Dear 100 Hour Board,
I've read before that reptiles can go very long periods of time without eating. A reptile expert today asserted to me that he has a shake that can survive two years between find it necessary.
Warm blooded animals however must eat daily. What then is the biological advantage of being warm blooded? What do we gain for that massive energy expenditure?
I’ve never found a shake that survived two years, unless their owners were lactose intolerant...
-Sunday Night Banter
Big brains need fast metabolisms. Snakes are pretty dumb (no offense to my pet snake). So that's one thing we gain!
The one I've heard the most is that warm-blooded animals are free-roaming. We regulate our own body temperature which allows us a wider range of suitable habitat. That's true in the long-term, but also just in daily movement. Cold-blooded animals have to warm up in the sun or find shade to stay cool. Find a snake and put it in a bucket on a hot day and, depending on the species, it will likely be dead in a few hours (please don't go frying snakes.) Reptiles have to make food last because they don't always get to choose where they go, and therefore can't always find food. Another way to say it is that reptiles don't have to move around a lot because they don't need as much food.
When an evolutionary tactic is more advantageous, it tends to result in higher genetic diversity. Ferns, for example, are non-flowering and non-seeding. They still exist but not nearly as vastly and diversely as flowering plants (which make up over 80% of all plants on earth.) All the energy flowering plants put into producing flowers, pollen, and sex organs are clearly paying off. It's a highly efficient trade-off.
In true Mythbuster's fashion, I'd like to take your question and have some fun with it if you don't mind.
WHO IS WINNING? Endotherms or ectotherms?
Mammals and birds are our homeotherms, and they're clocking in at about 16,000 species (give or take A LOT). Reptiles, amphibians, fish, and all invertebrates are our poikilothermic or ectothermic groups. For the sake of comparing apples to apples, we'll exclude invertebrates (1,305,250 species) from our contest. Vertebrate poikilotherms make up a solid 50,000 species (also give or take A LOT). Even with such a wide standard of error, I think it's pretty obvious that ectothermy is winning. If genetic diversity is your standard for a successful evolutionary tactic, ectothermy is the way to go.
That does not mean, however, that endothermy is less valuable to a given species. It means the endothermic species that do survive are highly specialized to use endothermy effectively. We humans are really friggin' smart and we've done a lot of dope things because of endothermy. We've screwed over a ton of ectotherms with our big brains and maybe also played ourselves. We'll find out if we should have gone with ectothermy but at the very least I think endotherms have way way more fun.
BUT WAIT A SECOND! Should we also remove fish from the contest? They live exclusively in water which completely changes the advantages of both temperature regulation and mobility. If I decide to only compare land-dwelling endotherms (15,938) with land-dwelling ectotherms (17,340) we have a much closer call. So close in fact and with such a terrible standard of error on both estimates, I would say that there is NO STATISTICAL SIGNIFICANCE. Basically, I'm saying that we're so uncertain about those numbers that it doesn't matter that ectotherms have 1000 more species. They're effectively the same number.
If you want to survive in this world, be a fish (32,900 species). If you want to have fun in this world, be an endotherm.