Rainforest along the bank of the Tambopata river in Peru. (Photo by R. Butler)
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SOLAR ENERGY/CLIMATE
The hot and humid climate plays an important role in rainforest
variety. As a general rule, diversity and ecosystem productivity increase with the amount of solar energy available to the
system. Sunlight is captured in the leaves of canopy plants via photosynthesis,
converted into simple sugars, and transferred throughout the forest
energy system as the leaves and fruit are eaten or decomposed by various
organisms. The primary measure of ecosystem net primary production is
the fixation of carbon by plants. Tropical rainforests have the highest
mean net primary production of any terrestrial ecosystem, meaning an
acre of rainforest stores more carbon than an acre of any other vegetation
type. The humid climate adds another ingredient essential to rich diversity:
water.
STABILITY
The stable tropical rainforest environment promotes diversity by allowing
plants and animals to interact all year round without needing to develop
protection against cold or frost. In addition, because the sun shines
all year long providing plants with the energy to manufacture food via
photosynthesis there is no seasonal food shortage in the ecosystem.
The abundant food source for plants (sunlight) is passed up through
the system to herbivores, which consume the plant leaves, seeds, and
fruits, to carnivores which consume the herbivores. Over the course
of millions of years, with abundant food, rainforest species have adapted
to take full advantages of all the available niches.
Millions of years of battle between predator and prey have resulted
in an extensive array of defenses, weapons, and specializations. Camouflage,
mimicry, specialized breeding and feeding habits, symbiotic relationships
with other species, and other complex adaptations have allowed species
to out-compete rivals by making use of resources not available to generalists.
Virtually no niche in the rainforest is unfilled and many different
species can coexist in a relatively small area, without encroaching
on their neighbors. The evolutionary process continues and species are
pushed into narrower and narrower niches until they are unbelievably
specialized to their particular way of life.
This evolutionary process
ensures that no one well-adapted species (i.e. beetle) dominates the
whole population of beetles because that one species cannot be possibly
adapted to all the niches available in the forest. As a generalist,
the species would be quickly out-competed by more specialized species.
Generalists appear to thrive most under disturbed conditions, such as
areas cleared for agriculture. Here these "weedy" species
may be quite common. Furthermore, any species abundant in natural forest
faces the threat that a predator would adapt to exploit its abundance.
For example, the failure of rubber tree (Hevea brasiliensis)
plantations in the Amazon is due to leaf blight. In the ordinary rainforest,
rubber trees are widely dispersed so blight can never wipe out more
than one individual tree at a time.
Tropical rainforests are markedly different from temperate forests.
In temperate regions many plant and animal species have wide distributions,
and a forest may consist of a half dozen or so tree
species. In contrast, tropical species have evolved to fit narrow niches
in a relatively constant environment, producing grandiose diversity.
For example, more than 480 tree species have been identified in a single
hectare of tropical rainforest.
Visitors to the rainforest are often disillusioned by what they see
because they confuse the word "diversity" with "abundance."
They visit the rainforest expecting to see ten jaguars, dozens of iguanas
lying on the lodge patio, and large toucans waiting for them
with breakfast. You will not encounter giant herds of wildebeest or
zebra as on the African savanna. Nor will you find an eruption of flowers
or even an abundance of colorful birds. Life in the rainforest is strikingly
subtle.
Rainforests are diverse, in terms of numbers of species, but any one
given species is not necessarily plentiful. Some rainforest
species have populations that number in the millions, whereas others
may consist of a handful of individuals. The biology of tropical rainforests
is a biology of rare species. The reason for this occurrence is that
the majority of rainforest species are scarce over the range of the
forest and may be common in only a few small areas where they are particularly
well adapted. A certain species may be quite common in one area
but exceedingly rare only 500 yards away, where it is replaced
by another similar, but distinct, species. There are a few common species
found in scattered patches and a great number of rare species scattered
throughout a forest. Some of these species are extremely rare and on
the verge of extinction, especially where the forest has been disturbed.
The reason for this pattern is that
many species are highly specialized to fit a particular niche. Where
that niche exists, that species may have a large population and constantly
produce offspring that head off to colonize new areas. However, the
colonizers almost always fail, because they cannot compete with the
specialized species of other areas. Thus these colonizers are rare in
the areas where they try to establish a foothold.
Review questions:
- Why does biodiversity generally increase towards the tropics?
- Where does the rainforest ultimately get its energy?
- Why are few species relatively abundant in the rainforest?
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Continued: Canopy structure, soils, effect of area on biodiversity
This article was written by Rhett A. Butler [bibliographic citation for this page] and was last updated on the most recent date listed in the column on the right side.
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WEEKLY NEWSLETTER
INTERACT
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Recent news
Some toilet paper production destroys Indonesian rainforests, endangering tigers and elephants
(02/09/2012) American consumers are unwittingly contributing to the destruction of endangered rainforests in Sumatra by purchasing certain brands of toilet paper, asserts a new report published by the environmental group WWF. The report, Don't Flush Tiger Forests: Toilet Paper, U.S. Supermarkets, and the Destruction of Indonesia's Last Tiger Habitats, takes aim at two tissue brands that source fiber from Asia Pulp & Paper (APP), a paper products giant long criticized by environmentalists and scientists for its forestry practices on the Indonesian island of Sumatra. The brands — Paseo and Livi — are among the fastest growing, in terms of sales, in the United States.
Vampire and bird frogs: discovering new amphibians in Southeast Asia's threatened forests
(02/06/2012) In 2009 researchers discovered 19,232 species new to science, most of these were plants and insects, but 148 were amphibians. Even as amphibians face unprecedented challenges—habitat loss, pollution, overharvesting, climate change, and a lethal disease called chytridiomycosis that has pushed a number of species to extinction—new amphibians are still being uncovered at surprising rates. One of the major hotspots for finding new amphibians is the dwindling tropical forests of Southeast Asia.
Fungus from the Amazon devours plastic
(02/02/2012) Students from Yale University have made the amazing discovery of a species of fungus that devours one of the world's most durable, and therefore environmentally troublesome, plastics: polyurethane. The new species of fungus, Pestalotiopsis microspora, is even able to consume polyurethane in zero-oxygen (anaerobic) conditions, which would be important in eating plastics in the deep dark layers of landfills where little sunlight, water, or oxygen is found.
Majority of Andes' biodiversity hotspots remain unprotected
(02/01/2012) Around 80 percent of the Andes' most biodiverse and important ecosystems are unprotected according to a new paper published in the open-access journal BMC Ecology. Looking at a broad range of ecosystems across the Andes in Peru and Bolivia, the study found that 226 endemic species, those found no-where else, were afforded no protection whatsoever. Yet time is running out, as Andean ecosystems are undergoing incredible strain: a combination of climate change and habitat destruction may be pushing many species into ever-shrinking pockets of habitat until they literally have no-where to go.
Protecting original wetlands far preferable to restoration
(01/26/2012) Even after 100 years have passed a restored wetland may not reach the state of its former glory. A new study in the open access journal PLoS Biology finds that restored wetlands may take centuries to recover the biodiversity and carbon sequestration of original wetlands, if they ever do. The study questions laws, such as in the U.S., which allow the destruction of an original wetland so long as a similar wetland is restored elsewhere.
More biodiversity news
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