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.