|An excerpt from
A Naturalist's Guide to the Tropics
Try to name ten wild animals, just off the top of your head, and you'll see that most of them are from the Tropics. When you try to imagine the vast African savannas, the dense Asian jungles, or the endless rainforests of the Amazon, doesn't your mind go naturally to the large and charismatic animals we know live in those wildernesses? The exciting flagship species living there have always stimulated the fantasies, not just of those who live far from the Tropics, but of the local populations as well.
During the age of modern exploration a few centuries ago, when some of these unusual animals first arrived at the ports of Europe after having traveled across the world, sometimes for months and months aboard sailing ships, they caused quite a commotion, inspiring thoughts about mysterious and faraway countries, the homelands of those and other formidable beings. That was the same time that the first zoos were organized in Europe, in Vienna and Madrid, during the second half of the eighteenth century, probably to satisfy some of that burning curiosity.
One could thinkand, certainly, a part of this would be truethat the fauna of the Tropics impressed, and continues to impress, the inhabitants of the Northern Hemisphere of the planet because they are curiously unfamiliar. But there's more; and even a preliminary glance at the variety within tropical zoology says a lot about the enticing universe of exotic species, the diversity of their adaptations, and the extravagance of their shapes and specialized behavior, all of which contribute to the extraordinary originality and spectacular character of tropical fauna.
An Extraordinary Wealth
As we've already seen regarding tropical vegetationor perhaps even more sothe fauna of the Tropics exhibits an astounding level of diversity and specialization.
Henry Bates, the English naturalist, first began visiting Amazonia in 1848; and over a period of eleven years of study, he was able to classify some 14,000 different animal species, of which 7,000 were yet unknown. Invertebrates make up by far the largest percentage of species that are yet unknown to science. It is estimated that from 6 to 30 million arthropods live in the tropical forests, and the great majority of these are yet unknown to science. This estimate represents over 96% of the total number of arthropods hypothesized to live on the planet. About one-third of the world's birds live in tropical forests, and many others use these habitats during migration or as wintering grounds. Some of the most reliable and generally accepted estimates recognize that the tropical latitudes may host up to 80% of all living animal species in the world.
Three Principles regarding Tropical Wildlife. The extraordinary wealth and variety of living forms lead us to consider the three primary characteristics of tropical zoology:
Great Diversity and Unexpected Look-Alikes
One of the biological factors markedly influencing the distribution of every individual species of living being on the planet, or even within a given habitat, is interspecific competition, or competition with other species for food and space. The success of a given species in terms of its expansion, resistance, or colonization within an environment depends upon how well it succeeds in overcoming or avoiding competition with other species that are present or attempting to colonize. For many animals, competition is a concern, not only for food, but also for territory, reproduction sites, and areas for refuge or repose.
Competition is best avoided by specializing. There are species that hunt during the day and others that hunt at night, for example, or those that hunt different prey, some larger, some smaller. Sometimes, when such "adjustments" have not been made, competition between species has caused widespread extinction. This was the case when monkeys appeared and came to colonize the African continent, clashing with the more primitive lemurs there. The latter have survived in Madagascar alone, and this is because the monkeys have never been able to cross the Mozambique Channel.
A high degree of competition, combined with a high availability and diversity of resources, stimulates species to differentiate their diets and habits, with the result that, from a few common progenitors, numerous distinct species originate over time, in a process referred to as adaptive radiation. When opportunities for specialization and differentiation are increased as a consequence of a complex environmental structure and favorable ecological conditions, as is the case in many tropical habitats, we are witness to a veritable explosion of different living species, each with its own exclusive forms and habits.
One further fascinating aspect regarding tropical zoology, again, is linked to the climatic stability and homogeneity of many tropical areas, even though they may be separated from one another geographically. This is the phenomenon known as evolutionary convergence, which occurs when two species that are isolated from one another evolve, by chance, to the point that they assume appearances, ecological roles, or behavior patterns that are extremely similar. This depends, logically, on their living in analogous habitats, having become adjusted to the same environmental characteristics, and having adopted the same strategies. The chance nature of the phenomenon is clearly demonstrated by the fact that, quite often, instances of evolutionary convergence involve species that have no relation to one another and no common ancestors. Cases of this type of convergence are very numerous in the Tropics. For some of the most striking examples, let us recall the South American toucans and the Afro-Asian hornbills, with their great, curved beaks, powerful yet light, used to feed on fruits and seeds. Or else, the similarity of the body structure and habits among ungulates in the African forest and Amazonian rodents, both of which are adapted to moving or running among the dense vegetation of the glades or the underbrush of primary jungles. And again, the myrmecophagous, or ant-eating, animals of the five continents: the Amazonian anteaters, the pangolins of the Asian forests and African savannas, the African aardvarks, and the Australian echidnas. All of these have forward-leaning carriage, prominent snouts, and extremely long, sticky tongues.
