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Size, shape, and surface area of beaver, Castor canadensis, a semiaquatic mammal
Canadian Journal of Zoology
Abstract
The beaver, Castor canadensis, is a large, herbivorous, semiaquatic rodent. Beaver forage on land as well as in water; thus functional compromise between competing activities should result in a less streamlined body shape than expected for a similarly sized marine mammal. Standard morphometrics and surface areas of 70 Wisconsin beaver ranging in size from 5 to 35 kg were measured. Geometric similarity of surface area was maintained during growth (i.e., area was proportional to body mass raised to the 2/3 power). Scaly-tail area was positively allometric with body mass; hind foot web area was weakly negatively allometric. The surface area of the unfurred extremities (hind feet and scaly tail) comprised 30% of the total surface area of adults and over 50% for younger beaver. The average surface area of 21 adult beaver (mean body mass = 20 kg) was 0.52 m2. This value was significantly lower (P < 0.001) than predicted from the Meeh equation for terrestrial mammals, but similar to that expected for a marine mammal of equivalent mass. Body shape was described by the fineness ratio (a hydrodynamic index of streamlining). The fineness ratio for beaver was 4.8, a value similar to that for phocid seals. Therefore, in spite of expected constraints on body shape imposed by herbivory and the competing demands of terrestrial and aquatic foraging, beaver do not differ significantly in overall shape from other, more aquatic, species. However, shape alone is not a reliable indicator of either hydrodynamic or energetic efficiency. Future comparative studies should incorporate both phylogeny and biomechanical data into evaluations of mammalian morphology.
... Fur can be an effective insulator for terrestrial lifestyle, but is it also in water? The presence of dense, waterproof fur is a characteristic of recent invaders of the aquatic environment, such as otters, polar bears, beavers and other rodents (Liwanag et al., 2012b;Reynolds, 1993). In this study, muskrats, beavers and otters were the species with the lowest degrees of desaturation and the highest hair densities (Fig. 4.3 and 4.4) which supports the idea that these mammals rely on dense waterproof fur, rather than the adipose tissue, as an insulator (Reynolds, 1993). ...
... The presence of dense, waterproof fur is a characteristic of recent invaders of the aquatic environment, such as otters, polar bears, beavers and other rodents (Liwanag et al., 2012b;Reynolds, 1993). In this study, muskrats, beavers and otters were the species with the lowest degrees of desaturation and the highest hair densities (Fig. 4.3 and 4.4) which supports the idea that these mammals rely on dense waterproof fur, rather than the adipose tissue, as an insulator (Reynolds, 1993). The efficiency of this coat relies on the air trapped in its hairs , which forms a protective warm layer and keeps the skin relatively dry (Dawson and Fanning, 1981). ...
... Recent entries to the aquatic environment possess drag-based propulsion in water and they have less fusiform body shapes, are shallower divers and slower swimmers compared to earlier entries, such as seals (Reynolds, 1993). However, the transition from a terrestrial to an aquatic lifestyle required adaptations for enhanced locomotory performance in water, which includes greater streamlining. ...
: Blubber was a crucial adaptation for mammals living in water. Blubber serves as an energy reservoir, where surplus energy is deposited in the form of fatty acids (FAs). Most FAs are obtained from an animal’s diet (dietary FAs), thus a predator’s FA signature has the potential to provide dietary information. However, some FAs in the predator may be synthesised or modified intrinsically to fulfil physiological demands (non-dietary FAs), which complicates dietary studies. The aim of this thesis was to understand how FAs signatures relate to the dietary and thermoregulatory roles of blubber. I analysed FAs of leopard and crabeater seals to determine how FAs vary across the blubber depth and how this variability influenced dietary interpretations.
I found that blubber is not uniform; where some FAs are abundant in the outer (superficial) layer others are dominant in the inner (deepest) layer. This suggests that the inner layer has a dietary role whereas the outer layer has a more structural role. The FA signatures from the predator’s inner layer resembled more closely those of their prey than the FAs in the outer layer. Trophic predictions were clearer when using only the dietary FAs rather than all FAs; this indicates that there are other factors influencing the metabolism of the non-dietary FAs. To examine if a mammal’s thermoregulatory requirements impact the shifts in FAs, I conducted a meta-analysis including 48 mammals from terrestrial, semi-aquatic, and fully-aquatic environments. I found that the FAs of aquatic mammals are more highly desaturated than those of terrestrial mammals. Higher desaturation helps reduce heat loss and ensures that blubber remains flexible in cold environments. FA desaturation is correlated with latitude and fur density in semi-aquatic mammals. Thus, they increase FA desaturation when living in colder habitats and when they have sparser fur. I compared the FAs of three sympatric Antarctic seals and found that FA desaturation changes as seals grow, which suggests that the thermal efficiency of blubber develops with age. In order to obtain better results in dietary studies, the effect of thermal habitat, fur density and age, on the metabolism of FAs must be considered.
... Additionally, they possess both fur and blubber insulation, which is an interesting aspect of mammalian thermoregulation. The presence of dense, waterproof fur is a characteristic of recent entries to the aquatic environment, such as otters, beavers and other rodents [19,48]. In this study, muskrats, beavers and otters, although living in cold regions, were the species with the lowest degrees of desaturation (Fig. 1b) suggesting that this is a pinniped-only phenomenon. ...
... Interestingly, these recent entries to the aquatic medium have the highest hair densities (See Additional file 1: Table S1.). This supports the idea that these mammals rely on dense waterproof fur, rather than the adipose tissue, as an insulator [48]. The efficiency of this coat relies on the air trapped in its hairs [49], which forms a protective warm layer and keeps the skin relatively dry [50]. ...
