The optimal allocation of time and respiratory metabolism over the dive cycle

Because anaerobic metabolism is much less efficient than aerobicmetabolism in supplying energy, it is widely believed that diversrely predominantly on aerobic metabolism for diving. In thispaper, a time budget model, which assumes that the diver canuse either completely aerobic or partially aerobic metabolismwith additional anaerobic metabolism for diving, is developedand is used to make predictions about patterns in optimal allocationof time and respiratory metabolism during the dive cycle. Theresults derived from the model are (1) a diver that can varythe ratio of energy supplied anaerobically to total energy spentduring dive time is favored by natural selection, but the patternsof time allocation over the dive cycle by the diver do not differ fromthose of a diver that cannot vary the ratio. (2) Even if itis assumed that divers switch their metabolism for diving, anobvious upturn in the surface time with respect to dive timedoes not occur at the aerobic dive limit (ADL) but occurs beyondthe ADL. (3) Use of additional anaerobic metabolism can be favoredfor dives shorter than the ADL. These findings provide a usefulguide to understanding the factors that limit diving behavior.     

Activity budget and diving behavior of gray whales (Eschrichtius robustus) in feeding grounds off coastal British Columbia

Behavior and diving patterns of summer resident gray whales ( Eschrichtius robustus ) foraging on mysids were studied in coastal bays along the north shore of Queen Charlotte Strait, British Columbia. In this region, gray whales were found to feed primarily on planktonic prey rather than on the benthos as in their primary feeding areas further north. During the summers of 1999 and 2000, whales spent most of their time actively feeding or searching for prey (77%), whereas only 15% of their time was spent traveling and 8% socializing. The majority of the dives were short; the mean dive duration was 2.24 min with approximately three respirations per surfacing and 15 s between blows. Whales dove frequently (26.7 h⁻¹), spending only 17% of their time at the surface with an overall blow rate of 1.14 respirations per minute. Activity states were characterized by significantly different diving and respiratory parameters; feeding whales dove more frequently, with shorter intervals between respirations, thus spending less time at the surface compared to when traveling or searching. This diving pattern differs from benthic-feeding whales and likely optimizes capture of the mobile mysid swarms in shallow waters.     

Effects of feeding time constraints on body mass regulation and energy expenditure in wintering dunlin (Calidris alpina)

We examined the effects of time-restricted feeding on regulationof body mass and activity energy expenditure in captive winteringdunlin (Calidris alpina) held in outdoor aviaries at TomalesBay, California. In the first of two experiments, we comparedbirds under 24 h : 24 h (fasting : ad libitum feeding) foodrestriction with controls under continuous ad libitum feeding. In the second experiment, we compared birds under 24 h : 6 h: 12 h : 6 h (fasting : ad libitum : fasting : ad libitum)food restriction with birds under 24 h : 24 h food restriction.We estimated total energy expended on activities from dailymass balance using an additive model based on measures of grossenergy intake, thermoregulation, basal metabolism, and a sensitivity analysis of gross utilization efficiency and energy densityof reserve body tissue. Dunlin under 24 h : 24 h food restrictionovercompensated for body mass lost while fasting, increasingtheir body mass relative to controls fed ad libitum. Dunlinunder 24 h : 6 h : 12 h : 6 h food restriction were unable to recover body mass lost during the first fasting day. Whenallowed to feed, food-restricted birds reduced the amount ofenergy spent on being active and increased food intake andenergy storage relative to controls, but when forced to fast,they increased their activity energy expenditure. These patterns suggest winter body mass regulation consistent with the behaviorsof free-living dunlin in winter.     

Disturbance does not have a significant impact on waders in an estuary close to conurbations: importance of overlap between birds and people in time and space

Disturbance of wildlife is a potential cause of conservation concern, not least to overwintering waders Charadrii inhabiting estuaries close to conurbations where human recreational and economic activities are often concentrated. Disturbance from people on and alongside intertidal foraging areas could make it more difficult for birds to survive until spring in good condition by reducing the time available for foraging, increasing energy requirements and displacing birds to poorer foraging areas. We adopted a two-part approach to testing whether such significant impacts occurred in a Special Protection Area where disturbance risk was high because of its small size and close proximity to conurbations. In part one, we recorded over the whole estuary during stages of the tidal cycle when part or all of the intertidal zone was exposed and so accessible to waders (i.e. on receding, low and advancing tides): (1) the numbers and activities of people on the intertidal flats and on the adjacent land in those places where people were visible to waders in the intertidal zone and (2) the numbers of waders present and disturbed into flight, the flight distance and flight duration in the ‘overlap’ areas where people did disturb waders. People occurred on < 25% of the 938 ha of intertidal flats, but most waders foraged on mudflats, whereas most people were on sandflats. People on land were visible to foraging waders along < 35% of the 16.5 km of shoreline. Waders and people were therefore substantially separated in space. Within overlap areas, people and waders were often frequently separated in time: for example, people on land mostly disturbed waders when only the upper shore levels were exposed. The average overwintering wader spent < 0.1% of its foraging time during daylight flying away from people and the additional energy expenditure was equivalent to < 0.02% of its daily requirements. The comparison made in part two between our study area and two comparable estuaries showed that the number of visits each day to the overlap areas would need to be 29 or 43 times greater for disturbance to have lowered the birds’ body condition and winter survival. Both parts of the study therefore suggested strongly that the amount of disturbance was too trivial to have a significant impact on waders. It is concluded that: (1) to properly assess disturbance risk to waders, both extensive and intensive observations must be made on the behaviour of people and birds to quantify the extent to which they overlap in space and time, and (2) it should not be assumed that an estuary's close proximity to conurbations, and the presence of large numbers of people in the vicinity of the SPA, necessarily implies a significant disturbance risk to waders.     

