A Phylogeny‐Based Comparison of Tarantula Spider Anti‐Predator Behavior Reveals Correlation of Morphology and Behavior

We studied anti‐predator strategies in nine species of tarantulas from Asia, Africa, and the Americas. Tarantulas in the New World possess urticating hairs which induce inflammation when in contact with vertebrate mucus membranes and skin. In contrast, tarantulas from the Old World lack this defense but are observed to exhibit a much greater willingness to escalate to an active defense when provoked. We had three goals: (1) describe the behaviors exhibited by each taxon in response to two levels of provocation, (2) look for the presence of alternative classes of anti‐predator strategy as predicted by the Old World–New World dichotomy in aggressive defense, and (3) examine the evolution of these behaviors in the context of the phylogeny of the group. We compared the response of nine different mygalomorph spider genera to two levels of aversive stimuli: puffs of air and prodding. We found that the overall structure of the defensive behavior was similar between the different taxa, consisting of fleeing, rearing, striking, and biting. Some genera did exhibit unique behaviors such as stridulating (Hysterocrates) or rocking (Haplopelma and Selenocosmia). We found that the genera from the New World exhibited low levels of escalation in their defense behaviors, while those from the Old World readily escalated to striking and biting. Our findings are consistent with the hypothesis that the possession of urticating hairs is associated with very low levels of active defense behaviors such as striking and biting. The phylogenetic analysis indicates that both the notable levels of aggression displayed by the African taxa tested and the relative passivity of the New World tarantulas each represents a synapomorphy.     

Chemical‐Mediated Predator Avoidance in the European House Cricket (Acheta domesticus) is Modulated by Predator Diet

Chemical information often mediates interactions between predators and prey, and threat‐sensitivity theory includes predictions that prey species should respond to chemical signatures of predators in a manner that is commensurate with the level of the assessed threat. Using the European house cricket (Acheta domesticus), we explored the influence of diet‐derived cues from the centipede Scolopocryptops sexspinosus on anti‐predator behavior in three laboratory experiments. In experiment 1, we compared the amount of time that adult female crickets spent on untreated filter paper and filter paper exposed to centipedes fed either the larvae of Hermetia illucens (black soldier fly), crickets, or a mixture of fly larvae and crickets. We discovered that crickets spent significantly less time on filter paper exposed to centipedes fed crickets only or a mixture of crickets and fly larvae compared with blank filter paper or filter paper exposed to centipedes fed fly larvae only. In our second experiment, we compared the amount of time that crickets spent on blank filter paper and filter paper exposed to adult female conspecifics to rule out the possibility that crickets simply avoid all filter paper exposed to metabolic by‐products, and crickets exhibited no discrimination. In our third experiment, we tested the potential effects of diet order on anti‐predatory behaviors. Specifically, we compared the amount of time that adult female crickets spent on filter paper exposed to centipedes fed fly larvae followed by crickets and filter paper exposed to centipedes fed crickets followed by fly larvae. We discovered no diet sequence effect. Our study demonstrates that European house crickets are sensitive to the chemical cues of their centipede predators, but only when centipedes have fed upon crickets.     

Olfactory Predator Discrimination in Yellow‐Bellied Marmots

The mechanism underlying olfactory predator identification may be relatively experience‐independent, or it may rely on specific experience with predators. A mechanism by which prey might identify novel predators relies on the inevitable creation of sulfurous metabolites that are then excreted in the urine of carnivorous mammals. We tested whether free‐living, yellow‐bellied marmots (Marmota flaviventris) and mid‐sized herbivores that fall prey to a variety of carnivorous mammals could discriminate herbivore (elk—Cervus elephas) urine from predator (red fox—Vulpes vulpes, coyote—Canis latrans, mountain lion—Felis concolor, wolf—Canis lupus) urine, a novel herbivore (moose—Alces alces), and a distilled water control. We further asked how specific this assessment was by testing whether marmots responded differently to predators representing different levels of risk and to familiar vs. unfamiliar predators. We found that marmots responded more to urine from coyotes (a familiar predator on adults), mountain lions (a potentially unfamiliar predator that could kill adults) and wolves (a locally extinct predator that could kill adults) than to elk urine (a non‐predator). Red fox (a predator that poses a risk only to recently emerged marmot pups) urine elicited a less substantial (but not significantly so) response than coyote urine. Marmots can identify predators, even novel ones, using olfactory cues, suggesting that experience with a specific predator is not required to identify potential threats.     