Background: Most fatty acids (FAs) making up the adipose tissue in mammals have a dietary origin and suffer little modification when they are stored. However, we propose that some of those FAs, specifically those that can be synthesised or modified by mammals, are also being influenced by thermal forces and used as part of the mechanism to regulate core body temperature. As FA desaturation increases, adipose tissues can reach colder temperatures without solidifying. The ability to cool the superficial fat tissues helps create a thermal gradient, which contributes to body heat loss reduction. Therefore, it is expected that animals exposed to colder environments will possess adipose tissues with higher proportions of desaturated FAs. Here, through a model selection approach that accounts for phylogeny, we investigate how the variation in FA desaturation in 54 mammalian species relates to the thermal proxies: latitude, physical environment (terrestrial, semi-aquatic and fully-aquatic) and hair density.
Results: The interaction between the environment (terrestrial, semi or fully-aquatic) and the latitude in which the animals lived explained best the variation of FA desaturation in mammals. Aquatic mammals had higher FA desaturation compared to terrestrial mammals. Semi-aquatic mammals had significantly higher levels of desaturated FAs when living in higher latitudes whereas terrestrial and fully-aquatic mammals did not. To account for dietary influence, a double bond index was calculated including all FAs, and revealed no correlation with latitude in any of the groups.
Conclusions: We propose that FA modification is an important component of the thermoregulatory strategy, particularly in semi-aquatic mammals. Potentially this is because, like terrestrial mammals, they experience the greatest air temperature variations across latitudes, but they lack a thick fur coat and rely primarily on their blubber. Unlike fully-aquatic mammals, extremely thick blubber is not ideal for semi-aquatic mammals, as this is detrimental to their manoeuvrability on land. Therefore, the adipose tissue in semi-aquatic mammals plays a more important role in keeping warm, and the modification of FAs becomes crucial to withstand cold temperatures and maintain a pliable blubber.
... Bipedal paddling is used by semiaquatic swimmers, such as the water-opossum (Chironectes minimus) and the rodents O. palustris, Ondatra zibethicus, and Hydromys chrysogaster ( Esher et al. 1978;Fish 1984Fish , 1992Fish , 1993bFish and Baudinette 1999). However, semiaquatic mammals such as the capybara (Hydrochoerus hydrochaeris) and the mink (Neovison vison) swim using all 4 limbs ( Dagg and Windsor 1972;Renous 1994;Williams 1983). ...
... during submerged swimming (Fig. 4) was similar to diagonal limb pairs, also used by quadruped primates, where thrust is generated by simultaneous action of a forelimb on 1 side and the hind limb on the opposite side of the body (Hildebrand and Goslow 2006). The swimming bound is similar to the half bound, a common asymmetric gait of small terrestrial mammals (Renous 1994), but in the half bound the right forelimb anticipates the power stroke by touching the ground before the opposite limb (Hildebrand and Goslow 2006). The change from bipedal paddling on the water surface to quadrupedal submerged swimming observed in N. rattus and Cerradomys sp. ...
A la fin du 19ème siècle, E.J. Marey et E. Muybridge ont séparément inventé les instruments permettant l'étude des mouvements locomoteurs des grands mammifères, en particulier du cheval. L'observation de la locomotion des petits mammifères est difficile, leurs mouvements étant plus rapides et leur pelage cachant leurs membres. La tachycinéradiographie, technique associant le cinéma à grande vitesse à la radiographie, permet de découvrir tout le système de la géométrie de leur squelette et d'analyser leurs mouvements rapides. Quelques-uns de ces animaux (la mérione, le rat...) sont plus particulièrement étudiés selon cette technique, à des cadences de 300 à 500 images/seconde. Les résultats de cette analyse mettent en évidence une géométrie particulière de leurs membres, dont la longueur n'est jamais pleinement utilisée au cours de leur déplacement. Les différences observées entre les espèces traduisent en particulier l'organisation structurale de leur propre groupe. Générique Direction scientifique : GASC Jean-Pierre, RENOUS Sabine et ROCHA BARBOSA Oscar (Adaptations et évolution des systèmes ostéomusculaires, URA CNRS, Paris). Réalisateur : DEVEZ Alain R. (Ecotrop, URA CNRS, Brunoy) Production : CNRS AV Diffuseur : CNRS Images http://videotheque.cnrs.fr/
... O. zibethicus (n = 12) δ13 C col = −22.7 to −10.7‰, with a mean of −15.3‰, and O. zibethicus δ 15 N col = +2.2 to +6.6‰, with a mean of +5.1‰. C. canadensis (n = 8) δ 13 C col varies very little, ranging from −24.0 to −23.2‰, with a mean of −23.5‰. ...
This is a multi-individual (n = 11), stable carbon and nitrogen isotope study of bone collagen (δ13Ccol and δ15Ncol) from the giant beaver (genus Castoroides). The now-extinct giant beaver was once one of the most widespread Pleistocene megafauna in North America. We confirm that Castoroides consumed a diet of predominantly submerged aquatic macrophytes. These dietary preferences rendered the giant beaver highly dependent on wetland habitat for survival. Castoroides’ δ13Ccol and δ15Ncol do not support the hypothesis that the giant beaver consumed trees or woody plants, which suggests that it did not share the same behaviours as Castor (i.e., tree-cutting and harvesting). The onset of warmer, more arid conditions likely contributed to the extinction of Castoroides. Six new radiocarbon dates help establish the chronology of the northward dispersal of the giant beaver in Beringia, indicating a correlation with ice sheet retreat.
... The beavers' fusiform body with short limbs, webbed hind feet, and waterproof fur reflects the animal's adaption to an amphibious life (Allers & Culik, 1997). In fact, it has been suggested that beaver streamlining is similar to that of fully aquatic animals such as phocid seals (Reynolds, 1993). In beavers, physiological adaptions to diving include bradycardia and a minor postdive tachycardia (Clausen & Ersland, 1970;Swain, Gilbert, & Robinette, 1988). ...
