The rainforest is a place of extravagance: beautiful, brightly colored and sometimes downright bizarre plants and animals of every conceivable form await those intrepid enough to travel to the tropics to seek them out. Here, the diversity of form is matched by a diversity in the way in which organisms survive, what biologists call their ecological ‘niche’. Many rainforest mammals, for example, live much the same way their temperate counterparts do—hunting for other animals in the dark of night, browsing for young leaves and shoots, or digging for roots and tubers. But in the tropics, where temperatures are higher and more constant, and where plants are orders of magnitude more diverse and abundant than in temperate regions, resources are available to support lifestyles that are impossible elsewhere.
In the photo above, a tiny pygmy marmoset, the world’s smallest monkey, clings nervously to the bark of a Parkia tree, taking turns between nervous vigilance and intense interest in a goopy sap that oozes from pockmarks scattered over the entire surface of the tree’s massive trunk. This sap, rich in sugars and nutrients, forms the basis of this tiny primate’s diet. What the marmoset does not receive from the Parkia’s sap it supplements with insects and whatever other small animals it can capture—weighing about a fifth of a pound, suitably-sized prey are few and far between.
Pygmy marmosets are not the only rainforest animals that feed on the nutrient rich gum produced by trees. Insects—butterflies, wasps, lantern bugs, cockroaches, ants, and beetles, to name a few—are attracted to the holes excavated by marmosets in the bark of trees such as the Parkia. For an insect, a visit to a marmoset’s gum hole is a risky affair, since sap flowing from a hole in the tree’s bark suggests a hungry marmoset is nearby. The nutrient- and energy-rich sap is clearly worth the risk, a fact attested to by the number and variety of insects visible at the holes.
The rainforest is also a place of extremes. In the western Amazon, pygmy marmosets feed from the same tree gum as the white witch (Thysania agrippina), a moth with the largest wingspan of any insect on earth. Measuring in at up to 13 inches across, the moth is as much as two times larger than the tiny marmoset!
Below, a lantern bug (Phrictus quinqueparitus) feeds on the sap of a Simarouba amara tree in the Costa Rican rainforest. The bug must often share its tree with the bizarre peanut-headed Fulgora laternaria, another lantern bug.
For those hoping to view wildlife, a visit to a tropical rainforest can be quite a frustrating experience. Unlike on the plains of Africa, rainforest animals can very easily conceal themselves among the dense vegetation, under a forest canopy that permits very little light to pass through. To make matters worse, many species avoid detection by resemblance to non-animal objects in their environment. Here, insects are the ultimate masters of disguise: stick insects and leaf-mimicking katydids imitate twigs and leaves—some even come complete with tiny spots meant to mimic diseased or chewed leaf bits. Still other insects sport patterns that allow them to blend in seamlessly on lichen-covered tropical tree trunks, some even with tiny frills and flourishes that bear an uncanny resemblance to mosses, fungi, and tree bark. By remaining unseen, small insects survive in a world teeming with hungry predators. Only one who is attuned to the jungle environment and the cryptic habits of its invertebrate denizens will appreciate the true, albeit hidden abundance of rainforest insects.
However, not all insects in the rainforest survive by hiding. Many biting and stinging insects—bees and wasps, mostly—invest little in camouflage, instead inviting hunters to attack with flashy colors and conspicuous behaviors. Those that do so are surprised by an unexpected counterattack and quickly learn that there are probably easier meals to be had. Importantly, predators are capable of remembering an unpleasant attempt to make a meal of an angry wasp, or an excited hive of stinging bees. So the rainforest, then, is full of predators, but those that have learned to avoid stinging insects—most predators probably learn this very early on—avoid insects that pack painful bites and stings. Given the extraordinary abundance of bees and wasps in the rainforest, this strategy appears to serve them well.
Below is a an example of just such a stinging insect: a wasp, right? Wrong. This is a picture of a katydid, a harmless relative of the crickets and grasshoppers. Biologists call such an animal a mimic: the katydid has escaped predation through protective resemblance—mimicry—of the much more noxious, stinging wasp, its model. In this case, the wasp must invest not only in a costly stinger and venom, but also in educating predators of its painful sting. The katydid knows nothing of these investments.
