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Thread: Speciation and Biodiversity

  1. #1

    Post Speciation and Biodiversity

    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. 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. 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. 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. 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. 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. 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. 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. 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.

 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. 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
    evolve. 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. 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? 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? 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.

  2. #2

    Arrow World Atlas of Biodiversity

    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.

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