Temperature Effects on Anti-Predator Behaviour in Rhabdophis tigrinus, a Snake with Toxic Nuchal Glands

Many contextual factors affect the anti-predator behaviour of animals. In ectotherms, in which most physiological activities depend on body temperature, ambient temperature is one of the most important of these factors. We examined the effects of temperature on the anti-predator behaviour of an ectotherm, the Japanese grass snake ( Rhabdophis tigrinus ). This species has a large repertoire of anti-predator behavioural responses. Among these responses are several anti-predator displays that appear to be unique to this species and perhaps others in a small group of closely related species possessing nuchal glands containing toxic secretions that may be derived from their toxic toad diet. Snakes were tested at room temperatures of 14, 22 and 30°C with order of temperatures balanced. A long wand modified to simulate initial contact by a predator was used as the stimulus. Snakes exhibited rather passive responses (neck flatten, body flatten, neck arch and immobile) more frequently at low temperatures, and fled more frequently at high temperatures. The dorsal facing posture, a characteristic posture directed against the stimulus, was observed more frequently at low temperatures. Threatening, assertive responses such as strike were rarely observed. These results showed that R. tigrinus shifts its anti-predator behaviour from multiple passive responses to active flight responses with increasing temperature. This snake species thus appears to rely more on its nuchal glands as a predator deterrent at low ambient temperatures. Consistent individual variation was also observed, and its adaptive and causal bases are discussed.     

GENETIC BASIS OF ACTIVITY METABOLISM. I. INHERITANCE OF SPEED,STAMINA, AND ANTIPREDATOR DISPLAYS IN THE GARTER SNAKE THAMNOPHIS SIRTALIS

Recent conceptual advances in physiological ecology emphasize the potential selective importance of whole-animal performance. Empirical studies of locomotor performance in reptiles have revealed surprising amounts of individual variation in speed and stamina. The present study is the first in a series examining the genetic basis of variation in locomotor performance, activity metabolism, and associated behaviors in garter snakes. Maximal sprint crawling speed, treadmill endurance, and antipredator displays (Arnold and Bennett, 1984; exhibited as snakes reached exhaustion on the treadmill) were measured for approximately six offspring (presumed to be full siblings) from each of 46 wild-caught gravid garter snakes (Thamnophis sirtalis). Each character was measured on two days; all were individually repeatable. Correlations of these characters with body mass, snout–vent length, age at testing, litter size, dam mass, and dam snout–vent length were removed by computing residuals from multiple-regression equations. These residuals were used in subsequent genetic analyses. Approximate coefficients of variation of residuals were 17% for speed, 48% for endurance, and 31% for antipredator displays. Broad-sense heritabilities were significant for all characters: speed h² = 0.58; stamina h² = 0.70; antipredator display h² = 0.42. All three residual characters showed positive and statistically significant phenotypic correlations (r = 0.19–0.36). Genetic correlations (estimated and tested by restricted maximum likelihood) among residuals were positive and highly significant between speed and endurance (0.58), but nonsignificant between speed and antipredator display (0.43), and between endurance and antipredator display (0.26). All environmental correlations were nonsignificant. These data suggest that, contrary to expectations based on previous physiological studies, there may be no necessary evolutionary trade-off between speed and stamina in these animals. This tentative conclusion will have important implications for future theoretical studies of the evolution of locomotor performance and associated antipredator behaviors.     

Antipredator Tactics of Amphibious Sea-Snakes (Serpentes, Laticaudidae)

