Versatile Predator Research Articles

Food Habits of the Javelin Sand Boa Eryx jaculus (Linnaeus 1758; Serpentes, Erycidae) in Sicily, Italy

The Javelin Sand Boa, Eryx jaculus, is reported to be a predator of mammals, lizards and their eggs, and occasionally of birds and invertebrates, but data on its diet are scarce and fragmentary. Here we describe some aspects of the feeding behavior of E. jaculus on the Mediterranean island of Sicily. A total of 132 individual snakes were examined. Prey remains were found in 43% of them, both in their feces (82.5%) and gut contents (17.5%). The number of snakes observed and their feeding rate decreased in August, probably as a result of the relatively higher temperatures. Feeding rate increases were observed in adult females in September, perhaps to enhance body reserves before hibernation. The overall prey spectrum is dominated by small mammals, with a frequency of occurrence of 71.4%, but also consisted of lizard eggs (30.2%) and lizards (7.9%). Lizards seem to be occasional prey, and our frequent detection of ingested autotomized tails suggests E. jaculus has low efficiency as a saurian predator. We observed a relationship between prey type and snout–vent length of the snakes. Lizard eggs are most frequently eaten by smaller snakes, which could be linked to gape size ontogenetic variation. We found differences in the prey spectrum between sexes and age classes. Our results indicate that juveniles, adult males, and females seem to adopt different foraging strategies. Females probably adopt ambush predation on small mammals, while juveniles are active foragers of lizard eggs. Adult males appear to be slightly more versatile predators, consuming both types of prey, probably because of their high mobility rates during the mating period.

Tracking killer whale movements in the Alaskan Arctic relative to a loss of sea ice

Killer whales (Orcinus orca) are highly intelligent and versatile predators. Though they have a consistent presence in southern Alaskan waters, they are not known to frequently or consistently venture into the typically ice-covered U.S. Arctic, where they risk ice entrapment. However, with the trend of decreasing sea ice in the Arctic Ocean, these top predators may be venturing into waters that were previously inaccessible to them. To expand our knowledge of killer whale movements in the Arctic, eight years of data (2010–2018) from four AFSC passive acoustic moorings (funded by NOAA S&T, the U.S. Navy, and BOEM) located in the Chukchi, Beaufort, and northern Bering Seas, were manually analyzed for the presence/absence of killer whale signals to examine interannual trends in the acoustic presence of killer whales. Results from our data indicate that killer whales spend more time than previously recorded in the Arctic, as far as the edge of the Chukchi Borderland, directly following the decrease in sea ice in these areas. These results speak to a changing Arctic, both in terms of the presence of killer whales themselves and in terms of the impact that increased killer whale predation could have on Arctic food webs.

Salvage logging after an insect outbreak reduces occupancy by snowshoe hares (Lepus americanus) and their primary predators

Salvage logging after a natural disturbance is controversial because it may disrupt forest succession and reduce the value of wildlife habitat, but few studies have examined consequences on predator-prey systems. For herbivores that consume early-seral vegetation, salvage logging may simultaneously improve food abundance and reduce protective cover, imposing trade-offs that influence their habitat selection and that of their predators. We examined habitat use by snowshoe hares (Lepus americanus)—a keystone prey species in the boreal forest—and their primary predators, Canada lynx (Lynx canadensis) and coyotes (Canis latrans), in response to salvage logging following a bark beetle outbreak in Yukon, Canada. We monitored hare, lynx, and coyote presence in beetle-affected forests and salvage-logged stands of different tree retention levels and ages (up to 25 years post-logging) using wildlife cameras, and modelled species occupancy as a function of forest structure at local and landscape scales. Snowshoe hares occupied stands with dense canopies and avoided salvage-logged stands regardless of retention class or age, selecting habitat with the most cover from aerial and terrestrial predators. Lynx and coyote generally used the same habitat as hares, selecting unsalvaged stands with high snowshoe hare occupancy. Habitat use by coyote and hare was more strongly linked than that of lynx and hare, perhaps because coyotes are versatile predators that can adjust their hunting tactics in dense habitat. Our study demonstrates that salvage-logged stands have lower value than beetle-affected forest for snowshoe hares and their predators in the short-term—regardless of retention levels—which may have localized impacts on boreal forest food webs. Higher tree retention, long harvest intervals, and small cut areas interspersed with large unlogged forest patches are recommended to mitigate negative impacts of salvage logging on these species.

