Predation Costs Research Articles

Female in-nest chatter song increases predation.

Female song is an ancestral trait in songbirds, yet extant females generally sing less than males. Here, we examine sex differences in the predation cost of singing behaviour. The superb fairy-wren (Malurus cyaneus) is a Southern Hemisphere songbird; males and females provision the brood and produce solo song year-round. Both sexes had higher song rate during the fertile period and lower song rate during incubation and chick feeding. Females were more likely than males to sing close to or inside the nest. For this reason, female but not male song rate predicted egg and nestling predation. This study identifies a high fitness cost of song when a parent bird attends offspring inside a nest and explains gender differences in singing when there are gender differences in parental care.

Immediate and carry-over effects of perceived predation risk on communication behavior in wild birds

Predation induces strong selection on phenotypic traits, affecting prey via consumptive and nonconsumptive effects. Communication is important for territorial behavior, but can increase susceptibility to predators. Therefore, predation risk should influence prey communication patterns, territoriality, and fitness. We evaluated how this trade-off is resolved via 2 manipulations of perceived predation risk using audio playback in wild great tits (Parus major). In the first experiment, we examined the immediate response of individuals to playback;the second experiment, replicated across 2 years, examined both immediate and carry-over effects (over days) of playback broadcast for a 5-month period (March-July) in 12 nest box populations. Birds exposed to predator sounds showed decreased singing and increased alarming compared to controls, both immediately and on days without play back exposure (carry-over effects). Perceived predation risk did not affect how birds responded to simulated territory intrusions. In combination, these studies' findings imply that individuals perceive predator vocalizations as risky up to days after exposure to predator cues, and adjust their behavior to minimize this risk. However, the lack of effects on territorial aggression implies that individuals are able to weigh the costs of predation against the benefits of each type of vocal behavior. Acknowledging that context changes the relative costs and benefits of antipredator behavior has important consequences for understanding predator-prey dynamics.

Antipredator defenses predict diversification rates

The "escape-and-radiate" hypothesis predicts that antipredator defenses facilitate adaptive radiations by enabling escape from constraints of predation, diversified habitat use, and subsequently speciation. Animals have evolved diverse strategies to reduce the direct costs of predation, including cryptic coloration and behavior, chemical defenses, mimicry, and advertisement of unprofitability (conspicuous warning coloration). Whereas the survival consequences of these alternative defenses for individuals are well-studied, little attention has been given to the macroevolutionary consequences of alternative forms of defense. Here we show, using amphibians as the first, to our knowledge, large-scale empirical test in animals, that there are important macroevolutionary consequences of alternative defenses. However, the escape-and-radiate hypothesis does not adequately describe them, due to its exclusive focus on speciation. We examined how rates of speciation and extinction vary across defensive traits throughout amphibians. Lineages that use chemical defenses show higher rates of speciation as predicted by escape-and-radiate but also show higher rates of extinction compared with those without chemical defense. The effect of chemical defense is a net reduction in diversification compared with lineages without chemical defense. In contrast, acquisition of conspicuous coloration (often used as warning signals or in mimicry) is associated with heightened speciation rates but unchanged extinction rates. We conclude that predictions based on the escape-and-radiate hypothesis must incorporate the effect of traits on both speciation and extinction, which is rarely considered in such studies. Our results also suggest that knowledge of defensive traits could have a bearing on the predictability of extinction, perhaps especially important in globally threatened taxa such as amphibians.

Titrating the Cost of Plant Toxins Against Predators: a Case Study with Common Duikers, Sylvicapra grimmia.

