Nearly everyone has heard of the “tropical rainforest” before, it practically rolls off the tongue every time somebody says “tropical” and “forest” together. There is, however, another type of tropical forest–the tropical dry forest–that is in far more trouble than the wetter kind.
Now before you get the wrong idea, let me be clear that it does rain quite a bit in the tropical dry forest, although these forests also have a dry season that can stretch anywhere between four and eight months. Right now in Panama, we are at nearly the height of the dry season, so the tropical dry forest that I visited at Parque Nacional Chagres was certainly very wet!
I went with another student who is conducting research with the Smithsonian Tropical Research Institute (STRI), although he is devoting his time to studying caterpillars and moths instead of spiders. I was told that the park had quite a few of the acacia plants where my Bagheera or Freya spiders might live, so we took a bus to the town of Chilibre, hailed a taxi to the entrance to the park, and hiked our way in. As I said before, this is now the height of the rainy season, so there were puddles everywhere!
The graduate student I was traveling with, who is studying at McGill University in Montreal, is studying a fascinating relationship that a particular species of butterfly has with a particular type of cycad, which is a very ancient sort of plant.
In this system my companion is studying, the cycads produce a chemical that damages DNA and therefore causes mutations (changes to DNA sequence), which in most cases can lead to cancer. In higher doses, it can even kill the animals that feed on it, and cows that have accidentally eaten this cycad will die within a day.
The particular caterpillar this graduate student is studying, however, along with the plant itself, maintain this highly toxic chemical in a state where it is attached to a sugar that keeps it from doing any harm. But once another animal eats the plant or the caterpillar (which stores up this chemical), then the sugar is broken off at the chemical does its damage. As a result, these caterpillars have extremely bright warning coloration (called aposematism) in order to signal other animals (birds, especially) that they shouldn’t be touched.
It appears to be an effective survival strategy for the caterpillars, because few creatures seem to touch them. The same can’t be said for the eggs, for it appears that there is a wasp that can lay eggs that will hatch into larvae that eat the developing caterpillar. Parasites are common in the tropics!
That said, tropical forests really are far from peaceful places where creatures live in harmony; it is the backdrop of an intense competition for survival. Sunlight, nutrients, space–all of them are in constant shortage in such an explosion of life. Therefore any strategy that an organism can employ to outcompete its neighbors will win, while the others are quickly recycled back into the ecosystem.
And when I say “recycled,” I really do mean it in the truest sense of the word. Decay is everywhere in the tropical dry forest, especially during the rainy season, as all sorts of organisms jump at the chance to get more nutrients.
While Parque Nacional Chagres was an active place for fungi, arthropods, and a wide variety of plants, I am sorry to say that there were not very many (or any) large animals. No monkeys in the trees, no tapir wallowing around, and no jaguars or toucans or harpy eagles. The problem is that the area has been heavily hunted in recent years, and none of the big animals are left. Deeper in the forest, where it is harder to reach on foot, there are probably still wild creatures, but I’m only saying that out of hope. This happens all over in Panama, even in the national parks. My hope is that this trend will not continue, and that these forests may be given a chance to fill again with creatures great and small.