Sexual selection,feather wear,and time constraints on the pre‐basic molt explain the acquisition of the pre‐alternate molt in European passerines

Avian feathers need to be replaced periodically to fulfill their functions, with natural, social, and sexual selection presumably driving the evolution of molting strategies. In temperate birds, a common pattern is to molt feathers immediately after the breeding season, the pre‐basic molt. However, some species undergo another molt in winter‐spring, the pre‐alternate molt. Using a sample of 188 European passerine species, Bayesian phylogenetic mixed models, and correlated evolution analyses, we tested whether the occurrence of the pre‐alternate molt was positively associated with proxies for sexual selection (sexual selection hypothesis) and nonsexual social selection (social selection hypothesis), and with factors related to feather wear (feather wear hypothesis) and time constraints on the pre‐basic molt (time constraints hypothesis). We found that the pre‐alternate molt was more frequent in migratory and less gregarious species inhabiting open/xeric habitats and feeding on the wing, and marginally more frequent in species with strong sexual selection and those showing a winter territorial behavior. Moreover, an increase in migratory behavior and sexual selection intensity preceded the acquisition of the pre‐alternate molt. These results provide support for the feather wear hypothesis, partial support for the sexual selection and time constraints hypotheses, and no support for the social selection hypothesis.     

Optimization of reproductive effort and foraging time in mammals: The influence of resource level and predation risk

Summary The trade-off between fitness benefits from foraging and associated costs in terms of predation risk is analysed by a simple model which takes into account the differential predation risk for reproducing and non-reproducing individuals. The currency that animals are assumed to maximize is their expected absolute fitness (probability of survival plus half of the expected litter size) after a potential reproductive period. Depending on resource levels and predation risk, this maximization can be achieved by (1) opting for individual survival and behaving as a strict time minimizer, (2) by reproducing at the maximal rate and behaving as a strict energy maximizer or (3) by submaximal reproductive effort and a behaviour intermediate between time minimization and energy maximization. Small changes in the availability of food or cover or in the density of predators can shift the optimum from one strategy to another. The shift is particularly abrupt, if predation pressure increases and the availability of resources remains high. This could explain the spatial and temporal variation in the reproductive effort and body weight observed in boreal small mammals with sustained, multiannual population fluctuations.     

The effect of age of current-year shoots of Picea glauca on survival, development time, and feeding efficiency of 6th-instar larvae of Choristoneura fumiferana

Diets prepared from lyophilized and powdered current-year (1983) shoots of white spruce Picea glauca (Moench) Voss were offered to 6th-instar larvae of spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). With increasing age of current-year shoots, time to pupation increased whereas survival, assimilation efficiency, efficiency of conversion of diet to moth biomass, and moth dry weight generally decreased. Sex of the larvae influenced amount ingested, time to pupation, and subsequent moth weight but not survival, assimilation efficiency, and efficiency of conversion of diet to moth biomass.