Foragers face many variables that influence their food intake. These may include habitat structure, time, climate, resource characteristic, food quality, and plant defenses. I conducted foraging experiments using common duikers that involved: 1) testing the effect of plant toxins on foraging, and 2) titrating toxin intake against safety. I used giving up densities (GUDs, food remaining after foraging) to test for selection among trays containing alfalfa pellets treated with water, with 10% oxalic acid, or 10% quebracho tannin. Pairs of trays were placed within islands of woody vegetation and out in open grass. I also conducted a titration experiment by offering the duikers a choice between a patch with water-treated pellets placed at a risky site, or a patch with one of three oxalic acid-treated pellets at a safe site. This made it possible to determine the concentration of oxalic acid at which the cost of toxin in the safe site equals the predation cost at the risky site. The common duikers showed no selectivity among the three treatments at 10% concentration, however, GUDs in the open grass (i.e., safe) were significantly lower than in the wooded islands (i.e., risky). As the oxalic acid concentration increased at the safe sites, the duiker's food intake from the risky sites increased significantly. The results demonstrate that foraging hazards may come in different forms such as predation and plant toxins, and their interactions may alter habitat use, foraging patterns, and perceptions of risk. These variables occur under natural situations, altering the overall habitat quality.

The impacts, characterisation and management of human–leopard conflict in a multi-use land system in South Africa

Human–carnivore conflict represents a global problem, negatively impacting carnivore populations and local livelihoods worldwide. Game farming in South Africa has increased introducing a new form of conflict due to predation on game, but is poorly understood. We contribute to this deficit by adopting an interdisciplinary research approach bringing together quantitative and qualitative data with longitudinal engagement with farmers. We assess the impacts, characteristics and management of human–leopard conflict on game and livestock in the Blouberg Mountain Range. Leopards represented 89 % of reported game attacks with the highest number of attacks on impala and 60 % of reported livestock attacks. The economic costs of leopard predation were highest for nyala compared to other game species and the financial cattle and donkey losses represented large economic costs for communal farmers compared to commercial farmers. Both farming communities experienced a reduced sense of wellbeing and for communal farmers, negative spiritual and cultural impacts. The spatial predation risk of game attacks were most affected by increasing distance to water and the risk of predation on livestock attacks increased further away from villages. Livestock attacks were associated with seasonal grazing patterns and the erosion of traditional management livestock strategies due to the economic costs of their implementation and the migrant labour system altering management roles in the community. The timing of game attacks by leopards was related to the birthing seasons for game and seasonal changes in water supply. Similarly, temporal patterns on livestock were related to the calving season and land degradation in communal areas.

Increases in food availability can tempt oribi antelope into taking greater risks at both large and small spatial scales

Differences in food availability and predation risk can influence how herbivores use landscapes. As a result, trade-offs between costs and benefits can influence habitat and patch selection. To determine how oribi antelope, Ourebia ourebi, weigh up costs and benefits when making habitat and patch level foraging decisions, we measured giving-up densities in artificial patches. First, we determined large-scale habitat use, and then explored how different variables explained patch use within habitats. When the availability of food within patches across the different habitats was equal, oribi preferred to feed in short and tall grasslands and avoided woodlands. Furthermore, the avoidance of woodlands extended into the surrounding grasslands, resulting in oribi feeding less intensively in grassland areas within 15 m of the woodlands. Within the safe grassland habitats, oribi preferred to feed in patches close to tall grass (i.e. escape cover), and where they could see beyond 2 m. These results suggest that oribi select habitats and patches in relation to perceived predation risk (i.e. predation costs outweigh potential food intake benefits). However, when we increased food availability within woodlands, oribi increased their large-scale risk-taking behaviour and fed in these woodlands. Furthermore, this increased risk taking extended to small-scale foraging decisions whereby an increase in food availability within woodlands caused oribi to increase their relative usage of patches that had sight lines as well as patches that were closer to potential ambush sites. Ultimately, these results highlight how changes in food availability can determine the degree to which herbivores are willing to increase their risk-taking behaviour, and how these changes can affect overall landscape use.

