Brian Green

Seasonal activity and energetics of two species of varanid lizards in tropical Australia

The field metabolic rates (FMR) and rates of water flux were measured in two species of varanid lizards over five periods of the year in tropical Australia. The energetics of these species were further investigated by directly measuring activity (locomotion) and body temperatures of free-ranging animals by radiotelemetry, and by measuring standard metabolic rate (over a range of body temperatures) and activity metabolism in the laboratory. Seasonal differences in the activity and energetics were found in these goannas despite similar, high daytime temperatures throughout the year in tropical Australia. Periods of inactivity were associated with the dry times of the year, but the onset of this period of inactivity differed with respect to habitat even within the same species. Varanus gouldii, which inhabit woodlands only, were inactive during the dry and late dry seasons. V. panoptes that live in the woodland had a similar seasonal pattern of activity, but V. panoptes living near the floodplain of the South Alligator River had their highest levels of activity during the dry season when they walked long distances to forage at the receding edge of the floodplain. However, during the late dry season, after the floodplain had dried completely, they too became inactive. For V. gouldii, the rates of energy expenditure were 196 kJ kg−1 day−1 for active animals and 66 kJ kg−1 day−1 for inactive animals. The rates of water influx for these groups were respectively 50.7 and 19.5 ml kg−1 day−1. For V. panoptes, the rates of energy expenditure were 143 kJ kg−1 day−1 for active animals and 56 kJ kg−1 day−1 for inactive animals. The rates of water influx for these two groups were respectively 41.4 and 21.0 ml kg−1 day−1. We divided the daily energy expenditure into the proportion of energy that lizards used when “in burrows”, “out of burrows but inactive”, and “in locomotion” for the two species during the different seasons. The time spent in locomotion by V. panoptes during the dry season is extremely high for a reptile (mean of 3.5 h/day spent walking), and these results provide an ecological correlate to the high aerobic capacity found in laboratory measurements of some species of varanids.

Water flux and energy use in wild house mice (Mus domesticus) and the impact of seasonal aridity on breeding and population levels

SummaryWater turnover rate (WTR), urine concentration and field metabolic rate (FMR) were examined in house mice, Mus domesticus, permanently inhabiting roadside verge areas and seasonally invading crops in semi-arid wheatlands in South Australia. FMR was approximately proportional to body mass0.5 and mean values varied from 4.8 ml CO2 g−1h−1 (2.9 kJ g−1d−1) in autumn and winter, to 7.0 ml CO2 g−1h−1 (4.2 kJ g−1d−1) in maturing crops during spring. WTR was independent of body mass, indicating that larger mice were selecting a diet containing moister foods. WTR was low in summer and high in winter, and in mice from crops varied from 165 ml l−1 body water d−1 (122 ml kg−1d−1) to 1000 ml l−1d−1 (725 ml kg−1d−1). Seasonal changes in WTR were less extreme on the roadside, where a greater diversity of food was available. In the crops, breeding occurred throughout summer during two of three years, but the population increased only in the one summer when mice had marginally higher WTR. On the roadside breeding and population growth were continuous during summer, except in a drought year. Avcrage urine concentration was inversely related to WTR, and varied from 2.0 to 4.8 Osm l−1. The data indicate that the water conserving abilities of mice equal those of many desert rodents. The water conserving abilities of mice living in crops during summer were fully extended, and in some years aridity limited breeding success and population levels. The degree of moisture stress to which mice are exposed during summer appears to depend not only on rainfall but also on other factors such as availability of food and shelter, and the level of weed infestation in crops.

Estimated Impact of feral house mice on sub-Antarctic invertebrates at Marion Island

SummaryThe energy metabolism of feral house mice Mus musculus was established on sub-Antarctic Marion Island, using the doubly-labelled water turnover technique. Mean water influx was 565 ml kg-1 day-1 and mean CO2 production was 5.41 ml g-1 h-1, i.e. 3375 kJ kg-1 day-1. From the energy content of the main items (Lepidoptera larvae, Curculionidae) in the diet of the mice it was estimated that the dry mass of food consumed was 3.5 g mouse-1 day-1. The overall impact of mice on invertebrates, based on mean mouse density and the mean percentage invertebrates in the diet, was estimated at 108 g ha-1 day-1 or 39.4 kg ha-1 y-1 (dry mass). Greatest predation pressure was on larvae of the flightless moth Pringleophaga marioni: 65 g ha-1 day-1 or 23.7 kg ha-1 y-1. Insect biomass is lower on Marion Island than on nearby Prince Edward Island, which is mouse-free. It is suggested that populations of certain insects on Marion Island are depressed by the alien mice.

Some Physiological Consequences of Estivation by Freshwater Crocodiles, Crocodylus johnstoni

Estivating crocodiles were studied at their dry season refuge in northern Australia over six years. The crocodiles spent three or four months a year underground without access to water. Doubly labeled water was used to measure field metabolic rates and water flux, and plasma and cloacal fluid samples were taken at approximately monthly intervals during some years to monitor the effects of estivation with respect to the accumulation of nitrogenous wastes and electrolyte concentrations. Estivating crocodiles expended a mean of 26.1 kJ kg- day-. Although environmental and, hence, body temperatures increased with increasing time in estivation, water efflux decreased with increasing time in estivation to 9.3 mL kg- day-1, which was only 23% of the flux rate of crocodiles in water before estivation (40.2 mL kg- day-l). The absolute size of body water pools declined proportionately with body mass and body solids; thus the crocodiles were not dehydrated even after three months without access to water. With increasing time in estivation, the following parameters increased in the cloacal fluid: osmolality, potassium, and magnesium; and the following increased in the blood plasma: osmolality, and protein concentration. Electrolytes in plasma were highest when the crocodiles were in the water and late in the estivation period. Freshwater crocodiles do not appear to have any specific adaptations for estivation, but given an adequate refuge, they can survive many months without access to water.