Also surprising are the instances of evolutionary convergence between the marsupials of Australia and placental mammals of the other continents. Having colonized Australia at a time when there were no competitors, the progenitor marsupial species differentiated profusely, so as to occupy the available space and numerous ecological niches. Examples of this are seen in the convergence between marsupial rats and the homologous rodents, the false marsupial "flying squirrels" and the true variety, the now extinct marsupial wolf and the canids, or the cuscus and the Neotropical sloth, and there are many other examples. Because of this, there are species belonging to widely different faunal categories all over the world that have remarkably similar counterparts in Australia, all belonging to the same order of marsupials!
American crocodile, Crocodylus acutus (Costa Rica).
Family of lemurs, Lemur rufus (Madagascar).
Multicolored grasshopper, Phymateus saxosus (Madagascar).
South American bats have evolved from their common insectivorous progenitors into various species, resorting to multiple strategies and specialized behavior adaptations in order to take best advantage of the available resources and avoid alimentary competition among themselves.
Thousand Strategies for Survival
The complexity of tropical ecology and its elevated biological diversity have pushed the process of adaptation to the extreme, giving origin to living beings with bizarre or even astonishing appearances. A couple of examples of these are seen in the four-eyed fishes of South America (Anableys spp.), with their two pupils and divided retinas, for seeing above and below the surface at the same time, and the electric eel (Electrophorus electricus), from the Amazon, which hunts by discharging powerful electric jolts in the water. The strength of these electrical jolts depends upon the length of the fish, because the negative and positive poles of the "battery" are located on the head and the tail, respectivelyfish 90 cm (35 in) long can emit discharges of about 350 volts. The same fish uses somewhat weaker discharges for orienting itself, for echolocating enemies, prey, or obstacles, or for communication (!) among its kind. Brightly colorful Central American poison dart frogs (genus Dendrobates) are more or less poisonous in accordance with the degree to which their "warning" colors are accentuated.
Then there is the universe of insects: there are carpenter wasps, which are capable of forcing entry into certain closed flowers; leaf-cutting ants, or weaver ants, which construct great nests by gluing and sewing plant cuttings to size; caterpillars that resemble the excrements of small birds; and butterflies, such as the plume moths of the Alucitidae family, which appear just like the small feathers lost by birds; or leaf butterflies, which are perfectly similar to green or dry leaves; or butterflies whose flight resembles the falling of leaves from the canopy layer. There are stick insects that are covered with protrusions exactly like the moss on which they live; treehoppers that pass the hours of the day fixed to branches or trunks, and which look like the thorns on a plant due to the odd form of their dorsal protuberances; "orchid" praying mantises of Borneo, whose lateral appendages are shaped and colored like the petals of their very beautiful epiphytic namesakes; and others, like the Amazonian Choeradodis, whose forms perfectly mimic the leaves of certain small climbersand this is just a brief selection of a few of the more striking examples.
Diversification among Neotropical Bats. A wonderful example of the accentuated diversification of forms and behavior within the fauna of the Tropics can even be found within a single animal group: the order of Chiroptera. It is true that the Tropics are an important center of differentiation for bats, and in South America, this reaches its maximum level. Although there are none of the megachiropterans (such as flying foxes or fruit bats) that are so abundant in Africa, Asia, and Oceania, we do find incredible examples of specialization among the microchiropterans.
As far as regards their alimentary strategies, it is believed that the ancestor of the current bats, that first mammal that succeeded in colonizing air space with its own active flight, was insectivorous, as are many currently living species, which feed upon flying insects using their exceptional "radar system" for echolocation. From one common progenitor, different species have evolved, exhibiting quite different instances of adaptation. Considering diversification in the diet alone of the bats of the American Tropics, we find those of the genus Noctilio, which emit sounds, not for echolocating insects within the air, but for finding fish and amphibians on the surface of the water. They have developed long claws and sharp teeth that are neatly adapted for capturing their prey. Vampire bats (Desmodus) are notoriously hematophagous. They detect their prey using eyesight and sense of smell, and often they approach by moving along the ground until they reach the preferred areas of the body (the hooves, ears, or muzzle), where they inflict wounds measuring about 5 by 10 mm (3/16 by 3/8 in), using their extremely sharp incisors. Utilizing an anticoagulant liquid, they extract about 15 to 25 ml (½ to 1 oz) of blood. False vampiressome of these have large dimensions, such as the Vampyrum spectrum, whose wingspans can reach 75 cm (30 in)catch prey such as small birds and mammals by surprising them while they sleep, possibly using their sense of smell to detect them. The Glossophaga are specialized in a totally different field, the gathering of pollen, and they have developed long, retractile tongues. The Macrophyllum and the Ectophylla, by contrast, are expert frugivores, while the Phyllostomus demonstrate, by their incredible and monstrous facial, foliaceous protuberances, an alimentary spectrum that is quite broad, including fruits as well as insects and animal prey of larger dimensions. Just as surprising are the adaptations involving the sites chosen for refuge and repose during the day. Among the South American species alone, those that belong to the genera Artibeus and Uroderma have the habit of weaving palm leaves into a comfortable sack. Many species choose grottos, caverns, or cavities in tree trunks, such as the Desmodus vampires. Bats of the Lasiurus genus conceal themselves simply among the leaves, and Hipposideres choose from among the numerous cavities at the bases of large forest trees. Equally innovative is the tiny Asiatic bat, which specializes in passing the entire day in the trunks of great bamboo plants. Meanwhile, the fruit bat and flying fox (Pteropus, which do not exist in South America) are famous for clinging onto the highest branches of trees, in clear view, in such a manner as to appear like hanging fruit.
