Impact of differential predation potential on eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) faunal community structure

The trophic structure of fauna within eelgrass beds (Zostera marina) was assessed at two sites in Little Egg Harbor, New Jersey, USA during the summer of 1999. Although the sites were similar with respect to both Z. marina shoot density and plant biomass, they differed significantly in the relative distribution of large predatory fish (e.g., Cynoscion regalis, Paralichthys dentatus, Morone saxatilis). Site One, Marsh Elder, was characterized by a significantly greater catch per unit effort for large predators than Site Two, Shelter Island. Gut content analysis provided direct evidence of trophic linking and significant declines between these fish and four of the five most abundant organisms collected in throw traps used to analyze the density of large benthic prey/small predators. The densities of grass shrimp (Palaemonetes spp. Hippolyte zostericola), blue crab (Callinectes sapidus), and small predatory fish (e.g., Syngnathus fuscus, Opsanus spp., Tautoga onitus) were significantly reduced at Marsh Elder, potentially as a direct impact of large predatory fish. In turn, the differences in the density of small predators observed between sites produced either a significant positive or negative effect on the distribution of small benthic prey (e.g., polychaetes, amphipods), resulting in a two-step trophic cascade within the system. Additionally, an analysis of similarities defined each site independently for both large prey/small predators and small benthic prey community structure. Although the mechanism which produced the differences in the distribution of large predatory fish remains unknown, their impact on faunal community structure mediated not only the distribution of their potential prey, but also subsequent lower trophic levels.     

The predatory ecology of Deinonychus and the origin of flapping in birds

Most non-avian theropod dinosaurs are characterized by fearsome serrated teeth and sharp recurved claws. Interpretation of theropod predatory ecology is typically based on functional morphological analysis of these and other physical features. The notorious hypertrophied 'killing claw' on pedal digit (D) II of the maniraptoran theropod Deinonychus (Paraves: Dromaeosauridae) is hypothesized to have been a predatory adaptation for slashing or climbing, leading to the suggestion that Deinonychus and other dromaeosaurids were cursorial predators specialized for actively attacking and killing prey several times larger than themselves. However, this hypothesis is problematic as extant animals that possess similarly hypertrophied claws do not use them to slash or climb up prey. Here we offer an alternative interpretation: that the hypertrophied D-II claw of dromaeosaurids was functionally analogous to the enlarged talon also found on D-II of extant Accipitridae (hawks and eagles; one family of the birds commonly known as "raptors"). Here, the talon is used to maintain grip on prey of subequal body size to the predator, while the victim is pinned down by the body weight of the raptor and dismembered by the beak. The foot of Deinonychus exhibits morphology consistent with a grasping function, supportive of the prey immobilisation behavior model. Opposite morphological trends within Deinonychosauria (Dromaeosauridae + Troodontidae) are indicative of ecological separation. Placed in context of avian evolution, the grasping foot of Deinonychus and other terrestrial predatory paravians is hypothesized to have been an exaptation for the grasping foot of arboreal perching birds. Here we also describe "stability flapping", a novel behaviour executed for positioning and stability during the initial stages of prey immobilisation, which may have been pivotal to the evolution of the flapping stroke. These findings overhaul our perception of predatory dinosaurs and highlight the role of exaptation in the evolution of novel structures and behaviours.     

Evolution of reversed sexual size dimorphism and role partitioning among predatory birds, with a size scaling of flight performance

