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Rainforest along the bank of the Tambopata river in Peru. (Photo by R. Butler)
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.
An alternative theory of why rainforests are so diverse
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?
Deforestation emissions should be shared between producer and consumer, argues study
(11/19/2009) Under the Kyoto Protocol the nation that produces carbon emission takes responsibility for them, but what about when the country is producing carbon-intensive goods for consumer demand beyond its borders? For example while China is now the world's highest carbon emitter, 50 percent of its growth over the last year was due to producing goods for wealthy countries like the EU and the United States which have, in a sense, outsourced their manufacturing emissions to China. A new study in Environmental Research Letters presents a possible model for making certain that both producer and consumer share responsibility for emissions in an area so far neglected by studies of this kind: deforestation and land-use change.
REDD may increase the cost of conservation of non-forest ecosystems
(11/19/2009) Policy-makers designing a climate change mitigation mechanism that will reduce emissions from deforestation and degradation (REDD) aren't doing enough to ensure that the scheme protects biodiversity outside carbon-dense ecosystems, argues an editorial published in Current Biology by a group of scientists.
Countries that invest in conservation will see higher financial returns, argues report
(11/13/2009) A new report issued by the The Economics of Ecosystems and Biodiversity (TEEB) initiative makes a strong case for valuing the planet's ecosystem services. The report calls for investments in "ecological infrastructure" to protect wildlands and the services they provide; market-based valuation of ecosystem services; reductions in environmentally harmful subsidies; recognition of the link between environmental degradation and poverty; and a strong climate deal that includes forest carbon.
Declaration calls for more wilderness protected areas to combat global warming
(11/11/2009) Meeting this week in Merida, Mexico, the 9th World Wilderness Congress (WILD9) has released a declaration that calls for increasing wilderness protections in an effort to mitigate climate change. The declaration, which is signed by a number of influential organizations, argues that wilderness areas—both terrestrial and marine—act as carbon sinks, while preserving biodiversity and vital ecosystem services.
How rainforest shamans treat disease
(11/10/2009) Ethnobotanists, people who study the relationship between plants and people, have long documented the extensive use of medicinal plants by indigenous shamans in places around the world, including the Amazon. But few have reported on the actual process by which traditional healers diagnose and treat disease. A new paper, published in the Journal of Ethnobiology and Ethnomedicine, moves beyond the cataloging of plant use to examine the diseases and conditions treated in two indigenous villages deep in the rainforests of Suriname. The research, which based on data on more than 20,000 patient visits to traditional clinics over a four-year period, finds that shamans in the Trio tribe have a complex understanding of disease concepts, one that is comparable to Western medical science. Trio medicine men recognize at least 75 distinct disease conditions—ranging from common ailments like fever [këike] to specific and rare medical conditions like Bell's palsy [ehpijanejan] and distinguish between old (endemic) and new (introduced since contact with the outside world) illnesses. In an interview with mongabay.com, Lead author Christopher Herndon, currently a reproductive medicine physician at the University of California, San Francisco, says the findings are a testament to the under-appreciated healing prowess of indigenous shaman.
