To minimize foraging time,use high‐efficiency,energy‐expensive search and capture methods when food is abundant but low‐efficiency,low‐cost methods during food shortages

Based on a mathematical model, I show that the amount of food in the habitat determines which among alternative methods for search of prey, respectively, for pursuit‐and‐capture give the shortest daily foraging time. The higher the locomotor activity, the higher the rate of energy expenditure and the larger the habitat space a predator can search for prey per time unit. Therefore, I assume that the more efficient a foraging method is, the higher its rate of energy expenditure. Survival selection favors individuals that use foraging methods that cover their energy needs in the shortest possible time. Therefore, I take the optimization criterion to be minimization of the daily foraging time or, equivalently, maximization of the rate of net energy gain. When time is limiting and food is in short supply, as during food bottleneck periods, low‐efficiency, low‐cost foraging methods give shorter daily foraging times than high‐efficiency, energy‐expensive foraging methods. When time is limiting, food is abundant and energy needs are large, as during reproduction, high‐efficiency high‐cost foraging methods give shorter daily foraging times than low‐efficiency low‐cost foraging methods. When time is not limiting, food is abundant, and energy needs are small, the choice of foraging method is not critical. Small animals have lower rates of energy expenditure for locomotion than large animals. At a given food density and with similar diet, small animals are therefore more likely than large ones to minimize foraging time by using high‐efficiency energy‐expansive foraging methods and to exploit patches and sites that require energy‐demanding locomotion modes. Survival selection takes place at food shortages, while low‐efficiency low‐cost foraging methods are used, whereas reproduction selection occurs when food is abundant and high‐efficiency energy‐expensive foraging methods do better. In seasonal environments, selection therefore acts on different foraging methods at different times. Morphological adaptation to one method may oppose adaptation to another. Such conflicts select against foraging and morphological specialization and tend to give species‐poor communities of year‐round resident generalists. But a stable year‐round food supply favors specialization, niche narrowing, and dense species packing.     

Whole Body Mechanics of Stealthy Walking in Cats

The metabolic cost associated with locomotion represents a significant part of an animal''s metabolic energy budget. Therefore understanding the ways in which animals manage the energy required for locomotion by controlling muscular effort is critical to understanding limb design and the evolution of locomotor behavior. The assumption that energetic economy is the most important target of natural selection underlies many analyses of steady animal locomotion, leading to the prediction that animals will choose gaits and postures that maximize energetic efficiency. Many quadrupedal animals, particularly those that specialize in long distance steady locomotion, do in fact reduce the muscular contribution required for walking by adopting pendulum-like center of mass movements that facilitate exchange between kinetic energy (KE) and potential energy (PE) [1]–[4]. However, animals that are not specialized for long distance steady locomotion may face a more complex set of requirements, some of which may conflict with the efficient exchange of mechanical energy. For example, the “stealthy” walking style of cats may demand slow movements performed with the center of mass close to the ground. Force plate and video data show that domestic cats (Felis catus, Linnaeus, 1758) have lower mechanical energy recovery than mammals specialized for distance. A strong negative correlation was found between mechanical energy recovery and diagonality in the footfalls and there was also a negative correlation between limb compression and diagonality of footfalls such that more crouched postures tended to have greater diagonality. These data show a previously unrecognized mechanical relationship in which crouched postures are associated with changes in footfall pattern which are in turn related to reduced mechanical energy recovery. Low energy recovery was not associated with decreased vertical oscillations of the center of mass as theoretically predicted, but rather with posture and footfall pattern on the phase relationship between potential and kinetic energy. An important implication of these results is the possibility of a tradeoff between stealthy walking and economy of locomotion. This potential tradeoff highlights the complex and conflicting pressures that may govern the locomotor choices that animals make.     