To explain the adaptive significance of sex role partitioning and reversed sexual size dimorphism among raptors, owls and skuas, where females are usually larger than males, we combine several previous hypotheses with some new ideas. Owing to their structural and behavioural adaptations for prey capture, predatory birds have better prospects than other birds of defending their offspring against nest predators. This makes sex role partitioning advantageous; one parent guards the offspring while the other forages for the family. Further, among predators hunting alert prey such as vertebrates, two mates because of interference may not procur much more food than would one mate hunting alone. By contrast, two mates feeding on less alert prey may together obtain almost twice as much food as one mate hunting alone. For these reasons, partitioning of breeding labours might be adaptive only in predatory birds. An initial imbalance favours female nest guarding and male foraging: the developing eggs might be damaged if the female attacks prey; their mass might reduce her flight performance; she must visit the nest to lay; and the male feeds her before she lays (‘courtship feeding’). Increased female body size should enhance egg production, incubation, ability to tear apart prey for the young, and, in particular, offspring protection in predatory birds. Efficient foraging during the breeding period then becomes most important for the male. This imposes great demands on aerial agility in males, particularly among predators of agile prey. Flight performance decreases with increasing size in five of six aspects explored. The male must therefore not be too large in relation to the most important prey. For these reasons, he should be smaller than the female. Among predatory birds, size dimorphism increases with the proportion of birds in the diet, which may be explained as follows. Adult birds have mainly one type of predators: other predatory birds. Because almost only these specialists exploit adult birds, they carry out most of the cropping of this prey. A predator of easier prey competes with many other kinds of predators, which considerably reduce prey abundance in its territory. This is not so for predators of adult birds. Further, because birds are extremely agile, the specialized predator can hunt efficiently only within a limited size range of birds, whose flight skill it can match. Increased size dimorphism among these predators therefore should be particularly important for enlarging the combined food base of the pair. A bird specialist may consume much of the available prey in the suitable size range during the breeding period. When the predator's young are large enough to defend themselves, the female aids better by hunting than by guarding the chicks. It is advantageous among bird specialists if she hunts prey of other sizes than does the male, who has by then reduced prey abundance in his prey size class. But among predatory birds hunting easier prey the female gains little by hunting outside the male's prey spectrum, because other kinds of predators will have reduced the prey abundance outside as well as inside the male's preferred size range. Intra-pair food separation through large sexual size dimorphism therefore should be particularly advantageous among predators of birds. This may be the main reason why the degree of size dimorphism increases with the dietary proportion of birds.     

Post-Strike Behavior of Timber Rattlesnakes (Crotalus horridus) During Natural Predation Events

The complexity of natural environments is an important component of animal behavior, and laboratory environments often cannot reproduce that complexity. Strike‐induced chemosensory searching (SICS) is a robust phenomenon among venomous snakes that has been studied extensively in the laboratory. To date, observations of this behavior in the field have been limited largely to anecdotes; the extent to which post‐strike behaviors in the laboratory accurately reflect what occurs in nature has not been examined. In this study, I use time‐lapse video equipment in the field to record the predatory behavior of timber rattlesnakes (Crotalus horridus). This represents the first quantitative analysis of post‐strike predatory behaviors associated with natural feeding events. As in the laboratory, stereotyped post‐strike behaviors were only observed after successful strikes, and not after missed strikes. Snakes in the field were observed to proceed through the same basic behavioral stages that have been documented in the laboratory: striking prey, releasing prey immediately after strike, post‐strike immobility, location of the chemosensory trail, trail following, and prey swallowing. However, the duration of post‐strike immobility, trail location, and prey swallowing was substantially longer in field than in laboratory studies. Additionally, post‐strike immobility was significantly longer when snakes struck large prey (prey over 100 g) than when they struck small prey. Overall, these results indicate that the behavioral challenges associated with SICS may be more robust than laboratory studies have indicated.     

