Prey Size Research Articles

Variation of parental and chick diet in opportunistic insectivorous European Bee-eaters

Insectivorous Palaearctic bird species associated with open habitats rely on high prey abundances, which are currently declining due to habitat loss and intensive agricultural practices. The European Bee-eater (Merops apiaster) is an opportunistic insectivore of open habitats, preying mainly on medium to large-sized flying insects. Its diet composition received some attention in the past, but the current variation in diet composition of birds breeding across different habitats, and between adults and chicks remains poorly known. In this study, we determine variation in bee-eaters’ diet in colonies located in five common habitats at the Iberian Peninsula. We also assess differences in the diet composition of chicks and adults and investigate seasonal diet selectivity of adults. Finally, we explore the variability in the size of prey provided to chicks throughout their growth period. Hymenoptera and Coleoptera were the most important groups for bee-eaters, with adults and chicks consuming 58.8% and 64.1% of hymenopterans and 37.6% and 28.6% of coleopterans, respectively. The proportion of Hymenoptera (42.3–55.7%) and Coleoptera (43.3–53.5%) in the diet was similar in colonies in pasture and oak habitats. But Hymenoptera dominated (83.8% and 95.7%) in meadow and mixed forest colonies. Despite being a generally opportunistic predator, adult bee-eaters provide their progeny with an increasing proportion of larger insects through chick development. Moreover, they equally take Hymenoptera and Coleoptera for themselves and their chicks, even when the abundance of these insects decreases seasonally. Overall, these results suggest that local prey availability associated with specific habitats influences diet composition and that regional declines in certain groups may, therefore, affect insectivore species differently according to their dietary and habitat preferences.

Feeding habits of the longfin goatfish Upeneus supravittatus Uiblein and Heemstra, 2010, along Chennai coast, south India

Recognising the need to understand the feeding habits of marine fishes, a study was undertaken on the longfin goatfish Upeneus supravittatus Uiblein and Heemstra, 2010, which contributed to trawl fisheries along Chennai coast (south-east coast of India). Dataon trophic attributes such as mouth gape area, gill raker counts, stomach and intestine lengths and gut condition and contents were collected and analysed to determine condition index, index of relative importance (IRI), niche breadth and trophic level (TrL) with reference to two variables, namely, body size (small, medium and large) and season (post north-east monsoon (PNE); summer (SUM); south-west monsoon (SW); north-east monsoon (NE). The mouth gape area of U. supravittatus was 129.3 mm2. The maximum body depth-total length ratio was 1:5.0; gill rakers in lower arch was 29 and the relative intestine length was 0.48. Empty stomach contributed 56.1% of the samples. U. supravittatus fed on prey belonging to 25 Orders and >40 Genera. Decapods such as shrimps and crablets were the main prey followed by fishes. The IRI of decapods was 6474 and that of fishes was only 193. The maximum prey size predated by the fish was 33.5 and 9.8% in terms of the predator’s length and weight, respectively. Higher prey diversity was noticed in small size group and during south-west monsoon season. The narrow niche breadth of 0.20 showed the selective nature of the fish to feed on decapods. The fish is a benthic carnivore with a mean trophic level of 3.58. The trophic level decreased with body size. Diet similarity was evident between north-east and post north-east monsoon and between summer and south-west monsoon seasons. Diversity indices showed marginal variation in prey diversity among size groups and among seasons. This study paves way for estimating production efficiency of U. supravittatus. Keywords: Diet composition, Index of relative importance, Trophic level, Trophic morphology, U. supravittatus

Variable juvenile growth rates and offspring size: a response to anthropogenic shifts in prey size among populations.