Because the antipredator behavior that an animal displays depends upon the context in which it encounters the predator, apparent interspecific differences in antipredator tactics may result from ecological rather than behavioral differences among taxa. We approached 127 free-ranging laticaudid sea-snakes on small islands in Noumea Lagoon, New Caledonia, prodded the animals midbody, and recorded their responses. One species (Laticauda colubrina) usually remained immobile (relying on crypsis) whereas another (L. laticaudata) generally fled. However, multivariate analysis shows that the two species actually responded in very similar ways to any given stimulus; the species differed overall because colubrina was generally encountered on land during the day whereas laticaudata was more often encountered in the ocean at night. Thus, apparent interspecific differences in antipredator responses were secondary consequences of interspecific differences in the times and places that predators were encountered. Snakes were more likely to flee rather than remain immobile when rapid locomotion was possible (i.e. juveniles rather than adults; in water rather than on land) and pursuit by a predator was difficult (i.e. at night rather than during the day). These patterns suggest that snakes adjust their antipredator tactics in ways that maximize the chances of surviving the encounter, although the remarkable docility of these highly venomous snakes remains puzzling.     

Behavioural variation in natural populations. III: Antipredator displays in the garter snake Thamnophis radix

Recently born garter snakes (Thamnophis radix) were subjected to a variety of threatening stimuli. The would crawl away from the investigator until high levels of lactate were attained, and then adopt one of a variety antipredator displays. These antipredator behaviours were surprisingly variable between individuals of a single population, but behaviours of individuals were consistent in replicate trials and in response to different stimuli. Snakes became more defensive when simulated predator attacks were more severe, but they became more offensive when tested at a lower temperature. Analysis of behavioural variation within and between 15 litters of full-sibling (172) snakes gave heritability estimates of 0.37 for single trials and 0.45 for the average of two replicate trials. This is the first study to examine the heritability of antipredator behaviour in any terrestrial vertebrate species.     

Managing predators: The influence of kangaroo rat antipredator displays on sidewinder rattlesnake hunting behavior

Upon sensing predators in their vicinity, many prey species perform antipredator displays that are thought to provide information to the predator that deters it from attacking (predator‐deterrent signals). These displays can be complex, incorporating a variety of signaling elements as well as direct physical harassment of the predator. Although the display behaviors in these communication systems are often well characterized, evidence of the efficacy of these displays in deterring predators is limited due to the challenges associated with studying free‐ranging predators. Here, we examine how the anti‐snake signals of the desert kangaroo rat (Dipodomys deserti) influence the ambush hunting behaviors of sidewinder rattlesnakes (Crotalus cerastes). We found that, although desert kangaroo rats incorporate a number of signal elements into their antipredator display, only sand kicking behavior was a significant factor in motivating sidewinder rattlesnakes to cease hunting: high rates of sand kicking led to early abandonment of ambush coils. These results indicate that anti‐snake displays of small mammals may be especially effective at mitigating the threat posed by rattlesnakes when those displays incorporate physical harassment as well as signaling.     

Meal Size Effects on Antipredator Behavior of Hatchling Trinket Snakes, Elaphe helena

Current foraging models limit the decision‐making process of animals to the food searching and consuming phase. The post‐consummatory phase of feeding may influence optimal meal size for some species as a morphologic change often results from feeding. In snakes, a single prey item can lead to abrupt increases in body mass, thus influencing locomotor performance. Identifying factors affecting locomotor performance can help predict behaviors that should maximize an animal's chance of evading predators. Although many snakes ingest large percentages of their body mass, not much work has examined the post‐consummatory effects of ingesting bulky prey differing in relative mass. I examined the locomotor performance and antipredator tactics of hatchling trinket snakes (Elaphe helena) after subjecting snakes to mice prey varying by relative mass differences of 20–35%, 50–59% or 70–79% of an individual hatchling's body mass. Snakes in treatment groups were compared with snakes in a control group (0%). Meal size‐affected locomotor parameters such as burst speed, endurance, and endurance times for hatchlings that ingested 50–59% and 70–79% of their body mass (p < 0.001). Recent feeding also affected the types of antipredator modes employed. Hatchlings in the 0% and 20–35% treatments exhibited behaviors that were categorized as active and threatening, while hatchlings in the 50–59% and 70–79% treatments exhibited stationary, neutral, and cryptic behaviors. Although snakes may become more reclusive following a meal, this study demonstrates that relative prey mass affects the ability of hatchling trinket snakes to flee from a predator. In turn, these results suggest that the post‐consummatory effects of foraging should be considered in optimal foraging models for organisms that consume a substantial portion of their body mass during a single feeding.     