Alterations of Hippocampal Place Cells in Foraging Rats Facing a “Predatory” Threat

Fear is an adaptive mechanism evolved to influence the primal decisions of foragers in "approach resource-avoid predator" conflicts. To survive and reproduce, animals must attain the basic needs (food, water, shelter, and mate) while avoiding the ultimate cost of predation. Consistent with this view, ecological studies have found that predatory threats cause animals to limit foraging to fewer places in their habitat and/or to restricted times. However, the neurophysiological basis through which animals alter their foraging boundaries when confronted with danger remains largely unknown. Here, we investigated place cells in the hippocampus, implicated in processing spatial information and memory, in male Long-Evans rats foraging for food under risky situations that would be common in nature. Specifically, place cells from dorsal cornu ammonis field 1 (CA1) were recorded while rats searched for food in a semi-naturalistic apparatus (consisting of a nest and a relatively large open area) before, during, and after encountering a "predatory" robot situated remotely from the nest. The looming robot induced remapping of place fields and increased the theta rhythm as the animals advanced toward the vicinity of threat, but not when they were around the safety of the nest. These neurophysiological effects on the hippocampus were prevented by lesioning of the amygdala. Based on these findings, we suggest that the amygdalar signaling of fear influences the stability of hippocampal place cells as a function of threat distance in rats foraging for food.

Individual boldness is linked to protective shell shape in aquatic snails.

The existence of consistent individual differences in behaviour ('animal personality') has been well documented in recent years. However, how such individual variation in behaviour is maintained over evolutionary time is an ongoing conundrum. A well-studied axis of animal personality is individual variation along a bold-shy continuum, where individuals differ consistently in their propensity to take risks. A predation-risk cost to boldness is often assumed, but also that the reproductive benefits associated with boldness lead to equivalent fitness outcomes between bold and shy individuals over a lifetime. However, an alternative or complementary explanation may be that bold individuals phenotypically compensate for their risky lifestyle to reduce predation costs, for instance by investing in more pronounced morphological defences. Here, we investigate the 'phenotypic compensation' hypothesis, i.e. that bold individuals exhibit more pronounced anti-predator defences than shy individuals, by relating shell shape in the aquatic snail Radix balthica to an index of individual boldness. Our analyses find a strong relationship between risk-taking propensity and shell shape in this species, with bolder individuals exhibiting a more defended shell shape than shy individuals. We suggest that this supports the 'phenotypic compensation' hypothesis and sheds light on a previously poorly studied mechanism to promote the maintenance of personality variation among animals.

The influence of food chemistry on food-safety tradeoffs in samango monkeys

Foraging animals must weigh the benefit of seeking food against the risk of becoming food, and the value of a given food should factor into this decision. We examined the separate and joint effects of food-safety tradeoffs and food chemistry on the foraging of free-ranging samango monkeys (Cercopithecus (nictitans) mitis erythrarchus) at Lajuma, South Africa. We conducted giving up density (GUD, the amount of food left behind by a forager) experiments with peanuts treated with secondary compounds (quebracho tannin, tannic acid, or oxalic acid) offered in safe and risky microhabitats. Effects of the compounds would manifest as higher GUDs relative to a control treatment. Moreover, secondary compounds should cause a greater increase in GUDs in the risky microhabitat. GUDs were higher in patches containing oxalic acid–treated peanuts than in patches with either of the tannin–treated or the untreated peanuts. Moreover, the samangos experienced an interaction of predation costs and secondary compounds: the GUDs on oxalates relative to control peanuts were higher in the risky microhabitat. As predicted, the samangos traded food for safety, and the effect was most pronounced when the control was paired with the least desirable food (oxalic acid). We provide evidence that the marginal value of energy is influenced by the presence of plant toxins, the predation cost of foraging, and the interaction of the two.

Prevalence, consequences, and mitigation of fireworm predation on endangered staghorn coral