Environmental variables, such as resource quality, shape growth in organisms, dictating body size, an important correlate of fitness. Variation in prey characteristics among populations is frequently associated with similar variation in predator body sizes. Anthropogenic alterations to prey landscapes impose novel ecological pressures on predators that may shift predator phenotypes. Research has focused on determining the adaptability of the phenotypic response by testing its genetic heritability. Here, we asked if anthropogenic shifts in prey size across the landscape correlate with juvenile growth rates among populations of watersnakes with divergent life-history phenotypes. We sought to determine if growth rate variation is the product of genetic adaptation or a non-heritable phenotypic response. Using a common-garden design, we measured growth of neonate snakes from fish farms varying in prey size. We found juvenile growth rates are faster for snakes with larger initial body sizes and from populations with larger average prey sizes. Our data suggest variability in juvenile grow rates within and among populations are not the product of genetic adaptation, but the indirect consequence of initial offspring size variation and prey consumption. We propose larger offspring sizes may favor increased juvenile growth rates, mediated through a larger morphological capacity to consume and process energy resources relative to smaller individuals. This experiment provides evidence supporting the growing body of literature that non-heritable responses may be significant drivers of rapid phenotypic divergence among populations across a landscape. This mechanism may explain the stability and colonization of populations in response to rapid, human-mediated, landscape changes.

Flash behaviors protect prey from avian predators

Abstract It has been proposed that flash behaviors, defined as the transient display of conspicuous color patches during escape, serve as an anti-predator defense in camouflaged prey. While recent studies in humans have demonstrated the effectiveness of flash behaviors in improving the survival of artificial prey, it remains unclear whether these benefits also arise in more natural systems involving non-human predators. This study investigated the adaptive significance of flash behaviors using chicks (Gallus gallus domesticus) as predators and virtual prey. Our experiments revealed that prey employing flash behaviors consistently enhanced their survival rate compared to non-flashing prey. Additionally, prey with non-conspicuous escape colors, though distinct from their resting colors, also showed a higher survival rate than non-flashing prey, challenging the conventional belief that conspicuous colors are required for search interference. An interplay between prey size and flash behaviors in enhancing survival was evident, with larger prey benefiting more than smaller prey. We found no evidence to suggest that being hidden before initiating an escape confers a survival advantage to flashing prey compared to being visible before escape. This study sheds light on the adaptive benefits of flash behaviors against natural predators and contributes to our understanding of the widespread occurrence of hidden color signals in camouflaged prey. We encourage further studies to explore the effectiveness of remaining hidden in flashing prey when confronted with natural predators, as well as how predators might learn to overcome the deception of flash behaviors.

Feeding mode drives mandibular shape in extant Delphinidae

AbstractDelphinidae is the most diverse family within the toothed whale clade, displaying two biosonar modes, different feeding strategies, and diving and habitat adaptations. This work examines the delphinid mandible to determine the association between shape, size and ecological variables in extant species. Geometric morphometric analysis on 95 mandibles belonging to 30 (out of 38) extant species, representatives of all 17 extant genera, was performed in occlusal (or dorsal) and lateral (or labial) view. The results reveal that feeding mode and climate primarily drive mandibular shape in extant species. Biosonar mode is an evolutionary driver in mandibular shape in occlusal view, while diet and maximum prey size play a significant role in size only in both views. By contrast, Diving Ecology, Superficial Temperature and Rostral index do not play a significant role in driving delphinid mandibular shape and size.

Prey size and ecological separation in spinosaurid theropods based on heterodonty and rostrum shape.

Members of the dinosaur clade Spinosauridae had numerous traits attributed to feeding in or around water, and their feeding apparatus has often been considered analogous to modern crocodylians. Here we quantify the craniodental morphology of Spinosauridae and compare it to modern Crocodylia. We measured from spinosaurid and crocodylian skeletal material the area of alveoli as a proxy for tooth size to determine size-heterodonty. Geometric morphometrics were also conducted on tooth crowns and tooth bearing regions of the skull. Spinosaurids overall had relatively large alveoli, and both they, and crocodylians, had isolated regions of enlarged alveoli. Spinosaurines also had enlarged alveoli along the caudal dentary that baryonychines lacked, which instead had numerous additional caudal tooth positions. Size-heterodonty was positively allometric, and spinosaurids overlapped with generalist/macro-generalist crocodylians of similar sizes. Spinosaurid crown shape morphologies overlapped with certain slender-longirostrine crocodylians, yet lacked molariform distal crowns typical of most crocodylians. Spinosaurid rostra and mandibles were relatively deep with undulating margins correlating with local tooth sizes, which may indicate a developmental constraint. Spinosaurines had a particularly long concavity caudal to their rosette of anterior cranial teeth, with a corresponding bulbous rostral dentary. The spinosaurid feeding apparatus was well suited for quickly striking and creating deep punctures, but not cutting flesh or durophagy. The jaws interlocked to secure prey and move it deeper into the mouth. The baryonychines probably did little oral processing, yet spinosaurines could have processed relatively large vertebrates. Overall, there is no indication that spinosaurids were restricted to fish or small aquatic prey.

