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Non-caloric essential nutrients big vs small animals

  1. May 24, 2017 #1
    It is true that big animals contain more calories than small animals. However, are the figures for the content of essential nutrients that are not calories different? Such nutrients may be limiting factors and require foraging strategies that would be suboptimal from a simple calory point of view.

    Are there also differences between parts of the body in the content of essential nutrients other than calories? Is it possible that the presence of more of those may favor hunting of animals of small overall size but with more of an organ that contain higher levels of some essential nutrients?
     
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  3. May 24, 2017 #2

    jim mcnamara

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    Interesting question.
    Trying an example:
    Let's use a micronutrient all mammals require - iodine. Also let's limit it to mammalian predators. It works the same for other clades of animals. Some soils are deficient in iodine, so all of the vegetation and animals grazing on it will have a sub-optimal supply. "Everybody" is short on iodine. No matter what animal the predator consumes gives a suboptimal amount of the micronutrient. The thyroid gland concentrates iodine, so if the predator was somehow aware of that would it limit feeding to just eating the thyroid gland?

    Energetics says no. Predators are successful in capturing prey circa one success per 10 tries. Since the thyroid makes up less than 1% of the prey body mass, the predator would have to go into super-overdrive (whatever that is) to capture enough prey to provide sufficient calories, consuming only thyroid glands of prey. So instead of 10 to 20 hunting forays per day, the predator would have to expend at least 100 times more energy getting enough food to live. Thousands of hunts per day. Cannot happen.

    What happens in the real world is population levels of prey are much more limited in those areas of low nutrient availability, because they have nutrient problems, too. The predator that has that nutrient poor territory is essentially doomed to very poor survival and reproductive success.

    BTW before human agricultural practices depleted iodine from large areas (example: India, which is fixing the problem see below) the pockets of low nutrient soils were geographically small.
    Not any more. See:
    800px-World_map_iodine_status_2007.jpg
     
  4. May 24, 2017 #3

    Andy Resnick

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    There is some (very scant) evidence that some forms of pica, specifically geophagia, may be related to an iron deficiency. Animals are known to engage in geophagy as well.

    https://www.ncbi.nlm.nih.gov/pubmed/11001006
    http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2005.00002.x/abstract
     
  5. May 24, 2017 #4
    I never claimed that it was about predators categorically never eating anything other than one body part. I was thinking of some hunters needing more of a nutrient hunting animals with a higher percentage of some nutrients but with lower overall energy. Especially in the case of animals that evolve a higher need for some nutrients that puts non-caloric limiting factors that force them to search for prey in strategies that favor specific essential nutrients over empty calories. For example, humans evolving bigger brains that require more of specific nutrients. May this have something to do with the archaeological correspondence between the rise of herding of select meat animals and the decline of brain-eating human cannibalism?
     
  6. May 24, 2017 #5

    jim mcnamara

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    Okay. Then predator population levels cannot go for very long above scarce available prey - prey limited by deficiency - if predators exceed the carrying capacity their population crashes. Classic example - Lynx hare cycle. http://www.enr.gov.nt.ca/node/3052

    Can you provide a citation for this?
    How about: https://en.wikipedia.org/wiki/Kuru_(disease)
    If you read this it appears to be a counterexample of your claim: disease transmission from ritual cannibalism in the Fore people. (now prevented by outsiders). The study documented prions and won a Nobel prize for Carlton Gadjusek.
     
  7. May 25, 2017 #6
    It is possible that the selective hunting may indeed have decreased the stocks of the high-essential prey, and the downswings accompanied by "calory hunting" of other species may have forced our ancestors into cannibalistic brain eating. This would explain why big-brained human ancestors before herding was invented all over the then-inhabited world often cannibalized brains, while it was much rarer both among the earlier small-brained australopithecines (possibly nonexistent among them) and among the later herding and/or farming humans.

    Also, prion diseases often take a long time to become manifest, which gave many brain-eating cannibals time to procreate before they became truly sick. Is there any research on whether a drop in the frequency of "slow down prions" genes show a general tendency to coincide with the rise of herding?
     
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