Fly Farther Afield



Now it’s time to take what you’ve learned about energy and the environment and apply it to the place you’ll be heading for your real trip in just a few weeks. You should know now that the first step to understanding the place will be to analyze the abiotic conditions.


So take a look at the climatogram to the right. What do you see? What’s in plenty of supply? Do you see a limiting factor?


Iquitos, Peru offers an environment that has plenty of light, heat, and plenty of water. Its location is 3 51 S 73 13 W; that’s just 3 degrees latitude below the equator, and directly south of the central United States. It’s inland, without the moderating effect of the ocean on temperature. (The Galapagos Islands, at about the same latitude but farther west, are much cooler.) For more on climate, follow the link.


From the climatogram, it’s easy to see that rainforest is warm year round. In Iquitos, Peru the temperature hovers around 28o C. The rainfall there, from 500 to 650 mm per month, is also characteristic of the biome. In a tropical rainforest, trees rarely lose their leaves all at the same time. (There are tropical deciduous trees, of course, but they generally lose their leaves at times of stress like dry periods, storms, or after floods.)


But by now you should realize that there’s no area on Earth where everything is in great supply. The dynamics among the organisms would insure that couldn’t happen. You also know that the organisms themselves modify the environment as they grow, compete and interact. In the rainforest, it’s the organisms—chiefly the plants—that create the challenges, blocking out light as they grow.


So it should be clear that the most important factor that determines survival and fitness in the rainforest is the ability to compete for light. In this rich, rapidly-changing environment expect creativity, biodiversity and amazing variation.


Competition in the Rainforest

For the rich plant life in the rainforest, competition for light and space is constantly in overdrive. With lots of energy to grab, organisms grow quickly, biological innovation is the rule. Here’s a chart that compares the light that penetrates the canopy of a tropical rainforest to one in a temperate area that also receives high levels of precipitation all year round.


Comparison of light in various strata of forests (measured in moles*):

Trophic Layer

Tropical Rainforest

Temperate Rainforest


47 mol/m2/day of light

702 mmol/m2/sec

Primarily reds



15% of the canopy light

No data

Shrub layer

3% of canopy light

No data


1% of canopy light

7% of canopy light

*1 mole of light = 6.02 × 1023 photons, Avogadro's number


It’s clear that light is the prize, and that the competition is stiff. Some have unique metabolic adaptations; rainforest plants have diverse chemical pathways that sometimes poison neighbors or put them at a disadvantage. Some plants use cooperation and partnerships. In the photo above, a “ball moss” (T. recurvata) uses the trunk of a tree to gain access to a little more light.


When you took a virtual visit to other biomes, you could often predict the species you’d see with relative ease. In an old growth forest in the Midwest U.S., oaks and maples will predominate; in Canada, it’s likely to have fir and spruce. But in the rainforest there is far greater biodiversity. Rainforests contain approximately 50 percent of the species on the planet--from 5 to 50 million species—although biologists admit they’ve only categorized a small fraction of them. In a single hectare (2.5 acres) of rainforest in Peru, biologists have categorized ~300 species of trees. Some (like the Clusia here) have seeds that actually glue themselves to other trees like this mangrove and begin life as an epiphyte. (This is the tree from which gutta-percha is derived.) 


When a road or a power line route is cut through a forest, the “rules of the competition” change. Plants that could never exist in the center of the ecosystem begin to creep in. Since today’s forests are only small fragments of what they were ten thousand years ago, development is often a case of “divide and conquer.” The challenge of preserving rainforests is much greater than just preserving individual plants or species; the whole is much greater than its parts.