In accordance with ecological rules, such an abundance and diversity of species has, as a response, predators of a superior degree. In the case of bats, these predators are the raptors, or birds of prey. There are falcons (Machaerhampus alcinus) that become active around twilight, which are specialized in hunting bats at the moment they leave their diurnal shelters. The technique is rather simple, in theory: they drop suddenly upon their prey from behind, taking advantage of the one "blind spot" within the bats' extremely sensitive radar range. Bats are mammals capable of such lightning-quick swerves and veers that, unless they are unaware of their danger, they are virtually ungraspable.
Accentuated specialization often restricts species to particular ecological niches, microhabitats, or periods of activity. Spider monkeys (genus Ateles) of the Central and South American rainforests are agile climbers that move among broad expanses of the jungle in nuclear families. They inspect the trees in search of food, fruits, and leaves. If, however, we observe them for a bit of time, we will discover rather easily that they pass the larger part of their time and perform the majority of their patrolling in the lowest stratum of the forest canopy, especially on the small, peripheral branches. The motive for this is simple. Their alimentary adaptationtheir dietis composed principally of fruits and nuts that only grow on the young, lateral branches. This part of the forests represents, for the Ateles, a habitat within a habitat, a small preferred portion within the larger environment of the forest.
A dangerous place to live . . . Still more amazing is the true microhabitat of certain forest insects, which choose as a habitat the "pitcher" of a special carnivorous plant, the Nepenthes, living in Asia, Oceania, and Madagascar. This pitcher plant has a cylindrical flower covered with a flap that acts as a sort of half-closed cover. Sacchariferous substances attract the insect prey, and, once they have oriented themselves facing the inside, they slip down along the edges and remain trapped within the chamber, ending up snared within the dense digestive liquid at the base of the chalice. The Nepenthes flower, a death trap for most, is, however, also the favorite habitat for certain super-specialists, making this an eerie microcosm of life and death. Within the liquids where the prey are slowly decomposed live numerous insect larvae that are able to resist the digestive enzymes. Many draw nutrients directly from the substances resulting from the plant's digestion, while others prey upon the bacteria and protozoa that abound in these highly specialized chemical conditions. Other, larger larvae prey upon the smaller larvae. Near the opening of the pitcher plant's flower, certain thomasiid spiders wait patiently, and the predatory larva of the mycetophilid fly is capable of extending its tiny nets to capture the incoming insects before they fall into the deadly liquids. There are even certain parasitical wasps that enter into the flower to deposit their eggs on these larvae, upon which the newly hatched wasps will feed and nourish themselves. Two-thirds of the animals found in the Nepenthes live nowhere else. Others are also able to live apart from the plant, though they simply exhibit a predilection for this habitat, which, despite its being a deadly trap for some, provides food and shelter to a variety of others. A study in Sumatra and Singapore registered the presence of twenty-five different species of insects and three species of spiders living in just three species of Nepenthes. This is truly an exemplification of the difficult struggle for survival, waged through invention and adaptation, all enclosed within the restricted and hostile environment of the flower of a "fearsome" carnivorous plant.
Living on Decay. One ecological category that is well represented in the tropical latitudes, and distributed somewhat throughout all habitats, is that of the decomposers, meaning those organisms that feed by degrading organic matter. The great biomass of plants, in particular, offers food to an immense number of small organisms, from bacteria to insects, that are capable of decomposing, absorbing, and permitting the recycling of this precious source of nutrients. Among the insects, both ants and termites exhibit an enormous number of different species, passing their lives and building nests either on the ground or in trees, and with habits that are either predatory, herbivorous, or parasitic. One single, huge tree of the Leguminosae family, towering above the Amazonian forest, has been found to play host to forty-three different species of ants, nearly the same number existing in all of Great Britain.