A new species of Gulo from the Early Pliocene Gray Fossil Site (Eastern United States); rethinking the evolution of wolverines.

The wolverine (Gulo gulo) is the largest living terrestrial member of the Mustelidae; a versatile predator formerly distributed throughout boreal regions of North America and Eurasia. Though commonly recovered from Pleistocene sites across their range, pre-Pleistocene records of the genus are exceedingly rare. Here, we describe a new species of Gulo from the Gray Fossil Site in Tennessee. Based on biostratigraphy, a revised estimate of the age of the Gray Fossil Site is Early Pliocene, near the Hemphillian—Blancan transition, between 4.9 and 4.5 Ma. This represents the earliest known occurrence of a wolverine, more than one million years earlier than any other record. The new species of wolverine described here shares similarities with previously described species of Gulo, and with early fishers (Pekania). As the earliest records of both Gulo and Pekania are known from North America, this suggests the genus may have evolved in North America and dispersed to Eurasia later in the Pliocene. Both fauna and flora at the Gray Fossil Site are characteristic of warm/humid climates, which suggests wolverines may have become ‘cold-adapted’ relatively recently. Finally, detailed comparison indicates Plesiogulo, which has often been suggested to be ancestral to Gulo, is not likely closely related to gulonines, and instead may represent convergence on a similar niche.

Dietary composition and spatial patterns of polar bear foraging on land in western Hudson Bay

BackgroundFlexible foraging strategies, such as prey switching, omnivory and food mixing, are key to surviving in a labile and changing environment. Polar bears (Ursus maritimus) in western Hudson Bay are versatile predators that use all of these strategies as they seasonally exploit resources across trophic levels. Climate warming is reducing availability of their ice habitat, especially in spring when polar bears gain most of their annual fat reserves by consuming seal pups before coming ashore in summer. How polar bears combine these flexible foraging strategies to obtain and utilize terrestrial food will become increasingly important in compensating for energy deficits from lost seal hunting opportunities. We evaluated patterns in the composition of foods in scat to characterize the foraging behaviors that underpin the diet mixing and omnivory observed in polar bears on land in western Hudson Bay. Specifically, we measured diet richness, proportions of plant and animal foods, patterns in co-occurrence of foods, spatial composition and an index of temporal composition.ResultsScats contained between 1 and 6 foods, with an average of 2.11 (SE = 0.04). Most scats (84.9%) contained at least one type of plant, but animals (35.4% of scats) and both plants and animals occurring together (34.4% of scats) were also common. Certain foods, such as Lyme grass seed heads (Leymus arenarius), berries and marine algae, were consumed in relatively higher proportions, sometimes to the exclusion of others, both where and when they occurred most abundantly. The predominance of localized vegetation in scats suggests little movement among habitat types between feeding sessions. Unlike the case for plants, no spatial patterns were found for animal remains, likely due the animals’ more vagile and ubiquitous distribution.ConclusionsOur results suggest that polar bears are foraging opportunistically in a manner consistent with maximizing intake while minimizing energy expenditure associated with movement. The frequent mixing of plant-based carbohydrate and animal-based protein could suggest use of a strategy that other Ursids employ to maximize weight gain. Further, consuming high rates of certain vegetation and land-based animals that may yield immediate energetic gains could, instead, provide other benefits such as fulfilling vitamin/mineral requirements, diluting toxins and assessing new foods for potential switching.

Trophic ecology of the black drum, Pogonias cromis (Sciaenidae), in Mar Chiquita coastal lagoon (Argentina)

Summary This is the first documentation on the feeding habits of the black drum, Pogonias cromis, in waters of South America. The aim of the investigation was to determine the trophic ecology of P. cromis in the Mar Chiquita coastal lagoon (37°32′–37°45′S; 57°19′–57°26′W) from stomach content analyses of 109 P. cromis specimens. Samples in various sizes were collected monthly using various types of fishing gear. The results showed that this species is a benthic predator focusing on bivalves and crabs. permanova results indicated significant seasonal differences in the diet. This pattern reflected seasonal changes in prey abundance and availability, which produced changes in both foraging strategy and trophic niche breadth. This indicates that P. cromis is a versatile predator, adapting its feeding strategy in response to a seasonal shift of prey abundance, and indicating an opportunist behavior.