Spider Web DNA: A New Spin on Noninvasive Genetics of Predator and Prey

Noninvasive genetic sampling enables biomonitoring without the need to directly observe or disturb target organisms. This paper describes a novel and promising source of noninvasive spider and insect DNA from spider webs. Using black widow spiders (Latrodectus spp.) fed with house crickets (Acheta domesticus), we successfully extracted, amplified, and sequenced mitochondrial DNA from spider web samples that identified both spider and prey to species. Detectability of spider DNA did not differ between assays with amplicon sizes from 135 to 497 base pairs. Spider and prey DNA remained detectable at least 88 days after living organisms were no longer present on the web. Spider web DNA as a proof-of-concept may open doors to other practical applications in conservation research, pest management, biogeography studies, and biodiversity assessments.     

Extreme Behavioral Adjustments by an Orb‐Web Spider to Restricted Spaces

Adaptive flexibility in response to environmental variation is often advantageous and occurs in many types of traits in many species. Although the basic designs of the orb webs of a given species are relatively uniform, spiders can adjust their webs to some types of environmental variation. This study of adult female Leucauge argyra tests the extremes to which they can adjust with respect to reduced area in which to build, and documents probably the most pronounced flexibility in orb design ever recorded. These adjustments revealed several behavioral rules that guide orb construction behavior. Spiders adjusted at least seven probably independent aspects of orb design when confined in tiny spaces that spanned about 7% of the maximum distance normally spanned by webs in the field and that had diameters that were only about three times the length of the spider itself. Webs in intermediate sized containers had intermediate designs, and many of the adjustments appear to result from extensions of the behavioral rules guiding orb construction in less severely restricted spaces in the field.     

The Effect of Predator Chemical Cue Age on Antipredator Behavior in the Wolf Spider Pardosa milvina (Araneae: Lycosidae)

The wolf spider, Pardosa milvina, exhibits reduced movement when detecting chemical cues (silk and excreta) from a larger wolf spider, Hogna helluo. We tested if cue age influenced Pardosa activity. Pardosa response was measured during 1-h trials using video-tracking equipment. Five treatments of predator cues were used: 5-day-old, 1-day-old, 1-h-old, and fresh cues and a control lacking predator cues. Pardosa moved significantly more slowly on substrates with fresh or 1-h-old cues compared to all other treatments and spent less time walking in all Hogna treatments relative to the control except with 5-day-old cues. Pardosa survived longer in the presence of Hogna with fresh compared to older cues. Prey may evaluate cue age as a measure of predation risk and grade antipredator behavior accordingly.     

The Influence of Predator Sex on Chemically Mediated Antipredator Response in the Wolf Spider Pardosa milvina (Araneae: Lycosidae)

The wolf spider, Pardosa milvina, reduces activity in the presence of chemical cues (silk and excreta) from a larger predatory wolf spider, Hogna helluo. Hogna is sexually dimorphic in body size and males and females differ in their propensity to attack prey. Consequently, each sex may present different levels of risk to Pardosa. We measured predation risk of Pardosa in the presence of male or female Hogna. We also assessed Pardosa antipredator responses and survival in the presence or absence of previously deposited chemical cues from male or female Hogna. In the absence of predator chemical cues, Pardosa survived significantly longer in the presence of male Hogna compared with female Hogna. We then assessed Pardosa survival in the presence of chemical cues from each Hogna sex by placing Pardosa in containers previously occupied by a female Hogna, a male Hogna, or no Hogna (control). We then introduced a female Hogna into each container and measured predation latency. Pardosa survived significantly longer in the presence of female and male cues compared with the control treatment. Median survival time of Pardosa was over four times longer on substrates with female Hogna cues compared with male cues, but this difference was not statistically significant. We tested Pardosa activity levels in the presence of chemical cues from male or female Hogna. Both Hogna sexes were maintained in separate containers after which we placed an adult female Pardosa in one of the containers or a blank control container. Pardosa significantly decreased activity in the presence of chemical cues from either sex relative to the control. Activity was lowest on substrates with female Hogna cues, but not significantly lower than on substrates with male Hogna cues. Results suggest that chemical information from male or female Hogna significantly reduces Pardosa activity which results in increased survival.     

