions found in the hard water stagnant in shallow household wells were the major causative factors of the disease. Similar incidence of CKDu found in other hot tropical climates is likely to have similar origins.     

Transport of butyltins at the water‐air interface and the adsorptive behavior of tributyltin in the surface microlayer

The transfer dynamics and enrichment phenomena of monobutyltin chloride(MBT), dibutyltin chloride(DBT) and tributyltin chloride(TBT) at the water‐surface microlayer (SM) interface were studied. The transport processes of the three compounds at the interface are very fast in the estuarine environment. The mass transfer coefficients are 1.54 m/h for MBT, 2.16 m/h for DBT, 1.56 m/h for TBT. The effect of various factors, including pH, salinity, suspended particulate and temperature, on the adsorptive behavior of TBT in the water's surface microlayer was also studied.     

Inhibition of glycosidases by Lepidoptera; roles in the insects and leads to novel compounds?

Summary Glycosidase inhibitors are widespread in plants and can be sequestered by Lepidoptera, for which they can presumably serve as defences by making the insects indigestible to a range of potential predators. As a result of this study of eight British species of moth and butterfly it was found that glycosidase inhibitors in the insects could then be detected in the larval food plants which were not previously known to contain them; however, some were only detectable in the plants after concentration. In some cases the inhibition of specific glycosidases by Lepidoptera was detected even though the insects had not apparently acquired them from their food plants. Inhibition of-N-acetylglucosaminidase was observed in most of the adult Lepidoptera analysed but further work is required to identify the inhibitors, though they are likely to be nitrogen-containing compounds. Weak anti-HIV activity was also observed in the glycosidase-inhibiting fractions ofAcherontia atropos and the plantUrtica dioica.     

Echolocation and foraging behavior of the lesser bulldog bat, Noctilio albiventris : preadaptations for piscivory?

We studied variability in foraging behavior of Noctilio albiventris (Chiroptera: Noctilionidae) in Costa Rica and Panamá and related it to properties of its echolocation behavior. N. albiventris searches for prey in high (>20 cm) or low (<20 cm) search flight, mostly over water. It captures insects in mid-air (aerial captures) and from the water surface (pointed dip). We once observed an individual dragging its feet through the water (directed random rake). In search flight, N. albiventris emits groups of echolocation signals (duration 10–11 ms) containing mixed signals with constant-frequency (CF) and frequency-modulated (FM) components, or pure CF signals. Sometimes, mostly over land, it produces long FM signals (duration 15–21 ms). When N. albiventris approaches prey in a pointed dip or in aerial captures, pulse duration and pulse interval are reduced, the CF component is eliminated, and a terminal phase with short FM signals (duration 2 ms) at high repetition rates (150–170 Hz) is emitted. Except for the last pulses in the terminal phase N. albiventris avoids overlap between emitted signals and echoes returning from prey. During rakes, echolocation behavior is similar to that in high search flight. We compare N. albiventris with its larger congener, N. leporinus, and discuss behavioral and morphological specializations that can be interpreted as preadaptations favoring the evolution of piscivory as seen in N. leporinus. Prominent among these specializations are the CF components of the echolocation signals which allow detection and evaluation of fluttering prey amidst clutter-echoes, high variability in foraging strategy and the associated echolocation behavior, as well as morphological specializations such as enlarged feet for capturing prey from the water surface. Received: 21 April 1997 / Accepted after revision: 12 January 1998     

An approach for particle sinking velocity measurements in the 3–400?μm size range and considerations on the effect of temperature on sinking rates

The flux of organic particles below the mixed layer is one major pathway of carbon from the surface into the deep ocean. The magnitude of this export flux depends on two major processes—remineralization rates and sinking velocities. Here, we present an efficient method to measure sinking velocities of particles in the size range from approximately 3–400?μm by means of video microscopy (FlowCAM^?). The method allows rapid measurement and automated analysis of mixed samples and was tested with polystyrene beads, different phytoplankton species, and sediment trap material. Sinking velocities of polystyrene beads were close to theoretical values calculated from Stokes’ Law. Sinking velocities of the investigated phytoplankton species were in reasonable agreement with published literature values and sinking velocities of material collected in sediment trap increased with particle size. Temperature had a strong effect on sinking velocities due to its influence on seawater viscosity and density. An increase in 9?°C led to a measured increase in sinking velocities of ~40?%. According to this temperature effect, an average temperature increase in 2?°C as projected for the sea surface by the end of this century could increase sinking velocities by about 6?% which might have feedbacks on carbon export into the deep ocean.     