Active foraging for toxic prey during gestation in a snake with maternal provisioning of sequestered chemical defences

Many animals sequester dietary defensive compounds and incorporate them into the offspring, which protects the young against predation. One possible but poorly investigated question is whether females of such species actively prey upon toxic diets. The snake Rhabdophis tigrinus sequesters defensive steroids from toads consumed as prey; it also feeds on other amphibians. Females produce chemically armed offspring in direct proportion to their own level of toad-derived toxins by provisioning the toxins to their eggs. Our field observations of movements and stomach contents of radio-tracked R. tigrinus showed that gravid snakes preyed upon toads by actively foraging in the habitat of toads, even though toads were a scarce resource and toad-searching may incur potential costs. Our Y-maze experiments demonstrated that gravid females were more likely to trail the chemical cues of toads than were males or non-gravid females. These results showed behavioural switching in females and active foraging for scarce, toxic prey during gestation. Because exploitation of toads by gravid females results in their offspring being more richly endowed with prey-derived toxins, active foraging for toxic prey is expected to be an adaptive antipredator trait, which may enhance chemical defence in offspring.     

EVOLUTIONARY RESPONSE OF PREDATORS TO DANGEROUS PREY: PREADAPTATION AND THE EVOLUTION OF TETRODOTOXIN RESISTANCE IN GARTER SNAKES

Coevolutionary interactions typically involve only a few specialized taxa. The factors that cause some taxa and not others to respond evolutionarily to selection by another species are poorly understood. Preadaptation may render some species predisposed for evolutionary response to new pressures, whereas a lack of genetic variation may limit the evolutionary potential of other taxa. We evaluate these factors in the predator-prey interaction between toxic newts (Taricha granulosa) and their resistant garter snake predators (Thamnophis sirtalis). Using a bioassay of resistance to tetrodotoxin (TTX), the primary toxin in the prey, we examined phenotypic evolution in the genus Thamnophis. Reconstruction of ancestral character states suggests that the entire genus Thamnophis, and possibly natricine snakes in general, has slightly elevated TTX resistance compared to other lineages of snakes. While this suggests that T. sirtalis is indeed predisposed to evolving TTX resistance, it also indicates that the potential exists in sympatric congeners not expressing elevated levels of TTX resistance. We also detected significant family level variation for TTX resistance in a species of Thamnophis that does not exhibit elaborated levels of the trait. This finding suggests that evolutionary response in other taxa is not limited by genetic variability. In this predator-prey system, species and population differences in resistance appear to be largely determined by variation in the selective environment rather than preadaptation or constraint.     

Evolution of coloration, urotomy and coral snake mimicry in the snake genus Scaphiodontophis (Serpentes: Colubridae)

