look up the law of conservation of matter. it's a complicated topic. the animal doesn't just "change shape", it literally breaks down fats to convert them to proteins, but in many species, there's a requirement to feed after emergence to have optimized protein/fat amounts
I still need the article title at least, then I can do that. At the moment, the pic won't even load
god dammit lemme explain real slowly for you
the gut-load is metabolized by the FEEDER, which converts the amino acids within the food into its own biological molecules, which the predator can then absorb
we're only talking the 3 macronutrients here, not minerals or vitamins and such
gecko gut-load is NOT "mostly calcium". every living organism needs calcium. can excess calcium cause an issue? yes. but I don't think we're even close to that point yet
*you're
every organism has more or less the same biological needs. all animal cells are made up of the same molecules and the same elements are required in basically the same quantities to function
the question is how does that organism obtain those molecules
herbivores, for example, have the enzymes necessary to break down plant cells and pull those materials out and convert them to their own biomass. the nutrient profile of say a hickory leaf is going to be about the same as that of a blade of grass. Now, you're probably thinking "well then why can't every herbivore just eat ANY plant?" good question. the answer is that aside from the proteins/AA, fats, carbohydrates, vitamins, minerals, etc within that plant tissue are various chemicals that "lock" up the nutrients. Without an enzyme to break that chemical down, the animal cannot actually use the material. It may even make the material toxic. Why does cyanide kill us? Because we don't have enzymes called P450s to break it down, and so it stays in our cellular machinery and inhibits the actions, leading to cell death. This is why most herbivorous insects will die if they're not eating the plant they've evolved to eat. Some generalists exist, but even they have their limits.
now let's talk about carnivores. carnivorous animals cannot digest things like cellulose or lignins, and so they would die if they ate a plant (ok there's nuance here like pollen is usually edible to everything and a bite of a leaf may not kill something). Why? Because they don't have the enzymes required to unlock the nutrients within a plant cell. That's what it comes down to
the reason we want to gut-load feeders is because that feeder isn't just some carrier of all of the nutrients for its predators. It is itself an organism that has its own biological processes that require energy and nutrients. I do not know why this is a difficult concept. Did you ever see those energy flow pyramids in 4th grade about each trophic level only getting 10% (ok the range is actually between 8 and 15%) of the available energy from the previous trophic level? Metabolism is hella inefficient. You know how foods have calories on the nutrition facts? Well, the actual calories in that food is about 10 times higher, but your body can't possibly absorb all of it. Most of it gets lost as heat. Don't believe me? Hydrate some yeast in some molasses water and wait about a day, then feel how much warmer the solution becomes. It's basic physics, chemistry, and biology. god damn!
this is only partially true. later I'll post references (right now I'm on the toilet and my roommate and I are off to the recycling center before we feed our mantises today, plus it's cleaning day) about this, but there are studies done on various predatory arthropods (including mantises but also spiders, assassin bugs, predaceous stinkbugs, etc) that show a few things
1: when prey has extra protein in its diet, predator survival and growth rate tend to be higher
2: most predators benefit from a multi-species diet. Those that do not either don't do any worse on the mixed diet or are specialists to begin with
3: I have my own data on mantis performance on fruit flies gut-loaded versus not gut-loaded
calcium is crucial to the fertilization of eggs in animals. the other thing we haven't even touched on here is transient gut microbes. but I think Craigey-poo needs to learn the basics first
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