Having spent the better part of two weeks moving down the Amazon River from Tabatinga to Belém, I’m now in the midst of the last 2-1/2 weeks of my year-long sabbatical leave, working on all things ants with my friend and colleague Rogério Silva at the Museu Paraense Emilio Goeldi. Rogério and I have been working on ecological similarities and differences between temperate and tropical ants. He’s visited me twice at Harvard Forest and now, with support from the Museum in Belém, I have an opportunity to learn first-hand about the ants of the Brazilian rainforest.
But first we have to get there.
30 November 2016
We have reservations on an evening boat, the Bom Jesus VI from Belém to Breves. We left Rogério’s apartment at 16:00; the taxi took more than 40 minutes to navigate the Belém traffic the handful of kilometers to the waterfront. With reservations in hand, Rogério, his graduate student Rony, and I skipped the various queues and piled into our cabin. We finally left the Bom Jesus dock at 18:30, bidding farewell to the Belém harbor with herons in the trees, kites overhead and the ubiquitous trash and decay in the water (click on any of the images to start a slideshow).
The pair of Bom Jesuses (V and VI) that make the nightly runs to and from Breves each hold about 250 people on three decks of hammocks and cramped 4-bed camarotes. Bathrooms, not especially clean, are shared and I decide early on that my shower will wait until we get to Caxiuanã.
Despite the pleasant breeze and picturesque sunset on the top (fourth) deck, the loud bar with flashing blue LEDs drives us below to the lanchenette for a Brazilian cheeseburger: small patty, ham, lettuce, tomato on white bread. The sweet strawberry yogurt drink helped wash it all down before turning in early with the diesel humming away.
1 December 2016
After a reasonable night’s sleep, we arrived around 06:30 at Breves. Bom Jesus Inc. does not have as nice a dock as where the Amazon Star had berthed last weekend, but all we needed to do was leap from the Bom Jesus VI onto its little sister, the Bom Jesus II Express, an enclosed fast skiff seating about 110 for the 1-1/2-hour trip further upriver to Portel, stopping at Melgaço along the way (click on any one of the three images to view larger ones).
On a bright day, with clear weather expected for the next week (and welcome after yesterday’s torrential rains presaging the coming rainy season), we head west from the dock on the Rio Parauaú across what Google maps thinks is land, but is clearly water. A nice forest-lined small river takes us directly to the junction of the Furo Oléria and the Furo Tajapuru where they formed the Furo Grande. Houses and small villages again dot the banks.
The Furo Grande empties into the Rio Campina Grande, which flows out of the Baía do Melgaço just northeast of our first stop at the eponymous town. Then it’s on to Portel, where we spend 2 hours buying food for the next ten days (a list thoughtfully provided by the cook at the station), buy a quick chicken fritter of the dock, and then hop onto the day’s final boat—a 6-person outboard that looks like a Brazilian copy of a Boston Whaler—for the two-hour bounce to the Caxiuanã National Forest Reserve (click on either image to view larger ones).
We arrive near 15:00, buns sore from the bounce, ears deafened by the whining outboard. We eat a late lunch (the first of a seemingly endless series of meals consisting of rice, spaghetti, something made with potatoes, beans, and chicken), unpack gear into the lab and ourselves into our rooms, have an early dinner, not much different from lunch—only the potato varies—and call it a night.
2-3 December 2016
The primary focus of our work here at Caxiuanã is to see if we can measure how much carbon dioxide is being emitted to the atmosphere from ant nests. Standard models of the exchange or carbon between Earth’s ecosystems and the atmosphere include plants and soils, but rarely account for animals, even common ones. And ants are the most common. It is thought, for example, that if you put all the ants in a rainforest on one side of a scale, and all the other animals on the other, that the ants would be heavier. So if we were going to try to include animals in models of ecosystem carbon exchange, ants seem like the animals with which to start.
But it’s not a trivial task to measure carbon dioxide escaping from an ant nest. First, ants nest in a wide variety of habitats, including underground, sandwiched between rotting leaves, and high up in trees. Second, they don’t really like being disturbed. When you put a respiration collar (a 10-cm diameter piece of plastic tubing) into a nest, the ants get annoyed (how would you like it if some giant stuffed a big plastic ring through the roof of your house?). Sometimes they pour out of the nest, biting and stinging anything that moves, eventually settling back down after a few hours. But if you’re really unlucky, they just up and move the whole colony (click on the four-second video below to watch Azteca ants swarm the respiration collar)
We decided initially to focus on the large hanging nests of Azteca ants. These nests not only are works of art but also are comparatively easy to find. The ants don’t move them, and they persist in one place for a long time. On the other hand, the hundreds-of-thousands to millions of tiny Azteca ants in a single nest are extraordinarily aggressive. As soon as we start poking around a nest for a good place to put the collar, the ants come pouring out—literally, it looks like a river of ants—covering every exposed surface and ready for battle with us intruders. They bite, but do not sting, and although being covered with biting ants is not for the faint-hearted. Fortunately, they don’t leave any lasting welts.
