In general, the two main differences between '99 South and the main common garden (for damage assessment and herbivory) appears to be less damage in '99 South and more ants (and less ant diversity).
When doing phenology in the '99 common garden about a week ago I noticed that the plants in the eastern-most row (those along the very edge) appeared to be more likely to have ants and (very anecdotally) seemed to have a different amount of florivery damage and browning than the rest of the garden (it's been too long owing to my laxness in flogging and I can't remember if it was less or more, though I am inclined to say less). Whether there actually is a difference in damage and whether this difference results from ants, edge effects, or chance remains to be seen.
A few days ago when I was doing phenology in the '99 South common garden I noted that the majority of plants in the garden had ants and that there was low variability in ant species composition - virtually all I saw where the large black ones with red heads. These ants were very aggressing and would leap off the flower head onto my stylus as I was pointing at the anthers to count them. I could practically hear them sharpening their mandibles. The northern-most row (those along the very edge) had few ants and the ants were of different species, including small black ones and light-colored ones. Interestingly, there was much more damage in this row.
Are these large ants actively defending their flower heads and increasing plant fitness?
Do other species of ants contribute less to the echinacea in terms of defense? Do they take more away in terms of pollen and nectar? It is not uncommon to see ants covered/dusted in pollen (I never observed this of the large black species) and I have twice seen a small black ant actively carrying pollen in its mandibles.