Phagocytosis in Dictyostelium: Nibbling, Eating and Cannibalism

ABSTRACT. Phagocytosis is a highly conserved biological process that serves numerous functions in a wide variety of organisms. Over the past few decades Dictyostelium has proven to be an excellent organism for investigations in cell biology and this is certainly no less the case for a study of phagocytosis. This review examines three distinct phagocytic activities which have been characterized in Dictyostelium. The first, "vegetative phagocytosis," represents the classical eukaryotic microbial uptake of food particles (bacteria). The second, a predatory form of phagocytosis, arises when one species such as Dictyostelium caveatum attacks another species of slime mold, engulfing small pieces of the target prey. This has been termed "cell nibbling." The third phagocytic process is "sexual cannibalistic phagocytosis." In this situation a zygote giant cell, having arisen from the fusion of gametic amoebae, attracts unfused nonzygotic amoebae of the same species and engulfs them as a food source. While cell nibbling has not been actively studied, vegetative and sexual cannibalistic phagocytosis have received varying amounts of attention leading to the idea that some of the elements (e.g., glycoprotein receptors and a G_αs subunit) involved in certain of these phagocytic events may be the same. On the other hand, some unique events (e.g., filopodial induction in prey by D. caveatum ) are also worthy of further investigation. Among other things, the presence of self-nonself recognition, the existence of opsonin-like substances and the presence of signal transduction elements (e.g., an A2-like receptor that negatively modulates sexual phagocytosis) once considered to be extant only in higher organisms suggest that much can be learned about phagocytosis in general by further studies in the classic, eukaryotic microbe Dictyostelium discoideum and related species.     

Invasions by ladybugs,ladybirds, and other predatory beetles

Species of predatory Coleoptera have become abundant in new geographic regions recently, raising concerns for invaded ecosystems. We address this topic by focusing on invasive alien ladybird beetles (Coccinellidae; known also as ladybugs). Humans appear directly or indirectly responsible for all or most ladybird invasions. Factors hypothesized to have promoted ladybird invasions include genetic diversity (e.g., for polymorphism), phenotypic plasticity, adaptation and genetic shift, generalized diet and habitat preferences, flexible life history and reproduction, large body size, and release from enemies. Factors such as climate, habitat and prey availability, and biotic resistance may sometimes prevent or slow ladybird invasions. Indigenous species (e.g., herbivores) may suffer from invasions, and biological control programs may be affected. Species of indigenous ladybirds throughout the world are reported to have declined in abundance following ladybird invasions, with increased competition and/or intraguild predation most often hypothesized or inferred. Similar recent studies especially of ground beetles (Carabidae) also make clear the potential of invasive alien predatory Coleoptera to disrupt invaded natural and agricultural ecosystems.     

Morphological integration and adaptation in the snake feeding system: a comparative phylogenetic study

A long-standing hypothesis for the adaptive radiation of macrostomatan snakes is that their enlarged gape--compared to both lizards and basal snakes--enables them to consume "large" prey. At first glance, this hypothesis seems plausible, or even likely, given the wealth of studies showing a tight match between maximum consumed prey mass and head size in snakes. However, this hypothesis has never been tested within a comparative framework. We address this issue here by testing this hypothesis in 12 monophyletic clades of macrostomatan snakes using recently published phylogenies, published maximum consumed prey mass data and morphological measurements taken from a large sample of museum specimens. Our nonphylogenetically corrected analysis shows that head width--independent of body size--is significantly related to mean maximum consumed prey mass among these clades, and this relationship becomes even more significant when phylogeny is taken into account. Therefore, these data do support the hypothesis that head shape is adapted to prey size in snakes. Additionally, we calculated a phylogenetically corrected morphological variance-covariance matrix to examine the role of morphological integration during head shape evolution in snakes. This matrix shows that head width strongly covaries with both jaw length and out-lever length of the lower jaw. As a result, selection on head width will likely be associated with concomitant changes in jaw length and lower jaw out-lever length in snakes.     