Energetics in Homo erectus and other early hominins: the consequences of increased lower-limb length

Previous studies of daily energy expenditure (DEE) in hominin fossils have estimated locomotor costs using a formula that was based on six species, all 18 kg or less in mass, including no primates, and that has a number of other problems when applied in an ecological context. It is well established that the energetic cost of human walking is lower than that of representative mammals, particularly for individuals with long lower limbs. The current study reevaluates the daily energy expenditures of a variety of hominin species using more appropriate approaches to estimating locomotor costs. To estimate DEE for primates, I relied on published data on body mass, day range, and the percentage of time spent in various activities. Based on those data, I calculated a value for nonlocomotor DEE. I then used a variant of a method that I have suggested elsewhere to calculate the daily cost due to locomotion (DEEL) and summed the two to calculate total DEE. The more up-to-date methods for calculating the cost of travel result in lower estimates of this aspect of the energy budget than seen in previous studies. Values obtained here for DEE in various representatives of Australopithecus are lower than reported previously by around 200 kcal/day. Taking into account the greater economy of human walking, particularly the effect of the longer lower limbs found in many later Homo species, also results in lowered estimates of DEE. Elongation of the lower limbs in H. erectus reduced relative travel costs nearly 50% in comparison to A.L. 288-1 (A. afarensis). The present method for calculating DEE indicates that female H. erectus DEE was 84% greater than that of female Australopithecus; this disparity is even larger than that suggested by previous workers.     

Resting and swimming metabolic rates in juvenile walruses (Odobenus rosmarus)

Changes in Arctic ice conditions have raised concerns regarding potential impacts on energy expenditure and food requirements of walruses. Modeling the repercussions of environmental changes requires accurate species-specific measures of bioenergetic expenditures. This is particularly true for walruses, who have a unique anatomy and foraging ecology from other pinnipeds. This study measured resting metabolic rate (RMR) and subsurface swimming metabolism in two juvenile walruses over a 13-month period. The walruses had relatively low RMR compared to studies of other young pinnipeds. RMR was greater for the male than the female, as expected given its larger size; the reverse was true on a mass-specific basis. There was also considerable variability in RMR for each walrus during the year that could not be accounted for by changes in body mass. Metabolism while swimming was about twice RMR, and locomotor costs were higher than generally predicted for other marine mammals. The lower calculated swimming efficiency may reflect the fact that walruses are not “high velocity” pursuit predators. The estimates of metabolic expenditure obtained in this study for young walruses are invaluable for quantifying the energetic consequences of behavioral changes induced by environmental shifts in the wild.     

Daily Energy Expenditure and the Cost of Activity in Mammals

Among 17 species of mammals, field metabolic rates exclusiveof thermoregulatory and productive costs (designated FMR*) averaged2.65 x standard metabolism (SMR). Daily activity costswere calculatedby subtraction from FMR* of the daily energy expenditure associatedwith SMR and assimilation of nutrients. Total expenditure foractivity was of a similar magnitude to that for daily standardmetabolism. Calculations indicate that expenditures by mammalsfor locomotion probably account for less than half of dailyactivity costs. Expenditures by mammals engaged in other kindsof activities are also reviewed. During their daily activityperiods, terrestrial mammals expend energy at a rate of about4.1 x SMR. The utility of energetic increments for activityin time-energy budgets, thermal energy budgets, and analysesof the economics of foraging are discussed.     

Ecological and biomechanical insights into the evolution of gliding in mammals

Gliding has evolved independently at least six times in mammals. Multiple hypotheses have been proposed to explain the evolution of gliding. These include the evasion of predators, economical locomotion or foraging, control of landing forces, and habitat structure. Here we use a combination of comparative methods and ecological and biomechanical data collected from free-ranging animals to evaluate these hypotheses. Our comparative data suggest that the origins of gliding are often associated with shifts to low-quality diets including leaves and plant exudates. Further, data from free-ranging colugos suggest that although gliding is not more energetically economical than moving through the canopy, it is much faster, allowing shorter times of transit between foraging patches and therefore more time available to forage in a given patch. In addition to moving quickly, gliding mammals spend only a small fraction of their overall time engaged in locomotion, likely offsetting its high cost. Kinetic data for both take-off and landing suggest that selection on these behaviors could also have shaped the evolution of gliding. Glides are initiated by high-velocity leaps that are potentially effective in evading arboreal predators. Further, upon landing, the ability to control aerodynamic forces and reduce velocity prior to impact is likely key to extending distances of leaps or glides while reducing the likelihood of injury. It is unlikely that any one of these hypotheses exclusively explains the evolution of gliding, but by examining gliding in multiple groups of extant animals in ecological and biomechanical contexts, new insights into the evolution of gliding can be gained.     

