The Jungle

I needed to sit and read a meter every 5 minutes or so, and was able to observed the stream more closely. While sitting on the stream bank, the diversity of types of tadpoles was unbelievable. I had been told how many species could be found in the sream, but the words did not convey the reality. Herpetology in general, and immature frogs in specific are not my areas of expertise, so I could not identify individual tadpole species. Actually, very few people can accurately identify most of the species in these streams from the tadpoles. In our group Edgardo and Scott were the specialists and the rest of us were just learning. Still, even to my unpracticed eye there was a clear variety present.

Some tadpoles were larger than my thumb and had very streamlined bodies. These used the suckers on their mouth to attach to rocks in faster waters. A large rock could have 10 or 20 of these. The scrape marks where these tadpoles had fed on the algae attached to the rock were apparent.

Chubby tadpoles with bodies that looked like slightly flattened spheres with a diameter wider than a quarter squiggled along the bottoms of the pools. These were not extremely fast and I caught one and its body felt like a bag of water. I released it and it skittered away. I wondered how such a slow large animal could exist without being preyed upon by snakes, lizards, and birds around the stream? Perhaps the fact that they were like a bag of water indicated that there was very little nutrition to be had in one of them, or maybe they were toxic. Given the impending extinctions, it is possible nobody will ever know the answer to the question.

Small tadpoles with bodies the sizes of orange seeds were wriggling around in shallow waters. I turned over some of the large wads of leaves on the stream bottom. Tadpoles with bright red blood vessels skittered away.

The open areas of the pool were perhaps 10 feet long, 10 feet wide and a half foot deep. Every one of these areas had herds of hundreds of small tadpoles, each the size of a pea, grazing on the microbes (algae, fungus, and bacteria) that lived attached to the sand and gravel. Any sudden movement would cause them to scatter for a while and hide, only to emerge a few minutes later and continue their incessant eating. Their only job in life was to gain enough energy to emerge from the stream, morph into an adult, mate, and produce more offspring.

Ecology is full of technical words, and the film of organism the tadpoles eat that is found on the bottom of the streams is called periphyton, a biofilm, or in more old fashioned terms, aufwuchs (one of my favorite words for some reason). In some strange way these tadpole flocks (there is no technical term for a group of them that I am aware of, maybe they school like fish) reminded me of the herds of bison that roam across the Kansas Prairie grazing the grass. Oh give me a home, where the tadpoles roam! Both the tadpoles and the bison are mainly eating machines and consume for most of their time. This constant eating is a requirement for any animal that eats relatively low quality food like grass or periphyton.

Time between writing down numbers offered me my first chance this trip to contemplate the riot of diversity that is a tropic rain forest. Evolution is occurring at breakneck speed relative to temperate systems. This has led to far more complex and diverse systems than occur in temperate habits. There are so many species of plants and animals that it is difficult to know how they interact, and fascinating to consider the linkages.

Plants struggle for light and nutrients. Water is not a problem here. Trees soar hundreds of feet upward into the canopy to intercept light. The trees have shallow roots that spread to intercept nutrients as soon as they reach the forest floor in the form of a fallen leaf, dissolved in a rain drop, or in animal excreta. The trunks of trees have wide buttresses (flared ribs spreading to the forest floor) to support their tall trunks. The buttresses give the jungle floor the feel of a green cathedral. The trunks and branches of all trees are covered with vines, mosses and other plants. Every square inch of available space is used.

The forest cuts the wind so flowers must be pollinated by birds, insects or bats. Each flower has its own tricks to lure the specific pollinator it needs and to exclude animals trying to steal the reward they offer to the type of pollinators they are trying to attract.

Exotic orchids offer odors as rewards that iridescent bees use to attract their mates. Each species of bee has its own cocktail of scents it harvests from different orchids, pollinating the flowers as they collect their scents. Humans were not the first species to discover the use of perfumes harvested from the surrounding to attract the opposite sex.

Some species of orchids are shaped to mimic bees. These flowers trick the male bees into attempted copulation, and deposit a pollen packet on to the presumably frustrated male. The bee goes on and if it makes the same mistake, it pollinates the next flower that fools it again (do they ever learn?).

This is not stark beauty like desert or tundra. It is diversity in your face with life evolved to use every nook and cranny. You cannot see far in the jungle, but there is lots to see right in front of you. There is something new for the observant biologist at every turn. If you sit still in one place in the jungle, the diversity will come to you. A mixed feeding flock of birds will eventually come foraging through the jungle. There are a half dozen species of birds in these flocks. Some eat bugs from the bottoms of leaves, others move up and down the trunks. Some of the species catch the insects that fly up when they are disturbed by the other birds. The birds receive benefits from feeding as a group; they are more likely to detect predators such as forest hawks, and their feeding habits complement each other.