Predatory behavior of the snake Bothrops jararaca and its adaptation to captivity

Habituation to captivity is difficult for some species. Understanding the motivational elements involved in predation may ease this habituation. Seventy‐one Brazilian jararaca snakes (Bothrops jararaca [Wied, 1824], Viperidae, Crotalinae) recently captured and never fed in captivity were tested for predatory behavior on rodents. Lighting was adapted to allow predatory sessions to occur during the first hours of the night when these animals are more active. Up to three prey subjects were presented in a session. In the first experiment, the preference for prey size and color was assessed using albino and dark‐colored rodents. In a second experiment, a group of snakes was submitted to 12 sessions during a period of almost 2 years. The strike strategy was classified in one of two categories: envenomation (E) or seizing (S). Envenomation involved a bite delivered by the snake with prompt retrieval of the head; holding the rodent in the snake’s jaws since the first strike, without retrieving the fangs and holding the prey during venom action, characterized S strike. Trailing and swallowing the dead prey always followed E strike. Results suggest that snakes fed more often on larger subjects. The color of the prey was not a relevant factor. E strike was predominant in the first predatory event in captivity. After habituation, S strike was predominant. Snakes may have a poor perception of the prey objects in captivity and adopt a strike strategy that assures the control of the prey. Also, the use of small prey subjects to ease feeding during adaptation to captivity may be less effective. Zoo Biol 20:399–406, 2001. © 2001 Wiley‐Liss, Inc.     

Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique

Despite the ubiquity of raptors in terrestrial ecosystems, many aspects of their predatory behaviour remain poorly understood. Surprisingly little is known about the morphology of raptor talons and how they are employed during feeding behaviour. Talon size variation among digits can be used to distinguish families of raptors and is related to different techniques of prey restraint and immobilisation. The hypertrophied talons on digits (D) I and II in Accipitridae have evolved primarily to restrain large struggling prey while they are immobilised by dismemberment. Falconidae have only modest talons on each digit and only slightly enlarged D-I and II. For immobilisation, Falconini rely more strongly on strike impact and breaking the necks of their prey, having evolved a ‘tooth’ on the beak to aid in doing so. Pandionidae have enlarged, highly recurved talons on each digit, an adaptation for piscivory, convergently seen to a lesser extent in fishing eagles. Strigiformes bear enlarged talons with comparatively low curvature on each digit, part of a suite of adaptations to increase constriction efficiency by maximising grip strength, indicative of specialisation on small prey. Restraint and immobilisation strategy change as prey increase in size. Small prey are restrained by containment within the foot and immobilised by constriction and beak attacks. Large prey are restrained by pinning under the bodyweight of the raptor, maintaining grip with the talons, and immobilised by dismemberment (Accipitridae), or severing the spinal cord (Falconini). Within all raptors, physical attributes of the feet trade off against each other to attain great strength, but it is the variable means by which this is achieved that distinguishes them ecologically. Our findings show that interdigital talon morphology varies consistently among raptor families, and that this is directly correlative with variation in their typical prey capture and restraint strategy.     

Variation in Vertebral Number in Galaxiid Fishes,How Fishes Swim and a Possible Reason for Pleomerism

The number of vertebrae in fishes is widely variable, with this variation having connections to phyletic position, geography, various environmental factors such as temperature and salinity, biome occupied and life history pattern. Variation is sometimes a response to environment, sometimes explicitly adaptive and probably often both. Swimming mode is likely to be influenced by body flexibility, which in turn is influenced by vertebral counts. Since vertebral number is fixed early in ontogeny, there is a predictive element in the choice of vertebral number during development that affects later adaptiveness. Pleomerism, the relationship between vertebral number and body size across the diversity of fishes, may be driven by the square/cube relationships between length, cross-sectional area and volume. Pleomerism in diadromous galaxiid fishes probably reflects adaptive advantages achieved during marine juvenile life and in non-diadromous species may reflect the size at which mid-water, shoaling juveniles become to benthic, cryptic, within-substrate behaviours.     

