1,721,162 research outputs found
Allometry of thermal variables in mammals: consequences of body size and phylogeny
No full textA large number of analyses have examined how basal metabolic rate (BMR) is affected by body mass in mammals. By contrast, the critical ambient temperatures that define the thermo-neutral zone (TNZ), in which BMR is measured, have received much less attention. We provide the first phylogenetic analyses on scaling of lower and upper critical temperatures and the breadth of the TNZ in 204 mammal species from diverse orders. The phylogenetic signal of thermal variables was strong for all variables analysed. Most allometric relationships between thermal variables and body mass were significant and regressions using phylogenetic analyses fitted the data better than conventional regressions. Allometric exponents for all mammals were 0.19 for the lower critical temperature (expressed as body temperature - lower critical temperature), −0.027 for the upper critical temperature, and 0.17 for the breadth of TNZ. The small exponents for the breadth of the TNZ compared to the large exponents for BMR suggest that BMR per se affects the influence of body mass on TNZ only marginally. However, the breadth of the TNZ is also related to the apparent thermal conductance and it is therefore possible that BMR at different body masses is a function of both the heat exchange in the TNZ and that encountered below and above the TNZ to permit effective homeothermic thermoregulation
Developmental phenotypic plasticity in a marsupial
No full textClimate change is likely to substantially affect the distribution ranges of species. However, little is known about how different mammalian taxa respond morphologically and physiologically to a rapid change of climate. Our objective was to provide the first quantitative data on the effect of continuous cold exposure during development on morphological and functional variables of a marsupial. Fat-tailed dunnarts ('Sminthopsis crassicaudata', Dasyuridae) were reared at an ambient temperature (Ta) of 16°C [cold-reared (CR)] or 22°C [warm-reared (WR)] until they reached adult age (>200 days). Body and head length of CR animals were significantly longer than in WR animals (mean ± s.e.m.; body: CR 80.8±6mm, WR 76.4±5mm; head: CR 29.4±3mm, WR 27.5±2mm), but other body attributes were not significantly different. Use of torpor was more frequent, torpor bout duration was longer and average daily metabolic rate and percentage of savings when using torpor were significantly higher (P200 days). Body and head length of CR animals were significantly longer than in WR animals (mean ± s.e.m.; body: CR 80.8±6mm, WR 76.4±5mm; head: CR 29.4±3mm, WR 27.5±2mm), but other body attributes were not significantly different. Use of torpor was more frequent, torpor bout duration was longer and average daily metabolic rate and percentage of savings when using torpor were significantly higher (
Heterothermy in pouched mammals – a review
No full textHibernation and daily torpor (i.e. temporal heterothermy) have been reported in many marsupial species of diverse families and are known to occur in ~15% of all marsupials, which is a greater proportion than the percentage of heterothermic placentals. Therefore, we aimed to gather data on heterothermy, including minimal body temperature, torpor metabolic rate and torpor bout duration for marsupials, and relate these physiological variables to phylogeny and other physiological traits. Data from published studies on 41 marsupial species were available for the present analysis. Heterothermic marsupials ranged from small species such as planigales weighing 7 g to larger species such as quolls weighing up to 1000 g. We used the marsupial phylogeny to estimate various heterothermic traits where the current dataset was incomplete. The torpor metabolic rate in relation to basal metabolic rate (%) ranged from 5.2 to 62.8% in daily heterotherms and from 2.1 to 5.2% in marsupial hibernators, and was significantly correlated with the minimum body temperature in daily heterotherms (R² = 0.77, P 0.05). The mean torpor bout duration ranged from 2 to 15 h in daily heterotherms and from 85 to 342 h in hibernators, and decreased significantly with increasing minimum body temperature in daily heterotherms (R² = 0.31,
Thermobiology, energetics and activity patterns of the Eastern tube-nosed bat (<i>Nyctimene robinsoni</i>) in the Australian tropics: effect of temperature and lunar cycle
No full textSUMMARY