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Résumé De la poudre lyophilysée de pousses de l'année de Picea glauca a été introduite dans le régime de chenilles du 6ème stade de Choristoneura fumiferana: 20% de poudre de pousses, 1.2% de gélifiant, 78.8% d'eau. Il est ainsi possible de déterminer à 2 mg près la quantité d'aliment consommée par chaque chenille, et, ainsi, de calculer, pour chacune, l'indice alimentaire, dont la prise de nourriture est l'une des variables. Avec de tels régimes préparés à partie de pousses recueillies au cours de 1983, on a constaté que la date de nymphose, la quantité consommée, et le poids ultérieur des papillons dépendaient du sexe de la chenille. En général, les chenilles femelles se nymphosent plus tard, consomment plus et donnent des papillons plus lourds (poids sec) que les chenilles mâles. L'efficacité de l'assimilation et celle de la transformation en biomasse de papillon ne différent pas suivant les sexes, c'est-à-dire qu'ils ont la même aptitude à digérer les pousses. Les taux de survie de chenille à nymphe et de nymphe à imago ne différent donc pas.Cependant, certains de ces paramètres et d'autres changent en fonction de l'âge des pousses annuelles. Quand elles ont été récoltées 7 jours après le débourrement (il a lieu le 20 mai), la survie jusqu'en nymphe est de 93% contre 74% de survie totale; avec des pousses récoltées 52 jours après le débourrement (11 juillet) les taux de survie sont respectivement 7% et 1.4%; avec des pousses récoltées 146 jours après le débourrement (13 octobre) les survies sont 71% et 50%. Des pousses récoltées 28 jours ou plus après le débourrement, retardent la date de nymphose de 25% par rapport à celles récoltées entre 7 et 14 après le débourrement; parallèlement, elles abaissent l'efficacité de l'assimilation de 39%, l'efficacité de conversion de la biomasse de 125%, et le poids des papillons de 54%. Ces changements sont liés à une diminution de la teneur en azote des pousses de 2.1% à environ 1% du poids sec. Cependant la corrélation entre la survie des chenilles et la teneur en azote n'est pas rigoureuse et un facteur encore inconnu est supposé responsable de l'augmentation de la mortalité quand les chenilles consomment (dans leur régime) des pousses récoltées début juillet, 52 jours après le débourrement. Les travaux destinés à identifier ce facteur inconnu sont en cours.

     

The effect of temperature on digestive and assimilation efficiency,gut passage time and appetite in an ambush foraging lizard,<Emphasis Type="Italic"> Cordylus melanotus melanotus</Emphasis>

In ectotherms, an increase in body temperature increases metabolic rate and may increase rates of digestive processes. We measured the thermal dependence of the apparent digestive and apparent assimilation efficiencies (ADE and AAE), gut passage time (GP) and appetite in Cordylus melanotus melanotus, a medium sized Crag Lizard, which is endemic to South Africa. Trials were conducted at 20, 22, 25, 30, 32 and 35 °C under controlled conditions. Trials lasted 14 days, during which, lizards were fed ca. 1 g mealworms per day. Glass beads were used as markers to determine GP at the beginning and end of trials. Faeces and urates were collected daily and oven dried at 50 °C. The energy content of egested matter was then measured using bomb calorimetry. ADE and AAE were not affected by temperature for either males or females. The mean±SE ADE and AAE were 94.4±0.3% and 87.2±0.6%, respectively. GP was not significantly different between males and females at any temperature, but decreased significantly with increasing temperature. Appetite was significantly different between the different temperatures measured. The decrease of gut passage time with increasing temperature was expected, since the digestive and assimilation efficiencies are similar over the range of temperatures tested. Lizards are thus assimilating a similar proportion of ingested energy, but at faster rates at higher temperatures. The results indicate that the digestive physiology of this species results in maximum energy gain per meal in environments where food is scarce.Abbreviations AAE apparent assimilation efficiency - ADE apparent digestive efficiency - AE assimilation efficiency - DE digestive efficiency - GP gut passage rate - NEA net energy absorbed through gut - NER net usable energy retained - SVL snout-vent length - T _b body temperature Communicated by G. Heldmaier     

The synchrony effect revisited: chronotype,time of day and cognitive performance in a semantic analogy task

ABSTRACT

The synchrony effect (i.e. superior performance at optimal, inferior performance at suboptimal times of day) has been broadly studied within the context of circadian rhythms. Whether one chronotype copes better with the synchrony effect than the other received only insufficient empirical attention. We report on an applied experimental study investigating the impact of chronotype on the synchrony effect in a semantic analogy task. To detect an analogy, 36 participants (12 males) aged between 18 and 40 had to decide whether the relation between events of a source pair was mirrored by the relation between events of a target pair (e.g. to cook: to eat = to saddle: to ride). Temporal orientation of the relation within each event pair was varied corresponding either to the chronological or reverse order. Response times (RTs), error rates, as well as the psychophysiological parameters pre-experimental pupil baseline and peak pupil dilation replicate findings of a synchrony effect (shorter RTs and allocation of less cognitive resources at optimal times of day) and show an impact of chronotype (morning types generally outperforming evening types). Most importantly, morning types appeared to cope better with the synchrony effect than evening types: At suboptimal times, morning types solved the analogy detection task more efficient; that is faster with the same accuracy and without the investment of more cognitive resources. They also showed greater alertness and wakefulness indexed by greater pre-experimental pupil baselines. At optimal times of day, morning types have more cognitive resources available to allocate these to the more demanding conditions to outperform evening types. We interpret these findings to suggest that morning types are more able to adapt to unfavourable circumstances (for instance, by avoiding wasteful resource allocation when there are less cognitive resources available). Evening types appear less able to adapt to suboptimal times than morning types, because they have to deal with social jetlag and decreased self-control.     

