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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?
Reptiles underrepresented on the IUCN Red List
(11/04/2009) Currently there are an estimated nearly 9,000 reptiles in the world, while the International Union for Conservation of Nature (IUCN) Red List has assessed all of the world's described mammals, birds, and amphibians, reptiles have yet to be fully assessed, leaving herpetologists with an unclear picture of how reptiles are faring in the world. Currently, 1,677 reptiles have been assessed (less than 20 percent of the total number of reptile species known) with 293 added this year.
Governments, public failing to save world's species
(11/04/2009) According to the International Union for the Conservation of Nature's (IUCN) 2008 report, released yesterday, 36 percent of the total species evaluated by the organization are threatened with extinction. If one adds the species classified as Near Threatened, the percentage jumps to 44 percent—nearly half.
REDD in Colombia: using forests to finance conservation and communities in Colombia's Choco, a former war zone
(11/03/2009) Reducing Emissions from Deforestation and Degradation (REDD), a climate change mechanism proposed by the U.N., has been widely lauded for its potential to simultaneously deliver a variety of benefits at multiple scales. But serious questions remain, especially in regard to local communities. Will they benefit from REDD? While much lip-service is paid to community involvement in REDD projects, many developers approach local communities as an afterthought. Priorities lie in measuring the carbon sequestered in a forest area, lining up financing, and making marketing arrangements, rather than working out what local people — the ones who are often cutting down trees — actually need in order to keep forests standing. This sets the stage for conflict, which reduces the likelihood that a project will successfully reduce deforestation for the 15-30 year life of a forest carbon project. Brodie Ferguson, a Stanford University-trained anthropologist whose work has focused on forced displacement of rural communities in conflict regions in Colombia, understands this well. Ferguson is working to establish a REDD project in an unlikely place: Colombia's ChocĂł, a region of diverse coastal ecosystems with some of the highest levels of endemism in the world that until just a few years ago was the domain of anti-government guerillas and right-wing death squads.
Language and conservation: why words matter
(10/28/2009) The words we choose matter. Benjamin Lee Whorf, an influential American linguist theorized that the language one speaks directly impacts our thoughts; he is quoted as saying, "language shapes the way we think, and determines what we can think about". If this is the case then those who believe in conservation must select their words wisely. My wife and I recently traveled to Africa where we visited wildlife parks in both Zimbabwe and Botswana. The animals we encountered and the scenes we were fortunate enough to witness proved so beautiful and wondrous that I have a difficult time describing them—at least in any way that accurately depicts the experience.
Crisis averted for now, Peruvian natives will meet with Hunt Oil
(10/28/2009) Indigenous groups in a dispute with Hunt Oil, over the company performing seismic tests their land, have scheduled a meeting with the Texas based oil corporation, according to Reuters.