Evidence for a by‐product mutualism in a group hunter depends on prey movement state

Abstract Group‐hunting animals have been shown to engage their prey in long pursuits (kms) to increase capture success, but the evidence for this is limited to a few terrestrial species. This predation strategy may be effective in the open‐ocean, where group‐hunts are characterised by large predator–prey size ratios and there are few places for prey to hide. However, recording the attack rates, capture rates and capture success probabilities of grouping predators during long‐distance pursuits through the open ocean, remains a significant challenge. Here we use a combination of underwater and aerial video to assess the attack and capture behaviour of striped marlin, Kajikia audax, in relation to the movement of their schooling prey (‘stationary’ and ‘mobile’ movement states) during group hunts. We found that the attack rate was higher when the prey school was ‘stationary’ and, during these times, individual marlin could make longer sequences of uninterrupted attacks on the prey school, effectively monopolising the prey resource for short periods over conspecifics. When the prey school was ‘mobile’, the attack pattern changed and individual marlin alternated their attacks on the prey school more frequently. Capture success probability (likelihood of capture per attack) was not affected by prey movement state. However, attacks on ‘mobile’ schools resulted in more prey fish becoming isolated from the school, and these isolated prey were easily captured—not by the attacker but by conspecifics swimming nearby. The likelihood of a prey becoming isolated from a ‘mobile’ school was predicted by prey school speed, with a 0.1 m s−1 increase leading to an 18.01% increase in the chance of isolation. Altogether this meant the capture rate at the group level was highest when the prey school was ‘mobile’ rather than ‘stationary’ because the predators that were pursuing the ‘mobile’ prey school had an increased availability of isolated and easy to capture prey. This mechanism provides evidence for a by‐product mutualism selecting for conspecific group formation and we discuss our findings in consideration of the social structure of the hunting group and the type of prey. Read the free Plain Language Summary for this article on the Journal blog.

Gelatinous filter feeders increase ecosystem efficiency

Gelatinous filter feeders (e.g., salps, doliolids, and pyrosomes) have high filtration rates and can feed at predator:prey size ratios exceeding 10,000:1, yet are seldom included in ecosystem or climate models. We investigated foodweb and trophic dynamics in the presence and absence of salp blooms using traditional productivity and grazing measurements combined with compound-specific isotopic analysis of amino acids estimation of trophic position during Lagrangian framework experiments in the Southern Ocean. Trophic positions of salps ranging 10–132 mm in size were 2.2 ± 0.3 (mean ± std) compared to 2.6 ± 0.4 for smaller (mostly crustacean) mesozooplankton. The mostly herbivorous salp trophic position was maintained despite biomass dominance of ~10-µm-sized primary producers. We show that potential energy flux to >10-cm organisms increases by approximately an order of magnitude when salps are abundant, even without substantial alteration to primary production. Comparison to a wider dataset from other marine regions shows that alterations to herbivore communities are a better predictor of ecosystem transfer efficiency than primary-producer dynamics. These results suggest that diverse consumer communities and intraguild predation complicate climate change predictions (e.g., trophic amplification) based on linear food chains. These compensatory foodweb dynamics should be included in models that forecast marine ecosystem responses to warming and reduced nutrient supply.