Field energetics of a large carnivorous lizard, Varanus rosenbergi

SummaryField metabolic rates (FMRs; CO2 production) and water influx rates of Varanus rosenbergi were measured seasonally by means of doubly-labelled water (3H218O). Metabolic rates and water influexes were highest in summer (0.18 ml CO2 g−1 h−1 and 17.9 ml H2O kg−1 day−1) and lowest in winter (0.04 ml CO2 g−1 h−1 and 6.5 ml H2O kg−1 day−1). FMRs and water fluxes were intermediate in spring. It is estimated that a 1-kg V. rosenbergi would need to consume 4.7 kg of prey each year to remain in energy balance and that the energy commitment to egg production requires a 40% increase in the food acquisition of a gravid female in late spring and early summer. It is calculated that water influxes in summer are totally provided from food but in other seasons, particularly winter, pulmocutaneous water exchange and/or drinking are significant avenues of water intake.

Water and Sodium Turnover and Estimated Food Consumption in Free-Living Lions (Panthera leo) and Spotted Hyaenas (Crocuta crocuta)

Water and sodium influx rates were measured in free-living lions and spotted hyaenas by means of isotope turnover. Mean water influx rates were 53.7 ± 12.5 and 64.4 ± 30.0 ml kg−1 day−1 for lions and spotted hyaenas, respectively; mean sodium influx rates were 2.16 ± 0.84 and 3.47 ± 1.66 mmol kg−1 day−1, respectively. Sodium influx rates were used to derive mean rates of food consumption; 5.97 ± 1.53 kg fresh food per day for lions and 3.79 ± 1.24 kg day−1 for spotted hyaenas. Drinking did not contribute significantly to water influxes in winter, but with the advent of hotter weather in spring, drinking became an important avenue of water influx in two lions.

Energy allocation for reproduction in a marsupial arboreal folivore, the common ringtail possum (Pseudocheirus peregrinus)

This study examines the annual energetics of a small folivorous marsupial, Pseudocheirus peregrinus. Particular attention was given to the energy and time allocated to reproduction by the females. Daily energy expenditure was measured directly using the doubly labelled water technique. Energy transferred to the young via the milk was estimated from information on milk composition and production. There was no significant seasonal variation in the energy expenditure or water influx of males or females. The mean daily energy expenditure of a 1-kg non-lactating adult ringtail possum was 615 kJ day−1 or 2.2 times standard metabolic rate. Females showed significant changes in daily energy expenditure according to their reproductive status. Without the burden of lactation the total annual energy expenditure of an adult female was estimated as 212.4 MJ kg−1 year−1. The total annual energy expenditure of a female rearing two young was 247.5 MJ kg−1 year−1, with the late stage of lactation constituting the most energetically expensive period accounting for 30% of the total yearly energy expenditure during 24% of the time. Total metabolisable energy allocation during reproduction (22 MJ kg) was similar to estimates available for other herbivores, although, the peak metabolisable energy allocation during lactation (759 kJ day−1) was lower than values available for other herbivores. The total energy requirement for reproduction (metabolisable energy plus potential energy exported to young via milk) suggests that the ringtail possum also has a relatively low overall energy investment in reproduction. It is suggested that the lactational strategy of the ringtail possum has been selected in order to spread the energy demands of reproduction over time due to constraints on the rate of energy intake imposed by a leaf diet and/or to prolong the mother-young bond. The strategies a female ringtail possum may employ to achieve energy balance when faced with the energy demands of reproduction are discussed.

Effects of Seasonal Variation in Prey Abundance on Field Metabolism, Water Flux, and Activity of a Tropical Ambush Foraging Snake

The responses of animals to seasonal food shortages can have important consequences for population dynamics and the structure and function of food webs. We investigated how an ambush foraging snake, the northern death adder Acanthophis praelongus, responds to seasonal fluctuations in prey availability in its tropical environment. In the dry season, field metabolic rates and water flux, as measured by doubly labeled water, were significantly lower than in the wet season. Unlike some other reptiles of the wet‐dry tropics, death adders showed no seasonal difference in their resting metabolism. About 94% of the decrease in energy expended in the dry season was due to a decrease in activity and digestion, with lower body temperatures accounting for the remainder. In the dry season, death adders were less active and moved shorter distances between foraging sites than in the wet season. Analysis of energy expenditure suggested that adders fed no more than every 2–3 wk in the dry season but fed more frequently during the wet season. Unlike many lizards that cease feeding during the dry season, death adders remain active and attempt to maximize their energy intake year‐round.

Thermoregulation, water turnover and energetics of free-living Komodo Dragons, Varanus komodoensis

Abstract 1. Body temperatures, water influxes and metabolic rates were determined for free-living Komodo Dragons ( Varanus komodoensis ) on Komodo Island, Republic of Indonesia. 2. Body temperatures, daily activity patterns and variations in water influx rates were similar to those of other species of varanid lizards. 3. Field metabolic rates were higher than predicted values.

Milk composition in an American marsupial (Monodelphis domestica).

1. Twenty one sequential milk samples from an American marsupial (Monodelphis domestica) were analyzed. 2. The solids fraction was relatively low initially (10% w/w) and then increased to about 30% at mid-lactation where it remained until lactation ceased. 3. During the first 50 days of lactation the relative proportions of protein, fat and carbohydrate were 36, 28 and 34%, respectively, of the solids fraction. 4. Sodium and magnesium concentrations were constant; however levels of potassium and magnesium varied substantially. 5. The milk of M. domestica exhibits a similar pattern of quantitative and qualitative changes to that seen in Australian marsupials.