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 516:187-194 (2014) - DOI: https://doi.org/10.3354/meps10996 Prevalence, consequences, and mitigation of fireworm predation on endangered staghorn coral M. W. Miller1,*, C. Marmet2, C. M. Cameron1,2, D. E. Williams1,2 1National Marine Fisheries Service, Southeast Fisheries Science Center, 75 Virginia Beach Drive, Miami, FL 33149, USA 2Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA *Corresponding author: margaret.w.miller@noaa.gov ABSTRACT: In the current era of reduced coral populations, the effects of predation are likely to compromise the growing investment in restocking of imperiled coral populations and may be a strong, chronic deterrent of natural population recovery. A 2 yr surveillance study documented highly variable prevalence of predation by the fireworm Hermodice carunculata on both wild (0 to 51%) and restocked (0 to 53%) populations of the Caribbean staghorn coral Acropora cervicornis, but significantly higher prevalence overall in 2012 than 2011. In addition, individual predation scars (branch tips) were tagged to determine the costs of predation both in terms of healing time (i.e. to recover positive rates of branch growth) and in terms of likelihood of progressive disease-like tissue loss on preyed branch tips. The risk of preyed branches showing progressive tissue loss at the subsequent survey was 10 times higher than for non-preyed branches. A survival analysis indicated an estimated mean time to healing for preyed branch tips of 110 ± 6 d (95% confidence). Finally, an experiment conducted in 2013 tested whether removing the dead skeleton from preyed branch tips could accelerate recovery. Indeed, this intervention shortened the mean time to formation of a new apical tip to 46 d (range: 22 to 92 d). Thus, fireworm predation imposes significant costs on both remnant wild and restocked staghorn colonies, but removing dead tips, rather than leaving them to bioerode, is a useful strategy to accelerate recovery from predation. KEY WORDS: Hermodice carunculata · Acropora cervicornis · Corallivory · Florida Keys · Restoration Full text in pdf format PreviousNextCite this article as: Miller MW, Marmet C, Cameron CM, Williams DE (2014) Prevalence, consequences, and mitigation of fireworm predation on endangered staghorn coral. Mar Ecol Prog Ser 516:187-194. https://doi.org/10.3354/meps10996 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 516. Online publication date: December 03, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Caddisfly egg mass morphology mediates egg predation: potential costs to individuals and populations

Summary Egg predation is seldom considered in life‐history studies of freshwater insects, but could be an important source of mortality with potential to limit population numbers. Costs of egg predation to prey can be considered at two levels: (i) fitness costs to individuals via reduced reproductive output; and (ii) population costs via reduced recruitment of benthic larvae. Larvae of Orthotrichia armata (Trichoptera: Hydroptilidae) feed on the egg masses of caddisflies in the Little River, central Victoria, Australia, but the small size of O. armata suggests that they may be unable to penetrate egg masses that are covered with a thick layer of spumaline jelly. We predicted that predation by O. armata would be more severe for egg masses with thinner spumaline. With field surveys throughout the peak caddisfly oviposition period (summer), we compared predation by O. armata on the egg masses of nine caddisfly taxa. Egg masses were categorised, according to the thicknesses of spumaline, into bulbous (thickly jellied), thinly jellied and jelly‐free morphotypes, with three species per morphotype. Bulbous egg masses were rarely consumed. Thinly jellied egg masses comprised just 4–13% of all egg masses in each survey, but attracted 52–93% of all egg predators. Jelly‐free egg masses were readily consumed, but O. armata were disproportionately scarce on them. In a second survey, we compared the proportions of eggs that were consumed from egg masses with small and large clutch sizes, by monitoring the thinly jellied egg masses of Taschorema sp. (598 ± 95 eggs per mass) and Ethochorema turbidum (1195 ± 192 eggs per mass) to eclosion. More than 25% of Taschorema sp. egg masses were entirely consumed, causing complete reproductive failure of parent females (fitness costs to individuals). Consumption rates were < 25% for most egg masses of E. turbidum. Orthotrichia armata consumed 48% of all Taschorema sp. eggs and 20% of E. turbidum eggs, suggesting that egg predation may substantially curb larval recruitment (costs to populations), particularly for species with small clutch sizes. Our results demonstrate that egg mortality varies for aquatic insect species that package their eggs in different ways. Combined with recent data from the same system, our results suggest egg mass morphology–mortality trade‐offs, with bulbous egg masses particularly vulnerable to flow forces (shear) and thinly jellied/jelly‐free egg masses particularly vulnerable to predation. Given the wide array of aquatic invertebrate species that lay single egg masses on hard substrata, it is feasible that this is a common trade‐off that warrants more research on the impacts of egg predation on aquatic species.

