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- Jun 10, 2010
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In answer to the raised question — "how about vertebrates?" — there are a couple of interesting answers.
In one case, insects are compared to mammals, by a group that is seriously devoted to insects as food. I imagine that they were somewhat disappointed at this Q&A bit:
Here's the article, with the Q&A toward the bottom. By the way, "the FIN" is the Food Insect Network. Yum!
FINL Vol. 6, No. 1 Insect Food Conversion Efficiencies
None of these references, by the way, come close to octopuses. And there's the additional complication of dry mass (grain) becoming wet mass (flesh, mostly water). Octopus growth is also sometimes measured the same way -- a paper up this thread calculated the dried mass of crabs involved.
I'm not getting any good comparable numbers for small mammals. I've learned that cavies generally break the rodent model by having a small number of very large babies (up to 18% of the parent's mass each!) and other interesting tidbits, but not closely relevant to our pursuits.
But it does seem that even on land, invertebrates (insects) are the champion individual converters of food to body mass.
A related term, assimilation efficiency, does not take into account the use of some of the assimilated material as energy. Here's one quote:
Natural History-Natural Cycles
But not, alas, for a very long time. I still don't see an obvious relationship between lifespan and conversion efficiency.
In one case, insects are compared to mammals, by a group that is seriously devoted to insects as food. I imagine that they were somewhat disappointed at this Q&A bit:
In short: "Why not raise and eat insects instead of beef?" and the answer is "Cattle conversion of grasslands are more efficient than you'd think, because the grasslands themselves are very productive and have evolved to deal with grazing."Doesn't it seem that, even with ECIs at the relatively low range of 10-15%, if the forest was properly managed for caterpillar (and termite) preservation (as has been recommended in several instances by researchers in Africa), it would be about as productive for animal agriculture as grassland? Is there a short answer for this complex question, or is the question not as complex as it seems?
Dr. Lindroth: On the surface the reasoning seems sound. But a number of complicating factors come to mind; the answer really is complex. For example, because grasslands have coevolved with large grazing mammals grasses can recover remarkably well from extensive grazing. Remove the same percentage of green foliage from a forest habitat and you'll not have the forest for long. And then there are the practical matters of harvest, etc. It is probably much easier to harvest 1000 lbs of large animal biomass from a grassland than an equivalent amount of insect biomass from a forest! This is not to say that management of forests for insect production should not be considered, just that the comparison with grassland systems is fraught with problems.
Here's the article, with the Q&A toward the bottom. By the way, "the FIN" is the Food Insect Network. Yum!
FINL Vol. 6, No. 1 Insect Food Conversion Efficiencies
None of these references, by the way, come close to octopuses. And there's the additional complication of dry mass (grain) becoming wet mass (flesh, mostly water). Octopus growth is also sometimes measured the same way -- a paper up this thread calculated the dried mass of crabs involved.
I'm not getting any good comparable numbers for small mammals. I've learned that cavies generally break the rodent model by having a small number of very large babies (up to 18% of the parent's mass each!) and other interesting tidbits, but not closely relevant to our pursuits.
But it does seem that even on land, invertebrates (insects) are the champion individual converters of food to body mass.
A related term, assimilation efficiency, does not take into account the use of some of the assimilated material as energy. Here's one quote:
Natural History-Natural Cycles
Octopuses are capable of not only getting a lot out of their food, they're also quite efficient at conserving the energy of the result.Some approximate percentages of assimilation efficiency are shown in various diets below:
* 15% of the energy from decomposing material
* 30-40% of the energy from grasses
* 60-70% of the energy in young plant materials
* up to 80% from seeds.
***
As with primary producers and herbivores, energy is also lost by secondary consumers through respiration and organism death. The assimilation efficiencies of animal food by carnivores vary between 60% and 90%. And within those foods, vertebrate (species with spinal columns or backbones) prey are more efficiently digested than insect prey, as the indigestible insect exoskeletons make up a larger portion of the prey body than do scales, feathers, or hairs on vertebrates. Assimilation efficiencies of insectivores are between 70% and 80% and carnivores is 90%.
Omnivores are part of both the second and third trophic levels. Humans are omnivores because we are physiologically capable of eating animal flesh and vegetation. Some humans, however, choose not to eat animal protein.
But not, alas, for a very long time. I still don't see an obvious relationship between lifespan and conversion efficiency.