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Terence J. Dawson - One of the best experts on this subject based on the ideXlab platform.
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ventilation patterns in red kangaroos Macropus rufus desmarest juveniles work harder than adults at thermal extremes but extract more oxygen per breath at thermoneutrality
The Journal of Experimental Biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:SUMMARY Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos ( Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25°C) and extreme (–5°C and 45°C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (–0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25°C, the juveniles9 resting metabolic rate was 1.6 times that of the mature females (ml min –1 kg –0.75 ), accommodated by significantly higher levels of oxygen extraction of 21.4±1.8% versus 16.6±1.9% ( P <0.05). At thermal extremes, juveniles showed typical mammalian responses in their ventilation, mirrored by that of adults, including higher metabolic and ventilation rates at ambient– 5°C and shallow panting at 45°C. However, at thermal extremes the juvenile kangaroos needed to work harder than adults to maintain their body temperature, with higher rates of ventilation at ambient –5°C and 45°C, accomplished via larger breaths at –5°C and higher respiratory rates at 45°C.
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Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutrality.
Journal of Experimental Biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:SUMMARY Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos ( Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25°C) and extreme (–5°C and 45°C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (–0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25°C, the juveniles9 resting metabolic rate was 1.6 times that of the mature females (ml min –1 kg –0.75 ), accommodated by significantly higher levels of oxygen extraction of 21.4±1.8% versus 16.6±1.9% ( P
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Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutrality.
The Journal of experimental biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos (Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25 degrees C) and extreme (-5 degrees C and 45 degrees C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (-0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25 degrees C, the juveniles' resting metabolic rate was 1.6 times that of the mature females (ml min(-1) kg(-0.75)), accommodated by significantly higher levels of oxygen extraction of 21.4+/-1.8% versus 16.6+/-1.9% (P
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University of Wollongong Research Online
2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutralit
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forage fibre digestion rates of feed passage and gut fill in juvenile and adult red kangaroos Macropus rufus desmarest why body size matters
The Journal of Experimental Biology, 2006Co-Authors: Adam J. Munn, Terence J. DawsonAbstract:SUMMARY Using red kangaroos Macropus rufus Desmarest, a large (>20 kg) marsupial herbivore, we compared the digestive capabilities of juveniles with those of mature, non-lactating females on high-quality forage (chopped lucerne Medicago sativa hay) of 43±1% neutral-detergent fibre (NDF) and poorer quality, high-fibre forage (chopped oaten Avena sativa hay) of 64±1% NDF. On chopped lucerne apparent dry matter (DM) digestibilities by young-at-foot (YAF) red kangaroos (an age that would normally be taking some milk from their mother), weaned juveniles and mature females were similar (55–59%). On chopped oaten hay apparent DM digestibility was lower in the YAF (35.9±2.3%) followed by weaned (43.4±2.8%) and mature females (44.6±1%). The digestion of NDF and its components (mainly cellulose and hemicellulose) was lowest among the YAF followed by weaned and then mature females. The YAF and weaned kangaroos could not sustain growth on the poor-quality diet, and appeared to be at or near maximal gut fill on both forages; the values being 114–122 g DM for YAF and 151–159 g DM for weaned kangaroos. Mean retention times (MRT) of particle and solute markers were significantly longer for the YAF and weaned kangaroos on oaten hay than on lucerne hay, and DM intake (g d –1 ) was ∼50% lower on the oaten hay. In contrast, solute and particle MRTs in the mature females were not significantly affected by diet; they maintained DM intakes by increasing DM gut fill from 264±24 g on chopped lucerne to 427±26 g DM on chopped oaten hay. Clearly, the mature female kangaroos did not maximise gut fill on the high-quality forage, presumably as a consequence of their proportionally lower energy requirements compared with still-growing juveniles. Overall, we have provided the first mechanistic link between the physiological constraints faced by juvenile red kangaroos in relation to their drought-related mortalities, rainfall and forage quality.
Adam J. Munn - One of the best experts on this subject based on the ideXlab platform.