The Neotropical hinged-tooth, coral snake mimics of the genus Scaphiodontophis are characterized by extremely long and disproportionately thick tails that are extremely fragile. Both the coloration and tail structure are putative antipredator devices. While all examples have components of the coloration that match those of the venomous coral snakes (family Elapidae), the range of variation is extreme, leading to controversy on the status of various populations, including nine named taxa. Individual, ontogenetic and geographic variation in scutellation and head, body and tail coloration were analysed to evaluate population status and possible evolutionary trends based on a sample of 183 examples from Mexico, Central America and Colombia. Variation in subcaudal counts show population differences (higher in Mexico and upper Central America) but are not congruent with geographic variation in coloration. Generally snakes from north of Nicaragua and from central and eastern Panama have a pattern of dyads (black-light-black bands separating red bands), those from Atlantic slope Nicaragua to western Panama a pattern of monads (light-black-light bands separating the red ones) and those from Colombia have both pattern types on the same snake. The dyads and/or monads may be present the length of the body and tail, restricted to the anterior part of the body or on the entire body or on the anterior part of the body and on the tail. Two or more of these variants may occur at a single geographic locality or only a single one may be present. Head and nuchal colour patterns (Z, A, V and Du) are relatively consistent geographically. The Adantic slope Guatemala, Belize and Honduras population have the A pattern, those of Nicaragua, Costa Rica and western Panama the V pattern, and those in Colombia a Du pattern. Other populations have the Z coloration. Intermediate conditions in coloration of the body and tail and head and neck are found at localities intermediate between the main pattern types, indicating intergradation among adjacent populations. Consequently, we regard these snakes as representative of a single species, Scaphiodontophis annulatus Dumeril and Bibron and the eight other names applied to various populations and individuals as synonyms. Analysis of colour pattern leads us to the conclusion that the tricolour pattern evolved from a uniform one through a lineate-spotted condition (usually present on the non-tricolour portions of the snake) through a bicolour red and black pattern to the dyadal condition. The monadal pattern in turn was derived from the dyadal one. The data further indicates that tricolour components first appeared anteriorly and progressively expanded posteriorly. The evolutionary sequence for the head and nuchal pattern appears to be A → Z → V → Du S. annulatus has a series of jaw and tooth specializations designed for rapid processing of hard-bodied prey found during diurnal foraging in the leaf-litter. Urotomy in this species involves intervertebral tail-breakage (pseudoautotomy) without regeneration. Evidence is presented supporting the long-tail multiple break hypothesis as applicable to Scaphiodontophis and other snakes with similar tail morphology (specialized pseudoautotomy). This is in contrast to snakes with similar tail morphology (specialized pseudoautotomy). This is in contrast to Coniophanes and other snakes with a high incidence of urotomy having long but unspecialized tails (unspecialized pseudoautotomy) without multiple breaks over time. All Scaphiodontophis colour patterns have a general resemblance to that of venomous coral snakes and offer protection from generalizing predators having innate or other triggered responses to coral snake colours. The aposematic effect is enhanced by tail thrashing and head twitching behaviours. The characteristic foraging pose of S. annulatus, which tends to expose the head and anterior body, makes even the incomplete tricolour pattern effective as an antipredator defence. No evidence supports the idea that tail thrashing or the incomplete tricolour pattern directs the predator attacks to the tail to expedite pseudoautotomy. Coral snake mimicry and specialized pseudoautotomy are shown not to be co-evolved and pseudautotomy seems to have evolved long before mimetic coloration in this genus.     

Predatory Attacks to the Head vs. Body Modify Behavioral Responses of Garter Snakes

An animal's response to predatory attack may depend upon which part of its body is the focus of that attack, because of differential vulnerability to injury. Many avian and mammalian predators direct attacks preferentially toward the prey's head, so simulated attacks that do not have this focus may elicit non‐natural responses. We ‘pecked’ 152 free‐ranging adult male garter snakes (Thamnophis sirtalis parietalis) in Manitoba either on the head or the midbody, and recorded their responses. The snakes’ antipredator tactics were affected not only by body size (larger snakes performed threat displays more often) and body temperature (hotter snakes were more likely to flee), but also by location of the attack. Pecks to the head generally resulted in snakes coiling and hiding their heads, often simultaneously elevating and wriggling their tails in an apparent distraction display. In contrast, pecks to the midbody stimulated either escape responses, or (in snakes that did not flee) open‐mouthed threat displays. More generally, antipredator tactics may respond in flexible ways to details of the predator–prey encounter (including attributes of the habitat as well as the morphology and behavior of both participants) and hence, experimental studies need to carefully simulate such details. The part of the body under attack may be an important factor in this respect.     