Semi-aquatic mammals have secondarily returned to the aquatic environment, although they spend a major part of their life operating in air. Moving both on land, as well as in, and under water is challenging because such species are considered to be imperfectly adapted to both environments. We deployed accelerometers combined with a depth sensor to study the diving behavior of 12 free-living Eurasian beavers Castor fiber in southeast Norway between 2009 and 2011 to examine the extent to which beavers conformed with mass-dependent dive capacities, expecting them to be poorer than wholly aquatic species. Dives were generally shallow (<1 m) and of short duration (<30 s), suggesting that the majority of dives were aerobic. Dive parameters such as maximum diving depth, dive duration, and bottom phase duration were related to the effort during different dive phases and the maximum depth reached. During the descent, mean vectorial dynamic body acceleration (VeDBA—a proxy for movement power) was highest near the surface, probably due to increased upthrust linked to fur- and lung-associated air. Inconsistently though, mean VeDBA underwater was highest during the ascent when this air would be expected to help drive the animals back to the surface. Higher movement costs during ascents may arise from transporting materials up, the air bubbling out of the fur, and/or the animals’ exhaling during the bottom phase of the dive. In a manner similar to other homeotherms, beavers extended both dive and bottom phase durations with diving depth. Deeper dives tended to have a longer bottom phase, although its duration was shortened with increased VeDBA during the bottom phase. Water temperature did not affect diving behavior. Overall, the beavers’ dive profile (depth, duration) was similar to other semi-aquatic freshwater divers. However, beavers dived for only 2.8% of their active time, presumably because they do not rely on diving for food acquisition.
... This latter phenomenon is expressed as either a resource defence polygyny or female (harem) defence polygyny, and it usually results in males being larger than females [18, 19]. Therefore, the vast majority of studies of sexual dimorphism in mammals have focused on SSD, while relatively few examined variation in shape [20, 21, 22, 23, 24, 25], especially in Cetaceans [26]. Odontocetes cetaceans (toothed whales) show different degrees of SSD, from the sperm whale having males 1.6 times larger than females, to the monomorphism of Delphinidae [11, 27]. ...
Feeding adaptation, social behaviour, and interspecific interactions related to sexual dimorphism and allometric growth are particularly challenging to be investigated in the high sexual monomorphic Delphinidae. We used geometric morphometrics to extensively explore sexual dimorphism and ontogenetic allometry of different projections of the skull and the mandible of the bottlenose dolphin Tursiops truncatus. Two-dimensional landmarks were recorded on the dorsal, ventral, lateral, and occipital views of the skull, and on the lateral view of the left and the right mandible of 104 specimens from the Mediterranean and the North Seas, differing environmental condition and degree of interspecific associations. Landmark configurations were transformed, standardized and superimposed through a Generalized Procrustes Analysis. Size and shape differences between adult males and females were respectively evaluated through ANOVA on centroid size, Procrustes ANOVA on Procrustes distances, and MANOVA on Procrustes coordinates. Ontogenetic allometry was investigated by multivariate regression of shape coordinates on centroid size in the largest homogenous sample from the North Sea. Results evidenced sexual dimorphic asymmetric traits only detected in the adults of the North Sea bottlenose dolphins living in monospecific associations, with females bearing a marked incision of the cavity hosting the left tympanic bulla. These differences were related to a more refined echolocalization system that likely enhances the exploitation of local resources by philopatric females. Distinct shape in immature versus mature stages and asymmetric changes in postnatal allometry of dorsal and occipital traits, suggest that differences between males and females are established early during growth. Allometric growth trajectories differed between males and females for the ventral view of the skull. Allometric trajectories differed among projections of skull and mandible, and were related to dietary shifts experienced by subadults and adults.
... Semi-aquatic mammals carry large volumes of air in both the respiratory tract and the pelage during dives. Air trapped in the pelage is a property of the dense waterproof fur possessed by semi-aquatic mammals (Sokolov, 1962Sokolov, , 1982Reynolds, 1993). The waterproof fur will confer protection against heat loss in water and also contributes to the positive buoyancy of individual animals. ...
... Conversely, terrestrial and semiaquatic species employ drag-based paddling motions (Williams 1983, Fish 1993a, 1996. This swimming mode is considered primitive and of low performance efficiency compared to the swimming behavior of fully aquatic mammals (Reynolds 1993, Fish 1996. Swimming through quadruped gaits is not the most efficient way to move in an aquatic environment, as it has a strong negative effect on hydrodynamics (Fish 1993b), although swimming below the water surface minimizes or obviates the increased energy expenditure and speed limitations imposed by wave drag (Lang andDaybell 1963, Hertel 1966). ...
This note reports the first record of undulatory swimming mode by the black-eared opossum Didelphis aurita. The record was made in a stream running through the Atlantic Rain Forest in Southern Brazil. After the individual was released, it dove into the stream to escape, swimming using undulation of its trunk and tail. In general, terrestrial mammals use similar gaits to walk and swim. The lateral undulation of the trunk and tail observed during the diving of D. aurita was similar to that seen in quadruped diagonal gaits in terrestrial habitats, but swimming without use of fore and hind limbs is a behavior unique to aquatic locomotion, increasing the locomotor repertoire of this species.
... The semiaquatic muskrat, however, has arrector pili muscles, which will be of benefit for insulation when out of the water. When models of a seal with and without hair covering were compared, a reduction of the drag with the hair covering was reported for flow velocities of 8-10 m s-' (Romanenko et al. 1973). However, Kooyman (1989) noted that these results may not be ecologically relevant, because seals normally swim at lower speeds (Williams and Kooyman 1985; Ponganis et al. 1990; LeBoeuf et al. 1972). ...