Strength of asymmetric competition between predators in food webs ruled by fluctuating prey: the case of foxes in tundra

In food webs heavily influenced by multi-annual population fluctuations of key herbivores, predator species may differ in their functional and numerical responses as well as their competitive ability. Focusing on red and arctic fox in tundra with cyclic populations of rodents as key prey, we develop a model to predict how population dynamics of a dominant and versatile predator (red fox) impacted long-term growth rate of a subdominant and less versatile predator (arctic fox). We compare three realistic scenarios of red fox performance: (1) a numerical response scenario where red fox acted as a resident rodent specialist exhibiting population cycles lagging one year after the rodent cycle, (2) an aggregative response scenario where red fox shifted between tundra and a nearby ecosystem (i.e. boreal forest) so as to track rodent peaks in tundra without delay, and (3) a constant subsidy scenario in which the red fox population was stabilized at the same mean density as in the other two scenarios. For all three scenarios it is assumed that the arctic fox responded numerically as a rodent specialist and that the mechanisms of competition is of a interference type for space, in which the arctic fox is excluded from the most resource rich patches in tundra. Arctic fox is impacted most by the constant subsidy scenario and least by the numerical response scenario. The differential effects of the scenarios stemmed from cyclic phase-dependent sensitivity to competition mediated by changes in temporal mean and variance of available prey to the subdominant predator. A general implication from our result is that external resource subsidies (prey or habitats), monopolized by the dominant competitor, can significantly reduce the likelihood for co-existence within the predator guild. In terms of conservation of vulnerable arctic fox populations this means that the likelihood of extinction increases with increasing amount of subsidies (e.g. carcasses of large herbivores or marine resources) in tundra and nearby forest areas, since it will act to both increase and stabilize populations of red fox.

Simultaneous defense against shell entry and shell crushing in a snail faced with the predatory shorecrab Carcinus maenas

Prey with versatile predators need diverse defenses. Such an example of a versatile predator is the voracious European green crab Carcinus maenas. Green crabs prey on snails by either crushing shells or, when shells are too tough to break, by extracting flesh through the shell opening (aperture). Among populations in the northwest Atlantic, the claw size of green crabs (an indicator of crushing strength) co-varies with shell mass of the intertidal snail Littorina obtusata (mass is an indi- cator of a shell's crushing resistance); thus shell-crushing predation appears to be an important part of the predator-prey interaction. We report that aperture occlusion and soft tissue withdrawal depth (two shell-entry defenses) of L. obtusata snails co-vary with their shell mass (an anti-crushing trait) among populations. When snails were fed directly to green crabs in the laboratory, populations with smaller shell openings and deeper withdrawal depths were less frequently killed by shell-entry attacks, and these same populations, with more massive shells, were also better at resisting shell- crushing attacks. Results provide compelling evidence that greater shell mass, a smaller shell open- ing, and deeper withdrawal depth are adaptive traits for snails faced with green crab predators. Furthermore, results suggest that American L. obtusata responded to the introduction of green crabs by escalating both anti-crushing and anti-entry defenses.

Toward a Quantitative Typology of Burglars: A Latent Profile Analysis of Career Offenders

Burglary is a serious, costly, and prevalent crime but prior typologies of burglars are mostly speculative and based on qualitative data. Using a sample of 456 adult career criminals, the current study used latent profile analysis to construct a methodologically rigorous quantitative typology. Four classes of burglars emerged: young versatile, vagrant, drug-oriented, and sexual predators. All groups demonstrated significant involvement in varied forms of crime, but the sexual predator group was the most violent and had the most serious criminal careers. Connections to the criminal career literature are offered and suggestions for further empirical study of offender typologies are discussed.