Mixed feeding flocks are but one example of the co-evolution that is so common in the tropics. Species in this habitat are more likely than any other, with possible exception of coral reefs, to have evolved characteristic in response to the other species in the environment. Many species have complex adaptations to the others found in their environment.

The bull-horn acacia, Acacia cornigera, found on forest edges, is but one example. Ants protect trees and shrubs from grazers. If you hit the trunk of the shrub, the ants create a sharp smell which is the chemical (pheromone) that the ants use to signal each other that there is an invader. The ants swarm to attack any animal that tries to eat the tree. At night, the ants descend to clip back seedlings of other plants that might compete with the acacia. In return, the ants make their nest in large hollow thorns, and eat food bodies with fats and proteins, and nectar with carbohydrates produced by the plant. An acacia that has the ants removed is quickly consumed by the many herbivores found in the forest, including the ever-present leaf cutting ants. The ants and the acacias have evolved a tight cooperative (mutualistic) relationship in response to the benefits each can provide.

Many more examples of co-evolution exist. Toxic butterflies are brightly colored to advertise “don’t eat me”. Other species of butterflies have evolved color patterns that mimic the toxic butterflies so they are protected form predators. Every species of insect seems to have a specialized species of wasp that is parasitic upon it. This list of entangled interrelationships goes on and on and provides endless fascination for those interested in biology.

The First Experience with the Jungle Stream

After each of us had walked up and down the stream, the lead researchers met up and settled on the experimental reach. This was a 300-yard long stretch of stream surrounded by jungle with no major side channels and a variety of pools and shallow areas (riffles) characteristic of the stream. Most streams naturally sort themselves into a series of pools and riffles through the natural processes of erosion. These processes also lead to the typical meanders or “S” shaped bends that characterize flowing waters.

We picked out sampling sites from the top down, each one a bit farther apart from the next, so we could sample correctly. Once the experimental area was set, we worked with Edgardo and the other Panamanian helpers and found the best way to get from each sampling site along the stream to the next. They then used their machetes (a standard item of hiking and work equipment for most rural Panamanians) to clear a rough path. We marked each of the sampling sites along the stream with fluorescent tape, and set up our equipment for the initial measurements.

The trail had its hazards. We could not step in the stream while the experiment was going on, so needed to have minimal crossings and placed logs and rocks to get across where we did need to go. The trail wound its way through a bit of sparse jungle, but the animal trials made false leads and it was easy to wander off the wrong part and we had to pay careful attention. I hoped we would not be caught on the trail after dark. After the sparse jungle the trail went across a marsh, which we filled with logs, but they kept sinking as we would walk across them and the crossing was precarious at best. Right on the edge was a palm tree, and it was natural to grab the tree if you slipped into the mud off the logs. Unfortunately the tree had huge spines and the spines had an irritating substance on them. More than one of us grabbed the tree by mistake and was impaled. It is the kind of mistake you only make once; unfortunately I made that mistake several times.

The trail went next to the stream in parts and up and down steep-slippery sections, and included some logs. At the top of the trial was a large rock bar where we were setting up our system to add the chemicals to the stream. Just above this part there was a branch in the stream and the jungle was a bit more open, so large shafts of sunlight played through the branches onto the stream. This was a beautiful spot where we could see a slope too steep to climb rising between the two stream branches and huge trees towering hundreds of feet above our heads up the slope. Boulders the size of shuttle busses had fallen off the sides of the steep slope and lodged in the stream channel, and massive tree trunks had recently fallen across the stream above taking out many others on their way down. Above our top location, the stream was a jumbled mass, and it was very difficult to get through to the stream above, but the effect was wonderful.

Since we were going to use an inert chemical tracer to follow how nitrogen moved into the animals in the stream, samples needed to be collected to establish a baseline, and also to establish our basic protocols of measurement. Our group split into smaller groups.

One group collected the leaves and algae in the stream that form the base food source for all the animals in the stream. These samples were collected from a known area so we could estimate the relative amount of each that were present in the stream. At previous streams where the frogs had gone extinct the algae had exploded, so we wanted to catch that with detailed measurement. Even in these shaded streams there was enough light to allow some algae to grow.

Other groups collected the tadpoles, insect larvae, crabs, fishes and shrimps that populate the stream. These collections required careful netting and counting of individuals. We needed to be absolutely certain to quantify the existing conditions, because we knew of the changes that were coming and there was no going back. All these collections also needed to be made with much caution to minimize the disturbance of the stream channel so as not to interfere with our measurements in the following days.

Simultaneously, Bob, Alex, Matt and I set about making additional basic preliminary measurements required to start the experiments. Measurements were made with chemical sensors (measuring oxygen gas dissolved in the stream water, temperature, and other important water quality parameters). We started electrodes that would record the chemical conditions and temperature in the stream for the entire duration of the experiment. We took chemical samples required to calculate how to start the experiment the next day.

