Hello again AAB,

I am a biology teacher and I am sitting with my A-level class as I type this (we are posing it as a class question). We were talking about elephants and then someone asked why all the biggest land animals tend to be herbivores (cows, elephants, buffalos etc) when a carnivorous diet surely provides more energy.

The best answer I can give is that very large animals tend to be slow and therefore would be unable to chase and catch prey.

Is this right? Are there any alternative theories or other contributing factors at play?

We eagerly await your answer...

Thanks as always!

Jim Farlow wrote a nice paper on this:

James O. 1993. On the rareness of big, fierce animals: Speculations about the body sizes, population densities, and geographic ranges of predatory mammals and large carniverous dinosaurs: American Journal of Science 293-A:167-199.

You can read it at http://earth.geology.yale.edu/~ajs/1993 … Farlow.pdf

To summarise, a large standing biomass of herbivores and only support a certain much smaller biomass of carnivores. At a given total biomass, you can either have a few giant carnivores or many smaller ones. But if the number of individuals becomes too low, there's no longer a sustainable breeding population. So in order to maintain enough individuals of any given predatory species without exceeding the total possible biomass enabled by the herbivore crop, there has to be a maximum size.