Energetics of foraging and locomotion in the platypus Ornithorhynchus anatinus

We measured the energy requirements of platypuses foraging, diving and resting in a swim tank using flow-through respirometry. Also, walking metabolic rates were obtained from platypuses walking on a conventional treadmill. Energy requirements while foraging were found to depend on water temperature, body weight and dive duration and averaged 8.48 W kg(-1). Rates for subsurface swimming averaged 6.71 W kg(-1). Minimal cost of transport for subsurface swimming platypuses was 1.85 J N(-1)m(-1) at a speed of 0.4 m s(-1). Aerobic dive limit of the platypus amounted to 59 s. Metabolic rate of platypuses resting on the water surface was minimal with 3.91 W kg(-1) while minimal RMR on land was 2.08 W kg(-1). The metabolic rate for walking was 8.80 W kg(-1) and 10.56 W kg(-1) at speeds of 0.2 m s(-1) and 0.3 m s(-1), respectively. A formula was derived, which allows prediction of power requirements of platypuses in the wild from measurements of body weight, dive duration and water temperature. Platypuses were found to expend energy at only half the rate of semiaquatic eutherians of comparable body sizes during both walking and diving. However, costs of transport at optimal speed were in line with findings for eutherians. These patterns suggest that underwater locomotion of semiaquatic mammals have converged on very similar efficiencies despite differences in phylogeny and locomotor mode.     

Migration and spawning energetics of the anadromous sea lamprey,Petromyzon marinus

Synopsis Energy expended in migration and reproduction was determined from measurements of caloric concentration and body and gonodal weight for nontrophic sea lampreys collected from different sites along the St. John River, New Brunswick. The estimated cost of locomotion in swimming the 140 km which separates the estuary from the spawning redds was 300 and 260 kcal for males and females respectively. Acutal distance which lampreys swam as well as mean swimming speed were estimated from a linear regression equation relating energy expenditure for locomotion and body weight. Energy expenditure for breeding was considerably greater than that catabolized throughout the upstream migration.     

Running energetics of the North American river otter: do short legs necessarily reduce efficiency on land?

Semi-aquatic mammals move between two very different media (air and water), and are subject to a greater range of physical forces (gravity, buoyancy, drag) than obligate swimmers or runners. This versatility is associated with morphological compromises that often lead to elevated locomotor energetic costs when compared to fully aquatic or terrestrial species. To understand the basis of these differences in energy expenditure, this study examined the interrelationships between limb morphology, cost of transport and biomechanics of running in a semi-aquatic mammal, the North American river otter. Oxygen consumption, preferred locomotor speeds, and stride characteristics were measured for river otters (body mass=11.1 kg, appendicular/axial length=29%) trained to run on a treadmill. To assess the effects of limb length on performance parameters, kinematic measurements were also made for a terrestrial specialist of comparable stature, the Welsh corgi dog (body mass=12.0 kg, appendicular/axial length=37%). The results were compared to predicted values for long legged terrestrial specialists. As found for other semi-aquatic mammals, the net cost of transport of running river otters (6.63 J kg(-1)min(-1) at 1.43 ms(-1)) was greater than predicted for primarily terrestrial mammals. The otters also showed a marked reduction in gait transition speed and in the range of preferred running speeds in comparison to short dogs and semi-aquatic mammals. As evident from the corgi dogs, short legs did not necessarily compromise running performance. Rather, the ability to incorporate a period of suspension during high speed running was an important compensatory mechanism for short limbs in the dogs. Such an aerial period was not observed in river otters with the result that energetic costs during running were higher and gait transition speeds slower for this versatile mammal compared to locomotor specialists.     

