Question

If being mesothermic can be an advantage, why are there not more more mesotherms at this time?

Answer 1

Mesotherms are not totally extinct. Extant species like the great white shark, tuna and leatherback sea turtle are mesotherms. Endotherms have an advantage over mesotherms, that is they have metabolic control of a particular body temperature, whereas mesotherms do not or have little control, but they do produce heat through metabolism, which ectotherms cannot. When direct competition occurs, endotherms suppress mesotherms, mesotherms suppress active but cold-blooded ectotherms, and active ectotherms suppress more lethergic sit-and-wait ectotherms. This is because, endotherms have higher metabolic rates compared to that of mesotherms and ectotherms, which allows them to grow faster and eventually reproduce faster. The same applies to advantage of mesotherms over ectotherms.

The mesotherms do require less food compared to endotherms, but when the cost of growth and reproduction rate is compared to that of the endotherms, the food cost becomes negligible.