Big pythons, big gape, and big prey

Knowing the size of prey that predators can consume facilitates understanding and predicting their ecological impact. Burmese Pythons (Python bivittatus) are apex predators that are larger than all but a few snake species, and their prey, which are swallowed whole, cannot exceed the size of their maximal gape. However, prey sizes smaller than maximal gape may occur because of what snakes select or if capturing and swallowing certain prey is prohibitively difficult. Our study quantified the maximal gape of three large Burmese Pythons (SVLs 410-520 cm), including the longest specimen captured in Florida (where they are invasive) and one specimen that was captured while eating a deer. All three specimens had maximal gape diameters of 26 cm that exceeded the previously reported maximal value of 22 cm, and the soft tissues between the lower jaws accounted for 56-59% of the maximal gape area. Combining our new data with previous data significantly affected the scaling equations predicting maximal gape. The smallest specimen in our study ate a 35 kg deer, which was 93% of its maximal gape area. Hence, in addition to eating prey with large absolute size, Burmese Pythons in nature also eat prey with a size near the limit imposed by gape, but how frequently this occurs remains unclear.

Individual dietary specialization and intraspecific morphological divergence of an endemic fish species: the case of Glanidium ribeiroi in the Iguassu ecoregion

ABSTRACT Because of the importance of information about endemic species and global biodiversity ecoregion, we tested the hypothesis that individuals of Glanidium ribeiroi (endemic species in the Iguassu ecoregion) are specialists and that this specialization decreases with increasing body size, especially concerning the size of the mouth and head, which can be limiting for the quantity and size of prey consumed by smaller individuals. Fish sampling was conducted monthly using gill nets and longlines from 2013 to 2016 in the main channel of the Iguaçu River and two tributaries. We observed the consumption of aquatic insects by smaller individuals and seeds, unidentified fish, and Decapoda by larger individuals. Individual dietary specialization was high and related to head width. The morphological traits of smaller-sized individuals were related to displacement and movement (larger peduncle), and the larger-sized individuals were related to high performance in the exploitation and prey acquisition (larger head and mouth, dorsal eyes, longer intestines). Our results highlight the importance of assessing individual variations within a population, favoring an understanding of population dynamics. In addition, morphological differences may imply differences in the use of habitat and food resources between individuals of larger and smaller body sizes and influence individual specialization.

Saugeye diets in southern reservoirs and insight for predatory control of stunted crappie

AbstractObjectiveSaugeye (Sauger Sander canadensis × Walleye S. vitreus) have been introduced in reservoirs for several purposes, including as a top‐down control to combat stunting in crappie Pomoxis spp. populations. However, no comprehensive diet evaluation has been completed in southern reservoirs. Our objectives were to assess variability in saugeye diet compositions, explore factors influencing crappie presence in saugeye diets, and investigate trends in prey size to inform management strategies regarding predatory control of crappie populations.MethodsWe collected 2638 saugeye diets from six Oklahoma reservoirs. We used permutational multivariate analysis of variance to test differences in diet compositions among saugeye lengths, study reservoirs, and seasons, and we used logistic regression models to correlate the presence of crappie in diets with saugeye size, season, crappie abundance, productivity, and turbidity. Finally, we used bivariate plots of diet indices and quantile regression to explore trends in prey importance and prey size relative to saugeye size.ResultSaugeye diet compositions were best explained by saugeye size, followed by study reservoir and season. Saugeye exhibited an ontogenetic shift from Inland Silverside Menidia beryllina to shad Dorosoma spp., and crappie were eaten infrequently in comparison. The presence of crappie prey in diets was most correlated with saugeye size (primarily large saugeye), followed by higher crappie abundance, lower reservoir productivity, and season (highest in fall). Saugeye consumed larger prey than most piscivores relative to predator size.ConclusionOur results indicated that dominant prey of saugeye transitioned from smaller‐bodied fishes to larger shad as they grew when both prey types were available, which may have implications for growth and recruitment. Ultimately, the low and variable use of crappie prey may lead to inconsistent predatory effects on crappie populations, and large saugeye may exert greater top‐down pressure on crappie in lakes with lower productivity or higher crappie abundance.

Integrating eDNA metabarcoding and citizen science enhances avian ecological research.

