I did a test with a Network render of a scene with a looped camera animation and a Dynamic Ecosystem. Each lap is 400 frames. The pre-calculation time is the time before actual rendering starts. Since it is a looped animation the render time is exactly the same at the beginning of each lap. 

Frame 0: pre-calculation time 3 seconds 
frame 400: pre-calculation time 2 min 20 sec 
frame 800: pre-calculation time 4 min 30 sec 
frame 1600: pre-calculation time 9 minutes 

I'm not a scientist, but I would say this proves that the pre-calculation time doubles with each next lap.... 

This was a very simple scene with low density growth. With a more complicated scene, like the one I just did, pre-calculation times went up to 30 minutes per frame after 1600 frames.

For me this renders (no pun intended!) the use of Dynamic Ecosystem useless for now......