In the animal kingdom there is a tremendous range in animal size. Bacteria are 1000x smaller than protozoa which are 1000x smaller than plankton which are 1000x smaller than mice which are 1000x smaller than jungle cats which are 1000x smaller than blue whales. (Don’t hold me to those numbers, I’m just creating an example)
Why don’t we see the next step in that progression? Like, say, 300ft-tall herbivores the size of small office buildings that graze on the amazonian canopy the way a cow might graze a field. Surely the amazon could support a small population of such a creature?
Why does the magnitude of animal size “max out” at Blue Whale?
It doesn’t “max out” as much as “becomes biologically inefficient to become larger”. Animals that large have to consume LARGE amounts of food to maintain that size. Ocean creatures are larger because the water supports their weight. You COULD have larger animals if the environmental variables (food supply, oxygen, gravity, etc) changed.
ETA: Life here hasn’t maxed out at the blue whale. That organism just so happens to be the largest yet (so far as we’ve discovered). In millions of years, something larger could very well evolve.
Evolution works by filling niches. If there’s some kind o phase space available, it will/might get exploited. Nature didn’t decide to ‘max out’ with the blue whale, there simply isn’t a niche available for a bigger animal.
As or 100ft herbivores… How would they evolve? What untapped resource is there which is feasible to strive for which might trigger evolution.
[/] and waiting for **Colibri ** and other smarter minds to fill in/correct me.
But couldn’t the proverbial plankton make that same argument about the mouse, having never seen a jungle cat?
Yes, the amount of food that a large animal has to consume is large, relative to you and me, but is it large in proportion to the size of the animal? Is the amount of food a blue whale eats any larger in proportion than the amount a mouse eats? Mouse food is abundant, why don’t mice grow to the size of blue whales (or at the least - jungle cats - oxygen and gravity being the same.)
I understand what you mean and perhaps I should have worded my answer better. The proportion organism size to it’s capability to injest food is not by any means an indicator to how massive an organism is. There are very small organisms that eat many times their weight/size and very large objects that eat very little. That particular ratio depends on the organism. Whether or not the plankton can make an argument to a mouse is more of a philosophical question. Hence the reason for the follow in line in my reply:
It leaves room for other possibilities. If a Unicron-like organism comes to devour our planet, then THAT will be the new reigning champ regardless of whether or not my pet bunny is aware of it.
In the context of the OP, I’m guessing he meant biological life as we know it. Life has evolved to fill the specific needs of the species. To big and it dies, to small and it dies. Life has to find the happy medium. If the environment allows for a larger animal to live, than it can. I’m sure you could breed blue whales to be larger if you wanted to. Also, since the environment has varied wildly in the existence of life on earth, the conditions for a “largest possible animal” have changed with it.
Breeding patterns are a huge factor in the evolution of size, and may even hint at the existence of the maximum size the OP touched on. The larger an animal is, the larger the habitat required, and thus the fewer the number of individuals able to survive in any particular ecological niche. Also, large animals are going to take longer to grow to reproductive age. A small population coupled with a long time between generations means that the species is not going to be very evolutionarily agile. It’s going to take a long time for it to adapt to changing environmental conditions. If it’s too big, it may die out before it can.
We joke that the human species will be survived by the cockroach, and we probably will. The small, fast breeding, and extremely numerous cockroaches will be quicker adapters to whatever environmental change kills us off.
I remember reading in grade school that insects couldn’t ever get as big as they did in the movies, because the weight of their exoskeletons would immobilize them. Thinking back on that, it would seem that the various structures of living things impose their own size limitations: get too big and you couldn’t move, reproduce, or get enough to eat. But even that is theoretical, because you don’t outgrow your niche.
Scaling is a significant constraint on just how big things can get. As linear dimensions increase, relative surface area decreases while volume increases. Further, cross-sectional area for bones and such increase slower than the mass increases. Thus, even aside from food intake problems, you have the basic problems of overcoming structural failure, overheating, and limited oxygen supply. Dinosaurs got to be big by evolving big empty spaces in their bones; for large sauropods, almost any bone area which wasn’t actually weight-bearing was done away with. Those may well represent the maximum sizes possible for terrestrial animals under Earth conditions (or, rather, Earth conditions at the time).
Sea creatures can usually get around the weight aspects, but they still suffer from heat and oxygen limitations. All that extra mass has to get energy somehow, and all that extra mass generates a lot of heat. Living in cold water may also help with the heat aspect, but you still have heat transfer issues acting as a constraint.
Not necessarily. There is much debate as to the status of “niche” independent of a species occupying it (that is, do niches really exist independently from any organism?). There may be no such things as “vacant niches”; if true, then evolution cannot work to fill them because they were never empty in the first place. A niche is, if anything, an adapative morphospace; as a population adapts, its niche necessarily changes along with it.
That doesn’t seem right to me. Whales have huge amounts of insulating fat to protect them from the cold water. Evaporative cooling is very efficient, and works well for pretty much all land animals. I doubt that animals the size of the blue whale would have serious heat dissipation issues on land; they’d just have major structural issues.
The thing about day to day evolution is that it tends toward moderate sizes for each species.
This is called “regression to the norm”.
Thus even if there is a size advantage/disadvantage, the whole species will average out.
The advantage has to be related to mating, rather than just existing, for it to change the whole species.
Thus, the giant antlers of the extinct Irish Elk arose because among herd animals the alpha male gets the most action among his harem.
In non-herd (or small herd) animals like whales, that is not a factor and all sizes that have any survivor skills at all will continue, whether “best of breed” or not.