Optimisation of energy by aquatic mammals requires adaptations that reduce drag, and improve thrust production and efficiency. Drag is minimised by streamlining the body and appendages. Highly derived aquatic mammals have body shapes close to the optimal hydrodynamic design for drag reduction. There is no conclusive evidence for specialised drag reduction mechanisms, although decreasing hair density is associated with reduced drag. Improvement in thrust production and efficiency is accomplished by changes in propulsive mode and appendage design. Semiaquatic mammals employ. drag-based propulsion using paddles, whereas fully aquatic mammals use lift-based propulsion with hydrofoils. Because paddling generates thrust through half the stroke cycle, propulsive efficiency is low and energetic cost is high compared with that for mammals using hydrofoils. Lift-based swimming is a rapid and high-powered propulsive mode. Oscillations of the hydrofoil generate thrust throughout the stroke cycle. For cetaceans and pinnipeds, propulsive efficiency is approximately 80%, and transport cost is below that of semiaquatic mammals. Behavioural adaptations help minimise energy expenditure by swimming mammals. Submerged swimming avoids increased drag from energy lost in formation of surface waves. Porpoising and wave riding, characteristic of dolphins, can reduce the transport costs, allowing for longer-duration swimming at high speeds.
... insulating fat layer, semi-aquatic mammals are protected from colder temperatures by a dense hair coat, in which an air layer is trapped (Sokolov 1962, Frisch et al. 1974, Reynolds 1993. Semiaquatic mammals have hair densities of: 36 000 hairs/cm 2 for the water rat Hydromis chrysogaster, between 30 000 and 38 000 for the European beaver Castor fiber, and between 67 000 and 84 000 for the platypus Ornithorhynchus anatinus (Grant and Dawson 1978, Dawson and Fanning 1981, Sokolov 1982, Fish et al. 2002. ...
The hair density of adult Eurasian otters Lutra lutra (Linnaeus, 1758) and sea otters Enhydra lutris (Linnaeus, 1758) was analysed using skin samples taken from frozen carcasses. Lutra lutra exhibited a mean hair density of about 70 000 hairs/cm2 (whole body, appendages excepted), the mean individual density ranging from about 60 000 to 80 000 hairs/cm2. The dominant hair type were secondary hairs (wool hairs), the hair coat comprising only 1.26% of primary hairs (PH). Secondary
hair (SH) density remained constant over the body (appendages excepted), whereas a few variations in PH density were observed.
Neither an influence of the sex, nor a seasonal variation of the hair coat was found, moulting seems to be continuous. Enhydra lutris had a hair density between 120 000 and 140 000 hairs/cm2, the primary hairs representing less than 1% within the hair coat. Hair density remained quite constant over the regions
of the trunk but was lower at the head (about 60 000 hairs/cm2 on the cheek). The hair follicles were arranged in specific groups with different bundles of varying size, normally comprising
dominant numbers of wool hair (SH) follicles. Invariably there was always a large central primary hair follicle and numerous
sebaceous glands between the bundles and principally around the PH follicles. The results are discussed related to possible
ecological influences on hair coat density.
Key wordsLutrinae-hair coat-hair follicles-hair group structure-seasonal variation-insulation
Many animals exhibit morphological changes across ontogeny associated with adaptations to their environment. Sea otters ( Enhydra lutris ) have the densest fur of any animal, which is composed of guard hairs, intermediate hairs, and underhairs. Sea otters live in cold water environments, and their fur traps a layer of air to remain properly insulated, due to morphological adaptations that allow the hairs to trap air when submerged. When a sea otter is born, it has a natal pelage which it will eventually molt and replace with a pelt resembling the adult pelage. Past studies have investigated the morphology and hair density of adult sea otter fur, but these characteristics have not been measured for other age classes, including for the natal pelage. This study quantified ontogenetic changes in hair morphology of southern sea otter ( E. lutris nereis) pelts. We measured guard hair length and circularity, shape of cuticular scales on guard hairs and underhairs, and overall hair density for sea otter pelts across six age classes: neonate (<1 month), small pup (1–2 months), large pup (3–5 months), juvenile (6 months–1 year), subadult (1–3 years), and adult (4–9 years). Neonate and small pup pelts had significantly longer guard hairs than older age classes. Natal pelage guard hairs were similarly shaped but smaller in diameter than adult guard hairs. Hairs of the natal pelage had similar cuticular scale patterns as adult hairs, indicating the importance of this structure for the function of the fur. Natal pelage had a lower hair density than the pelage of older age classes, with the adult pelage exhibiting the highest hair density. Overall, the morphological differences between natal and adult pelage in sea otters suggest functional differences that may make sea otter pups more vulnerable to heat loss.
The exploration of underwater narrow space is of great significance to study the phenomena, process and laws of life in the ocean. The existing underwater robots are not suitable for the underwater narrow area exploration. Beavers use the hind limbs with webfeet to provide power for flexible movement and possess certain underwater operation ability. In this study, based on the bionic prototype of beaver hind limb, the system structure of beaver-like hind limb is designed, and the paddling motion of beaver-like hind limb is realized by combining servos with rope drive. On this basis, the concept of swimming gait is proposed, and swimming process of beavers with one leg and two legs is analyzed, and the movement sequence of various joints and parts in the swimming is studied. Then, the joint angle data of beavers from the video are obtained and a nonlinear oscillation swimming controller based on Fourier technology is proposed to plan the bionic swimming trajectory of the beaver. Further, the swimming efficiency of the beaver-like hind limb is analyzed, and a model of the swimming efficiency is proposed, which can provide a basis for evaluating its swimming effect. Finally, an experimental platform for the swimming of the beaver-like hind limb is set up, and bionic and reconstruction of the swimming gaits are generated by the nonlinear oscillation swimming controller, and the swimming experiment is carried out. The results show that the propulsion efficiencies of the alternate and synchronous bionic gait are 0.5 × 10−3 and 0.6 × 10−3, higher than those of the generated gaits which are 0.2 × 10−3 and 0.3 × 10−3. This verifies the rationality of the beaver swimming, and lays a theoretical foundation for the swimming realization of the beaver-like hind limb, which provides theoretical support for us to further understand the swimming mechanism of the beaver.