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THE ECOPHYSIOLOGY OF SURVIVAL IN JUVENILE RED KANGAROOS Macropus rufus: GREATER DEMANDS AND HIGHER COSTS
2015Co-Authors: Adam J. Munn, J. DawsonAbstract:Red kangaroos (Macropus rufus) are large (> 20 kg) herbivorous marsupials common to the arid and semi-arid regions of inland Australia. The population dynamics of M. rufus is tightly linked to environmental factors, which operate partly through the survival of juveniles. A crucial period is the young-at-foot (YAF) stage when juveniles have permanently left the mother’s pouch. YAF and weaned kangaroos have the highest drought-related mortalities of any cohort and show notable differences from adults in their basic physiology. YAF and weaned M. rufus, for example, had a resting metabolic rate (kJ kg-1 d-1) twice that of mature females and 1.5 times that expected for an adult marsupial of equivalent body mass (i.e., kJ kg-0.75 d-1). This greater energy turnover was largely explained by their metabolic demands for growth; juveniles required 70- 95 % of the digestible energy intake (kJ d-1) of mature, non-lactating females. Meeting these costs may not be a problem for juveniles when high-quality, low-fibre forage is available, but they were constrained when only hard-to-digest, high-fibre forage was available. YAF and weaned kangaroos, for example, were unable to sustain growth on forages of more than 40 – 50 % fibre, fibre levels characteristic of forages in arid regions during drought. Yet mature, non-lactating females were capable of maintainin
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Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutrality.
Journal of Experimental Biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:SUMMARY Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos ( Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25°C) and extreme (–5°C and 45°C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (–0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25°C, the juveniles9 resting metabolic rate was 1.6 times that of the mature females (ml min –1 kg –0.75 ), accommodated by significantly higher levels of oxygen extraction of 21.4±1.8% versus 16.6±1.9% ( P
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ventilation patterns in red kangaroos Macropus rufus desmarest juveniles work harder than adults at thermal extremes but extract more oxygen per breath at thermoneutrality
The Journal of Experimental Biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:SUMMARY Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos ( Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25°C) and extreme (–5°C and 45°C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (–0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25°C, the juveniles9 resting metabolic rate was 1.6 times that of the mature females (ml min –1 kg –0.75 ), accommodated by significantly higher levels of oxygen extraction of 21.4±1.8% versus 16.6±1.9% ( P <0.05). At thermal extremes, juveniles showed typical mammalian responses in their ventilation, mirrored by that of adults, including higher metabolic and ventilation rates at ambient– 5°C and shallow panting at 45°C. However, at thermal extremes the juvenile kangaroos needed to work harder than adults to maintain their body temperature, with higher rates of ventilation at ambient –5°C and 45°C, accomplished via larger breaths at –5°C and higher respiratory rates at 45°C.
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Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutrality.
The Journal of experimental biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos (Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25 degrees C) and extreme (-5 degrees C and 45 degrees C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (-0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25 degrees C, the juveniles' resting metabolic rate was 1.6 times that of the mature females (ml min(-1) kg(-0.75)), accommodated by significantly higher levels of oxygen extraction of 21.4+/-1.8% versus 16.6+/-1.9% (P
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University of Wollongong Research Online
2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutralit
Shane K. Maloney - One of the best experts on this subject based on the ideXlab platform.
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Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutrality.
Journal of Experimental Biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:SUMMARY Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos ( Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25°C) and extreme (–5°C and 45°C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (–0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25°C, the juveniles9 resting metabolic rate was 1.6 times that of the mature females (ml min –1 kg –0.75 ), accommodated by significantly higher levels of oxygen extraction of 21.4±1.8% versus 16.6±1.9% ( P
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ventilation patterns in red kangaroos Macropus rufus desmarest juveniles work harder than adults at thermal extremes but extract more oxygen per breath at thermoneutrality
The Journal of Experimental Biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:SUMMARY Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos ( Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25°C) and extreme (–5°C and 45°C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (–0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25°C, the juveniles9 resting metabolic rate was 1.6 times that of the mature females (ml min –1 kg –0.75 ), accommodated by significantly higher levels of oxygen extraction of 21.4±1.8% versus 16.6±1.9% ( P <0.05). At thermal extremes, juveniles showed typical mammalian responses in their ventilation, mirrored by that of adults, including higher metabolic and ventilation rates at ambient– 5°C and shallow panting at 45°C. However, at thermal extremes the juvenile kangaroos needed to work harder than adults to maintain their body temperature, with higher rates of ventilation at ambient –5°C and 45°C, accomplished via larger breaths at –5°C and higher respiratory rates at 45°C.