The functional meaning of “prey size” in water snakes (Nerodia fasciata, Colubridae)

The evolutionary success of macrostomatan (enlarged-gape) snakes has been attributed to their ability to consume large prey, in turn made possible by their highly kinetic skulls. However, prey can be “large” in several ways, and we have little insight into which aspects of prey size and shape affect skull function during feeding. We used X-ray videos of broad-banded water snakes (Nerodia fasciata) feeding on both frogs and fish to quantify movements of the jaw elements during prey transport, and of the anterior vertebral column during post-cranial swallowing. In a sample of additional individuals feeding on both frogs and fish, we measured the time and the number of jaw protractions needed to transport prey through the buccal cavity. Prey type (fish vs. frog) did not influence transport kinematics, but did influence transport performance. Furthermore, wider and taller prey induced greater movements of most cranial elements, but wider prey were transported with significantly less anterior vertebral bending. In the performance trials, heavier, shorter, and wider prey took significantly more time and a greater number of jaw protractions to ingest. Thus, the functional challenges involved in prey transport depend not only upon prey mass, but also prey type (fish vs. frog) and prey shape (relative height, width and length), suggesting that from the perspective of a gape-limited predator, the difficulty of prey ingestion depends upon multiple aspects of prey size.     

Prey attack and predators defend: counterattacking prey trigger parental care in predators

That predators attack and prey defend is an oversimplified view. When size changes during development, large prey may be invulnerable to predators, and small juvenile predators vulnerable to attack by prey. This in turn may trigger a defensive response in adult predators to protect their offspring. Indeed, when sizes overlap, one may wonder "who is the predator and who is the prey"! Experiments with "predatory" mites and thrips "prey" showed that young, vulnerable prey counterattack by killing young predators and adult predators respond by protective parental care, killing young prey that attack their offspring. Thus, young individuals form the Achilles' heel of prey and predators alike, creating a cascade of predator attack, prey counterattack and predator defence. Therefore, size structure and relatedness induce multiple ecological role reversals.     

Species-Specific Effects of Ant Inhabitants on Bromeliad Nutrition

Predator activities may lead to the accumulation of nutrients in specific areas of terrestrial habitats where they dispose of prey carcasses. In their feeding sites, predators may increase nutrient availability in the soil and favor plant nutrition and growth. However, the translocation of nutrients from one habitat to another may depend on predator identity and diet, as well as on the amount of prey intake. Here we used isotopic (¹⁵N) and physiological methods in greenhouse experiments to evaluate the effects of the identity of predatory ants (i.e., the consumption of prey and nest sites) on the nutrition and growth of the bromeliad Quesnelia arvensis. We showed that predatory ants with protein-based nutrition (i.e., Odontomachus hastatus, Gnamptogenys moelleri) improved the performance of their host bromeliads (i.e., increased foliar N, production of soluble proteins and growth). On the other hand, the contribution of Camponotus crassus for the nutritional status of bromeliads did not differ from bromeliads without ants, possibly because this ant does not have arthropod prey as a preferred food source. Our results show, for the first time, that predatory ants can translocate nutrients from one habitat to another within forests, accumulating nutrients in their feeding sites that become available to bromeliads. Additionally, we highlight that ant contribution to plant nutrition may depend on predator identity and its dietary requirements. Nest debris may be especially important for epiphytic and terrestrial bromeliads in nutrient-poor environments.     

Predatory functional response and prey choice identify predation differences between native/invasive and parasitised/unparasitised crayfish

Background

Invasive predators may change the structure of invaded communities through predation and competition with native species. In Europe, the invasive signal crayfish Pacifastacus leniusculus is excluding the native white clawed crayfish Austropotamobius pallipes.

Methodology and Principal Findings

This study compared the predatory functional responses and prey choice of native and invasive crayfish and measured impacts of parasitism on the predatory strength of the native species. Invasive crayfish showed a higher (>10%) prey (Gammarus pulex) intake rate than (size matched) natives, reflecting a shorter (16%) prey handling time. The native crayfish also showed greater selection for crustacean prey over molluscs and bloodworm, whereas the invasive species was a more generalist predator. A. pallipes parasitised by the microsporidian parasite Thelohania contejeani showed a 30% reduction in prey intake. We suggest that this results from parasite-induced muscle damage, and this is supported by a reduced (38%) attack rate and increased (30%) prey handling time.