Investigation of fluorescence characterization and electrochemical behavior on the catalysts of nanosized Pt-Rh/γ-Al2O3 to oxidize gaseous ammonia

This work describes the environmentally friendly technology for oxidation of ammonia (NH₃) to form nitrogen at temperatures range from 423K to 673K by selective catalytic oxidation (SCO) over a nanosized Pt-Rh/γ-Al₂O₃ catalyst prepared by the incipient wetness impregnation method of hexachloroplatinic acid (H₂PtCl₆) and rhodium (III) nitrate (Rh(NO₃)₃) with γ-Al₂O₃ in a tubular fixed-bed flow quartz reactor (TFBR). The characterization of catalysts were thoroughly measured using transmission electron microscopy (TEM), threedimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic lightscattering (DLS), zeta potential meter, and cyclic voltammetry (CV). The results demonstrated that at a temperature of 673K and an oxygen content of 4%, approximately 99% of the NH₃ was removed by catalytic oxidation over the nanosized Pt-Rh/γ-Al₂O₃ catalyst. N₂ was the main product in NH₃-SCO process. Further, it reveals that the oxidation of NH₃ was proceeds by the over-oxidation of NH₃ into NO, which was conversely reacted with the NH₃ to yield N₂. Therefore, the application of nanosized Pt-Rh/γ-Al₂O₃ catalyst can significantly enhance the catalytic activity toward NH₃ oxidation. One fluorescent peak for fresh catalyst was different with that of exhausted catalyst. It indicates that EEFM spectroscopy was proven to be an appropriate and effective method to characterize the Pt clusters in intrinsic emission from nanosized Pt-Rh/γ-Al₂O₃ catalyst. Results obtained from the CV may explain the significant catalytic activity of the catalysts.     

Does cannibalism in Spodoptera frugiperda (Lepidoptera: Noctuidae) reduce the risk of predation?

The incidence of cannibalism of larval Spodoptera frugiperda (Lepidoptera: Noctuidae) on maize under field conditions was investigated using field cages. Cannibalism was found to account for approximately 40% mortality when maize plants were infested with two or four fourth-instar larvae over a 3-day period. Field trials examined the effect of larval density on the prevalence of natural enemies of S. frugiperda. The abundance of predators (earwigs, staphylinids, other predatory beetles, and Chrysoperla spp.) was significantly greater on maize plants with higher levels of larval feeding damage, while the relationship between predator abundance and number of S. frugiperda larvae per plant was less clear. As larval damage is probably a more reliable indicator of previous larval density than numbers collected at an evaluation, this indicates that predation risk will be greater for larvae living in large groups. Parasitism accounted for 7.1% mortality of larvae in sorghum, and involved six species of Hymenoptera and Tachinidae. There was no effect of larval density or within-plant distribution on the probability of larval attack by parasitoids. The selective benefits of cannibalism, in relation to the risk of predation and parasitism, are discussed. Received: 23 March 2000 / Accepted: 24 June 2000     

Susceptibility to oxidative stress of the Mediterranean demosponge Petrosia ficiformis : role of endosymbionts and solar irradiance

 The effects of elevated pO₂ and irradiance as inducers of prooxidant conditions have been investigated in the Mediterranean demosponge Petrosia ficiformis (Poiret, 1789). This species lives symbiotically with the autotrophic cyanobacterium Aphanocapsa feldmanni, the abundance of which is controlled by the intensity of light irradiance. In the presence of symbionts, tissues of P. ficiformis were characterized by a general enhancement of antioxidant defenses as compared to aposymbiotic specimens. The main differences included higher activities of several antioxidant enzymes and a greater capability to neutralize various forms of oxyradicals, as indicated by the total oxyradical scavenging capacity (TOSC) assay. Elevated pO₂, more than light, appeared to be the primary factor inducing prooxidant pressure in the Mediterranean sponge; in fact, irrespective of the solar irradiance experienced by the sponge, symbiotic specimens showed comparable activities of antioxidant enzymes and a similar scavenging capacity towards various reactive oxygen species. However, the potential toxicity of photodynamic production of reactive oxygen species was demonstrated in organisms from more irradiated sites, as the levels of antioxidant defenses were lowered in the outer layer of the sponge. The role of enhanced antioxidant defenses in protecting symbiotic specimens, also from oxyradical-mediated toxicity of light exposure, was supported by translocation experiments; aposymbiotic sponges did not survive when moved to conditions of elevated solar irradiance, while no effects were observed in symbiotic specimens if translocated and/or deprived of symbionts. Received: 23 November 1999 / Accepted: 13 June 2000     

How do simple energy activities comprise complex behavior of life systems?: A conceptual synthesis and decomposition of the energy structure of life systems