We started other measurements to determine how the stream responded to pulses of nitrogen and how pulses of tracers we released at the top moved down the stream. The results from these releases allowed us to account for how quickly the water moved through the system, and how much water was flowing. We took background samples of water to measure nitrogen so we could calculate how much nitrogen tracer to add and for how long. All these water samples would be analyzed later that same evening. Bob had a very nice approach where we could add the chemicals streamside and the samples would incubate and be ready to analyze that evening. Length, width and depth of every few feet of stream over the 300 yards or more of the experimental reach needed to be recorded.

Some time was spent just sitting on the stream bank and waiting between measurements, occasionally writing down numbers in the field book. Field research can be a curious mix of rapid, hard, physical work, then intense calculation and concentration, interspersed with waiting and observing.

Rio Maria and the jungle

Our research group had a central goal of finding out what would happen to the high elevation jungle streams after the tadpoles disappeared, so it was necessary to measure everything we could about the biology of the streams while the frogs and tadpoles were still there. Part of the process of scientific understanding is detailed observation, and we needed to be sharp and pick out the most important details to measure in this stream, to capture the true way the system worked. The baseline conditions of how the organisms influenced their environment, which organisms were there, and how they interacted all needed to be measured. We had limited time on this trip and had to make the best use of that time. This is the scientific way to talk about the environment we were about to enter, but there is more to biology than just measuring things.

It was hot in the sun out with the trucks as we fussed around with our gear. We got all the stuff we needed for our first set of measurements and started loaded up for our first trip into the jungle. The edges of the road were overgrown with a tangle of grass and bushes, as is always the case in the tropics; a road cut lets in valuable light and the plants fight for a toehold in this newly opened habitat. We needed to force our way through this on a tiny trail that had been hacked out by machete a few days before, and there were holes, fallen logs, and slippery muddy bits that needed to be negotiated with heavy loads of equipment. Our gum-boots did not making the footing easier, but they probably would protect from the fangs of a snake, and did keep our feet dry. Of course, we needed to also keep an eye out for sunning fer-de-lance, the extremely toxic snake that frequented the area.

As I entered the damp shade of the dense jungle near the stream, the temperature became more pleasant. This was another world. Rio Maria was a beautiful stream as it flowed through the jungle. A few shafts of sunlight found their way through the riot of tangled green to dance on the surface of the stream and dapple the rocks at the bottom of the clear waters.

Clear-winged butterflies flitted through the forest. These butterflies are fantastic as they have a rim of color around one or two almost completely clear wings. The oval-winged butterflies appear to fly slowly, but prior experience with a butterfly net convinced me that the clear wings make it difficult to see them and judge what direction they are going to fly. Or maybe I just suck at catching flying insects. Clear wings are probably a good predator defense, at least against inexperienced collectors.

Garish red flowers (hibiscus, passion flowers) dangled from overhanging vines or grew from the jungle floor. The vegetation is not extremely dense at the forest floor because so little light reaches it. Mosses covered most surfaces, including the tree trunks, fallen logs, older leaves, and the edges of the rocks near the streams. Tropical rainforest is part of what lured me back to Central America, and reality exceeded memory.
There were frog calls from hundreds of feet above in the tree canopy, down in the low vegetation, near the stream, and from the hillsides that surrounded us. The sound of chirping frogs constantly came from all directions. The calls blended with the insect sounds (cicadas and others) and bird calls.

Our first task was to decide which section of the stream would serve as the research site, so we set off through the jungle upstream to have a look. With each step in the forest, small brown frogs jumped out from under our feet. We had to be careful not to step on them. At the stream crossing (chosen with care so as to not disturb the bottom of the stream for our experiment) the pool had hundreds of small tadpoles swarming along the bottom.

I have spent quite a bit of time studying aquatic systems and the only time I have ever seen so many frogs and tadpoles at these densities was in the quaking bogs surrounding small lakes high in the Oregon Cascades in the 1980’s. These bogs form at the upstream end of lakes and have floating vegetation mats and deep water holes that the unwary will fall into. The conditions, once the snow melts, are perfect for breeding frogs, and they are everywhere there. My mind drifted back to Oregon, and then snapped into focus on the jungle frogs at hand.

Water in the stream gurgled between the rocks, rocks rounded by the many floods over the centuries rolling them along the stream channel and grinding them to smoothness. First they were eroded by the weather until were free from the volcanic hillsides above, then they fell and washed down the outer slopes of the crater, and eventually they would be ground by the energy of the water scraping them against other rocks to end up as grains of sand on the ocean beaches tens of miles away.

Occasionally parrots would make a racket in the distance, a toucan would fly high overhead, or a blue butterfly with a wingspread wider than my head (Morpho) would glide past. I found myself looking for monkeys and sloths, but found none.