Correlated geographic variation in predation risk and antipredator behaviour within a wide‐ranging snake species (Notechis scutatus,Elapidae)

Geographic variation in antipredator behaviour within wide‐ranging species may be driven by both genetic and environmental influences. We quantified antipredator responses in neonatal (laboratory born, n = 555) and adult (field caught, n = 346) tiger snakes (Notechis scutatus) from 11 mainland and island sites in southern Australia. We used these data to test predictions from Bonnet et al.'s hypothesis that the vigour of antipredator responses in this species reflects behavioural plasticity (in turn, driven by an individual snake's exposure to predators during its lifetime) rather than by genetic variation in this trait. We used the number of predator taxa in each area as an index of predator risk. As predicted, adult snakes from predator‐rich areas had more vigorous defensive responses when handled, whereas neonatal behaviour (although also variable among populations) was unrelated to predator species richness. Adult males bit more readily than adult females (as expected from the greater predation exposure of males during mate searching) but no such sex difference was evident in neonates. Although alternative models remain possible, our data are most consistent with the hypothesis that geographic divergence in antipredator tactics within this species primarily reflects developmentally plastic responses to local predation risk.     

Predator response to the coloured eyespots and defensive posture of Colombian four-eyed frogs

Deimatic displays, where sudden changes in prey appearance elicit aversive predator reactions, have been suggested to occur in many taxa. These (often only putative) displays frequently involve different components that may also serve antipredator functions via other mechanisms (e.g., mimicry, warning signalling, body inflation). The Colombian four-eyed frog, Pleurodema brachyops, has been suggested to gain protection against predation through putative deimatic displays where they inflate and elevate the posterior part of their body revealing eye-like colour markings. We exposed stationary artificial frogs to wild predators to test whether the two components (eyespot/colour markings, defensive posture) of their putative deimatic display, and their combination, provide protection from predation without the sudden change in appearance. We did not detect any obvious additive effect of defensive posture and eyespots/colour markings on predation risk, but found a marginally significant trend for model frogs in the resting posture to be less attacked when displaying eyespots/colour markings than when they were not, suggesting that the presence of colour markings/eyespots may provide some protection on its own. Additionally, we found that models in a resting posture were overall more frequently attacked on the head than models in a defensive posture, indicating that a defensive posture alone could help redirect predator attacks to non-vital parts of the body. The trends found in our study suggest that the different components of P. brachyops' coloration may serve different functions during a deimatic display, but further research is needed to elucidate the role of each component when accompanied by sudden prey movement.     

Correlations between Ontogenetic Change in Color Pattern and Antipredator Behavior in the Racer, Coluber constrictor

Differences in snake color pattern have been demonstrated to affect behaviors involved in antipredator defense. Snakes with blotched or banded color patterns are concealed when not moving, and tend to rely on concealment and aggression for defense. In contrast, snakes with uniform or striped color patterns are easily seen when stationary, but their speed and direction are difficult to track when moving. They tend to rely on flight for protection. Some snake taxa exhibit ontogenetic change in color pattern, but the behavioral consequences of this change have not been investigated. I present results of a behavioral study in the racer, Coluber constrictor, which has a blotched juvenile color pattern but is uniformly colored as an adult. Hatchling racers were significantly more likely than adults to show aggressive behavior when confronted with a model predator, whereas adults were more likely to flee. This supports the hypothesis that changes in behavior and color pattern are correlated in this species to provide effective antipredator defense at different stages of life history. I also examined sprint speed, which may be an important factor in antipredator defense. Juvenile and adult racers showed a similar relationship between length and speed, a pattern also seen in other species that lack color change. This result suggests that sprint speed is not a causal factor in the evolution of ontogenetic color change.     

Nuchal ligament reconstructions in diplodocid sauropods support horizontal neck feeding postures

Historically, sauropods have been largely perceived as having vertical, ‘S’-curved necks which were hypothesised to allow them to feed from the canopy of trees. Within the past two decades, this popular perception has been questioned, resulting in a debate over neck posture. The osteological differences between sauropods with horizontal neck posture (Diplodocus), and less horizontally inclined necks (Brachiosaurus) suggest differing life and feeding styles. One differing vertebral feature between these polarised bauplans is the bifurcated neural spine. Regardless of the spine condition, sauropods with and without bifurcated spines have been reconstructed exhibiting the same neck posture. Corroborating histology and morphology in extant taxa highlights the presence of modified vertebral ligaments associated with bifurcated spines. Using these extant taxa to better understand the biomechanics of bifurcated spines, this study proposes alternative soft tissue reconstructions. Previous depictions had the bifurcation trough entirely open or harbouring pneumatic diverticula or muscles; conversely this study proposes that the apices of the bifurcated spines were the anchoring points for a split nuchal ligament, and that the trough of bifurcation was predominantly filled with interspinal ligaments. Ligaments provide energy-efficient elastic rebound, and a paired ligament in the cervical series would aid in prolonged, lateral movement in a horizontal plane (i.e. feeding).     