Construction of energy landscapes can clarify the movement and distribution of foraging animals

Variation in the physical characteristics of the environment should impact the movement energetics of animals. Although cognizance of this may help interpret movement ecology, determination of the landscape-dependent energy expenditure of wild animals is problematic. We used accelerometers in animal-attached tags to derive energy expenditure in 54 free-living imperial cormorants Phalacrocorax atriceps and construct an energy landscape of the area around a breeding colony. Examination of the space use of a further 74 birds over 4 years showed that foraging areas selected varied considerably in distance from the colony and water depth, but were characterized by minimal power requirements compared with other areas in the available landscape. This accords with classic optimal foraging concepts, which state that animals should maximize net energy gain by minimizing costs where possible and show how deriving energy landscapes can help understand how and why animals distribute themselves in space.     

Predictive Simulation Generates Human Adaptations during Loaded and Inclined Walking

Predictive simulation is a powerful approach for analyzing human locomotion. Unlike techniques that track experimental data, predictive simulations synthesize gaits by minimizing a high-level objective such as metabolic energy expenditure while satisfying task requirements like achieving a target velocity. The fidelity of predictive gait simulations has only been systematically evaluated for locomotion data on flat ground. In this study, we construct a predictive simulation framework based on energy minimization and use it to generate normal walking, along with walking with a range of carried loads and up a range of inclines. The simulation is muscle-driven and includes controllers based on muscle force and stretch reflexes and contact state of the legs. We demonstrate how human-like locomotor strategies emerge from adapting the model to a range of environmental changes. Our simulation dynamics not only show good agreement with experimental data for normal walking on flat ground (92% of joint angle trajectories and 78% of joint torque trajectories lie within 1 standard deviation of experimental data), but also reproduce many of the salient changes in joint angles, joint moments, muscle coordination, and metabolic energy expenditure observed in experimental studies of loaded and inclined walking.     

Growth and energetics of a small shorebird species in a cold environment: the little stint Calidris minuta on the Taimyr Peninsula, Siberia

The little stint Calidris minuta is one of the smallest shorebird species breeding in the Arctic (weighing 4.3  g on hatching). Their chicks are small and have a high surface area-to-volume ratio. We determined prefledging growth, energy expenditure and time budgets for little stint chicks in northwestern Taimyr, Siberia. A modified power curve was introduced to model the relationship between daily energy expenditure and body mass. Total metabolisable energy, TME, over the 15-d prefledging period was 107% greater than the allometric prediction for a bird the size of a little stint. Their growth rate coefficient was 14% greater than the prediction for a bird their size. The growth of young chicks was reduced in cool weather, possibly due to a reduction in foraging time in order to be brooded and reduced food availability which impact foraging efficiency. We did not detect weather effects on energy expenditure of chicks, but lack of temperature variation during energy expenditure measurements may have prevented this. In sum, both growth rate coefficient and energy expenditure of little stint chicks were greater than predicted and this is similar to that observed in other arctic shorebird species.     

A field experiment on the influence of load transportation and patch distance on the locomotion velocity of <Emphasis Type="Italic">Dorymyrmex goetschi</Emphasis> (Hymenoptera,Formicidae)