Influence of climate on the presence of colour polymorphism in two montane reptile species

The coloration of ectotherms plays an important role in thermoregulation processes. Dark individuals should heat up faster and be able to reach a higher body temperature than light individuals and should therefore have benefits in cool areas. In central Europe, montane local populations of adder (Vipera berus) and asp viper (Vipera aspis) exhibit a varying proportion of melanistic individuals. We tested whether the presence of melanistic V. aspis and V. berus could be explained by climatic conditions. We measured the climatic niche position and breadth of monomorphic (including strictly patterned individuals) and polymorphic local populations, calculated their niche overlap and tested for niche equivalency and similarity. In accordance with expectations, niche overlap between polymorphic local populations of both species is high, and even higher than that of polymorphic versus monomorphic montane local populations of V. aspis, suggesting a predominant role of melanism in determining the niche of ectothermic vertebrates. However, unexpectedly, the niche of polymorphic local populations of both species is narrower than that of monomorphic ones, indicating that colour polymorphism does not always enable the exploitation of a greater variability of resources, at least at the intraspecific level. Overall, our results suggest that melanism might be present only when the thermoregulatory benefit is higher than the cost of predation.

Relaxed predation hinders development of anti‐predator behaviors in an aposematic beetle

AbstractPredation is a key force constraining the time and space in which prey can forage. Theoretical models propose that warning coloration (aposematism) may help unprofitable prey to extend their foraging niche without suffering the costs of predation. In this study, we show that aposematism can alter the development of those behaviors that are associated with detection by predators. The aposematic rove beetle Paederus fuscipes Curtis (Coleoptera: Staphylinidae) harbors a symbiotic bacterium, which produces a non‐proteinaceous compound named pederin. We showed that pederin is highly toxic orally to insect predators and that adult P. fuscipes are well protected against predators. Field analysis revealed that Paederus is the most abundant genus of the tribe Paederini compared to five other closely related genera and that adult Paederus beetles are much more likely to be discovered during the day in open areas. In addition, laboratory analysis of common anti‐predator behaviors in P. fuscipes and three closely related, but non‐toxic, rove beetles revealed that non‐toxic beetles tend to seek refuge immediately after stimulation. Conversely, adult P. fuscipes are not adapted to conceal themselves even when intensely threatened. Instead, they walk in open areas and climb plant stalks, two behaviors that expose them to predators. These results imply that the chemical defense of P. fuscipes may have relaxed selective pressures on the development and maintenance of anti‐predator behaviors. These findings explain the unique biological characteristics of P. fuscipes beetles and provide evidence that aposematic animals may gain benefit by extending their foraging activities across both time and space.

English

Several papers have been written on the experiences, successes and challenges facing compensation schemes for wildlife, some of whom criticize the strategy while others support it.  What is clear among the Maasai is that the burden of conserving wildlife, particularly predators that roam freely on their land and predate upon their livestock, is too great to bear: support in terms of financial compensation and mitigation strategies to reduce socio-economic loss from livestock deaths would help communities tolerate predators, and discourage some among them to kill carnivores in retaliation. Such programs in the Amboseli ecosystem are critical for the long term future of wildlife conservation. The Mbirikani Predator Compensation Fund (MPCF) is such a compensation scheme administered by the Big Life Foundation since 2003.  Data from Big Life Foundation’s monitoring records of compensation paid between 2008 and 2012 were analyzed in order to establish insights into the pattern and cost of predation in the Amboseli ecosystem.  Results show that predation has been increasing with time, especially in recent years and during droughts; it is widespread across the Amboseli Ecosystem, but the frequency and intensity is higher near protected areas. The most common predators in the area studied are hyena, jackal, cheetah, lion and leopard; hyenas are the major predators, targeting all livestock types, while lion primarily target cattle. Between 2008 and 2012, more than KSh28 million was spent on compensation for over 9,000 livestock killed in bomas only.  Poor Maasai homestead (boma) maintenance encouraged predation further.  We recommend the compensation scheme to continue so that it cushions the Maasai from predation costs. Also, current measures of predation prevention such as improved livestock husbandry, construction of predator proof fences, and vigilance at night by the Maasai (especially the morans) should be encouraged, as it is within the MPCF.  Benefit systems that complement predator compensation, such as generation of local employment, educational opportunities and involvement in carnivore conservation strategies, will help to conserve predators in the Amboseli ecosystem.   Key words: Amboseli ecosystem, human-carnivore conflict, compensation scheme, cost of conservation.