Activity, habitat use, feeding behavior, and diet of four sympatric species of Serranidae (Actinopterygii: Perciformes) in southeastern Brazil

Diplectrum formosum (the sand perch), Diplectrum radiale (the aquavina), Epinephelus marginatus (the dusky grouper) and Mycteroperca acutirostris (the comb grouper) are four sympatric serranid of remarkable ecological and commercial importance. This study investigated the feeding of these four species in the São Sebastião Channel, São Paulo State (southeastern Brazil), comparing their diet, habitat utilization and morphological features related to foraging. These four serranids are opportunistic visual predators that use a total of nine different tactics to capture their preys, feed mostly on crustaceans during the day and twilight, and keep stationary and quiescent at night. The ecomorphological study was conducted to test its predictive value to infer lifestyles. It was verified that such analysis should be used carefully and must be complemented by field observations. Although morphologically and behaviorally very similar, D. formosum and D. radiale showed different preferences to the substratum type used by large individuals, which are exclusively sit-and-wait predators. On the other hand, E. marginatus displayed more sedentary habits than M. acutirostris, the most versatile predator from the studied species. The studied species of Diplectrum and E. marginatus can be regarded as benthic serranids, while M. acutirostris could be viewed as a nektobenthic species.

Feeding habits of the sandskate Psammobatis extenta (Garman, 1913): sources of variation in dietary composition

Understanding the variation in the diet of skates is crucial for determining their roles in marine ecosystems. The diet of 458 sandskates, Psammobatis extenta, from Puerto Quequén, Argentina was quantified to determine whether there was geographical, sexual, ontogenetic, and/or seasonal variation in dietary composition. Cumulative prey-diversity curves reached a stable level at ~30 stomachs and thus the sample size was large enough to describe the overall diet of the sandskate. The diet comprised a variety of small invertebrates, suggesting that the sandskate is a secondary consumer (trophic level of 3.5). The most important prey items were gammarids, shrimps and, to a lesser extent, polychaete worms. A significant correlation was found between the diets of sandskates from south-eastern Brazil and Puerto Quequén, suggesting that in both locations they used similar resources and would have similar ecological roles. No difference was found between the diets of males and females, but ontogenetic and seasonal patterns were detected. Small sandskates preyed largely on gammarids and shrimps but consumed fewer polychaetes and brachyurans than larger individuals. In summer and winter, the most important prey item by number was gammarids, whereas the consumption of shrimps peaked in autumn. This ontogenetic and seasonal pattern indicates that large and small sandskates are versatile predators that can shift their diets in response to prey abundance.

Parental and predatory behaviour of Scytodes sp., an araneophagic spitting spider (Araneae: Scytodidae) from the Philippines

AbstractParental care, especially as it relates to our understanding of sociality, is a topic that has received considerable recent attention in research on spiders (Aviles, 1997). Predatory strategies, including foraging decisions, prey preferences and predatory versatility, have also been emphasized in the recent literature. The present paper is concerned with both of these areas, parental care and predatory strategies. Scytodes sp. indet. is a versatile predator that captures prey either in its web or away from webs, and prey capture may be either by ambush or by active pursuit regardless of whether in the presence and absence of webs. The web is a sparsely woven sheet across a concave upper leaf surface, with a three‐dimensional tubular nest linked to the sheet via a small opening. Leaves may be green and living or brown and dead. In the field, a wide range of insects and spiders is taken, but jumping spiders (Salticidae) are the dominant prey. Predatory attacks are by spitting, with large prey being spat at repeatedly before being subdued. After spitting, the scytodid wraps prey in silk before feeding. Eggs are enclosed in a silk egg sac. The female uses her chelicerae to hold her eggs until hatching. After hatching, there is an extended mother–offspring association, with juveniles tending to remain in their mother's web until after the third moult. Females take prey to their juveniles and either feed alongside the juveniles or leave the juveniles to feed alone.