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Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutrality.
The Journal of experimental biology, 2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:Juvenile mortalities in large mammals are usually associated with environmental extremes, but the basis for this vulnerability is often unclear. Because of their high surface area to volume ratio, juveniles are expected to suffer greater thermal stresses relative to adults. Coping with thermal stress requires the ventilatory system to accommodate increases in oxygen demand and respiratory water loss at thermal extremes. Because juveniles are smaller than adults, these demands may set up different constraints on their ventilatory system. Using red kangaroos (Macropus rufus Desmarest), an arid zone species, we compared the ventilatory capabilities of juveniles and adults at thermoneutral (25 degrees C) and extreme (-5 degrees C and 45 degrees C) ambient temperatures. We used an allometry to compare juvenile to adult ventilation, using predicted body mass scaling exponents for oxygen consumption (0.75), respiration rate (-0.25), tidal volume (1.0), ventilation rate (0.75) and oxygen extraction (0.0). At ambient 25 degrees C, the juveniles' resting metabolic rate was 1.6 times that of the mature females (ml min(-1) kg(-0.75)), accommodated by significantly higher levels of oxygen extraction of 21.4+/-1.8% versus 16.6+/-1.9% (P
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University of Wollongong Research Online
2007Co-Authors: Adam J. Munn, Terence J. Dawson, Shane K. MaloneyAbstract:Ventilation patterns in red kangaroos (Macropus rufus Desmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutralit
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Ventilatory accommodation of oxygen demand and respiratory water loss in kangaroos from mesic and arid environments, the eastern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus).
Physiological and biochemical zoology : PBZ, 2000Co-Authors: Terence J. Dawson, Adam J. Munn, Cyntina E. Blaney, Andrew K. Krockenberger, Shane K. MaloneyAbstract:Abstract We studied ventilation in kangaroos from mesic and arid environments, the eastern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus), respectively, within the range of ambient temperatures (Ta) from −5° to 45°C. At thermoneutral temperatures ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $T_{\mathrm{a}\,}=25^{\circ }\mathrm{C}\,$ \end{document} ), there were no differences between the species in respiratory frequency, tidal volume, total ventilation, or oxygen extraction. The ventilatory patterns...
Alan J. Lymbery - One of the best experts on this subject based on the ideXlab platform.
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western australian marsupials are multiply infected with genetically diverse strains of toxoplasma gondii
PLOS ONE, 2012Co-Authors: Shuting Pan, R. Andrew C. Thompson, Michael E. Grigg, Natarajan Sundar, Andrew Smith, Alan J. LymberyAbstract:Five different organs from 16 asymptomatic free-ranging marsupial macropods (Macropus rufus, M. fuliginosus, and M. robustus) from inland Western Australia were tested for infection with Toxoplasma gondii by multi-locus PCR-DNA sequencing. All macropods were infected with T. gondii, and 13 had parasite DNA in at least 2 organs. In total, 45 distinct T. gondii genotypes were detected. Fourteen of the 16 macropods were multiply infected with genetically distinct T. gondii genotypes that often partitioned between different organs. The presence of multiple T. gondii infections in macropods suggests that native mammals have the potential to promote regular cycles of sexual reproduction in the definitive felid host in this environment.
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Presence of Toxoplasma gondii in tissue samples from five different organs in 16 macropod marsupials of three species (Macropus rufus, M. fuliginosus and M. robustus) tested by direct PCR.
2012Co-Authors: Shuting Pan, R. Andrew C. Thompson, Michael E. Grigg, Natarajan Sundar, Andrew Smith, Alan J. LymberyAbstract:Presence of Toxoplasma gondii in tissue samples from five different organs in 16 macropod marsupials of three species (Macropus rufus, M. fuliginosus and M. robustus) tested by direct PCR.
