Dogs chase efficiently, but cats skulk counterintuitively
December 3, 2008A Duke University study suggests that evolution can behave as differently as dogs and cats. While the dogs depend on an energy-efficient style of four-footed running over long distances to catch their prey, cats seem to have evolved a profoundly inefficient gait, tailor-made to creep up on a mouse or bird in slow motion.
"It is usually assumed that efficiency is what matters in evolution," said Daniel Schmitt, a Duke associate professor of evolutionary anthropology. "We've found that's too simple a way of looking at evolution, because there are some animals that need to operate at high energy cost and low efficiency."
Namely cats.
In a report published online Nov. 26 in the research journal Public Library of Science (PLoS), Schmitt and two former Duke co-researchers followed up on a scientific hunch by measuring and videotaping how six housecats moved along a 6 yard-long runway in pursuit of food treats or feline toys.
Long-distance chase predators like dogs can reduce their muscular work needed to move forward by as much as 70 percent by allowing their body to rise and fall and exchanging potential and kinetic energy with each step. In contrast, the maximum for cats is about 37 percent and much lower than that in a stalking posture, the report found.
"An important implication of these results is the possibility of a tradeoff between stealthy walking and economy of locomotion," the three researchers wrote in PLoS. "These data show a previously unrecognized mechanical relationship in which crouched postures are associated with changes in footfall pattern, which are in turn related to reduced mechanical energy recovery."
In other words, they found that when cats slink close to the ground they walk in a way that "the movements of their front and back ends cancel each other out," Schmitt said. While that's not good for energy efficiency "the total movement of their bodies is going to be even and they'll be flowing along," he added
"If they're creeping, they're going to put this foot down, and then that foot down and then that one in an even fashion. We think it has to do with stability and caution, Schmitt said."
Walking humans recover as much energy as dogs, said Schmitt, who studies gaits of various mammals. "Our centers of mass rise and fall when we walk. And when we do that, humans and other animals exchange potential and kinetic energy. It's an evolutionary miracle in my view.
"But cats need to creep up on their prey. Most scientists think that energetic efficiency is the currency of natural selection. Here we've shown that some animals make compromises when they have to choose between competing demands."
Source: Duke University
Oct 14, 2009 |
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Bottom line question is... Who spends more of their daily lives in restful activities such as sleeping, and less time hunting? Feral dogs or Feral cats. IDK. Anyone have answer with data to back it up?
Dogs have yet to achieve this intellectual breakthrough.
It doesn't take much observational analysis to see that the efficiency crown goes to the cat.
I'd guess it would depend on how you look at it. Alligators and crocodiles can lay in wait using far less energy for far longer than either dogs or cats. On the other hand, reptiles are screwed in cold weather. Judging by how long they've been around though, that doesn't seem to be a huge problem for them.
Personally I'd say it just shows that energy efficiency isn't the only, and often not the most important, factor in natural selection.
Perhaps I'm misunderstanding.
Dogs hunt in packs and will run down their prey. When individuals run out of energy other pack members can fill in for them.
Cats, generally, are solo predators and only run fast for short distances. And when they run out of steam there is no one (other than a compeditor) to fill in.
Allowing the body to rise and fall is not enough to save energy, this energy has to be stored in elastic tissue like tendons so that it may be reused.
So just studying the gait is certainly not enough to know the efficiency.
This might be why they he talks about maximum possible recovery not the actual recovery, but this is pretty misleading, if the energy stored is lower then 37% then both species are equally efficient.
Claim that humans recover as much energy as dogs is also pretty unsubstantiated, the difference in mass, anatomy and the fact that we are bipedal all have to be taken into account. Basing such claims only on the fact that we also rise and fall as we walk is laughable.
And finally *everything* that rises or falls exchanges potential and kinetic energy, even rocks, so saying its an "evolutionary miracle" implies a complete misunderstanding of physics and evolution.