Summary Locomotion velocity during foraging activities is determined by factors such as travel distance, habitat structure and load mass among others. However, few studies on foraging behavior have analyzed the influence of spatial heterogeneity and food transportation on the locomotion velocity of ants under natural conditions. In order to study the mentioned factors, we selected 20 nests of the ant Dorymyrmex goetschi (subfamily Dolichoderinae), in a lower Andes locality of central Chile. Half of the nests were offered a food patch located at 10 cm from the nest entrance, and at 20 cm for the other half. We measured the duration of trips between nest and food patch and vice versa, and the distances traveled. We also recorded spatial heterogeneity of the substratum and soil temperature. Temperature was used as a covariate in the statistical analysis. Travel speed was significantly slower when worker ants returned to the nest with a food load, compared to the velocity of foragers without load that traveled from the nest to the patch. When the food patch was located at greater distance, locomotion velocity was significantly faster. Spatial heterogeneity did not affect movement speed. The reduction in locomotion velocity in ants carrying a load of 5.6 mg represents an energetic cost of transportation equivalent to 79% of the costs involved in moving a body mass of 1.6 mg. Faster velocities at larger patch distances can be interpreted as a strategy to maintain an efficient resource exploitation, by way of decreasing the time exposed to higher predation risk.Received 28 April 2003; revised 11 November 2003; accepted 22 January 2004.     

Modelling the energy budget of a colonial bird of prey, the Ruppell's griffon vulture, and consequences for its breeding ecology

Colonial nesting is rare in birds of prey. In this study we develop further Pennycuick's (1979 ) model of energy balance to consider the implications of colonial nesting for the breeding ecology of Ruppell's griffon vultures. To achieve a realistic foraging range, and remain in energy balance, the birds need to do more than fill their crop once on each foraging trip. They must remain in the feeding area and digest some of this food and refill the crop to obtain sufficient energy to pay for the flight costs and have sufficient energy to satisfy their own requirements and that of the chick. Given the known distances that the birds have to travel to forage, it would be impossible for them to rear more than one chick. The low growth rate of griffon vulture chicks may be an adaptation to the low rate at which energy can be delivered by the parents. The optimal time for a bird to be away from the nest changes with the distance they have to travel. Assuming that one parent remains on the nest at all times to guard the chick, it is optimal for both parents to take turns to forage on the same day if the distance to a feeding area is under 150 km, but to switch to each parent being away for a whole day when the distance is greater than this. Soaring flight is essential for such a scavenger, because of the low energy expenditure. If a vulture relied on the more energetically demanding flapping flight its maximum foraging range would be under 40 km. Griffon vultures are known to be able to depress their basal metabolic rate, and this has major implications for their foraging range, which then becomes constrained by the flight speed rather than by the amount of food they need to obtain. Griffon vultures minimize energy expenditure on all activities, because even small increases in their energy demands have a large impact on the foraging range that the bird can use.     

Substrate Size and Primate Forelimb Mechanics: Implications for Understanding the Evolution of Primate Locomotion

International Journal of Primatology - Did the anatomical and locomotor specializations of primates evolve in response to requirements of locomotion and foraging on thin branches? Laboratory...     

Cool running: locomotor performance at low body temperature in mammals

Mammalian torpor saves enormous amounts of energy, but a widely assumed cost of torpor is immobility and therefore vulnerability to predators. Contrary to this assumption, some small marsupial mammals in the wild move while torpid at low body temperatures to basking sites, thereby minimizing energy expenditure during arousal. Hence, we quantified how mammalian locomotor performance is affected by body temperature. The three small marsupial species tested, known to use torpor and basking in the wild, could move while torpid at body temperatures as low as 14.8-17.9°C. Speed was a sigmoid function of body temperature, but body temperature effects on running speed were greater than those in an ectothermic lizard used for comparison. We provide the first quantitative data of movement at low body temperature in mammals, which have survival implications for wild heterothermic mammals, as directional movement at low body temperature permits both basking and predator avoidance.     

Optimal body size and energy expenditure during winter: why are voles smaller in declining populations?

Winter is energetically challenging for small herbivores because of greater energy requirements for thermogenesis at a time when little energy is available. We formulated a model predicting optimal wintering body size, accounting for the scaling of both energy expenditure and assimilation to body size, and the trade-off between survival benefits of a large size and avoiding survival costs of foraging. The model predicts that if the energy cost of maintaining a given body mass differs between environments, animals should be smaller in the more demanding environments, and there should be a negative correlation between body mass and daily energy expenditure (DEE) across environments. In contrast, if animals adjust their energy intake according to variation in survival costs of foraging, there should be a positive correlation between body mass and DEE. Decreasing temperature always increases equilibrium DEE, but optimal body mass may either increase or decrease in colder climates depending on the exact effects of temperature on mass-specific survival and energy demands. Measuring DEE with doubly labeled water on wintering Microtus agrestis at four field sites, we found that DEE was highest at the sites where voles were smallest despite a positive correlation between DEE and body mass within sites. This suggests that variation in wintering body mass between sites was due to variation in food quality/availability and not adjustments in foraging activity to varying risks of predation.     