Potential ecological implications from the introduction of the European green crab, Carcinus maenas (Linneaus), to British Columbia, Canada, and Washington, USA

We evaluate the potential impact of the European green crab Carcinus maenas (Linneaus) (Decapoda: Portunidae) on possible prey species in British Columbia, Canada, and Washington State, USA. This crab was first observed on the west coast of North America in San Francisco Bay, CA, in 1989. In early 1997, adult green crab were found in Coos Bay, Oregon, about 300 km further north than its previous known range limit (Humbolt Bay, CA). Ocean current transport of larvae may introduce it to Canada in the near future. The green crab is a versatile predator with a preference for molluscan and crustacean prey. In the Pacific, green crab seem to thrive best in habitats protected from oceanic swell, and the Strait of Georgia/Puget Sound are expected to provide ideal habitat, as are coastal estuaries in Washington State. These areas are main production areas for both intertidal bivalves and Dungeness crab (Cancer magister Dana) fisheries. It is expected that both bivalve and crab fisheries will be negatively impacted by the presence of green crab. Deltas in the Strait/Sound also support extensive migrating shorebird populations. Any change in densities of small invertebrates arising from green crab occurrence and predation may affect these migrating species, with ecological implications extending far beyond the actual potential range occurrence of green crab. We discuss the need for monitoring measures which will document the impact of this exotic species on local ecosystems when it ultimately extends its range to Canada.

Role as consumers

Cephalopods are voracious, versatile predators. They generally have a short life span and a single spawning event followed by death. Populations are subject to dramatic fluctuations and their impact on prey populations is equally variable. The prehensile arms and tentacles of cephalopods, coupled with a highly evolved sensory system, allow them to occupy a broad trophic niche and migrations enable populations to exploit the temporal and spatial variability of production systems and populations of prey. Shoaling is a common behavioural feature of many species which facilitates prey capture and contributes to the impact of cephalopods on prey populations. Research on cephalopod stomach contents is hampered because the beak is used to bite the prey into small pieces so hard parts, which are usually needed for identification of prey species, are often rejected causing potential bias in estimation of diet. Cephalopods may also feed unnaturally in the presence of sampling gear. Despite these problems there is a growing body of data on cephalopod predation collected using direct observations, conventional visual analysis of stomach contents and serological methods. Most species feed on small crustaceans as juveniles and shift the diet to larger fish and other cephalopods during growth. This shift is accompanied by ontogenetic changes in the allometry of the brachial crown. There is increasing evidence that myctophid fishes are an important food resource for oceanic squid. The diet and stock size of some commercially exploited squid populations is sufficiently well known to quantify the impact of a single generation on the prey community. Where there is predation on commercial stocks of fish and crustaceans, the effect of cephalopod feeding on recruitment may be significant. Cephalopods are trophic opportunists in marine food webs from polar to equatorial seas.

General activity and foraging tactics in a water bug

Diplonychus indicus is a highly versatile predator that forages both actively and from ambush. However, no correlations between predatory mode changes and predatory performance have yet been evidenced. The hypotheses that time spent foraging actively was proportional to time spent locomotory active and that time spent ambushing was proportional to time spent quiescent were tested during animal development. Locomotory activity increases during development due to increases in both frequency and duration of swimming bouts. The frequency of position changes increases as well. Eggbearing males were less active than other adults. However, the proportion of active foraging did not vary significantly with developmental stage and no correlations between activity level and predatory mode were found. Changes in predatory tactics inDiplonychus indicus differ from those reported in other predators as they are not related to any of the usual biotic or abiotic factors.

Craniodental remains ofPapio angusticeps from the haasgat cave site, South Africa

Haasgat is a fossil-bearing cave site that has yielded 83 craniodental fossils of early Papio.All of the Haasgat cave baboon fossil collection may be identified as Papio angusticeps.The Haasgat fossils of P. angusticepsextend the previously known size range of the species as identified at other sites. The concordance of this and other fauna with that of Kromdraai suggest that Haasgat probably dates to the terminal Pliocene. We hypothesize that the Haasgat baboons and associated fauna were accumulated by versatile predators operating in a cave in a montane forest environment with savannah or open woodland nearby.