Predation costs of impaired chemosensory risk assessment on acid-impacted juvenile Atlantic salmon (Salmo salar)

Weak levels of acidification (pH < 6.6) inhibit the ability of fishes to assess predation risk via interference with damage-released chemical alarm cues. While survival benefits associated with behavioural responses to alarm cues have been demonstrated under laboratory conditions, it remains largely unknown whether fishes under natural conditions experience similar benefits. Using hatchery-reared juvenile Atlantic salmon (Salmo salar) as a model organism, we conducted a tethering experiment in reaches of neutral (pH ≥ 6.6) and acidic (pH < 6.6) salmon nursery streams, plus one additional stream that varied between pH classes. Despite exposure to fewer predatory fish species, similar availability of physical refugia, and similar threat from terrestrial predators, tethered fish in acidic streams were significantly more likely to be predated over the course of a trial than their counterparts in neutral streams. These results suggest that (i) in the absence of compensatory mechanisms, juvenile Atlantic salmon under acidic conditions may experience greater rates of predation as a result of impaired chemosensory risk assessment, and (ii) brook trout (Salvelinus fontinalis) appear to play the greatest role in limiting the survival of young-of-the-year (0+) salmon.

Are the Costs of Site Unfamiliarity Compensated With Vigilance? A Field Test in Eurasian Siskins

AbstractDetermination of fitness differentials between individuals adopting different migratory and dispersal strategies is basic to understand the evolution of migration. In the Eurasian siskin Carduelis spinus, both resident and transient birds forage within the same wintering area, providing the rare opportunity to compare their foraging behaviour in the same area and habitat. The aim of this study was to test the predictions associated to the different hypothesized costs of transience by studying the vigilance and foraging behaviour of wild wintering siskins foraging at three bird tables with different predation risk and interference competition levels. Transient siskins showed longer scan durations than residents, either because of site unfamiliarity or subordination (i.e. prior‐occupancy effect). However, residents and transients did not differ in aggression rates, contrary to the dear‐enemy effect. Transient siskins did not show a higher allocation of time to vigilance, contrary to the hypothesis of compensation vigilance to reduce predation risk by dispersing animals. Moreover, transients increased pecking rate with increasing predation risk, showed lower scan rates, longer foraging bouts and, in males, presented marginally higher proportions far from cover. Altogether these results strongly support the hypothesis that transients incur a predation cost due to a less efficient vigilance and foraging system.

Association between shell morphology of micro-land snails (genusPlectostoma) and their predator’s predatory behaviour

Predator–prey interactions are among the main ecological interactions that shape the diversity of biological form. In many cases, the evolution of the mollusc shell form is presumably driven by predation. However, the adaptive significance of several uncommon, yet striking, shell traits of land snails are still poorly known. These include the distorted coiled “tuba” and the protruded radial ribs that can be found in micro-landsnails of the genus Plectostoma. Here, we experimentally tested whether these shell traits may act as defensive adaptations against predators. We characterised and quantified the possible anti-predation behaviour and shell traits of Plectostoma snails both in terms of their properties and efficiencies in defending against the Atopos slug predatory strategies, namely, shell-apertural entry and shell-drilling. The results showed that Atopos slugs would first attack the snail by shell-apertural entry, and, should this fail, shift to the energetically more costly shell-drilling strategy. We found that the shell tuba of Plectostoma snails is an effective defensive trait against shell-apertural entry attack. None of the snail traits, such as resting behaviour, shell thickness, shell tuba shape, shell rib density and intensity can fully protect the snail from the slug’s shell-drilling attack. However, these traits could increase the predation costs to the slug. Further analysis on the shell traits revealed that the lack of effectiveness in these anti-predation shell traits may be caused by a functional trade-off between shell traits under selection of two different predatory strategies.