Research Highlight: Bourbour etal., 2024. Feeding en route: Prey availability and traits influence prey selection by an avian predator on migration. Journal of Animal Ecology. Diet selection plays a key role in the eco-evolutionary dynamics of animals, exhibiting substantial variability across species, environments and seasons. The complex interplay between movement capability, hunting strategies, habitat use, prey traits and availability shapes the foraging patterns of avian predators. However, detailed information on how these birds exploit their extensive territories remains limited. In this study, Bourbour etal. utilised a novel integration of eDNA metabarcoding and citizen science to explore predator-prey interactions between migrating sharp-shinned hawks (Accipiter striatus) and an ephemeral avian prey community along North America's Pacific flyway. The research identified 1396 detections from the diet (65 species) of 588 migrating sharp-shinned hawks. Hawks' diet composition correlated with prey abundance indices sourced from the eBird database throughout the migration season, highlighting the significant impact of prey availability-shaped by migration tendency, flocking behaviour, and habitat-on raptor-songbird interactions. Notably, the study also found significant differences in prey size between male and female hawks, indicating that sexual dimorphism has led to diverse foraging strategies during migration. These findings underscore the potential of combining eDNA metabarcoding with citizen science to deepen our understanding of the foraging ecology of highly mobile and wide-ranging birds, as well as to monitor complex and vast ecosystems.

Omega-3 fatty acids-critical for the marine food web and for seabird productivity

Abstract Seabird reproductive success in northern latitudes is often linked with prey abundance, availability, size, or species. Causes are often broadly explained as changes in ocean currents/temperatures, or diets. Few studies trace diets down the food web to primary producers, thus missing what I propose as an underlying cause of seabird colony failure, dietary abundance of essential omega-3 polyunsaturated fatty acids (PUFA). PUFA differ from other nutrients because they are, in part, ligands—critical for reproduction and other physiological processes for the entire marine food web, not just for seabirds. Diatoms are one of the few life forms that can produce PUFA de novo, and a lack of PUFA in zooplankton and fish reduces their abundance and productivity, with consequences up the food web. Since the mid-1980s, historical prey of breeding seabirds has decreased, and frequency of colony failures has increased. In years of failure, prey often had less fat than historically preferred species. Likewise, proportions of alternate species’ PUFA, from published papers, show lower values than in historical prey. Production of PUFA by diatoms is depressed in warmer and more acidic environments, and I hypothesize that these warmer and more acidic seas have affected production of PUFA over the past 3–4 decades. Assuming this is true, I propose that these lower amounts of PUFA have negatively impacted the breeding success of all members of the marine food web, not just seabirds.

Gape-limited invasive predator frequently kills avian prey that are too large to swallow.

Gape-limited predators (e.g., snakes, many fish) are not generally expected to pose a predation threat to prey that are too large for them to swallow. However, the extent to which snakes predate on prey that exceed their gape limitation remains largely unknown. We conducted the first study to investigate the influence of both prey and predator sizes on the frequency of ingestion success by snakes in a natural system. We combined survival monitoring of an avian prey species (Aplonis opaca) via radio-telemetry with a survey of the size distribution of their major predator (Boiga irregularis) on Guam. This allowed us to assess (1) the frequency of unsuccessful ingestion by the predator, (2) whether the size of the prey predicts ingestion success, (3) whether the size of the predator predicts ingestion success, and (4) the relationship between prey and predator sizes in successful ingestion attempts. We found that nearly half (47.95%) of ingestion attempts by snakes on fledgling birds were unsuccessful, and no instances where unsuccessful ingestion caused the mortality of the snake. Attempts to consume smaller fledglings were as likely to be unsuccessful as attempts to swallow larger fledglings. However, snakes that successfully ingested fledglings were among the largest snakes in the population, and larger than average conspecifics attracted to endothermic prey. The smallest snakes that successfully ingested fledglings attained remarkably high relative prey mass values for their species, consuming prey weighing up to 79.9% of their own mass. Our study indicates that B. irregularis routinely predate prey that are too large for them to successfully ingest, which causes mortality to the prey but poses little risk to the predator. The potential reward for snakes in consuming oversized prey may outweigh the inherent risks, while instances of predation that do not result in consumption may have considerable impacts on prey populations.