Stable isotope analysis of diet has become a common tool in conservation research. However, the multiple sources of uncertainty inherent in this analysis framework involve consequences that have not been thoroughly addressed. Uncertainty arises from the choice of trophic discrimination factors, and for Bayesian stable isotope mixing models (SIMMs), the specification of prior information; the combined effect of these aspects has not been explicitly tested. We used a captive feeding study of gray wolves (Canis lupus) to determine the first experimentally-derived trophic discrimination factors of C and N for this large carnivore of broad conservation interest. Using the estimated diet in our controlled system and data from a published study on wild wolves and their prey in Montana, USA, we then investigated the simultaneous effect of discrimination factors and prior information on diet reconstruction with Bayesian SIMMs. Discrimination factors for gray wolves and their prey were 1.97‰ for δ13C and 3.04‰ for δ15N. Specifying wolf discrimination factors, as opposed to the commonly used red fox (Vulpes vulpes) factors, made little practical difference to estimates of wolf diet, but prior information had a strong effect on bias, precision, and accuracy of posterior estimates. Without specifying prior information in our Bayesian SIMM, it was not possible to produce SIMM posteriors statistically similar to the estimated diet in our controlled study or the diet of wild wolves. Our study demonstrates the critical effect of prior information on estimates of animal diets using Bayesian SIMMs, and suggests species-specific trophic discrimination factors are of secondary importance. When using stable isotope analysis to inform conservation decisions researchers should understand the limits of their data. It may be difficult to obtain useful information from SIMMs if informative priors are omitted and species-specific discrimination factors are unavailable.
The transition from a terrestrial to an aquatic lifestyle in mammals required the evolution of specific adaptations for locomotion and stability in water. We postulated that the non-wettable fur of semi-aquatic mammals is an important adjunct to buoyancy control. Fur buoyancy characteristics and hair morphology were examined for two terrestrial mammals (opossum, Didelphis vivginiana and Norway rat, Rattus norvegicus), and seven semi-aquatic mammals, (beaver, Castor canadensis; sea otter, Enhydra lutris; Australian water rat, Hydronzys chrysogaster; river otter, Lutra can- adensis; American mink, Mustela vison; muskrat, Ondatra zibethicus; and platypus, Ornithorhynchus anatinus). We determined buoyancy hydrostatically, measured hair density on histological skin samples, and hair length and diameter. Buoyancy was posi- tively correlated with hair density, but was not with hair length or thickness. As expected, buoyancy was considerably greater in aquatic mammals than in terrestrial mammals. Enhydra displayed the greatest hair density (1188.8 hairs/mm2j with a buoyant force of 0.94 N, whereas Rattus had the lowest hair density (95.2 hairslmm2) and Didelphis had the lowest fur buoyancy of 0.12 N. High hair density of non-wettable fur traps large amounts of air and thus provides semi-aquatic mammals with positive buoyancy and decreases the effort needed to float.
My overall goal is to complete a synthesis of bioenergetics/behavior models with ecological interactions models. I will focus on terrestrial animals and the microclimates available to them at global localities in the past, present or future. The results will appear as a substantial paper and a book (11 of 15 chapters done already) with user friendly computer programs for research and teaching.
The Australian water rat, Hydromys chrysogaster, faces thermoregulatory problems due to the variation in its thermal environment. The influence of temperature on the rodent's heat budget in air and in water at three levels of activity was examined. The water rat maintained at low air temperatures, but hyperthermia occurred when approached . During thermoneutral conditions was 36.6 ± 0.6 C (mean ± SD) and standard metabolism was 3.28 ± 0.19 W kg⁻¹, similar to predicted values. In water, was not maintained at water temperatures below 25 C at any level of activity, suggesting thermoregulatory abilities inferior to the other Australian semiaquatic mammal, the platypus. The water rat possesses fur insulation comparable with that of the platypus, but the platypus has extensive vascular retia which the water rat lacks. In cold water the water rat may accept a degree of hypothermia, with the rate of heat loss being retarded by the maintenance of an air layer in the fur and by controlled regional heterothermia. An estimate of the cost of swimming gave values for water rats similar to those for ducks.
Standard morphometries and body surface areas were determined for 56 captive phocid seals. The mean Meeh constant, describing the relationship between maximum surface area (Amax) and body mass raised to the power 2/3 (m0.67), was 0.088 ± 0.011 m2∙kg−0.67. This value was not significantly different (P < 0.05) from the mean Meeh constant for 13 species of marine mammals (0.090 ± 0.018 m2∙kg−0.67), nor was it significantly different from the Meeh constants calculated for two samples of terrestrial mammals (0.097 ± 0.019 (N = 57) and 0.10 ± 0.013 m2∙kg−0.67 (N = 21)). The empirical allometric relationship between body mass and surface area for our phocid seals was log Amax = log 0.14 + 0.51 log m (R2 = 0.84). This relationship was not significantly different from that calculated for cetaceans, but was, however, significantly different from that calculated for terrestrial mammals. On average, surface areas of marine mammals (including pinnipeds, cetaceans, and the sea otter) were 23% smaller for their mass than those of terrestrial mammals.