Antipredator behavioural compensation of proactive personality trait in male Eurasian siskins

Many animals show behavioural syndromes (i.e. suites of correlated behaviours across multiple situations). These behavioural correlations, however, imply limitations in the behavioural plasticity of individuals when facing the trade-off between predation risk and starvation risk. Some models suggest that proactive animals prioritize the reduction of starvation risk, while reactive animals do the opposite. Therefore, fast explorers that are also bold (i.e. proactive) are assumed to pay a predation cost associated with their behavioural trait. However, it has recently been suggested that proactive individuals may be able to compensate for their higher risk of predation by adopting some antipredator behaviours. In this study we tested these two alternative hypotheses with wild wintering Eurasian siskins, Carduelis spinus, foraging at artificial feeders. Male siskins have a melanin-based black bib that has been found to be correlated with exploratory behaviour, aggressiveness and dominance, and therefore is a signal of proactivity. We found that male siskins with large black bibs uttered more distress calls upon capture and displayed a vigilance strategy that improved predator detection. Moreover, this vigilance strategy did not reduce food intake rate. These results show that proactive individuals are not reckless, but instead compensate for their personality trait with stronger antipredator behaviours, and thus, do not necessarily have to pay a predation cost. Our results support the view of a positive relationship between eumelanism, proactive personality and the display of antipredator behaviours.

Rhinoceros Beetles Suffer Male-Biased Predation by Mammalian and Avian Predators

Male sexually-selected traits often impose an increased risk of predation on their bearers, causing male-biased predation. We investigated whether males of the sap-feeding Japanese rhinoceros beetle Trypoxylus dichotomus were more susceptible to predation than females by comparing the morphology of beetles caught in bait traps with the remains of beetles found on the ground. The males of this species are larger than the females and have a horn on the head. We found that predation pressure was greater for males than for females, and that larger individuals of both sexes were more vulnerable to predation. We identified two predators, the raccoon dog Nyctereutes procyonoides and jungle crow Corvus macrorhynchos, by monitoring sap-site trees with infrared video cameras. Raccoon dogs visited sap-site trees at night, while crows came after daybreak. The highest frequency of visits by both predators was observed in the first half of August, which matches the peak season of T. dichotomus. Raccoon dogs often left bite marks on the remains of prey, whereas crows did not. Bite marks were found on most of the remains collected at two distant localities, which suggested that predation by raccoon dogs is common. Size- and sex-dependent differences in the conspicuousness and active period of T. dichotomus probably explain these biased predation patterns. Our results suggest that having a large horn/body is costly in terms of the increased risk of predation. Predation cost may act as a stabilizing selection pressure against the further exaggeration of male sexual traits.

Detection of predator cues alters mating tactics in male wolf spiders

Males of the wolf spider, Rabidosa punctulata, exhibit condition-dependent alternative mating tactics, whereby small, poor condition males engage in multimodal courtship while large, good condition males adopt a direct mount tactic that forgoes courtship. This study explores the possibility that tactic-specific costs can help explain this unintuitive pattern of mating tactic expression. Specifically, we hypothesize that courtship signaling is costly with respect to eavesdropping by predators and that males can alter their tactic expression based upon the perceived environmental predation risk. We test this by first examining the risk of predation associated with different mating tactics. We use a co-occurring predatory heterospecific, R. rabida as our predator. We found support for the prediction that courting R. punctulata males tended to be attacked more often than non-courting males, and the likelihood of being attacked was best predicted by courtship activity. Given this documented cost, we hypothesized that R. punctulata males would adjust their mating tactic based upon perceived predation risk. In a second experiment, we manipulated perceived predation risk by providing R. punctulata males with different female silk cues (conspecific; predatory heterospecific; conspecific + predatory heterospecific) and examined mating tactic expression. In support of our hypothesis, males were more likely to adopt the direct mount tactic in the presence of predatory heterospecific or mixed silk cues and were more likely to court in the presence of conspecific cues. These results support the hypothesis that the cost of predation from eavesdroppers may influence the evolution and expression of male alternative mating tactics in R. punctulata.