Optimal locomotion modes of foraging birds in trees

This paper compares the energy costs of various modes of locomotion of birds foraging in trees. For birds moving vertically in trees by climbing and hopping (but not by flying) the best choice of locomotion mode depends on the distance between visited trees in relation to the height h of the zone searched for food in trees.
When the distance between successively visisted trees is longer than about half the distance coverable in gliding flight with height loss h , then it is cheapest in energy to hop or climb upwards in a tree and fly downwards to the next tree. When the distance between successively visited trees is shorter than about half the distance coverable in gliding flight with height loss h , then it is cheapest in energy to move alternately downwards and upwards in trees (downwards in the first, upwards in the second, downwards in the third tree, etc.) and to fly level between trees.
Treecreepers and woodpeckers are adapted morphologically to the former mode, but more generalized tree foragers might use either mode depending on the spacing of trees.     

Intermittent Swimming by Mammals: A Strategy for Increasing Energetic Efficiency During Diving

The evolutionary history of marine mammals involved marked physiologicaland morphological modifications to change from terrestrial toaquatic locomotion. A consequence of this ancestry is that swimmingis energetically expensive for mammals in comparison to fish.This study examined the use of behavioral strategies by marinemammals to circumvent these elevated locomotor costs duringhorizontal swimming and vertical diving. Intermittent formsof locomotion, including wave-riding and porpoising when nearthe water surface, and prolonged gliding and a stroke and glidemode of propulsion when diving, enabled marine mammals to increasethe efficiency of aquatic locomotion. Video instrumentationpacks (8-mm camera, video recorder and time-depth microprocessor)deployed on deep diving bottlenose dolphins (Tursiops truncatus),northern elephant seals (Mirounga angustirostris), and Weddellseals (Leptonychotes weddellii) revealed exceptionally longperiods of gliding during descent to depth. Glide duration dependedon depth and represented nearly 80% of the descent for divesexceeding 200 m. Transitions in locomotor mode during divingwere attributed to buoyancy changes with compression of thelungs at depth, and were associated with a 9–60% reductionin the energetic cost of dives for the species examined. Bychanging to intermittent locomotor patterns, marine mammalsare able to increase travelling speed for little additionalenergetic cost when surface swimming, and to extend the durationof submergence despite limitations in oxygen stores when diving.     

Influence of fruit availability on macronutrient and energy intake by female chimpanzees

Daily energy intake of adult female mammals is influenced by environmental conditions and physiological requirements, including reproduction. We examined the effects of fruit availability on macronutrient and metabolisable energy (ME) intake by adult female chimpanzees (Pan troglodytes schweinfurthii) of the Kanyawara community in Kibale National Park, Uganda, from January 2014 through June 2015. Drupe fruits were abundant for 4 months, whereas the other 14 months were dominated by fig fruits. The mean daily intake of food (dry matter) and ME did not differ between drupe‐months and fig‐months. However, foraging costs were higher during fig‐months, as indicated by a 20% increase in feeding time. Furthermore, during drupe‐months female chimpanzees ingested more water‐soluble carbohydrates and lipids, and less available protein and neutral detergent fibre. Although ME intake did not differ consistently between drupe‐months and fig‐months, they consumed more on days when ripe fruit dominated the diet than when leaves and pithy stems dominated the diet. Our data suggest that differences in diet quality between drupes and figs can have important effects on frugivore foraging and that they influence net energy gain more by their effects on macronutrient composition or foraging cost than by their direct impact on energy intake.