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Western Australian Marsupials Are Multiply Infected with Genetically Diverse Strains of Toxoplasma gondii
2012Co-Authors: Toxoplasma Gondii, Shuting Pan, R. Andrew C. Thompson, Michael E. Grigg, Natarajan Sundar, Andrew Smith, Alan J. LymberyAbstract:Five different organs from 16 asymptomatic free-ranging marsupial macropods (Macropus rufus, M. fuliginosus, and M. robustus) from inland Western Australia were tested for infection with Toxoplasma gondii by multi-locus PCR-DNA sequencing. All macropods were infected with T. gondii, and 13 had parasite DNA in at least 2 organs. In total, 45 distinct T. gondii genotypes were detected. Fourteen of the 16 macropods were multiply infected with genetically distinct T. gondii genotypes that often partitioned between different organs. The presence of multiple T. gondii infections in macropods suggests that native mammals have the potential to promote regular cycles of sexual reproduction in the definitive feli
Gordon C. Grigg - One of the best experts on this subject based on the ideXlab platform.
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Fencing artificial waterpoints failed to influence density and distribution of red kangaroos (Macropus rufus)
Wildlife Research, 2009Co-Authors: Y. Fukuda, Hamish Mccallum, Gordon C. Grigg, A. R. PopleAbstract:Provision of artificial waterpoints in Australian rangelands has resulted in an increase in the range and density of kangaroos. At high densities, kangaroos can inhibit vegetation regeneration, particularly in some protected areas where harvesting is prohibited. Fencing off waterpoints has been proposed to limit these impacts. Our aim was to determine whether fencing off waterpoints during a drought (when kangaroos would be especially water-limited) would influence the density and distribution of red kangaroos (Macropus rufus). Two waterpoints were fenced within the first 6 months of the 27-month study and a further two waterpoints were kept unfenced as controls in Idalia National Park, western Queensland. We estimated kangaroo densities around waterpoints from walked line-transect counts, and their grazing distribution from dung-pellet counts. Fencing off waterpoints failed to influence either the density or distribution up to 4 km from the waterpoints. Our results indicate that food availability, rather than the location of waterpoints, determines kangaroo distribution. Few areas in the rangelands are beyond kangaroos' convenient reach from permanent waterpoints. Therefore, fencing off waterpoints without explicitly considering the spatial context in relation to other available water sources will fail to achieve vegetation regeneration.
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Population Dynamics Of Red Kangaroos (Macropus rufus) In Relation To Rainfall In The South Australian Pastoral Zone
The Journal of Applied Ecology, 1993Co-Authors: S. C. Cairns, Gordon C. GriggAbstract:1. Populations of red kangaroos (Macropus rufus) in the 282,000 km2 pastoral zone of South Australia were assessed by aerial surveys conducted each year in winter for the period 1978-88, inclusive. The results of these surveys are used in a kangaroo management programme, the basis of which is the control of kangaroo numbers through regulated culling. 2. Rainfall in the pastoral zone is generally low and unreliable. Comparatively good seasons, with rainfall near to, or above average prevailed from 1978 to 1981. During this period, red kangaroo numbers increased throughout the pastoral zone. A drought occurred between 1982 and 1983. Associated with this drought was a dramatic decline in red kangaroo numbers; to the lowest level since 1978. Following the drought, the populations recovered, with steady increases in numbers from 1984 onwards. 3. The changes in red kangaroo numbers, in the form of the yearly exponential rate of population increase (r) were found to correlate best with intervals of rainfall at short time-lags from the second of any two successive aerial surveys used to determine r. 4. The numerical response of the red kangaroo populations to rainfall was investigated. Asymptotic models in the form of the negative exponential Mitscherlich equation were fitted to data for the period 1978-84. The rainfall input into these models was that for the calendar summer-autumn period between successive aerial surveys (January-June). 5. The response to summer-autumn rainfall in the Western region of the pastoral zone was different to that in the Central & Eastern region. Separate numerical response models were derived for each of these two regions. These models implied positive rates of exponential population growth (r>O) when summer-autumn rainfall exceeded 74 mm in the Western region and 107 mm in the Central & Eastern region. They also implied maximum levels of r of 0.92 in the Western region and 0.38 in the Central & Eastern region. 6. Predictions by the numerical response models of the changes in red kangaroo numbers in relation to summer-autumn rainfall for the period 1984-88 proved to be rather poor, particularly for the years immediately following the drought. It is suggested that the reason for this was that the age structures and sex ratios of the post-drought populations were different from those of the populations used to develop the models. Drought is thought both to truncate the age structures of kangaroo populations and to bias the sex ratios towards the females. A result of this could be an increase in the numerical response to rainfall above that of a population near to the carrying capacity of its environment and with a near-stable age structure.