Classical heinrothian intimidation displays exhibited byGalago demidoff demidoff: A paradigm for pinpointing galagine species diversity

The existence of rhythmic micturation displays among bushbabies is well established but the function of such behavior has been a source of dispute, due largely to indiscriminate lumping of different kinds of phenomena. In this paper classical ethological evaluation of the rhythmic micturation intimidation displays regularly exhibited by dominant adult Galago demidoff demidoffallows comparison with other varieties of intra- /interspecific displaying and agression. These include (1) pure offensive behavior shared by both sexes; (2) defensively toned, antiintruder/antipredator displaying; (3) male- male rank demonstration confrontations; and (4) dominant- female, emotionally neutral self- advertising. The dominant- male, offensively toned displays couple the functions of rival intimidation and partner attraction; they vary between different species of bushbaby, and they represent an important taxonomic tool.     

Once Bitten,Twice Shy: Does Previous Experience Influence Behavioural Decisions of Snakes in Encounters with Predators?

Injuries are common in animals of diverse taxa and are usually attributed to encounters with predators. Although often non‐lethal, injuries nevertheless represent effects of predators that can have negative consequences for demography and fitness (e.g. reproductive costs). However, encounters with predators also represent experience through which animals can learn and positively adapt their future behaviour, potentially mitigating, at least partly, the negative effects of prior exposure to predators. I predicted that injured grass snakes (Natrix natrix), which presumably had been handled previously by a predator, would be more likely to move before capture than uninjured snakes. This prediction was borne out. Snakes with injuries also had lower body condition than uninjured snakes, although the effect was non‐significant. Snakes that had been previously captured also were significantly more likely to move before capture than snakes that had never been caught before. These results provide strong evidence for the role of experience and learning in modifying the antipredator behaviour of snakes.     

Extensive genetic divergence in the East Asian natricine snake,Rhabdophis tigrinus (Serpentes: Colubridae), with special reference to prominent geographical differentiation of the mitochondrial cytochrome b gene in Japanese populations

We investigated intraspecific phylogenetic relationships in the natricine snake, Rhabdophis tigrinus. A partial sequence of mitochondrial cytochrome b gene (990 bp) was sequenced for 220 individuals from 112 populations. The phylogeny indicated monophyly of the Japanese populations against the continental and Taiwanese populations, sister relationships of the Japanese and continental populations, and monophyly of the whole species. The results strongly suggested substantial genetic divergences among population assemblages from those three regions. We thus consider both lateralis from the continent, which is often synonymized to R. tigrinus, and formosanus from Taiwan, which is usually regarded as a subspecies of the latter, as distinct full species based on the evolutionary species concept. In the Japanese populations, haplotypes were classified to in two major clades (I and II) that were parapatric to each other. Clade I consisted of three distinct subclades (I‐A, I‐B, and I‐C), of which the former two were parapatric with each other, whereas the latter was sympatric with each of the former two subclades. The geographical haplotype structure exhibited by the Japanese populations is likely to have resulted from a series of allopatric differentiations with rapid range extensions of resultant lineages, leading to secondary contact or further admixture of mitochondrial haplotype clades and subclades. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 395–408.     