The Effect of Predator Hunger on Chemically Mediated Antipredator Responses and Survival in the Wolf Spider Pardosa milvina (Araneae: Lycosidae)

The wolf spider Pardosa milvina exhibits effective antipredator behavior (reduced movement) in the presence of silk and excreta from a larger co‐occurring predatory wolf spider Hogna helluo. As the quantity and quality of the silk and excreta may vary with the hunger state of the predator, we tested if chemical cues from a hungry vs. satiated H. helluo affected the activity level and survival of P. milvina. Pardosa milvina response was measured on substrates containing chemical cues from (1) a satiated H. helluo, (2) a H. helluo that had been withheld food for 2 wk, (3) cues from adult domestic crickets (Acheta domesticus), or (4) a blank test substrate (20 replicates/treatment). Pardosa milvina activity level was recorded on each substrate over a 30‐min period using video‐tracking equipment (Videomex‐I^®; Columbus Instruments, Columbus, OH, USA). We then measured P. milvina survival in the presence of hungry or satiated H. helluo on cues from a hungry H. helluo, satiated H. helluo, or a blank control (2 × 3 design). Pardosa milvina significantly reduced activity in the presence of H. helluo cues and showed significantly less activity in the presence of cues from a hungry H. helluo compared with a satiated one. Cue type and predator hunger state significantly affected P. milvina survival in the presence of live predators. However, cues from hungry vs. satiated H. helluo resulted in no difference in P. milvina survival. Pardosa milvina can discriminate between hungry vs. satiated predators based on silk and excreta cues alone, but differences in behavior as a result of this discrimination did not translate into increased survival in the presence of a live predator.     

Anti‐Predator Behaviour in a Nocturnal Primate,the Grey Mouse Lemur (Microcebus murinus)

Although one‐third of all primates are nocturnal, their anti‐predator behaviour has rarely been studied. Because of their small body size, in combination with their solitary and nocturnal life style, it has been suggested that they mainly rely on crypsis to evade predators. However, recent studies revealed that nocturnal primates are not generally cryptic and that they exhibit predator‐specific escape strategies as well as alarm calls. In order to add to this new body of research, we studied anti‐predator strategies of nocturnal grey mouse lemurs experimentally. In order to elicit anti‐predator behaviour and alarm calls, we conducted experiments with a carnivore‐, snake‐ and raptor model. We also conducted playback experiments with mouse lemur alarm calls to characterize their function. In response to predator models, they exhibited a combination of anti‐predator strategies: in response to carnivore and snake models, mouse lemurs monitored the predator, probably to assess the potential risk that emanates from the predator. In response to raptor models they behaved cryptically and exhibited freezing behaviour. All mouse lemurs, except one individual, did not alarm call in response to predator models. In addition, during playback experiments with alarm calls, recorded during real predator encounters, mouse lemurs did not emit alarm calls nor did they show any escape behaviour. Thus, as in other nocturnal primates/mammals, mouse lemurs do not seem to rely on routinely warning of conspecifics against nearby predators.     

The Use of Two‐Way Linear Mixed Models in Multitreatment Meta‐Analysis

Summary Meta‐analysis summarizes the results of a series of trials. When more than two treatments are included in the trials and when the set of treatments tested differs between trials, the combination of results across trials requires some care. Several methods have been proposed for this purpose, which feature under different labels, such as network meta‐analysis or mixed treatment comparisons. Two types of linear mixed model can be used for meta‐analysis. The one expresses the expected outcome of treatments as a contrast to a baseline treatment. The other uses a classical two‐way linear predictor with main effects for treatment and trial. In this article, we compare both types of model and explore under which conditions they give equivalent results. We illustrate practical advantages of the two‐way model using two published datasets. In particular, it is shown that between‐trial heterogeneity as well as inconsistency between different types of trial is straightforward to account for.     