Amazingly, this katydid takes its trade one big step further than mere resemblance. Not only has this species foregone the typical, protective green coloration of most katydids, it has abandoned nearly every characteristic that makes it identifiable as a katydid at all. Instead of using its powerful hind legs for jumping the way katydids, crickets and grasshoppers tend to do, this individual gets where it needs to go by flying—in precisely the manner the wasp does. When it flies, the long hind legs trail behind, making the katydid nearly indistinguishable from its wasp model in flight. Even the antennae contribute to the deception, gesticulating back and forth, side to side, in a decidedly unkatydid-like, but wholly wasp-like manner. The katydid’s mimicry is exact to the finest detail.
Mimicry—the convergence, in this case, of not only the appearance but also the behavior of creatures as distantly related as a wasp and a katydid—is a potent testament to the transformative power of natural selection. And the wasp-mimicking katydid is but one example. The rainforest is overflowing with such wonder, if only we have the patience, and the eye, to look for it.
Deep within Peru’s Bahuaja-Sonene National Park, two rivers—one crystal-clear and strewn with rapids, the other swirling and muddy—converge to drain the pulsing heart of one of the world’s richest rainforests, a place known as the Candamo Valley. The indigenous Ese Ejja Indians call the region the ‘Last Forest Without Man’—a reference to the area’s extreme remoteness and the fact that no people, not even the Indians themselves, have ever settled here.
Candamo is one of the few remaining large, pristine rainforests left on the planet—tropical forests nearly everywhere else have been destroyed or degraded as tropical countries have scrambled over the past few decades to convert their natural resources into quick wealth. Pristine areas like Candamo factor heavily in an ambitious plan by tropical conservationists to bring humanity into the age of globalization while losing as little of our biological heritage as possible; only large, undisturbed areas can harbor the high numbers of species that will allow this to happen as surrounding forests disappear.
I’m here to survey butterflies—while detailed information are still lacking, some evidence suggests that as many as several hundred butterfly species might be declining throughout the tropical Andes and western Amazonian ecosystems. The reason? A rapidly growing human population, agricultural expansion, and increasing global demand for oil, timber, gold, and other natural resources have all devastated the rainforest habitats that butterflies depend on for survival. In Candamo, butterflies have a safe haven.
And while biologists currently know almost nothing of Candamo’s rich plant and animal communities, news from other, better-studied protected areas in the region are promising. Peruvian researchers working in the nearby Tambopata Reserve, for instance, have found more than 1,300 butterfly species alone, in only a few months of sampling at a handful of locations. So far, the protected areas are working.
Butterflies, of course, aren’t the only beneficiaries of these conservation areas. As I patrol a floodplain forest in the Candamo Valley with my butterfly net, the telltale signs of another rainforest inhabitant call my attention—the sound of crackling twigs and leaves and crashing as dislodged dead branches tumble onto the forest floor belie the presence of primates. Judging by the noise they’re making, I guess they are spider monkeys, among the largest arboreal mammals in this part of the world. As they approach even closer, I see that I am right.
Before I realize what’s happening, a huge dead branch comes crashing towards me, and explodes above my head and all around me in a hail of decaying shrapnel, complete with a swarm of angry, biting ants. Five seconds later, as I furiously pluck the ants away, another one. And another. I quickly realize I’m under attack.
As I look up, I notice around 10 monkeys staring down at me. One is shaking violently on the branch he’s on, staring me dead in the eyes. Another announces to the rest of the group with a special vocalization, “Get over here, you gotta see this!” These monkeys have never seen a human being.
In one of those magical moments I thought only happened to National Geographic explorers or, more likely, adventurers from a time long passed, we exchange incredulous looks—me, astonished at the unusual curiosity displayed by the primates above my head, and they, not knowing what to make of the bizarrely-clad, clumsy ground monkey. These animals have no fear of humans, which can only mean they have never seen any; elsewhere, monkeys flee intruders that would put them on their dinner plates.