Size‐specific reduction in kelp consumption by New Zealand urchins exposed to chemical cues from the red rock lobster

AbstractSea urchins can strongly reduce their mobility, exposure to predation, and feeding rates upon detection of chemical cues produced by predators, driving behavioral effects on grazing activity that may contribute to macroalgal community dynamics. However, the extent of chemically induced antipredator behaviors in urchins can vary by predator–prey species pair and ecological context and is therefore important to characterize in novel settings. Additionally, the effect of predator and prey size on urchin reactions to predator cues has rarely been considered, with the few existing examples yielding mixed conclusions. Here, we used a replicated split‐plot experiment to measure the effects of red rock lobsters (Jasus edwardsii) on consumption of macroalgae by the New Zealand sea urchin (Evechinus chloroticus) across a range of predator and prey body sizes. Overall, per‐capita consumption rates of kelp by urchins declined by 30% in the presence of lobsters, though feeding activity varied widely among individuals. Based on mass‐specific measurements of feeding rates, responses to predator cues appeared similar across all urchin sizes but only yielded distinguishable differences in the amount of kelp consumed in trials with larger urchins due to their considerably higher feeding capacity. Conversely, consumption rates of kelp by urchins had no apparent relationship with lobster size, likely due to chemical cue saturation in our experimental setting or a risk gradient that was insufficient to elicit a graded behavioral response. Our findings provide new evidence for a nonconsumptive effect of lobsters on feeding rates of an important grazer that can potentially reinforce the ecological role of this key predator in New Zealand kelp beds.

Feeding en route: Prey availability and traits influence prey selection by an avian predator on migration.

During animal migration, ephemeral communities of taxa at all trophic levels co-occur over space and time. The interactions between predators and prey along migration corridors are ecologically and evolutionarily significant. However, these interactions remain understudied in terrestrial systems and warrant further investigations using novel approaches. We investigated the predator-prey interactions between a migrating avivorous predator and ephemeral avian prey community in the fall migration season. We tested for associations between avian traits and prey selection and hypothesized that prey traits (i.e. relative size, flocking behaviour, habitat, migration tendency and availability) would influence prey selection by a sexually dimorphic raptor on migration. To document prey consumption, we sampled trace prey DNA from beaks and talons of migrating sharp-shinned hawks Accipiter striatus (n = 588). We determined prey availability in the ephemeral avian community by extracting weekly abundance indices from eBird Status and Trends data. We used discrete choice models to assess prey selection and visualized the frequency of prey in diet and availability on the landscape over the fall migration season. Using eDNA metabarcoding, we detected prey species on 94.1% of the hawks sampled (n = 525/588) comprising 1396 prey species detections from 65 prey species. Prey frequency in diet and eBird relative abundance of prey species were correlated over the migration season for top-selected prey species, suggesting prey availability is an important component of raptor-songbird interactions during fall. Prey size, flocking behaviour and non-breeding habitat association were prey traits that significantly influenced predator choice. We found differences between female and male hawk prey selection, suggesting that sexual size dimorphism has led to distinct foraging strategies on migration. This research integrated field data collected by a volunteer-powered raptor migration monitoring station and public-generated data from eBird to reveal elusive predator-prey dynamics occurring in an ephemeral raptor-songbird community during fall migration. Understanding dynamic raptor-songbird interactions along migration routes remains a relatively unexplored frontier in animal ecology and is necessary for the conservation and management efforts of migratory and resident communities.

The trophic strategy of the European honey‐buzzard Pernis apivorus during breeding: extravagant specialization or ingenious solution?

This article provides insight into the trophic strategy of a little‐known top predator and allows for a better understanding of the selective pressures that shape its diet. We studied the diet of European honey‐buzzards, a raptor specialized in consuming social wasp brood. The ratio of predator to prey biomasses is one of the highest among raptors. Considering the prey size and ingestion rate hypothesis, we investigated the honey‐buzzard's preferences for native and exotic eusocial vespid species. We also described other prey items in the diet and how diet changes throughout the breeding season. We installed trail cameras in 24 honey‐buzzard nests in north‐western Spain in 2018–2021. We estimated the proportion and daily rate of delivery of native common‐wasps, invasive Asian‐hornets, reptiles, and birds and the honey‐buzzard's preferences for vespid species. We performed LMMs, GLMMs, and CLMMs to analyse relationships between response variables and predictors. Honey‐buzzards mainly consumed vespids (82% of prey). Common‐wasps and Asian‐hornets were almost the only two vespids consumed. The invasive hornet was the second most consumed prey, but common‐wasps were preferred. Vespids became more important as the age and number of nestlings increased. Our results suggest that this diet is the adaptive result of the conflict between being a median‐sized insect‐eating nidicolous raptor and collecting enough morsels for the growth of its nestlings. This would allow them to deliver a relatively large amount of biomass to the nest with a high ingestion rate. We discussed implications of our findings for the management of the invasive wasp.