Non‐Selective and Time‐Dependent Behavioural Responses of Common Toads (Bufo bufo) to Predator Acoustic Cues

Acoustic predator recognition has rarely been studied in anurans, in spite of the fact that hearing is widespread in these animals and that it has been demonstrated to play an important role in both arthropods and other vertebrates. Using field playback experiments, we tested the hypothesis that adult common toads (Bufo bufo) are capable of recognizing natural vocalizations of a common predator, the Eurasian otter (Lutra lutra), and show antipredator responses. We found that toads exposed to both natural (two types of otter sounds) and synthetic stimuli [white noise (WN) and otter sound‐based amplitude modulated WN] increased time allocated to locomotion and escape behaviour. These responses were correlated with time elapsed from sunset to the onset of testing and were independent from the type of acoustic signal, toad features and other environmental factors monitored. We conclude that B. bufo has not developed a selective recognition of predator vocalizations, suggesting that low‐frequency or seismic sounds associated with predator movements may provide anurans with better cues about an approaching risk. We propose that the time‐dependent response to acoustic stimuli of common toads represents a case of threat‐sensitivity and demonstrates that it can occur even when the response to the threat is not predator specific.     

Prey Selection by an Apex Predator: The Importance of Sampling Uncertainty

The impact of predation on prey populations has long been a focus of ecologists, but a firm understanding of the factors influencing prey selection, a key predictor of that impact, remains elusive. High levels of variability observed in prey selection may reflect true differences in the ecology of different communities but might also reflect a failure to deal adequately with uncertainties in the underlying data. Indeed, our review showed that less than 10% of studies of European wolf predation accounted for sampling uncertainty. Here, we relate annual variability in wolf diet to prey availability and examine temporal patterns in prey selection; in particular, we identify how considering uncertainty alters conclusions regarding prey selection.Over nine years, we collected 1,974 wolf scats and conducted drive censuses of ungulates in Alpe di Catenaia, Italy. We bootstrapped scat and census data within years to construct confidence intervals around estimates of prey use, availability and selection. Wolf diet was dominated by boar (61.5±3.90 [SE] % of biomass eaten) and roe deer (33.7±3.61%). Temporal patterns of prey densities revealed that the proportion of roe deer in wolf diet peaked when boar densities were low, not when roe deer densities were highest. Considering only the two dominant prey types, Manly''s standardized selection index using all data across years indicated selection for boar (mean = 0.73±0.023). However, sampling error resulted in wide confidence intervals around estimates of prey selection. Thus, despite considerable variation in yearly estimates, confidence intervals for all years overlapped. Failing to consider such uncertainty could lead erroneously to the assumption of differences in prey selection among years. This study highlights the importance of considering temporal variation in relative prey availability and accounting for sampling uncertainty when interpreting the results of dietary studies.     

Cascading trait‐mediation: disruption of a trait‐mediated mutualism by parasite‐induced behavioral modification

Trait‐mediated indirect interactions (TMII) are important driving‐forces causing trophic cascades in aquatic and terrestrial food webs. Furthermore, since most biological communities are not simple food chains but complex networks of interactions, one TMII within a community might easily be influenced by another TMII. In other words, TMII themselves can be cascades with potential implications for community dynamics. Here we report on one of such cascade, where a parasitic fly induces behavioral changes that disrupt a trait‐mediated ant–hemipteran mutualism. We show that during parasite‐induced low‐activity periods, the ant Azteca instabilis fails to protect its mutualistic scale‐insect partner against predatory ladybeetles. Thus, in the presence of the parasite, ladybeetles ate as many scales in ant‐patrolled plants as they did in ant‐free plants. These results demonstrate how, through a cascade of trait‐mediated interactions, associations between members of a community can be drastically altered.