After only a few short days I leave Candamo armed with a few new records for butterflies, but also with something greater. My experience here reminds me that there is still hope for conserving the greatest natural gift with which we humans have been endowed. In places like Candamo, monkeys live without fear of us, and we have a place where the raw, wild spirit of nature lives on. Indeed, we are greatly enriched by this place.
By Geoff Gallice
Bright colors in nature generally indicate danger. A brightly colored animal, for instance, typically uses its flashy hues to warn potential predators of a threat it might pose. Usually that threat is chemical: animals, ranging from insects and other invertebrates to frogs and snakes, have evolved a bewildering array of toxic poisons, venoms, and other chemical surprises that await would-be enemies. Bright colors help predators remember unpleasant experiences—they quickly learn to avoid the colorful meal that made them sick or stung them.
The passion-vine butterflies are a group of brightly colored or aposematic butterflies found throughout the rainforests of Central and South America. The most diverse genus is Heliconius and, as its common name suggests, this group of butterflies feeds on passion vines that are loaded with compounds known as cyanogenic glycosides—you don’t need to be a biochemist to guess that the cyan at the beginning of that name means it isn’t good to eat.
The glycosides are not harmful to Heliconiusbutterflies though. In fact, the butterfly larvae greedily devour vines that are high in these compounds. From them they are able to synthesize derivatives—similar chemical forms—that can be stored in the butterfly’s tissues.
Thanks to its diet of passion vines, a Heliconius butterfly is a mouthful of toxic, foul-tasting poison to a predator, which, in the day at least, is usually a bird. And since Heliconius are brightly colored, birds quickly learn to avoid them. Thus, the butterflies are chemically defended and, once the local birds have been educated, have essentially no diurnal enemies.
But what happens at night, when visual signals are less effective as a warning to nocturnal predators that hunt without good eyesight? Bats, for instance, hunt at night using echolocation or sonar, in which high-frequency sounds are produced and distance and direction to prey are judged largely by the time taken for the sounds to bounce, or echo, back to the bat’s ears. With echolocation, eyesight is unnecessary, and bats that echolocate are able to hunt very effectively even in total darkness. Many have monochromatic or otherwise very poor vision.
One peculiar aspect of Heliconius butterfly biology is their roosting behavior—that is, at night, they sleep collectively in aggregations. Roosts may contain as many as 10-15 individuals, although typically the number is less. The butterflies begin to gather at sunset and take as much as one hour to settle in for the night; they use tiny hooks at the ends of their feet to hang, upside down, from nearby small branches and the tips of dead twigs.
Many biologists believe that animals aggregate in order to dilute the effects of predation. Think of the chances of a buffalo being picked off by a lion alone versus in a large herd. The same should be true for aposematic butterflies in the daytime—considering that their bright colors most likely serve as a warning to birds, daytime Heliconius roosts would make a lot of sense. But the butterflies roost together at night, and it’s not clear why.
As a graduate student interested in tropical butterfly biology at the University of Florida, Christian Salcedo wanted to understand why Heliconius roost at night. Do the butterflies have any predators? Could they be using unseen signals to fend off attack, much in the way they use color in the day?
Salcedo decided to employ technology to study the question of Heliconius roosting at night. He created a camera system—he called it a “stand-alone nocturnal infrared camera system”—that would catch Heliconius predators in the act by activating video when an infrared beam was crossed.
After a number of nights the remote cameras had recorded several disturbance events, during which an animal—there was an agouti, an armadillo, a rabbit, and even a few stick insects—disturbed the butterflies, causing one or more of them to rouse momentarily from their sleep. In a jungle bumping with nocturnal creatures, this wasn’t very surprising. However, the most interesting event occurred when a bat was observed picking a Heliconius butterfly from its roost. Several moments later, the butterfly returned, apparently unharmed, to its roost-mates. Of course, Salcedo captured the event on video.