Oxygen consumption (VO2) during surface swimming and total body drag were investigated in the North American mink, Mustela vision Schreber. Over the range of 0.13-0.70 ms-1, VO2 increased curvilinearly with speed for minks swimming against a current in a water flume. Similarly, body drag of a mink carcass increased non-linearly with speed and was described by the equation, Drag = 1.24 velocity. A streamlined body shape, characteristic of many mustelids, aided in reducing drag at high speeds. Net swimming efficiencies were comparatively low (less than 2.8%) and were attributed to hig levels of drag when on the water surface and the absence of appendage specialization for aquatic locomotion. This lack of specialization probably contributes to high energetic costs but enables the mink to forage in both the aquatic and terrestrial environments.
Cold water has been described as the harshest thermal environment encountered by mammals anywhere on earth (Irving 1973). This is a perception undoubtedly reinforced by our own limited thermoregulatory competence in the aquatic medium. In 0°C water, the rectal body temperature (Tb) of an adult human may drop at a rate of 0.07–0.08°C min-1, resulting in a predicted survival time of 107 min (Hayward et al. 1975). Immersion hypothermia thus poses a serious risk in boating accidents, and not surprisingly, has provided the focus for much research in the past (see Hayward et al. 1975; McArdle et al. 1984). Far less attention has been directed to the truly aquatic mammals, many of which are much smaller than man. This is unfortunate, considering that there are close to 100 species of mammals, spanning 9 orders, that spend at least some part of their life in water (Irving 1973). Aquatic mammals frequent lakes and streams of virtually every continent, and occur in all the major oceans of the world. Yet despite the rich diversity of aquatic forms, our understanding of their thermal biology is based on investigations of but a few species, and clearly has not kept pace with advances in the study of terrestrial endotherms. This deficiency may in part reflect the logistical problems of studying aquatic species, especially large-bodied forms such as whales and seals.
Thermoregulation during swimming and resting in water was investigated for the North American mink (Mustela vision, Schreber) in summer and winter pelage by measuring total heat production, heat storage, and minimum thermal conductance. Swimming activity over the range of 0.13-0.60 m·s⁻¹ resulted in heat losses that exceeded metabolic heat production within 5 min of immersion. This imbalance, manifested as a decline in core body temperature (core ), resulted in negative levels of heat storage. Negative heat storage for mink was greatest at intermediate swimming speeds. Maximum levels were -14.28 W·kg⁻¹ at 0.29 m·s⁻¹ and -8.72 W·kg⁻¹ at 0.36 m·s⁻¹ for mink in summer and winter pelage, respectively. Thermal conductance determined from cooling curves of carcasses and a taxidermic mount increased linearly with water speed and was comparatively greater at all speeds for animals in summer pelage. Patterns of cooling for carcasses, the taxidermic mount, and swimming mink were similar. In combination with regional heterothermy and elevated heat production, insulation provided by an air layer pervading the fur will permit short bouts of swimming in which is maintained by foraging mink.
Hydrodynamic characteristics, including fineness ratios, coefficients of drag, and the influence of body size, shape, and position on drag were examined for harbor seals (Phoca vitulina). Drag for towing animals increased curvilinearly with velocity over the range 0.7 to 3.5 m·s⁻¹ and was described by the equations: Drag(N) = 6.49 velocity ( for a submerged adult seal, and Drag(N) = 1.29 for the seal towing at the water surface. The importance of streamlining was demonstrated by comparing these values with those of a towing human subject. At 2.0 m·s⁻¹ drag for a submerged human was 113 N, representing a 5.0-fold and a 1.9-fold increase in drag over submerged and surface towing seals, respectively. Coefficients of drag (Cd) followed this trend and were three times greater for the human subject. Alterations in body configuration of the seals, as occurs during stroking movements, resulted in an increase in body drag. From our calculations, body drag during gliding phases may more than double during active swimming by seals and influences the swimming performance of these animals.
During the last 55 million years of mammalian evolution, the order Rodentia has had an increasing success in terrestrial mammalian communities. No less than 330 to 400 genera, and 1800 to 2300 species, have been recorded in the Recent fauna, and the last number represents half of all species of mammals. All continents and all islands, including the smallest, are colonized by these small animals, sometimes with the aid of man himself. In deserts, mountains, rivers and cities, rodents are joining man in many of his activities, including exploitation of the earth.
Most biologists are now aware that ordinary least square regression is not appropriate when the X and Y variables are both subject to random error. When there is no information about their error variances, there is no correct unbiased solution. Although the major axis and reduced major axis (geometric mean) methods are widely recommended for this situation, they make different, equally restrictive assumptions about the error variances. By using simulated data sets that violate these assumptions, the reduced major axis method is shown to be generally more efficient and less biased than the major axis method. It is concluded that if the error rate of the X variable is thought to be more than a third of that on the Y variable, then the reduced major axis method is preferable; otherwise the least squares technique is acceptable. An analogous technique, the standard minor axis method, is described for use in place of least squares multiple regression when all of the variables are subject to error.
Muskrats experienced a steady decline in abdominal and subcutaneous body temperature (ΔTh) during unrestrained dives of 0.5- to 4-min duration. Extent of body cooling, postdive O2 consumption , and metabolic recovery time increased both with time submerged and declining water temperature (3 – 30 °C). For each additional minute that a muskrat remained submerged, cost increased by 99 mL O2∙kg−1 in 3 °C, compared with 71 and 43 mL O2∙kg−1 in 20 and 30 °C water, respectively. Postdive correlated strongly with ΔTh incurred during diving. Mean , during spontaneous activity in water, when animals were free to swim, dive, or float quietly on the surface, varied inversely with water temperature and directly with ΔTh. Temporal decline in Th during 25-min immersion was matched by a concurrent reduction in voluntary dive time. Mean , immediately following withdrawal from water exceeded that during an equivalent period of immersion.