Termites are even more closely bound to the decomposition of dead vegetation, and in particular, with ligneous structures. Thanks to their symbiosis with flagellate protozoa living in their intestines, they are able to digest and decompose lignin, something that few animals in the world can do. Besides performing the role of decomposing agents, these social insects, which group in colonies varying from a few hundred to millions of individuals, constitute an alimentary source for numerous species of myrmecophages on the different continents. The previously noted South American anteaters (Myrmecophagidae family) for example, have morphology and habits that are similar to the African aardvark (Orytteropus afer), to the pangolins of the African and Asian continents (Manidae family), and to the Australian echidnas (Tachyglossidae family). As a further consequence of their adaptation for hunting ants and termites, and in order to reduce competition, certain species of anteaters and pangolins live and feed on the ground, while others are tree dwellers. One pangolin can eat about seventy-five million ants and termites in one year, which is equivalent to about two hundred thousand a night! On the other hand, there is no lack of prey: a single nest of the African termite Atta cephalotes can occupy as much as 150 square meters (125 square yards) of surface area and house many millions of workers. Moreover, termites are an extremely nutritious source of food: 1 kg (2.2 lb) of termites is equivalent to 0.75 kg (1.7 lb) of fresh meat!
Many faunal groups are facilitated by advantageous climatic conditions. Amphibians, for example, are extremely widespread and diversified in the wet tropics, where, quite often, they do not even need to have direct contact with the water, except for when depositing their eggs and raising their tadpoles, because the elevated humidity of the atmosphere and of the microhabitats where they often live is sufficient for them. This is the case for the tree frogs (family Hylidae) or the poison dart frogs (family Dendrobatidae), of which there exist some striking species, such as the marsupial tree toad (genus Gastrotheca), which guards first its eggs and then its tadpoles within a dorsal pouch, until complete development. The Hyla faber is so named because of the metallic sound that it emits, which recalls the beating of a hammer upon an anvil. Within the ponds of water, the male constructs a bank of mud, often circular, within which he couples with the females, which then deposit their eggs. The tadpoles develop within this artificial bay, sheltered from the many predatory fish, until their metamorphosis into adults.
Homeland of the Great Fauna
Beyond these and an infinite number of other marvelous instances of specialization, the Tropics are characterized by great, legendary, and charismatic animals. The greater part of the largest felines in the world have mainly a tropical distribution, such as do the great reptiles, and, to a certain degree, all of the largest terrestrial species: elephants, rhinoceroses, hippopotamuses. Simians and prosimians are exclusively tropical, with the very few exceptions of some Asian macaques and langurs. The same exclusiveness applies to an innumerable list of species, families, and orders of birds, some among the most beautiful and striking on the entire planet: from the New Guinea birds of paradise to the toucans of Central and South America, from the African and Asian hornbills to the pantropical parrots, from the majority of the American hummingbirds to the African and Asian sunbirds (Nectariniidae).
With their privileged climate and luxuriant vegetationand above all, thanks to these animalsthe Tropics have consolidated the image of the exotic and the attractive. And this, more than anything else, evokes fascination and stimulates the imagination, whether of locals or visitors.
The abundance of ants and termites is a constant throughout the entire tropical region. This is why there are animals on the various continents that specialize in this form of nourishment (myrmecophagy). These animals exhibit a high degree of similarity, both in form and behavior.
Male impala enjoying acacia flowers (Zimbabwe).
The nations with "megadiversity"the planet's countries richest in animal and plant species, often including high percentages of endemic species (those that are typical of a restricted locality or region and found nowhere else).
|10||Papua New Guinea||200||67%|
|9||Papua New Guinea||305||30%|
Sources: P. R. Gil, 1997, Megadiversity and BirdLife International, 1998, Endemic Bird Areas of the World.
Copyright notice: Excerpted from pages 55-83 of A Naturalist's Guide to the Tropics by Marco Lambertini, translated by John Venerella and illustrated by Kitty Capua, published by the University of Chicago Press. ©2000 by the University of Chicago. All rights reserved. This text may be used and shared in accordance with the fair-use provisions of U.S. copyright law, and it may be archived and redistributed in electronic form, provided that this entire notice, including copyright information, is carried and provided that the University of Chicago Press is notified and no fee is charged for access. Archiving, redistribution, or republication of this text on other terms, in any medium, requires the consent of the University of Chicago Press.
A Naturalist's Guide to the Tropics
Translated by John Venerella and illustrated by Kitty Capua
Paper $25.00 ISBN: 0-226-46828-3
©2000, 336 pages, 11 color plates, 57 color photos, 21 maps, 76 line drawings
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