Numbats and aardwolves—how low is low? A re-affirmation of the need for statistical rigour in evaluating regression predictions

Comparative Biochemistry and Physiology Part A: Molecular &

2009

The chuditch is a large carnivorous dasyurid marsupial. Historically it had one of the widest geographical distributions of all marsupials, encompassing much of arid Australia, but it is now restricted to the mesic south-west of Western Australia. It is therefore of interest to determine if its physiology better reflects adaptation to its historically arid or present mesic habitat. The basic physiological parameters of the chuditch conform to other marsupials.Body mass of males (1385g) at an ambient temperature of 26.0°C, and increased at higher ambient temperatures due to panting and licking. Changes in wet thermal conductance largely reflected changes in evaporative heat loss, and dry thermal conductance increased at high ambient temperature due in part to posture change. Ventilatory parameters were consistent with metabolic demands in and below thermoneutrality, and suggested augmented evaporative heat loss above the thermoneutral zone. Chuditch had a high point of relative water economy of 22.6°C, indicating favourable water economy at even moderate ambient temperatures, due to its low evaporative water loss rather than high metabolic water production. Chuditch were physiologically more similar to marsupials from arid rather than mesic habitats, better reflecting their historical distribution than their current geographical range.

Section: Methodsmentioning

confidence: 99%

Metabolic, ventilatory and hygric physiology of the chuditch (Dasyurus geoffroii; Marsupialia, Dasyuridae)

Schmidt

Withers

Comparative Biochemistry and Physiology Part A: Molecular &

2009

“…However, compared to a more recent allometric relationship for FMR of marsupials (Cooper et al 2003), the honey possum has an FMR that is 133% of predicted. This falls within the 95% prediction limits for the relationship, but it is difficult to show statistical significance for FMR as the relationship is more variable and thus the prediction limits wider than for BMR, especially for a small species towards the lower limit of the regression (see 14 Cooper and Withers 2006). Thus it remains equivocal if the honey possum has an elevated FMR.…”

mentioning

confidence: 63%

“…Values of physiological variables for the honey possum were compared to standard (thermoneutral) values of other marsupials using the data summary of Withers et al (2006; where N = 61 for BMR, 59 for T b , 55 for C wet and 24 for EWL) and for ventilatory variables data of Hallam and Dawson (1993), Chappell and Dawson (1994), Dawson et al (2000), Larcombe (2002), Cooper and Withers (2004), , and . These comparisons were made by examining the position of the honey possum relative to the 95% prediction limits for the log 10 -transformed allometric regression (T b values were not log-transformed) after Cooper and Withers (2006). The magnitude of the difference between observed and predicted values was calculated using the minimum variance unbiased estimator (MVUE) of Shonkwiler (2006, 2007).…”

mentioning

confidence: 99%

Metabolic, hygric and ventilatory physiology of a hypermetabolic marsupial, the honey possum (Tarsipes rostratus)

Cruz‐Neto

2009

J Comp Physiol B

The honey possum is the only non-volant mammal to feed exclusively on a diet of nectar and pollen. Like other mammalian and avian nectarivores, previous studies indicated that the honey possum's basal metabolic rate was higher than predicted for a marsupial of equivalent body mass. However, these early measurements have been questioned. We re-examined the basal metabolic rate (2.52 ± 0.222 ml O 2 g -1 h -1 ) of the honey possum and confirm that it is indeed higher (162%) than predicted for other marsupials both before and after accounting for phylogenetic history. This, together with its small body mass (5.4 ± 0.14 g; 1.3 % of that predicted by phylogeny) may be attributed to its nectarivorous diet and mesic distribution. Its high basal metabolic rate is associated with a high standard body temperature (36.6 ± 0.48 °C) and oxygen extraction (19.4%), but interestingly the honey possum has a high point of relative water economy (17.0°C) and its standard evaporative water loss (4.33± 0.394 mg H 2 O g -1 h -1 ) is not elevated above that of other marsupials, despite its mesic habitat and high dietary water intake.

“…For mammals, low T b and low BMR correlate with the use of heterothermy and torpor (Geiser, 1998;Ruf and Geiser, 2014) and we assume a similarity in physiological drivers between convergently endothermic mammals and birds. We therefore compared here our standard physiological data for babblers with those of other birds (Table S6) using the 95% prediction limits (Cooper and Withers, 2006) for conventional and phylogenetically informed allometric regressions after Barker et al (2016), using the phylogenetic tree from birdtree.org (Jetz et al, 2012(Jetz et al, , 2014 with the Hackett backbone (Hackett et al, 2008).…”

Section: Standard Physiologymentioning

confidence: 99%

Avian torpor or alternative thermoregulatory strategies for overwintering?

Douglas

Journal of Experimental Biology

Withers

2017

It is unclear whether torpor really is uncommon amongst passerine birds. We therefore examined body temperature and thermoregulatory strategies of an Austral passerine, the white-browed babbler (Pomatostomus superciliosus), which has characteristics related to a high probability of torpor use; it is a sedentary, insectivorous, cooperative breeding species, which we studied during winter in a temperate habitat. Wild, free-living babblers maintained normothermy overnight, even at sub-zero ambient temperatures, with a mean minimum body temperature of 38.5±0.04°C that was independent of minimum black bulb temperature. Physiological variables measured in the laboratory revealed that babblers had a low basal metabolic rate and evaporative water loss, but their body temperature and thermal conductance were typical of those of other birds and they had a typical endothermic response to low ambient temperature. Huddling yielded significant energy savings at low temperatures and a roost nest created a microclimate that buffered against low temperatures. Low basal energy requirements, communal roosting and the insulation of a roost nest confer sufficient energetic benefits, allowing babblers to meet energy requirements without resorting to heterothermia, even in their depauperate, low-productivity landscape, suggesting that passerine birds use alternatives to torpor to balance their energy budgets when possible.