Both a landmark text and reference book, Steven Vogel's "Life in Moving Fluids" has also played a catalytic role in research involving the applications of fluid mechanics to biology. In this revised edition, Vogel continues to combine humor and clear explanations as he addresses biologists and general readers interested in biological fluid mechanics, offering updates on the field over the last dozen years and expanding the coverage of the biological literature. His discussion of the relationship between fluid flow and biological design now includes sections on jet propulsion, biological pumps, swimming, blood flow, and surface waves, and on acceleration reaction and Murray's law. This edition contains an extensive bibliography for readers interested in designing their own experiments.
Measurements have been made of the principal leg bones of 37 species representing almost the full range of sizes of terrestrial mammals. The lengths of corresponding bones tend to be proportional to (body mass)0·35 and the diameters to (body mass)0·36, except in the family Bovidae in which the exponents for length are much nearer the value of 0·25 predicted by McMahon's (1973) theory of elastic similarity. Comparisons are made between mammals of similar size belonging to different orders.
The aquatic and terrestrial locomotion of the walrus are described using the frame‐by‐frame analysis of 16 mm cine film and the manipulation of bone‐muscle preparations. The
hind limbs of the walrus are the major source of aquatic propulsion; the forelimbs are used for manoeuvring as well as for propulsion.
Daimonelix is a name given to terrestrial lebensspuren of the late Oligocene—early Miocene beaver genus Palaeocastor, and is not a plant or fresh-water sponge as was originally believed by Barbour. Palaeocastor belongs to a lineage of castorids always found in upland habitat, never near evidence of ponded water. Daimonelices are found in high concentrations in the Harrison Formation of western Nebraska and eastern Wyoming, which represents a semiarid, upland paleoenvironment of sandy substrate. Assignment of a large sample of contemporaneous Daimonelix to the species P. fossor is based on a series of incisor width measurements and on mean shaft diameters. The remarkable preservation of daimonelices, which permits detailed analysis of events in beaver burrow construction, is shown to be due to rapid silicification of plant roots invading the burrows. Some aspects of Palaeocastor ecology and ethology are also clarified. The spatial distribution of Daimonelix consists of scattered towns of high burrow density. One such colony is shown in a detailed paleogeographic map. Criteria for time equivalency of such burrow aggregations are established. The entoptychine gopher Gregorymys, the carnivore Zodiolestes, and the larger beaver P. magnus are also shown to be occasional inhabitants of Palaeocastor fossor colonies.
In situations such as allometry where a line is to be fitted to a bivariate sample but where an asymmetric choice of one or other variable as regressor cannot be made, the reduced major axis is often used. Existing tests of the slope of this line, particularly between samples, are not sufficiently accurate in view of the scarcity of the material to which such methods are often applied. Alternative test statistics are suggested and some of their properties derived from a computer implementation of k statistics.
We discuss and clarify several aspects of applying Felsenstein's (1985, Am. Nat. 125: 1–15) procedures to test for correlated evolution of continuous traits. This is one of several available comparative methods that maps data for phenotypic traits onto an existing phylogenetic tree (derived from independent information). Application of Felsenstein's method does not require an entirely dichotomous topology. It also does not require an assumption of gradual, clocklike character evolution, as might be modeled by Brownian motion. Almost any available information can be used to estimate branch lengths (e.g., genetic distances, divergence times estimated from the fossil record or from molecular clocks, numbers of character changes from a cladistic analysis). However, the adequacy for statistical purposes of any proposed branch lengths must be verified empirically for each phytogeny and for each character. We suggest a simple way of doing this, based on graphical analysis of plots of standardized independent contrasts versus their standard deviations (i.e., the square roots of the sums of their branch lengths). In some cases, the branch lengths and/or the values of traits being studied will require transformation. An example involving the scaling of mammalian home range area is presented. Once adequately standardized, sets of independent contrasts can be analyzed using either linear or nonlinear (multiple) regression. In all cases, however, regressions (or correlations) must be computed through the origin. We also discuss ways of correcting for body size effects and how this relates to making graphical representations of relationships of standardized independent contrasts. We close with a consideration of the types of traits that can be analyzed with independent contrasts procedures and conclude that any (continuous) trait that is inherited from ancestors is appropriate for analysis, regardless of the mechanism of inheritance (e.g., genetic or cultural).
The propulsive motions of swimming harp seals (Phoca groenlandica Erxleben) and ringed seals (Phoca hispida Schreber) were studied by filming individuals in a flume. The seals swam at velocities ranging from 0.6 to 1.42 m s-1. Locomotion was accomplished with alternate lateral sweeps of the hind flippers generated by lateral flexions of the axial body in conjunction with flexion of the flippers. The frequency of the propulsive cycle increased linearly with the swimming velocity, and the maximum angle of attack of the flipper decreased, but the amplitude remained constant. The kinematics and morphology of this hind flipper motion indicated that phocid seals do not swim in the carangiform mode as categorized by Lighthill (1969), but in a distinct mode that mimics swimming by thunniform propulsors. The hind flippers acted as hydrofoils, and the efficiency, thrust power and coefficient of thrust were calculated from unsteady wing theory. The propulsive efficiency was high at approximately 0.85. The thrust power increased curvilinearly with velocity. The drag coefficient ranged from 0.012 to 0.028 and was found to be 2.8-7.0 times higher than the theoretical minimum. The drag coefficient was high compared with that of phocid seals examined during gliding or towing experiments, indicating an increased drag encumbered by actively swimming seals. It was determined that phocid seals are capable of generating sufficient power for swimming with turbulent boundary layer conditions.
The surface swimming of muskrats (Ondatra zibethicus Linnaeus) was studied by forcing individual animals to swim against a constant water current, of velocity ranging from 0·2 to 0·75 ms−1, in a recirculating water channel. Lateral and ventral views of the swimming muskrats were filmed simultaneously for analysis of thrust by the propulsive appendages.
Drag measurements and flow visualization on dead muskrats demonstrated that these animals experience large resistive forces due to the formation of waves and a turbulent wake, because of the pressure and gravitational components which dominate the drag force.
