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The African Wild Dog
Metabolism & Energy
In the early Pliocene Epoch (i.e. the geologic time period that extends from ~5.3 million to ~2.6 million years before present) Canids arrived in Europe. They then diverged in the Old World during the late Pliocene and Pleistocene (1.5-2 Ma), by colonizing Europe, Asia, and Africa. An increase in their brain size during this period is thought to have encouraged the typical cooperative hunting in packs and social behavior they've adapted to. This process of evolution is known as adaptive radiation, in which organisms diversify rapidly from an ancestral species into various new forms. This can occur when there are abiotic, environmental changes creating additional resources, or influence from biotic factors within their ecosystem (i.e. plants, animals, and bacteria) creating a new environmental niche for the species. This adaptive radiation gave rise to Canid forms such as Wolves, Dholes and African Wild Dogs.
Typically, Canids body size is a response that's dependent upon food availability. Very small Canids (e.g. Fennec Fox) typically live in poor, dry habitats where only smaller body mass can be sustained year-round, while large Canids (e.g. African Wild Dog) are often associated with habitats (i.e. open plains, savannahs, and woodlands) where prey are abundant.
Fig.
10 of the 12 extant, living canid genera
Fig.
An African wild dog chewing on a young impala's face
African wild dogs are able to utilize their keen scent, hearing, and sight to track down prey over long distances, as opposed to a cheetah that uses high acceleration, speed, and maneuverability to typically capture its prey in a brief pursuit.
The dogs can kill medium-sized prey within 2–5 minutes, whereas larger prey (e.g. wildebeest) may take half an hour or more to pull down from exhaustion. The dogs begin to feed on their prey's bodies immediately without even taking a bite to initially kill. Their hunting behavior allows for instant energy and water replenishment.
Large mammals have a greater benefit than small ones from endogenous heat because of the allometric relation between an animal’s body size and its metabolic rate. Large mammals typically have lower weight-specific metabolic rates than small mammals, as well as lower weight-specific water costs to relieve their internal heat.
For large canids, the daily caloric requirement is roughly 22–32 kg, estimated at 1300 to 1800 kilocalories (kcal) metabolizable energy (ME) per day in a thermoneutral environment under moderate activity. Since wild dogs have a unique lifestyle, caloric requirements are generally based on the animal's life stage, activity, thermoregulatory needs, along with their body condition.
A study by Gorman et al. researched field metabolic rates in a group of adult African wild dogs via doubly labeled water (DLW) measurements. This method takes two forms of stable isotopically labeled water, (2)H2O and H2(18)O, are used, and the difference in the rate of loss in the two isotopes in an individual's body represents the energy expended over a period of 1 to 3 half-lives of the labeled water. This is typically done by sampling heavy isotope concentrations in body water, through saliva, urine, or blood samples.
Their results showed that rates were high, and their locomotion in pursuit to find food is where most energy is burned, where they create a net rate model that balance energy gains and losses.
A cross-study conducted by Hubel et. al show that brief opportunistic hunts of medium-sized prey are generally cheap in energy cost, and African wild dogs using this hunting strategy will most likely have a large safety margin with respect to the effects of kleptoparasitism.
Comparing the opportunistic hunting style of the African wild dog pack with the same calculations for high-investment cheetah chases, shows that the higher individual kill rate and gain-to-cost ratio are offset by the group sharing of kills by African wild dogs.
Research by Lifson, Gordon, Visscher, and Nier gathered in a brief summary from Wikipedia helps to explain the doubly labeled water process below in simple terms:
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Metabolism can be calculated from oxygen(O2)-in to carbon dioxide (CO2)-out.
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DLW ('tagged') water is traceable hydrogen (deuterium) and traceable oxygen [(18)O].
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The (18)O leaves the body in two ways:
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(i) exhaled CO2
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(ii) water loss in (mostly) urine, sweat, & breath
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BUT: the deuterium leaves only in the second way (water loss).
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SO: from deuterium loss, we know how much of the tagged water left the body as water. And, since the concentration of (18)O in the body's water is measured after the labeling dose is given, we also know how much of the tagged oxygen left the body in the water. (A simpler view is that the ratio of deuterium to (18)O in body water is fixed, so total loss-rate of deuterium from the body multiplied by this ratio, immediately gives the loss rate of (18)O in water.) Measurement of (18)O dilution with time gives the total loss of this isotope by all routes (by water and respiration). Since the ratio of (18)O to total water oxygen in the body is measured, we can convert (18)O loss in respiration to total oxygen lost from the body's water pool via conversion to carbon dioxide. How much oxygen left the body as CO2 is the same as the CO2 produced by metabolism, since the body only produces CO2 by this route. The CO2 loss tells us the energy produced, if we know or can estimate the respiratory quotient (ratio of CO2 produced to oxygen used)."
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Additional research by Shriver, Racine, Schoeller, and Coward explain that the DLW method is a form of indirect calorimetry because it measures a product produced during the oxidation of fuel in the body instead of directly measuring the heat released during that oxidation. Indirect calorimetry is considered "the measurement of a chemical produced during the oxidation of fuel in the body versus directly measuring the heat released during that oxidation." This method of indirect calorimetry is a standard when it comes to measuring the energy metabolism in free-living animals. The minimal sampling procedures is a great benefit when using the DLW method since other methods of calorimetry rely on frequent sample collection.
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