View Full Version : Speciation and Biodiversity

Sunday, May 2nd, 2004, 01:49 AM
Interview with Edward O. Wilson

The formation of new species can happen relatively quickly; however it cannot keep up with the current extinction rate.
Species require energy, stability, and enough space -- all of which are decreasing. Some populations are no longer healthy because there are too few individuals. In one human lifetime, half the world's species will disappear if the rate continues.

ActionBioscience.org: How is a biological species defined?

Wilson: The biological species concept is a classical concept. It applies, however, to species that reproduce sexually and is a
follows: a species is a population or a series of populations of individuals that interbreed freely with one another. In other words,
a species is a more-or-less genetically isolated element, evolving on its own. The species concept is not universal.

ActionBioscience.org: This concept implies a closed gene pool. Is this universal?

Wilson: It is not universal. It can be applied to the vast majority of animals and a great many flowering plants. It may be applicable
to many kinds of microorganisms. But there are many other organisms, especially plants and microorganisms, to which this concept cannot be applied, or at best applied with difficulty. Obviously, it cannot be applied if there is no sexual reproduction.

In the case of asexual species, it's possible to classify them arbitrarily based on genetic differences. For example, a standard
used for bacteria is when two strains of bacteria differ by as much as 30% of their DNA, they can be treated as different species. This is arbitrary, of course, but it's also reasonably workable. Subspecies refers to races that differ in certain traits.

ActionBioscience.org: Can a subspecies be defined as clearly as a species?

Wilson: Not to the same degree. In theory, a subspecies is a geographical race. A species may be divided into geographical races
that differ from one another consistently, in a set of diagnostic traits, such as color, length of wing, breeding habits. Overall,
subspecies have many difficulties that make them far more an arbitrary category than species. Defining subspecies is often difficult.

One of the difficulties is that traits tend to vary separately from one another. Take for example a butterfly species of Eastern Europe.
You might find that populations grow progressively larger going from north to south but are darker in color going from east to west. A
closer study may reveal that they have more spots on the wing going from southeast to southwest. So, what are you to do? Will you select one or two characteristics and define the subspecies that way? Or do you try to combine many characteristics and, if so, you get a jumble of many subspecies?

Discordance of traits is probably the most difficult aspect of applying the subspecies concept. However, subspecies is still used
and it has some validity, especially in the case of island races. It's also difficult to apply the biological species concept to
ancestral species.

ActionBioscience.org: What about chrono, or ancestral, species?

Wilson: A chronospecies is simply a necessity of science because we have to distinguish between populations that live today and
populations that are ancestral to them. They lived so long ago that they are very different. For example, we are the species Homo
sapiens -- and it is fairly certain that we descended directly from another species, Homo erectus -- and it would be very confusing,
somehow intuitively incorrect, to try to put them together. Even though Homo erectus evolved through stages into Homo sapiens, we
can't apply the biological species concept to this obviously. Nonetheless we want to make a distinction between them, even though it is arbitrary. Species tend to evolve rapidly on islands.

ActionBioscience.org: What are the origins of biodiversity?

Wilson: First is the apparent cycle that species go through in populating a new area and diversifying. When an island or an
archipelago is formed, for example, or an area is cleared by glaciation or other major physical event of its original biodiversity, there is first a flood of immigrant species. They interact with one another and form a community that we call an ecosystem. If the new area is left undisturbed, then typically there is an episode of rapid evolution -- an adaptation of new species to the environment. If there is enough area and enough geographically isolated parts in that area to sustain populations that have little contact with one another, then we also have rapid species formation.

Speciation slows down after the initial burst of diversification. A typical example would be Hawaii. Evidence shows that the archipelago filled up with a small number of species and that they evolved and diversified into many species over a relatively short period of time, by which I mean, centuries or thousands of years. That's short compared to the evolution we see in many other parts of the world.

Diversification finally reaches a level where the fauna and flora become stabilized, with coadaptation occurring. That means that one
species is dependent on another, such as one species specialized on feeding on another. At this point, speciation slows down. It's
similar to the growth of an organism - rapid at first with assembly of new parts that interact and finally a level of maturity can be
sustained for a long period of time. The number of species increases the closer you get to the equator.

The other set of principles of biodiversity have to do with amounts, or what determines the ultimate amounts. We know, for example, that tropical rainforests have many more species per unit area than do the tundra or coniferous forests of the northern hemisphere. The number of species in a given area, i.e., in a square mile or a square hundred miles, increases steadily as one approaches the
equator. The number also increases as you go from small islands to large islands, as in the Caribbean. Energy, stability, and area influence the number of species.

ActionBioscience.org: What determines this increase of species?