Coupled Versus Uncoupled Functional Systems: Motor Plasticity In The Queen Triggerfish Balistes Vetula

ABSTRACT Teleost fishes typically capture prey with the oral jaws and perform most types of prey-processing behavior with the pharyngeal jaw apparatus. In these fishes, the motor patterns associated with the different stages of feeding are quite distinct, and fish can modify muscle activity patterns when feeding on different prey. We examined motor pattern variation in the queen triggerfish, Balistes vetula, a versatile predator that both captures and processes prey with its oral jaws. During feeding on three prey that differed in hardness and elusiveness, three distinct patterns of behavior could be identified on the basis of patterns of muscle activity: prey capture, buccal manipulation and blowing. During prey capture by suction feeding, the retractor arcus palatini muscle (RAP) commenced activity before the levator operculi muscle (LOP). In both buccal manipulation and blowing, the RAP began activity well after the onset of activity in the LOP. Both prey capture and buccal manipulation motor patterns varied when fish fed on different prey. When capturing hard-shelled and non-elusive prey, B. vetula did not employ suction feeding but, instead, the fish directly bit parts of its prey. The motor pattern exhibited during direct biting to capture prey was different from that during suction feeding, but was indistinguishable from the pattern seen during the repeated cycles of buccal manipulation. Harder prey elicited significantly longer bursts of activity in the jaw adductor muscles than did soft prey. In spite of the involvement of the oral jaws in virtually all stages of feeding, B. vetula shows levels of variation between patterns of behavior and types of prey characteristic of previously studied teleost fishes. Thus, the coupling of capture and processing behavior patterns in the repertoire of the oral jaws does not appear to constrain the behavioral versatility of this species.

Use of prey‐specific predatory behaviour by North American jumping spiders (Araneae, Salticidae) of the genus Phidippus

Prey‐capture behaviour of seven species of Phidippus is studied using two types of prey, house flies (adult Musca domestica) and caterpillars (cabbage loopers, larval Trichoplusia ni). Each species is shown to be a versatile predator which uses a different prey‐specific prey‐capture behaviour depending on whether prey is a fly or a caterpillar: spiders approached the two types of prey differently and leapt on them from different distances. Interspecific differences among Phidippus species are not pronounced, cxcept for variation in the distance from which spiders jumped and the spider's success at capturing a fly on the first try.

Predatory versatility in the water bug Diplonychus indicus

First instar Diplonychus indicus Venk. et Rao (Heteroptera:Belostomatidae) larvae possess a behavioural plasticity similar to that of adults. This highly versatile predator alternates frequently from foraging actively to ambushing and vice versa. No significant variations in the use of these two predatory modes during post-embryonic development could be evidenced. The present study stresses similarities between the use of different predatory modes by young and old larvae and by adults. Changes per unit time from one predatory mode to the other increased with age, as frequency of attempts increased with age. Adults changed predatory modes approximately seven times per hour. Most changes were made after one, two, or, more rarely, three predatory attempts of the same mode. The maximum number of consecutive attempts of one predatory mode increased with age. There was no evidence that any specialization occurred during development. No proximal causes for these changes of predatory mode were found. Changes were not correlated with the outcome of previous predatory attempts, nor did changing predatory mode increase the probability that the next attempt would be successful.

Factors influencing the choice of predatory tactics in a water bug, Diplonychus indicus Venk. & Rao (Heteroptera: Belostomatidae)

The tropical water bug Diplonychus indicus is a highly versatile predator that alternates quickly from active foraging to ambushing. The influence of hunger level, the presence of prey and environmental complexity on swimming, diving resting and foraging by adult males was investigated at the individual level, in a factorial experiment with three main treatments. There were simple relationships between these factors and the water bug's behaviour, and interactions between these three factors also affected foraging. The general distribution of foraging tactics between active search and ambushing was significantly influenced by the presence of perching sites (vegetation), but not by hunger levels although hungry bugs as well as bugs in the absence of perching sites were significantly more active than well-fed subjects or bugs in the presence of perching sites. In the presence of vegatation, predatory attempts included fewer dives and more attempts from ambush including preliminary orientations. Hunger level, however, did influence the distribution of ambush predatory tactics; the attempts by hungry subjects included more preliminary orientations. Capture efficiency was not affected by hunger level, but it was affected by the presence of perching sites. Under these experimental conditions the bugs appeared to be capable of modifying, to a certain extent, their predatory tactics in relation to the environment. Nevertheless, the choice of a predatory tactic did not appear to be taken on an all or none basis.