Currently, there are no data on the thermal biology of free-ranging pteropodid bats (Chiroptera). Therefore, our aim was to investigate physiological and behavioural strategies employed by the fruit bat Nyctimene robinsoni (body mass ∼50 g) in winter in tropical Northern Queensland in relation to ambient temperature (Ta) and the lunar cycle. Daily body temperature (Tb) fluctuations in free-ranging bats were measured via radio-telemetry and metabolic rate was measured in captivity via open-flow respirometry (Ta, 15–30°C). Free-ranging bats showed a significant 24 h circadian cycle in Tb, with the lowest Tb at the end of the rest phase just after sunset and the highest Tb at the end of the activity phase just before sunrise. Average daily core Tb ranged from 34.7±0.6 to 37.3±0.8°C (mean ± s.d.) over an average daily Ta range of 17.1±1.1 to 23.5±1.8°C. Tb never fell below 30°C but Tb was significantly reduced during the full moon period compared with that during the new moon period. Tb was correlated with Ta during the second half of the rest phase (P&lt;0.001) but not during the active phase. Resting metabolic rate of bats was significantly affected by Ta (P&lt;0.001, R2=0.856). Our results show that tube-nosed bats exhibit reduced Tb on moonlit nights when they reduce foraging activity, but during our study torpor was not expressed. The energy constraints experienced here by tube-nosed bats with relatively moderate Ta fluctuations, short commuting distances between roosting and feeding locations, and high availability of food were probably not substantial enough to require use of torpor.</jats:p
Activity patterns and torpor in two free-ranging carnivorous marsupials in arid Australia in relation to precipitation, reproduction, and ground cover
No full textIt is generally assumed that in unpredictable environments, the use of daily torpor and its interaction with daily activity are largely dependent on environmental thermal conditions and resource availability. Using temperature telemetry, we compared the thermal biology and activity patterns of 2 species of mulgaras ('Dasycercus blythi' and 'D. cristicauda') at 3 sites of different habitat types in central Australia. The work compared a dry period with a wet period (resource pulse). The most obvious functional difference among populations was observed in the timing of the onset of activity, which began significantly earlier in dense unburned spinifex (on average 17.7min before sunset) than in burned spinifex (4.6min after sunset) or on gibber plains (21.8min after sunset). However, although the seasonal expression of torpor differed significantly between males and females, torpor use as well as seasonal timing was similar among sites and periods despite differences in rainfall and habitat. It appears that predominantly reproductive activity governed torpor depth and duration in all measured populations and both species. Our data suggest that while the timing of activity is modulated by the amount of vegetation cover and thus protection from diurnal predators, torpor expression and winter reproduction in mulgaras are functionally linked and surprisingly more or less independent of apparent resource availability. Consequently, in mulgaras, daily torpor does not seem to be employed in response to immediate energy shortage but more likely to allow reallocation of energy and nutrients towards reproduction
Seasonally constant field metabolic rates in free-ranging sugar gliders ('Petaurus breviceps')
No full textSugar gliders, 'Petaurus breviceps' (average body mass: 120 g) like other small wild mammals must cope with seasonal changes in food availability and weather and therefore thermoregulatory and energetic challenges. To determine whether free-ranging sugar gliders, an arboreal marsupial, seasonally adjust their energy expenditure and water use, we quantified field metabolic rates (FMR) and water flux at a seasonal cool-temperate site in eastern Australia. Thirty six male and female sugar gliders were labelled with doubly labelled water for this purpose in spring, summer and autumn. The mean FMR was 159 ± 6 kJ d⁻¹ (spring), 155 ± 8 kJ d⁻¹ (summer), and 152 ± 20 kJ d⁻¹ (autumn) and the mean FMR for the three seasons combined was 158 ± 5 kJ d⁻¹ (equivalent to 1.33 kJ g⁻¹ d⁻¹ or 780 kJ kg⁻0.75 d⁻¹). The mean total body water was 83 ± 2 g, equal to 68.5% of body weight. Mean water flux was 29 ± 1 mL day⁻¹. Season, ambient temperature or sex did not affect any of the measured and estimated physiological variables, but body mass and total body water differed significantly between sexes and among seasons. Our study is the first to provide evidence for a constant FMR in a small mammal in three different seasons and despite different thermal conditions. This suggests that seasonal changes in climate are compensated for by behavioural and physiological adjustments such as huddling and torpor known to be employed extensively by sugar gliders in the wild
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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