Wilson: There appear to be three factors, which I like to refer to as ESA. E is for energy, S for stability, and A for area. The more energy that is available to the evolving community of species, the more species there are. That maximizes as you go towards the equator. The more stable a region, as in a constant-climate area, the more species accumulate because they have more time to adapt and fit together. The larger the area, the larger the population and the more diverse it is. For example, South America
has more species than the West Indies.

These three driving forces working together appear to account for the large amount of variation of species in the world.
Behavior seems to play a larger role in speciation than geographical isolation.

ActionBioscience.org: What is the most prevalent form of speciation?

Wilson: If sympatric speciation occurs so widely in insects -- the
most diverse organisms on earth -- as our studies suggest it might,
it could be the most prevalent form of speciation. Sympatric
speciation is a more difficult phenomenon to study than the easily
observed and clearly observed allopatric speciation but it could be
very prevalent, we don't know.

Sympatric refers to similar organisms in close proximity that don't
interbreed because of differences in behavior, even though they
theoretically could. Allopatric refers to similar organisms that
don't interbreed, even though they theoretically could, because they
are geographically separated.

ActionBioscience.org: How quickly can these and other mechanisms
produce new species?

Wilson: Instantly. Well, in a few generations. First of all, in
plants, there's a mechanism -- called polyploidy -- which, in one
step, can create a strain that can't breed with the original stock
from which it came. In fact, it's called instantaneous speciation.
Speciation can happen relatively quickly but it is difficult to

Sympatric speciation can sometimes also take only a few steps to
produce new species in a short period time. For example, in certain
kinds of fruitflies one strain can prefer to breed on a different
kind of plant, and that can happen over several mutations. Another
strain comes to breed at a different season, and that can happen by
several mutations. Or incompatibility can exist between two strains
that differ by one gene or a very small number of genes. This can
occur by mutation or recombination of existing genes in a short
period of time.

So, it is theoretically possible to create new species within a few
years and probably some species formation does occur that rapidly
but it is difficult to observe. We are not certain how widespread
very rapid speciation really is.

An experiment proved that some species return quickly to an area
after extinction.

ActionBioscience.org: In 1966, you and Dr. Daniel Simberloff
conducted an experiment to determine the Minimum Critical Size of
Ecosystems (MCS). What did you discover?

Wilson: We were looking to determine how fast species invade an
empty island and whether or not they would be affected by area or
distance. What we did was to miniaturize the system in the Florida
Keys by selection of mangrove islets and then remove all the
organisms except trees. We then observed the return of the insects.
We demonstrated that
Small creatures, including insects and spiders, came back very
The island filled up with species until it reached approximately the
number of species it had before.
The more distant the area for immigrant species, the longer it took
to reach equilibrium in the area.
Although the number of species came back to original level, the
composition of the community differed from the original.
This is consistent with our theoretical conception of the turnover
of species, that is, extinction followed by colonization (and in the
long term, speciation).

Population size is critical to the genetic health of a species.

ActionBioscience.org: Is there is a threshold below which
populations are in imminent danger of extinction?

Wilson: Yes. Population size is critical to survival. Generally
speaking, when populations get below about 100 individuals, then
inbreeding depression happens. And, if there are deleterious, lethal
genes in the populations, e.g., cystic fibrosis in humans, then you
will get a higher incidence of this genetic trait, which leads to
death or sterility. In large populations, chances are that a lethal
gene will occur less often.

Species need at least 500 individuals to stay healthy.
Conservation biologists offer a 50-500 rule for the genetic health
of populations. As I explain this in my 1992 book, The Diversity of
Life: "a population of 50 or more is adequate for the short term
only, and one of 500 is needed to keep the species alive and healthy
into the distant future."

Rapid speciation cannot produce species that took along time to

ActionBioscience.org: If speciation can happen quickly, why should
we worry about species extinction?

Wilson: It can occur rapidly theoretically but the product would
relatively "cheapen" species differences. For example, if two
species of fish differed only by one or a few genes out of the tens
of thousands that they have, chances are they would differ very
little from one another. Compare this to two species that diverged a
million years ago and have been evolving genetically in many genes
and traits. If these were wiped out, we would lose a great deal more
than losing two species that differ only a little.
Species are vanishing a thousand times faster than they are being
In any case, whether species are slightly different or markedly
different, they are now disappearing at the rate somewhere of a
thousand times faster than they are born due to human activity. At
this rate, in one human lifetime, we can easily eliminate half the
species of the world. Many of these have developed over thousands or
millions of years. The clearly demarcated species that can be
tracked in the fossil record, before humanity originated, appeared
roughly on the order of about one species per million per year. Any
rapid process of speciation that would let them begin again can't
duplicate that.