Our first stop on the Azteca hunt was about 2-km upriver. We motored upstream in the aptly named Candiru I with two graduate students studying carbon flux at and around a 53-m-tall tower, which extends far above the rainforest canopy and measures exchanges of gases between the forest and the atmosphere. We thought that if we could measure carbon flux from ant nests in the “footprint” of the tower (i.e., that section of the forest being measured by the tower) then our measurements could add a piece to the overall carbon “budget” of the forest.
But in three hours of searching, we found only one Azteca nest in the footprint. We did use this one to develop a method for mounting a respiration collar on a nest, and we also climbed the tower to get a real bird’s-eye view of the forest, but we returned to the station for lunch somewhat chagrined that we didn’t find more nests (click on any one of the three images to view larger ones).
After lunch (the predictable rice, spaghetti, potato salad, chicken), we set off for a couple km walk to another gas-flux tower, this one—somewhat shorter at only 40-m tall—located adjacent to a long-term forest drought experiment (ESECAFLOR). Since 2002, researchers here have been preventing half of the rainfall from reaching the soil surface in a hectare (10,000 m2) of rainforest, which is no mean feat in this environment (a representative paper on this experiment was published in Nature last year).
On the trail out, we found two more Azteca nests, and a third on the way back in. We also put respiration collars on nests of Pheidole (1), Atta (the infamous leaf-cutters and fungus gardeners) (2), Mycocepurus (another fungus gardener) (3), Solenopsis (1), and Azteca (4) in and around the lab clearing. And finally, on 3 December, a respiration collar atop an Odontomachus nest adjacent to the ESECAFLOR experimental plots. We made it a point to avoid Paraponera nests, despite (or because of) the large size of these ants (the largest in the Neotropics).
Now we let the collared ants rest for a few days while the ants repair and re-seal the nests around where we put the collars.
Although we’re pretty focused on ants, there’s a lot more to see here. The trees are huge; of particular note is the Tauari (Couratari ?tauari), one of the largest rainforest trees. Many other trees are covered with termite trails. Some come in chevrons, which remind me of the lichen-covered Pacific silver fir trees in Oregon (click on either big tree to see it even larger).
Monkeys play in the trees above the dorms and bats flit in and out of our rooms. Birds call constantly but are, of course, difficult to see—I did manage to record the conspicuous call of the Screaming Piha (Lipaugus vociferans), more colloquially and congenially called the Voice of the Amazon. It will make a great ringtone!. Frogs are loud and abundant and small lizards, including anoles and Ameiva species, are seen on occasion. Snakes supposedly also are abundant (I’m told that “Caxiuanã” means “land of many snakes” in the language of the local indigenous people), but so far we’ve seen two: a small fossorial one named for its dark head (Tantilla melanocephala) and a coral-snake mimic, Oxyrophus sp., which we watched squeeze and swallow whole a lizard (Ameiva sp.) about one-third the size of the snake. There should be several species of Bothrops here, along with numerous coral snakes, but seen them yet, not (click on the either of the top two thumbnails to see larger versions of those, then click on the first of the 2nd set to see the snake swallow the lizard).
4 December 2016
While we’re waiting for the respiration collars to settle, we’re spending time on adding to the data on the diversity of ants here, collecting and sieving leaf litter and soil, as well as learning about how far ants will range from their nests in search of food. The latter is not nearly as easy as it sounds. We put out small baits—a mix of Farinha and sardines in oil—and wait for the ants to come to lunch. Then, we crawl around on our hands and knees following ants carrying bits of farinha back to their nest. If we can see the farina grains and don’t lose the ants in the leaf litter, then voilá! the nest. This morning, three of us crawling around for an hour-and-a quarter found 13 nests, and in the afternoon, another 15. Which felt really rewarding, given that most of the ants we were following were only 1-2 mm long, like the Pheidole species in the video below.
It was more fun, though, to follow the big ones! (the video below is of the Odontomachus ?hastatus nest atop which we installed a colony respiration collar).
5 December 2016
More baits, more ants, more data. And we walked into a wasp’s nest, which was somewhat unpleasant for all concerned.
But after 2 days of baiting, we have good data on more than 80 colonies in 12 genera—the most common of which is Pheidole—so in between colony respiration measurements, we’re going to move on to explore how far Pheidole will go to get food. Stay tuned!