Watch videos of Heliconius roost disturbances here:
In some ways, these experiments shed light on the mysterious Heliconius night roosts. Based on the footage gathered with the remote camera system, we now know that Heliconius probably do have nocturnal predators. But the fact that the cameras recorded a butterfly returning to the roost after an attack, unharmed, actually raises many more questions.
Did the cameras capture an instance of predator education? That is, the bat clearly tried but did not eat the butterfly—in the video, do we witness the learning event that results in other Heliconius avoiding attack by at least this individual bat? If so, how can the bat recognize future roosting Heliconius and know to stay away?
Some bats are able to see ultraviolet light, which is reflected by parts of the wings of Heliconius. Could that be the key mechanism? Or perhaps predators like bats are able to smell pheromones or other chemical signals produced by the butterflies that act in a similar way as bright colors in the daytime, preventing a repeat bad-taste experience. Do bats typically capture prey and assess their palatability before deciding to devour them or let them go unharmed?
Video footage of a nocturnal attack is tantalizing, but we still have a lot to learn about the roosting behavior of Heliconius butterflies. The rarity of nocturnal attacks on the butterflies—Salcedo’s experimental roosts were attacked only several times in hundreds of hours of filming—make the matter of studying them more difficult. But, as is increasingly the case, technology coupled with a curious, motivated young graduate student willing to brave long, late hours and harsh tropical conditions can make great discoveries regarding the fascinating phenomenon of the roosting passion-vine butterflies.
As you might intuitively guess, animals that are brightly colored are probably best avoided in the rainforest. One example that comes to mind are the showy dendrobatid frogs of the New World tropics. Known commonly as the ‘poison dart frogs,’ these amphibians are toxic and advertise that fact with flamboyant colors of bright reds, yellows, greens, and even striking blues. These colors warn would-be predators that ‘I taste bad at best, and at worst, I will kill you!’
Indeed, in nature many animals that are conspicuous in their coloration or behavior do not make a good meal. Most often, such animals are protected by toxins or poisons that they either manufacture de novo or acquire from their food. The famous dart frogs of American rainforests advertise their deadly batrachotoxins with gaudy and obvious colors, toxins which they acquire from the invertebrates—mostly ants and small beetles—that they eat.
Other animals, like an almost endless variety of colorful rainforest butterflies, feed on plants as caterpillars or flowers as adults that provide them with a wide range of noxious chemical compounds that they are able to store. These insects advertise their distastefulness with flashy colors, bold wing patterns, and slow, daring flight. Should a predator attack, it will quickly learn to avoid similar colors and patterns in the future; with these creatures, relatively few individuals bear the cost of educating predators of the toxicity of their species.
Butterflies, nearly without exception, fly during the day when they can use their flashy colors to warn their visually-oriented predators—birds, mostly—of their distastefulness. Moths, on the other hand, generally fly by night, when bright colors serve as a poor warning signal to nocturnal predators that generally hunt without the aid of good vision. In the rainforests of Madre de Dios, however, one group of moths stands as a striking exception to this rule. Here, a large number of species of clearwing moths have evolved a remarkable variety of garish colors, wing patterns, and strange forms; they fly boldly by day, practically daring prospective predators to attack them.
These clearwings belong to a subfamily of moths that entomologists have named the ‘Arctiinae.’ The name comes from the Greek αρκτος, which means ‘a bear’—this refers to the North American common name for their caterpillars: the wooly bears. Some species of wooly bear caterpillars feed on plants that provide them with toxic compounds that they can store in various parts of their bodies as larvae. As a result, the caterpillars are protected from attack by predators that have learned the hard way to avoid them. Other arctiine species acquire their chemicals as adults, often storing them in the integument—the entomological word for the insects’ skin or, more accurately, their exoskeleton.
The clearwing arctiine moths are a brilliant example of one an almost endless variety of incredible ways that rainforest animals protect themselves from the legions of predators that constantly patrol the forest floor, interior, and canopy looking for a meal. Whereas many animals—including most other moths—have opted to hide during the day, coming out cautiously only under the cover of darkness, these colorful moths fly by day, warning would-be attackers: “Eat me if you dare!