Functional morphology of the primate head and neck

The vertebral column plays a key role in maintaining posture, locomotion, and transmitting loads between body components. Cervical vertebrae act as a bridge between the torso and head and play a crucial role in the maintenance of head position and the visual field. Despite its importance in positional behaviors, the functional morphology of the cervical region remains poorly understood, particularly in comparison to the thoracic and lumbar sections of the spinal column. This study tests whether morphological variation in the primate cervical vertebrae correlates with differences in postural behavior. Phylogenetic generalized least-squares analyses were performed on a taxonomically broad sample of 26 extant primate taxa to test the link between vertebral morphology and posture. Kinematic data on primate head and neck postures were used instead of behavioral categories in an effort to provide a more direct analysis of our functional hypothesis. Results provide evidence for a function-form link between cervical vertebral shape and postural behaviors. Specifically, taxa with more pronograde heads and necks and less kyphotic orbits exhibit cervical vertebrae with longer spinous processes, indicating increased mechanical advantage for deep nuchal musculature, and craniocaudally longer vertebral bodies and more coronally oriented zygapophyseal articular facets, suggesting an emphasis on curve formation and maintenance within the cervical lordosis, coupled with a greater resistance to translation and ventral displacement. These results not only document support for functional relationships in cervical vertebrae features across a wide range of primate taxa, but highlight the utility of quantitative behavioral data in functional investigations. Am J Phys Anthropol 156:531–542, 2015. © 2015 Wiley Periodicals, Inc.     

Mother Cottonmouths (Agkistrodon piscivorus) Alter Their Antipredator Behavior in the Presence of Neonates

Neonate‐directed care is rare in non‐avian reptiles, but female pitvipers attend their young for a period of time after birth. One of the primary functions of parental care is the protection of offspring from predators, and parents of diverse taxa are able to modulate their antipredator behavior in the presence of offspring. To test the hypothesis that the antipredator behavior of post‐parturient pitvipers is altered during neonate attendance, we conducted behavioral trials on female cottonmouths (Agkistrodon piscivorus) in which we measured female response to a simulated predator encounter. Cottonmouths were divided into three treatment groups: (1) post‐parturient, attending neonates; (2) post‐parturient, not attending neonates; and (3) non‐reproductive. All females were subjected to a second trial approximately 3 wk later, when females in Group 1 were no longer attending neonates. When mothers were attending offspring, they were more hesitant to engage the predator and exhibited more warning than aggressive behaviors once they did, relative to non‐attending and non‐reproductive females. When these same mothers were no longer attending offspring, they significantly increased their antipredator behavior by engaging the predator quickly and displaying more aggressive than warning behaviors. This change in behavior was not observed in post‐parturient females who did not have neonates present during either trial, nor was it observed in non‐reproductive females, indicating that the presence of neonates directly affected the antipredator behavior of attending females. We discuss hypotheses concerning the possible adaptive value of reduced antipredator behavior in female pitvipers attending neonates.     

Density dependent and density independent relationships during a twenty-seven year study of the population dynamics of the benthic macroinvertebrate community of a chemically unstable lake

Data are given on net precipitation, water chemistry, vegetation cover and the population dynamics of 20 taxa of benthic macroinvertebrates from the total of 40 recorded ln the lake. The relationships between data sets were investigated by bivariate analysis. The relationships between abiotic factors are best described by linear equations as are some relationships between Sigara concinna, Sigara dorsalis, Potamopyrgus jenkinsi and environmental factors. The relationships of numbers of Gammarus tigrinus with temperature, Sigara stagnalis with conductivity, Corixidae with time and Sigara lateralis, Theromyzon tessulatum and Piscicola geometra with vegetation cover are best described by exponential equations. The relationships between the population dynamics of pairs of certain taxa viz. Gammarus tigrinus and G. duebeni, G. tigrinus and Asellus aquaticus, G. tigrinus and Corixidae, Sigara dorsalis and S. concinna, are best described by power equations. The relationship of vegetation cover with time and the population dynamics of many taxa are best described by logarithmic logistic equations.Both density dependent and density independent relationships appear to be responsible for changes in numbers and taxa within the total community. Density independent relationships are most important at times of environmental change while density dependent relationships, though operating continuously, are most important when conditions are stable.