The best way to see a sloth in the tropics is to scan large Cecropia trees, looking for a still, amorphous lump. The common knowledge is that they spend most of their time in Cecropia trees, preferring their leaves. But do they? It may be just a simple observation bias given that the minimal, elegant structure of the tree provides the best chance to spot something that doesn't fit. Either way, what I'm really interested in is their interaction with Azteca ants. Do ants somehow ignore these slow moving beasts? Or do the sloths ignore the potential onslaught? Or perhaps colonies differ in their response to sloths. I've gathered minimal anecdotal evidence for any of these ideas because it's hard to get up close to observe whats happening. I have seen sloths get deterred from a tree before they even reach the leaves, and I've seen sloths eating at their leisure. Perhaps it is the sloths that vary in boldness or pain tolerance. Experiment planning is underway.
These howler monkeys have very different foraging approaches depending on which Cecropia tree they are feeding on. In the first shot, the monkey seems to be minimizing its contact with the plant by reaching out from a another tree, retreats quickly after snapping off the soft meristem, and presumably scratches off the attacking Azteca ants. In the second shot, the money is chomping at its leisure, lounging on the Cecropia tree itself. Perhaps these monkeys are being met with differing levels of aggression by the resident Azteca guardians . . .
So far, I've been focusing on medium-aged colonies in medium-sized tree for standardization reasons. In a recent experiment conducted with Karla Moeller, we expanded our sampling to include young saplings and old giants. Here's a sneak peak at how one of our sapling colonies responded to leaf damage. Note that as the ant that discovered the damage returns to the stem to rally her nestmates, she is dragging her abdomen, laying a guiding chemical trail.
All in all, there were 31,054 ants from 17 colonies in the greenhouse by the end of the study. At least 22,554 were born there. More specific stats forthcoming.
One year ago, the great harvest took place. Harvest time is always an exciting, bittersweet scramble. I've been studying these colonies for these colonies for two years - discovering them in the field, getting to know their personalities, extracting them and implanting them into my greenhouse, watching them recover and grow, and studying their change in behavior, if any. Now to answer many fascinating questions about colony growth, morphology, plant investment, nutrient flow, and microbe communities, the colonies and plants must be sacrificed. With 42 plants, half of them hosting colonies, timely processing is an incredible feat - impossible for one person. It was at this time that I called on the other scientists at the Gamboa field site to volunteer their spare time to help with the harvest. I was overwhelmed with support, and together, we pulled it off. Sample analysis and behavioral scoring is underway. I could not have done this without you Sebastian Stockmaier, Agustin Diaz, Megan Pendred, Eloïse Lebrun, Yussef Castillo, May Dixon, Claire Hemingway, Krzysztof Kozak, Aaron Goodman, Eva Gril, Clément Aubert, Lynette Strickland, Barrett Klein, and Brendan Dula. Any time you need a helping hand, I'll be there.
The American Philosophical Society (APS) newsletter features my research and photos in their most recent Autumn 2016 issue. The APS played a key role in making my ambitious greenhouse transplant experiment possible by providing funding through their Lewis and Clark Fund for Exploration and Field Research grant. I'm honored to take part!
All of the transplanted greenhouse colonies have been thoroughly reassessed on their patrolling behavior and responses to vibrational disturbance, leafcutter intruders, army ant intruders, and leaf damage. A terabyte of videos await analysis, so stay tuned for the colony comparisons of how much they've changed since the transplant last year and if their behavior was affected by their host plant's soil nutrients.
Patrolling Azteca ants that discover freshly damaged leaf material recruit their nestmates to the damaged site to fend off any offenders (or even make a meal of them if they can). This robust, fascinating behavior is one of my favorites to watch unfold. However, it is very difficult to film this interaction in its entirety because tracking such small, fast individuals while maintaining a decent focus takes practice and luck. Recently, I was lucky enough to follow the discoverer from the damage site, along the leaf vein to the petiole junction, all the way across the petiole to the main stem, and back. If you look closely you can see her dragging her abdomen as she runs to lay a pheromone trail that her nestmates follow. She also seems to release an alarm pheromone at the leaf-petiole junction that activates all the poised workers waiting there.
After 5 years of dreaming about what Azteca colonies are like in the tops of the tallest Cecropia trees, my collaborator Karla Moeller and I have made it a reality by renting a boom lift and taking it into the jungle. Now we have answers to some very simple questions - are there separate colonies in these large branching trees? are giant colonies more or less aggressive? do they show variation in collective behavior like smaller trees? do they respond to leaf damage like younger colonies? do they colonies all branch tips, or just a few? what's the colony connectivity like between branches at opposite ends of the tree? Results are forthcoming, stay tuned.
My most aggressive greenhouse colony will not tolerate the presence of a single army ant (Eciton hamatum). Watch this colony's impressive response.