Biomechanical analysis demonstrated that thrust is mainly generated by alternating strokes of the hindfeet in the paddling mode. A general lengthening of the hindfeet and presence of lateral fringe hairs on each digit increase the surface area of the foot to produce thrust more effectively during the power phase of the stroke cycle. Increased energy loss from drag on the foot during the recovery phase is minimized by configural and temporal changes of the hindfoot. Employing the models developed by Blake (1979, 1980a,b) for paddle propulsion, it was found that as the arc through which the hindfeet were swept increased with increasing velocity the computed thrust power increased correspondingly. However, the frequency of the stroke cycle remained relatively constant across all velocities at a level of 2·5 Hz.
Both mechanical and aerobic efficiencies rose to a maximum with increasing swimming velocity. The aerobic efficiency, which examined the transformation of metabolic power input to thrust power output reached a value of 0·046 at 0·75 ms−1. The mechanical efficiency expressing the relationship of the thrust power generated by the paddling hindfeet and laterally compressed tail (Fish, 1982a,b) to the total mechanical power developed by the propulsive appendages increased to a maximum of 0·33 at 0·75 ms−1.
I conclude that the paddling mode of swimming in the muskrat is relatively inefficient when compared to swimming modes which maintain a nearly continuous thrust force over the entire propulsive cycle. However, the paddling mode permits the muskrat to generate propulsive forces effectively while swimming at the surface. The evolution of this mode for semi-aquatic mammals represents only a slight modification from a terrestrial type of locomotion.
198 1. Mechanics of drag-based mechanisms of propul-sion in aquatic vertebrates
- R W Blake
Blake, R. W. 198 1. Mechanics of drag-based mechanisms of propul-sion in aquatic vertebrates. In Vertebrate locomotion. Edired by M. H. Day. Symp. Zool. Soc. Lond. 48: 29-52.
A. 199 1. Phylogeny, ecology, and behaviour Metabolism of weasels: the cost of being long and thin
- D R Brooks
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- J H Brown
- R C Lasiewski
Brooks, D. R., and McClennan, D. A. 199 1. Phylogeny, ecology, and behaviour. University of Chicago Press, Chicago, 111. Brown, J. H., and Lasiewski, R. C. 1972. Metabolism of weasels: the cost of being long and thin. Ecology, 59: 939-943.
Manatees-Trichechus manarus, Trichechus senegalensis, and Trichechus inunguis The sirenians and baleen whales
- D K Caldwell
- M C S H Caldwell
- R Ridgeway
- Harrison
Caldwell, D. K., and Caldwell, M. C. 1985. Manatees-Trichechus manarus, Trichechus senegalensis, and Trichechus inunguis. In Handbook of marine mammals. Vol. 3. The sirenians and baleen whales. Edired by S. H. Ridgeway and R. Harrison. Academic Press Inc., Ltd., London. pp. 33-66.
Aquatic locomotion In Mammalian energetics: interdisciplinary views of metabolism and reproduction
- F E Fish
Fish. F. E. 1992. Aquatic locomotion. In Mammalian energetics: interdisciplinary views of metabolism and reproduction. Edired by T. Tomasi and T. Horton. Cornell University Press, Ithaca, N.Y. pp. 34 -63.
Temperature regulation in the Can Downloaded from www.nrcresearchpress.com by SAVANNAHRIVNATLABBF on 11/21/14 For personal use only. bolic heat in air and water
- T R Grant
- T J Dawson
Grant, T. R.. and Dawson, T. J. 1978. Temperature regulation in the Can. J. Zool. Downloaded from www.nrcresearchpress.com by SAVANNAHRIVNATLABBF on 11/21/14 For personal use only. bolic heat in air and water. Physiol. Zool. 51: 3 15 -332.
Digging of quadrupeds In Functional verte-brate morphology
- M Hildebrand
Hildebrand, M. 1985. Digging of quadrupeds. In Functional verte-brate morphology. Edited by M. Hildebrand, D. M. Bramble, K. F. Liem, and D. B. Wake. Belknap Press, Cambridge, Mass. pp. 89-109.
Hydrodynamic resis-tance of semiaquatic mammals. (In Russian)
- B V Kurbatov
- Y Y Mordvinov
Kurbatov, B. V., and Mordvinov, Y. Y. 1974. Hydrodynamic resis-tance of semiaquatic mammals. (In Russian). Zool. Zh. 53: 104 -110.
Wildlife ecology Applied linear statistical models: regression, analysis of variance and experimen-tal designs Linear relationships in biomechanics: the sta-tistics of scaling functions
- A N Moen
- San Freeman
- Calif Fran-Cisco
- J Neter
- W Wasserman
- M H Kutner
- J M V Rayner
Moen, A. N. 1973. Wildlife ecology. W. H. Freeman, San Fran-cisco, Calif. Neter, J., Wasserman, W., and Kutner, M. H. 1985. Applied linear statistical models: regression, analysis of variance and experimen-tal designs. 2nd ed. Richard D. Irwin, Inc., Homewood, Ill. Rayner, J. M. V. 1985. Linear relationships in biomechanics: the sta-tistics of scaling functions. J. Zool. (1965 -1984), 206: 4 15 -439.
Thermoregulation and bioenergetics: patterns for vertebrate survival
- H Swan
Swan, H. 1974. Thermoregulation and bioenergetics: patterns for vertebrate survival. Elsevier Science Publishing Co., Inc., New York.
Swimming. In Functional ver-tebrate morphology
- P W Webb
- R W Blake
- D B Wake
Webb, P. W., and Blake, R. W. 1985. Swimming. In Functional ver-tebrate morphology. Edited by M. Hildebrand, D. M. Bramble, K. F. Liem, and D. B. Wake. Belknap Press, Cambridge, Mass. pp. 110-128.