Conclusions and Significance

Our results indicate that the per capita (i.e., functional response) difference between the species may contribute to success of the invader and extinction of the native species, as well as decreased biodiversity and biomass in invaded rivers. In addition, the reduced predatory strength of parasitized natives may impair their competitive abilities, facilitating exclusion by the invader.     

Curvature facilitates prey fixation in predatory insect claws

Insects show a large variety in prey capture strategies, with a correspondingly large diversity in predatory adaptations. We studied a specific type of predatory claws, these can for example be found in praying mantis species. The claw is closeable over its entire length and the prey is fixed between the femur (upper arm) and the tibia (lower arm) of the insect leg. The morphology of these predatory claws is diverse. Some species have straight claws covered with spines, while other species have smooth, curved claws. We have studied the mechanics of this femur-tibia type of predatory insect claws, by making a physical model, eventually trying to explain why in some insect species the claws are curved instead of straight. The main results are (1) when comparing curved claws to straight claws, curvature leads to a strong reduction of forces driving the prey away from the pivoting point, thereby reducing the need for friction generating structures. (2) In the curved claw model a position exists where the resulting force on the prey is exactly zero. This is because the normal forces on the femur and tibia are opposed, and in line. At this position the prey is perfectly clamped and not driven out of the claw. This feature does not exist in straight claws. (3) In the curved claw, the prey cannot be placed at a position further than a certain maximum distance from the pivoting point. Near this maximum position, the resulting force on the prey reaches high values because moment arms are near zero. (4) Between the zero position and the maximum position the resulting force is directed toward the pivoting point, which stabilizes prey fixation.     

Is there safety‐in‐numbers for prey?

The abundance of prey affects the rate of predation, but little consensus exists on whether this enhances or reduces per capita mortality. Studies of aggregating prey in marine habitats generally emphasise that the probability of predation of any individual is the reciprocal of the number of prey within a school. A field experiment tested the alternative hypotheses that predation by predatory fish on schooling prey (1) increased with an increase in the number of prey per school and that this caused (2) survival to be lower in schools with more individuals. The number of prey (juvenile Acanthochromis polyacanthus ) per school was manipulated in replicate treatments with natural densities of large predatory fish (open plots) and treatments without large predatory fish (exclusion cages). Large predatory fish preyed on juveniles in a density-dependent manner and this was the key source of density-dependent mortality in plots open to all predators. There was some suggestion that small predatory fish also prey on juveniles in a density-dependent manner, but this was weak and did not translate into density-dependent mortality of juveniles. It would appear that aggregation of prey may be a successful strategy against predation from some predators, but not always every predator, or all predators in combination.     

Predatory Versatility in Females of the Scorpion <Emphasis Type="Italic">Bothriurus bonariensis</Emphasis> (Scorpiones: Bothriuridae): Overcoming Prey with Different Defensive Mechanisms

Scorpions are dominant predators in some environments. Nevertheless, most studies of predatory behavior in scorpions have focused on diet composition whereas some other relevant aspects, such as predatory strategy, have been poorly explored. Herein we evaluate the prey acceptance and predatory strategy of the scorpion Bothriurus bonariensis against sympatric prey with different defenses. As prey, we selected earwigs (Forficula cf. auricularia) which use pincer-like defensive appendages, hard-bodied isopods (Armadillium vulgare) known for their conglobation defensive strategy, soft bodied isopods (Porcellio cf. scaber), which secrete noxious substances as defense mechanisms, cockroaches with limited defensive mechanisms (Blatta cf. orientalis.) and spiders (Lycosa cf. poliostoma) which possess venomous fangs. Prey were offered to 21 adults of B. bonariensis in random order until all prey had been offered to all scorpions. Prey consumption and the number of attempts needed for capture were recorded. We also evaluated the effect of sting use on immobilization time as well as the prey capture strategies on the most consumed prey. We found that despite using a similar number of attempts for capturing all prey, spiders and armadillid isopods were less consumed than other prey. Immobilization times were longer for earwigs than for armadillid isopods and cockroaches. Scorpions used alternative predatory strategies against these aforementioned prey, although the stinger was used against all of them. These results show that scorpions are able to use different predatory strategies which might allow them to include prey with diverse defensive strategies in their diet.     