Conservation should focus on the hot spots of biodiversity.

ActionBioscience.org: With extinction happening globally, where
should we focus conservation efforts?

Wilson: On the hot spots, such as tropical forests. Hot spots are
the habitats that are most endangered and have the largest number of
species found nowhere else but in them. These include the forests of
Hawaii and Madagascar and the rich scrub lands of southwestern
Australia and southern Africa. Tropical wildernesses, such as the
Amazon and the Congo, have the last of the great frontier forests
able to support a mega fauna, i.e., large mammals and birds. The
preservation of these places is critical.
Hotspots include tropical forests and coral reefs.

Another area is the freshwater systems of the world, which are
generally neglected. They deserve special attention because they are
under the heaviest assault everywhere, as for example from pollution
or drainage. These systems have the largest concentration of
endangered species per unit area of any ecosystem in the world.
Their equivalent in oceans is the coral reefs, a large percentage of
which are now being destroyed or severely degraded. They also have a
high percentage per unit of area of endangered species.

Conclusion: Nature's services are worth $30 trillion a year. Why
destroy such a valuable commodity?

ActionBioscience.org: In your new book Future of Life you deflate
the myth that environmental policy is hostile to economic growth.
Can you elaborate?

Wilson: The living resources of the world -- ecosystems and its
species -- are still largely unexplored, much less studied for the
benefits they might hold for humans, for example, new
pharmaceuticals or water purification. Some ecologists and
economists have estimated that the total value of these natural
ecosystems, that's the total amount of services they provide to
humanity, is in the vicinity of 30 trillion dollars a year. That's
more than the total of the gross national products of all nations
combined. And it's free!

To save and make fuller use of them in a non-obtrusive way is
economically valuable to us. To destroy them is to force humanity
into an artificial world in which we have to personally manage our
water systems, our food supply, and our atmosphere by prosthetic
devices day by day instead of relying on powerful organisms to do
the work for us. Do we want to turn Earth literally into a spaceship
that requires constant tinkering?

ActionBioscience.org Editor's Note (11/02): The first World Atlas of
Biodiversity: Earth's Living Resources for the 21st Century was
released by the United Nations Environment Programme World
Conservation Monitoring Centre (UNEP-WCMC) in August 2002
(University of California Press). Its writers estimate that:
during the past 150 years, humans have directly impacted and
altered close to 47% of the global land area
under one bleak scenario, biodiversity will be threatened on almost
72% of Earth's land area by 2032
48% of South East Asia, the Congo Basin, and parts of the Amazon
will likely be converted to agricultural land, plantations and urban
areas -- compared with 22% today, suggesting wide depletions of
starting some 45,000 years ago a high proportion of larger land
animals became extinct in North America, Australia, the Caribbean,
and elsewhere, coinciding with human arrival

About the author: At Harvard University, E.O. Wilson, Ph.D., is
Honorary Curator in Entomology of the Museum of Comparative Zoology,
in addition to Pellegrino University Research Professor Emeritus.
Dr. Wilson, internationally regarded as the dean of biodiversity, is
the recipient of numerous honors, including the Gold Medal of the
Worldwide Fund for Nature (1990) for his conservation efforts. He is
on the Board of Directors of The Nature Conservancy, Conservation
International, and the American Museum of Natural History. Two of
his books have been awarded the Pulitzer Prize; his most recent is
titled Future of Life (2002). Dr. Wilson continues to give many
lectures throughout the world.

http://www.actionbioscience.org/biodiversity/wilson.html (http://forums.skadi.net/redirector.php?url=http%3A%2F%2Fwww.acti onbioscience.org%2Fbiodiversity%2Fwilson .html)

Friday, May 21st, 2004, 05:15 PM

The Biosphere
The biosphere is the thin and irregular envelope around and including the Earth's surface that contains all living organisms and the elements they exchange with the non-living environment.

Water makes up about two-thirds of an average living cell, and organic molecules based on hydrogen, carbon, nitrogen and oxygen make up the remaining one-third. These and other elements of living cells cycle repeatedly between the soil, sediment, air and water of the environment and the transient substance of living organisms.

The energy to maintain the structure of organisms enters the biosphere when sunlight is used by bacteria, algae and plants to produce organic molecules by photosynthesis, and all energy eventually leaves the biosphere again in the form of heat. Photosynthetic organisms themselves use a proportion of the organic material they synthesise; net primary production is the amount of energy-rich material left to sustain all other life on Earth.

Humans now appropriate a large proportion of global net primary production, and have caused planetary-scale perturbations in cycling of carbon, nitrogen, and other elements.