Reduction and synthesis has always been Science’s way to learn about complex systems. The problem is, of course, that after studying the behavior of the system components, the reconstruction of system behavior cannot be any simple summation of the behavior of the individual components. How should we go about with the reconstruction is an umbrella question addressed in the paper. In particular, one should ask what is the contribution of each component to the system, and what kind and quantitative relations do the connections among the components signify in the total system? Answering these questions is necessary to understand the internal mechanism of a life system, the regularity of its dynamics, and the nature of the control mechanisms.The general approach of the paper is based on the assumption that the life energy transmission structure of the system is the fundamental principle of reduction and synthesis.The paper generalizes the energy transmission in terms of two basic types, based upon the mode of linkage in energy activities, such as sequential or parallel. The basic mathematical concept is an eigenparameter analysis in a model called Life Energy System Model (LESM). Simple examples illustrate the models application. It is true that the energy transmission structure of a natural life system is usually very complex, in which case the analysis has to incorporate more details than shown in the paper. Yet, the analysis still follows the same fundamental principle as outlined.     

Sexual selection on mature male parr of masu salmon (Oncorhynchus masou): does sneaking behavior favor small body size and less-developed sexual characters?

In many salmonid species, males exhibit morphological dimorphism associated with alternative mating behaviors. ”Precocious males” have a small body size with little or no development of sexual characters and adopt sneaking to gain access to females, while ”migratory males” of large body size and well-developed secondary sexual characters fight. We quantified selection on precocious male parr of masu salmon (Oncorhynchus masou) under simulated natural conditions to examine the contribution of morphology to sneaking success. In contrast to the prediction that sneaking behavior favors small body size, we detected selection favoring relatively large body size for sneaking success. This selection pressure was caused by the dominance hierarchy within parr and may have been facilitated by indifference of dominant migratory males to parr. Unlike the secondary sexual characters exhibited by migratory male salmon, such as the hooked snout and humped back, no morphological characters other than body size contributed to the reproductive success of masu salmon parr. This non-contribution may have been responsible for the lack of development of sexual characters in precocious males. Received: 15 November 1999 / Accepted: 20 May 2000     

Two sides of the same coin? Rare and pest plants native to the United States and Canada

Plant biodiversity is at risk, with as many as 10% of native species in the United States being threatened with extinction. Habitat loss has led a growing number of plant species to become rare or threatened, while the introduction or expansion of pest species has led some habitats to be dominated by relatively few, mostly nonindigenous, species. As humans continue to alter many landscapes and vegetation types, understanding how biological traits determine the location of species along a spectrum from vulnerability to pest status is critical to designing risk assessment protocols, setting conservation priorities, and developing monitoring programs. We used boosted regression trees to predict rarity (based on The Nature Conservancy global rankings) and pest status (defined as legal pest status) from data on traits for the native vascular flora of the United States and Canada including Hawaii, Puerto Rico, and the Virgin Islands (n approximately = 15,000). Categories were moderately to highly predictable (AUCpest = 0.87 on 25% holdout test set, AUCrarity = 0.80 on 25% holdout test set). Key predictors were chromosome number, ploidy, seed mass, and a suite of traits suggestive of specialist vs. generalist adaptations (e.g., facultative wetland habitat association and phenotypic variability in growth form and life history). Specifically, pests were associated with high chromosome numbers, polyploidy, and seed masses ranging from 0.1 to 100 mg, whereas rare species were associated with low chromosome numbers, low ploidy, and large (>1000 mg) seed masses. In addition, pest species were disproportionately likely to be facultatively associated with wetlands, and variable in growth form and life history, whereas rare species exhibited an opposite pattern. These results suggest that rare and pest species contrast along trait axes related to dispersal and performance in disturbed or novel habitats.     

Can leftovers from predators be reliably used to monitor marine turtle hatchling sex-ratios? The implications of prey selection by ghost crabs

In marine turtles, the sex of an individual is determined by temperatures experienced during embryonic development. Gonad histological observation is still the only reliable way to determine hatchling sex, hampering the study of reproduction and of the demographic consequences of context-dependent sex-ratios, a subject of interest in a warming planet. We investigated whether hatchling remains from predation by Ocypode cursor can be used to estimate sex-ratio trends in a green turtle rookery at Poilão, Guinea-Bissau (10°52′N, 15°43′W). Sex could be readily determined in 77 and 79% of the predated hatchlings in 2008 and 2009, respectively. By comparing hatchlings killed by crabs, hatchlings accidentally dying on the reefs, and live hatchlings, we show that ghost crabs select the smaller prey, but do not select according to hatchling sex, which is explained by the lack of hatchling size dimorphism in this population. The proportion of male hatchlings was 0.45 ± 0.06 and 0.15 ± 0.06 for early and late-season clutches, respectively, these differences most likely being explained by rainfall. Using leftovers from predation by crabs may be a good solution to non-invasively monitor broad trends in sex-ratios of sea turtles.