Today was our second full day at Las Cuevas and we set up two more experiments. In the morning, we were testing nutrient limitations in the different layers of the forest. Nitrogen is the primary limiting nutrient that we wanted to focus on. In order to see just how limiting it was in the forest floor and the canopy, we set up multiple pitfall traps, evenly spaced along a trail. Some of these traps had a source of nitrogen in them (coming from the most readily-available source we had, urine) and some just had water. In theory, the traps with the nitrogen source should attract more insects, and the ones in the region which is more nitrogen limited—the canopy—should have a bigger difference between the water traps and the traps with nitrogen. The traps were a bit tough to set up, because we had to wire them to the trunks and dig them into holes at the vase, but we ended up managing to set them all up with a bit of group coordination and ingenuity.
That wasn’t our only experiment of the day. In the afternoon, we were looking into mutualistic relationships between ants and Trumpet trees, AKA cecropia trees. The ant colonies live inside the trunks and protect the trees from other insects and animals which might graze on them. We wanted to see if young specimens, without any colonies to protect them, had other defenses. In order to do this, we planned to capture some herbivorous insects — grasshoppers and katydids— and keep them in a container with cecropia leaves to see if there was a difference in how much they chose (or were able) to eat. These trees live along disturbed areas, so we ventured out along the road leading to Las Cuevas. It wasn’t long before we encountered a small mature tree, and we chopped it down to access the leaves, which are concentrated near the top, and to inspect the ant colonies inside. The ant colonies were so interesting—they live in these flat layered chambers and feed on nutrients that the plant supplies. When we opened up the tree, the ants were swarming all over, and it took a little while for them to calm down. There was also a tarantula den in the base of the tree. Amazing how one tree can host so much life.
It took us significantly longer to find a young tree. We walked pretty far along the main road, until we realized that, because it was maintained, young cecropia trees might have been removed. We walked back to the unmaintained San Pastor road, which we had walked along yesterday, and almost immediately found a young cecropia. We noticed a hole in it, but no ants came out when we disturbed it. We cut it at the hole and realized that there was an ant queen inside with larvae but no workers yet. we had caught it just in time! No colony had established itself yet. We got back just before dinner and set up the mini habitats. Tomorrow we’ll inspect them to see how much of the leaves the insects ate and perform some simple data analysis. I can’t wait!
