Manathermy: effects on the ecosystem

In the animal kingdom we have endotherms, ectotherms and a few things in-between. These are the methods by which animals thermoregulate themselves to survive.

But in this world there is a new kid in the metabolic block: Manatherms.

How it works:

Basically, they are mammal-like animals that can use magic to maintain their body temperature (and a few other cool tricks irrelevant to the question). They can't use mana to supply any other metabolic requirements, for reasons unknown.

The animals have to "filter-feed" mana from the air using visually impressive organs like antlers, horns, tusks, fangs, manes and others.

The setting

The environment in question is a massive Mediterranean oak savanna similar to the Spanish dehesa, crossed by many rivers and closely managed by local hunter gatherers to maximize animal populations.

The question

So the question is, taking into account these animals have the metabolic rate of mammals, and thus their growth, while having what I believe is a reptile caloric intake due to manathermy. What would the environment be like, in terms of animal population (biomass) and trophic levels?

The main difference that would be seen in environments with manatherms is that there would be many more predators for a given population of prey animals than is the case for non-manatherm homeotherms.

Paleontologist Robert Bakker has determined that homeothermic predators (such as 'warm-blooded' lions and tigers) are only 1-3% of the biomass of prey animals, while poikilothermic predators (such as 'cold-blooded' lizards or spiders) can be up to 40% of their prey's biomass. Why is this? Because poikilotherms can afford to sit still and wait for prey for long periods of time without having to spend much metabolic energy on staying warm.

So, manatherms would be like poikilotherms. They can afford to sit still and wait for prey to come along without having to worry about starving due to a need to fuel heat production. However, since they are homeotheric, even if not metabolic homeotherms, they would also not need to bask in the sun like poikilotherms - they would always be warm enough. That means that while poikilotherm predators may not always be ready to chase after prey, manatherm predators would be.

So, I expect that manatherm predator-prey biomass ratios would be very high compared to homeotherms that have to fuel their own body heat production from their diet, but lower than the predator-prey biomass ratios for poikilotherms, since manatherm predators would be more efficient.

I would expect that there might be around a 20% predator to prey biomass ratio (say 10-30%), which is around half-way between homeotherm and poikilotherm ratios.

Similarly, I would expect that there could be a great many more manatherm herbivores in a given environment than there could be homeothermic herbivores. Since the manatherms are using ever-present mana to fuel their body heat production, the manatherms would need to fuel only their other bodily functions, such as growth and the three "F's"... fleeing, fighting and reproduction. This would mean that manatherms would need smaller diets per unit body mass, and therefore the environment could support many more herbivores.

So, this environment would be packed with manathermic animals, relatively speaking, many of them predators. They might not be as common as poikilotherms could be, but they could be much more common than homeotherms. They could spend more energy on sexual display than a homeothermic animal, and still not spend as much energy in total... at least not energy that has to be gained from food. So, they would be flashy, fanciful creatures with seemingly meagre diets, but more energetic than poikilotherms.

Manatherms could also be expected to out-compete both poikilotherms and endotherms. Poikilotherms cannot meet the activity levels that a manatherm or endotherm could achieve, and a manatherm can wait just as well as a poikilotherm if need be. Endotherms would need to eat far more than manatherms or poikilotherms for the same body mass, and are less able to withstand periods of famine. Because manatherms have the advantages of both poikilotherms and endotherms and none of the disadvantages of either, they'll likely displace both of them.

The only problem that the manatherms might face is if the mana goes away. Then they'll likely starve, even if there's plenty of food. It's hard to suddenly boost the throughput of a digestive system used to small, frequent (or big but infrequent) poikilotherm-sized meals to handle big, frequent meals like endotherms.

Your biggest effect comes down to this, as an herbivore you can fill your daily nutritional in less than an hour so you have a lot more time and energy for other stuff.

More numbers, populations are just much larger. If you lean really far into this you will see less of the other stuff.

More variety, with much lower nutritional requirments but constant activity the can try all kinds of more exotic ways of living, maybe a huger herbivore that only eats fruit or seeds. Maybe somthing that eats trees and digest woodbecasue it can take days to digest it

More behavior and mating. These animals now have LOTS of free time, they are active but don't need to eat constantly so you have huge display structures, courtship dances that last days, constant noise, building massive constructions. All the time they used to waste on eating is now spent trying to mate. Look at birds of paradise for examples of what happens when a groups of active animals gains more free time. You may even get more territoriality since they have time to spend defending their territory.

You may also have animals with, Manoris, (lit mana mouth) or Manaretes (mana net) that are oversized and they have fiquired out how to use the extra mana for big mating displays, this depends on what else they can do with the mana.

More predators. Monty covers most of this but you also have a strongr incentive for everything to try more predation, they care more about nutrional value than pure calories so a big incentive for omnivory to get all nutrients.

For Plants this matter because either there are way more herbivores that can afford to spend a lot more time breaking down your stuff so you need even better defenses OR herbivores have a far weaker impact so you can afford to spend more on flowers and fruit and just growing faster.