Prey size reflected in tooth wear: a comparison of two wolf populations from Sweden and Alaska.

Ingesta leaves distinct patterns on mammalian teeth during mastication. However, an unresolved challenge is how to include intraspecific variability into dietary reconstruction and the biomechanical aspects of chewing. Two extant populations of the grey wolf (Canis lupus), one from Alaska and one from Sweden, were analysed with consideration to intraspecific dietary variability related to prey size depending on geographical origin, sex and individual age as well as tooth function. Occlusal enamel facets of the upper fourth premolars, first molars and the second lower molar were analysed via three-dimensional surface texture analysis. The Swedish wolves displayed facets characterized by higher peaks and deeper, more voluminous dales, featuring an overall rougher surface than the wolves from Alaska. Compared to females, the Swedish male wolves had a slightly larger dale area and hill volume on their facets. Upper fourth premolars are smoother and had higher values in texture direction compared to upper first molars. The upper first molars were rougher than the occluding lower second molars and were characterized by larger and deeper dales. We find evidence supporting intraspecific dietary segregation, and antagonistic asymmetry in occlusal wear signatures. The data offer new insights into the roles of apex predators like the grey wolf.

Fitness effects of symbiotic relationships between arthropod predators: Synergy in a three‐way spider symbiosis

Abstract Symbiotic relationships shape ecological communities and often involve more than two species. Yet few experimental studies examine the impact of symbioses involving three species, particularly any mediating role of third parties, and none involving symbioses of predators. We investigated experimentally the synergistic and antagonistic fitness effects of three symbiotic spider predators across a broad latitudinal range and involving different species combinations. The three‐dimensional web complex of Cyrtophora spiders is a habitat patch to different associates—species of Argyrodes and web‐building Leucauge spider guests. Our field experiments, which manipulated the presence of each guest species and determined the subsequent host weight change, revealed a remarkable consistency in fitness outcomes across the three populations, with the consequences of the interactions between two species depending upon the services provided by a third. Cyrtophora hosts intercepted more prey when web‐building Leucauge guests were present and thus gained more weight. In contrast, Argyrodes guests exerted a fitness cost on their Cyrtophora host, but only when Leucauge guests were absent. A comparison of the prey consumed by Cyrtophora hosts and Argyrodes guests revealed that their diets (reflected in the size of prey) overlapped less in the presence of Leucauge web‐building guests. Our novel experimental study highlights the importance of exploring synergistic effects in multi‐species symbioses. Read the free Plain Language Summary for this article on the Journal blog.

Evaluating the Use of Chemical Weapons for Capturing Prey by a Venomous Mammal, the Greater Slow Loris (Nycticebus coucang).

Few mammals are venomous, including one group of primates-slow (Nycticebus spp.) and pygmy (Xanthonycticebus spp.) lorises. Hypotheses for the evolutionary function of venom in these primates include defense from predators or ectoparasites, communication or competition with conspecifics, and the capture of prey. We tested the prey capture hypothesis in 75 trials with 22 wild-caught greater slow lorises (N. coucang) housed in a rescue center in Java, Indonesia. We experimentally offered the slow lorises arthropod prey items varying in size, escape potential, and toxicity and recorded venom-related and predatory behaviors using live and video observations. The slow lorises visually targeted arthropod prey, approached it quickly and efficiently, and captured it with a manual grasping motion. They rarely performed venom-related behaviors and seemed to do so in a defensive context. The slow lorises exhibited little variation in pre-capture behavior as a function of prey size or escape potential. In response to noxious prey, the slow lorises performed tongue-flicking and other investigative behaviors that indicate they are using chemosensory input to assess prey characteristics. These data suggest it is unlikely that slow lorises use chemical weapons to subdue arthropod prey and may support, instead, a defensive function for slow loris venom.