The effect of intra- and interspecific aggression on patch residence time in Negev Desert gerbils: a competing risk analysis

We observed patch-use behavior by two gerbil species in a fieldsetting and investigated how aggression and intrinsic decision-makinginteract to influence patch residence times. Results were interpretedby using a competing risk analysis model, which uniquely enabledus to estimate the intrinsic patch-leaving decisions independentlyof external interruptions of foraging bouts by aggression. Theexperiment was conducted in two 1-ha field enclosures completelysurrounded by rodent-proof fences and included allopatric (onlyGerbillus andersoni allenbyi) and sympatric (G. a. allenbyiand G. pyramidum) treatments. We predicted that increased foodpatch quality (i.e., habitat quality) should decrease intrinsicpatch-leaving rates and increase rates of aggressive interactionsinvolving the forager feeding in the patch (i.e., the occupantindividual). We also anticipated that increasing populationdensity should result in an increase in the rate of aggressiveinteractions involving the occupant individual. Our resultssupported the first two predictions, indicating a trade-offbetween foraging and aggression. However, the third predictionwas realized only for G. a. allenbyi in allopatry. Furthermore,in allopatry, occupant G. a. allenbyi individuals with highcompetitive ranks were involved in aggressive interactions atlower rates than those with low competitive ranks. However,in sympatry, patch-use behavior of occupant G. a. allenbyi individualswas mainly influenced by aggressive behavior of G. pyramidum,which did not respond to their competitive rank. Thus, it shouldpay less for G. a. allenbyi to be aggressive in sympatric populations.The observed reduction in intraspecific aggression among individualG. a. allenbyi in the presence of G. pyramidum supports thisassertion. We suggest that this reduction likely weakens thenegative effect of intra- and interspecific density on the percapita growth rate of G. a. allenbyi. Because this would changethe slope of the isocline of G. a. allenbyi, it could be animportant mechanism promoting coexistence when habitat selectionis constrained.     

The effect of dietary carbohydrate composition on apparent total tract digestibility,feed mean retention time,nitrogen and water balance in horses

A total of four diets with different carbohydrate composition were investigated in a 4×4 Latin square design experiment with four Norwegian Coldblooded trotter horses. The objective of the present study was to increase the fermentable fibre content and reduce the starch intake of the total ration obtained by partly substituting mature hay and barley with sugar beet pulp (SBP), a soluble fibre source. The diets investigated were hay only (HAY), hay (85% of dry matter intake (DMI)) and molassed SBP (15% of DMI) (SBP), hay (68% of DMI) and barley (32% of DMI) (BAR), and hay (68% of DMI), barley (26% of DMI) and SBP (6% of DMI) (BAR+SBP). The feeding level was 18.5, 17.3, 15.7 and 15.7 g DM/kg BW per day for the HAY, SBP, BAR and BAR+SBP diets, respectively. Each diet was fed for 18 days followed by 10 days of data collection, where apparent total tract digestibility (ATTD), total mean retention time (TMRT) of ytterbium-labelled hay, water balance, digestible energy (DE) intake and nitrogen balance were measured. An enzymatic chemical dietary fibre (DF) method was used to get detailed information on the composition and ATTD of the fibre fraction. Inclusion of SBP in the diet increased the ATTD of the constituent sugars galactose and arabinose (P<0.01). Feeding the HAY and SBP diets resulted in a lower TMRT owing to a higher DF intake than the BAR and BAR+SBP diets (P<0.01). There was no difference in water intake between HAY and SBP, but faecal dry matter was lower for HAY than the other diets (P=0.017), indicating that water was more tightly bound to fibre in the HAY diet. The diets were iso-energetic and provided enough DE and protein for light to moderate exercise for a 550 kg horse. In conclusion, this study showed that the DF intake had a larger effect on TMRT than partly substituting hay or barley with SBP, and that highly fermentable pectin-rich soluble DF from SBP maintains high nutrient utilization in horses.     

The effect of changing extracellular osmolality on water transport in the human red blood cell as measured by the cell water residence time and the activation energy of water transport

A pulse NMR technique employing low extracellular Mn²⁺ concentrations has been used in following the effect of variations in extracellular osmolality on water transport through the human red blood cell membrane. We report results including the effect of osmolality on the cell water lifetime (τ_a) and, for the first time, the effect on the proton spin-spin relaxation of the intracellular water (T_2a) and the activation energy for the water transport process. Current results are encouraging in correlating the effects seen in this study with suspected membrane functional changes occurring in both in vivo and in vitro aging and during in vitro preservation attempts.