Dangerous food: lacking venom and constriction,how do snake‐like lizards (Lialis burtonis,Pygopodidae) subdue their lizard prey?

Snakes are renowned for their ability to subdue and swallow large, often dangerous prey animals. Numerous adaptations, including constriction, venom, and a strike-and-release feeding strategy, help them avoid injury during predatory encounters. Burton's legless lizard ( Lialis burtonis Gray, Pygopodidae) has converged strongly on snakes. It is functionally limbless and feeds at infrequent intervals on relatively large prey items (other lizards) capable of inflicting a damaging bite. However, L. burtonis possesses neither venom glands, nor the ability to constrict prey. We investigated how L. burtonis subdues its prey without suffering serious retaliatory bites. Experiments showed that lizards modified their strike precision according to prey size; very large prey were always struck on the head or neck, preventing them from biting. In addition, L. burtonis delayed swallowing large lizards until they were incapacitated, whereas smaller prey were usually swallowed while still struggling. Lialis burtonis also displays morphological adaptations protecting it from prey retaliation. Its long snout prevents prey from biting, and it can retract its lidless eyes out of harm's way while holding onto a food item. The present study further clarifies the remarkable convergence between snakes and L. burtonis , and highlights the importance of prey retaliatory potential in predator evolution.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91 , 719–727.     

Effects of prey density, prey instar, and patch size on the development of the predatory mosquito, Toxorhynchites towadensis

Effects of prey density, prey instar, and patch size on the development of the predatory mosquito larva, Toxorhynchites towadensis, were investigated in the laboratory. Survivors of T. towadensis showed different developmental patterns in relation to prey age structure. All predatory larvae in containers with only second instar prey developed into the third instar. However, in several containers with fourth instar prey, mortality of predators was observed. During the third instar, no predatory larva died, but both prey density and prey instar significantly affected the survival of predators during their fourth instar. Large prey size promoted large predator adults, and predatory larvae which grew up in small surface containers responded by developing to large sizes than those in large containers. Larval developmental time of the predators differed in each treatment. During first and second instars, faster predator development was observed in containers with small surface areas and containing young prey individuals. However, when development was enhanced by the presence of old prey individuals, no surface effect was observed. The fastest predator development was observed with prey of mixed instars and high density. This study suggests that a small surface container containing prey of mixed instars and high density is suitable for development of predators.     

Contribution of the vertebral artery to cerebral circulation in the rat snake Elaphe obsoleta

Blood supplying the brain in vertebrates is carried primarily by the carotid vasculature. In most mammals, cerebral blood flow is supplemented by the vertebral arteries, which anastomose with the carotids at the base of the brain. In other tetrapods, cerebral blood is generally believed to be supplied exclusively by the carotid vasculature, and the vertebral arteries are usually described as disappearing into the dorsal musculature between the heart and head. There have been several reports of a vertebral artery connection with the cephalic vasculature in snakes. We measured regional blood flows using fluorescently labeled microspheres and demonstrated that the vertebral artery contributes a small but significant fraction of cerebral blood flow (∼13% of total) in the rat snake Elaphe obsoleta. Vascular casts of the anterior vessels revealed that the vertebral artery connection is indirect, through multiple anastomoses with the inferior spinal artery, which connects with the carotid vasculature near the base of the skull. Using digital subtraction angiography, fluoroscopy, and direct observations of flow in isolated vessels, we confirmed that blood in the inferior spinal artery flows craniad from a point anterior to the vertebral artery connections. Such collateral blood supply could potentially contribute to the maintenance of cerebral circulation during circumstances when craniad blood flow is compromised, e.g., during the gravitational stress of climbing. J. Morphol. 238:39–51, 1998. © 1998 Wiley-Liss, Inc.