This is a species of poison-dart frog from Tambopata, Allobates femoralis.
While not very large or particularly showy–or very poisonous, for that matter–these frogs are very interesting in that they show extreme variation throughout their range. Researchers have discovered that distinct populations that are separated by geologic barriers, such as large Amazonian rivers, have different calling patterns; some populations have a two-note call, whereas other populations have a three- or four-note call. These might seem like unimportant differences, but they may be all that are required to isolate populations and lead to speciation. For instance, if females in one region prefer males that have a four-note call, they might not breed with males that have, say, a two-note call, and over time this can cause a new species to arise from that population. Add in large rivers that form barriers to populations mixing, and you’ve got the potential for a huge amount of genetic diversity and confusion for biologists trying to understand the distribution of frog diversity here. Just another way in which the Amazon continues to reveal its biodiversity to those who pay close attention to it!
Another species of primate from Tambopata, this is the black-capped squirrel monkey (Saimiri boliviensis). Not counting the tiny tamarins, these are the smallest monkeys found in the rainforests of southeastern Peru and, as their common name suggests, are about the size of a squirrel. Squirrel monkeys forage in very large groups of up to one hundred animals or more, searching mostly for fruits and insects, although they will take small vertebrates like tree frogs or baby birds. Interestingly, here in Tambopata they can almost always be found foraging alongside the much larger brown capuchins (Cebus apella). Biologists have been trying to figure this out for decades: brown capuchins can be very aggressive, and animals the size of squirrel monkeys even make up an occasional part of their diet. So the question is this, Why do squirrel monkeys travel with the capuchins? Put another way, why do the capuchins tolerate the squirrel monkeys?
A recent study by Taal Levi et al. (2013) in northeastern South America showed that squirrel monkeys tended to be more abundant where brown capuchins were present, lending support to the long-standing hypothesis that the two species facilitate each others’ foraging. That is, more eyes on the forest might make it easier to find patchily distributed foods, such as fruiting trees or large caches of insects. Alternatively, larger groups might provide better protection from predators, as both species are food for a variety of species ranging from cats to snakes to even birds of prey. Teasing apart the importance of the various benefits associated with mixed-species groups has been difficult, and we still have much to learn.
A curl-crested aracari (Pteroglossus beauharnaesii) from the Tambopata Research Center. Why do the aracaris and the rest of the toucans have such big bills? At first glance, it might seem to be the result of sexual selection, the same force that drives many other tropical birds to exuberant coloration and ornamentation. However, in toucans, both males and females are essentially identical–they’re not sexually dimorphic–ruling out this possibility. A recent study in the journal Science suggested that the toucan’s bill performs quite an unexpected function–it acts as a radiator! By controlling blood flow to the bill, the toucan can control its body temperature, much in the same way an elephant uses its big ears to cool off. When the toucan warms up, say, after a long flight that increases metabolic heat by a factor of 10, it can send blood to the bill to dump that excess heat as the bill cools. The bill can also store heat, which explains why toucans sleep with their bills tucked under their feathers. The coolest thing about these findings might be how they were made. The researchers used thermal imaging cameras to measure blood flow to the bill, and changes in temperature, in a variety of rooms adjusted to different temperatures. Now, the biggest question that remains is whether the bill evolved first to regulate heat, or if it evolved for another reason, and the radiator function was a secondary benefit. That question will be much more difficult to answer.
Two more aracaris, part of a flock of 8 observed foraging through the Tambopata rainforest canopy. The bills of the two individuals shown here are different; however, it’s difficult to know if these differences are due to normal variation between individuals or some other factor, such as differences between adult and juvenile coloration. Whatever the case, male and female bills do not differ significantly among toucans, and there is no way to separate males from females apart from examining the sexual organs via endoscope; this provides strong evidence that the toucans’ large and colorful bills evolved that way for reasons unrelated to sex or sexual selection.