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<h1><b><font size=6 face="Times New Roman"><span style='font-size:24.0pt'>What
Triggers Mass Extinctions? Study Shows How Invasive Species Stop New Life<o:p></o:p></span></font></b></h1>
<p id=first><span class=date><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>ScienceDaily (Dec. 31, 2010)</span></font></span>
— An influx of invasive species can stop the dominant natural process of
new species formation and trigger mass extinction events, according to research
results published December 29 in the journal <em><i><font face="Times New Roman">PLoS
ONE</font></i></em>. The study of the collapse of Earth's marine life 378 to
375 million years ago suggests that the planet's current ecosystems, which are
struggling with biodiversity loss, could meet a similar fate.<o:p></o:p></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Although
Earth has experienced five major mass extinction events, the environmental
crash during the Late Devonian was unlike any other in the planet's history.
The actual number of extinctions wasn't higher than the natural rate of species
loss, but very few new species arose.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>"We
refer to the Late Devonian as a mass extinction, but it was actually a
biodiversity crisis," said Alycia Stigall, a scientist at <st1:place
w:st="on"><st1:PlaceName w:st="on">Ohio</st1:PlaceName> <st1:PlaceType w:st="on">University</st1:PlaceType></st1:place>
and author of the <em><i><font face="Times New Roman">PLoS ONE</font></i></em>
paper.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>"This
research significantly contributes to our understanding of species invasions
from a deep-time perspective," said Lisa Boush, program director in the
National Science Foundation (NSF)'s Division of Earth Sciences, which funded
the research.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>"The
knowledge is critical to determining the cause and extent of mass extinctions
through time, especially the five biggest biodiversity crises in the history of
life on Earth. It provides an important perspective on our current biodiversity
crises."<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The
research suggests that the typical method by which new species
originate--vicariance--was absent during this ancient phase of Earth's history,
and could be to blame for the mass extinction.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Vicariance
occurs when a population becomes geographically divided by a natural, long-term
event, such as the formation of a mountain range or a new river channel, and
evolves into different species. New species also can originate through
dispersal, which occurs when a subset of a population moves to a new location.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>In a
departure from previous studies, Stigall used phylogenetic analysis, which
draws on an understanding of the tree of evolutionary relationships to examine
how individual speciation events occurred.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>She
focused on one bivalve, <em><i><font face="Times New Roman">Leptodesma</font></i></em>
(<em><i><font face="Times New Roman">Leiopteria</font></i></em>), and two
brachiopods, <em><i><font face="Times New Roman">Floweria</font></i></em> and <em><i><font
face="Times New Roman">Schizophoria</font></i></em> (<em><i><font
face="Times New Roman">Schizophoria</font></i></em>), as well as a predatory
crustacean, <em><i><font face="Times New Roman">Archaeostraca</font></i></em>.
These small, shelled marine animals were some of the most common inhabitants of
the Late Devonian oceans, which had the most extensive reef system in Earth's
history.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The seas
teemed with huge predatory fish such as <em><i><font face="Times New Roman">Dunkleosteus</font></i></em>,
and smaller life forms such as trilobites and crinoids (sea lilies). The first
forests and terrestrial ecosystems appeared during this time; amphibians began
to walk on land. As sea levels rose and the continents closed in to form connected
land masses, however, some species gained access to environments they hadn't
inhabited before.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The
hardiest of these invasive species that could thrive on a variety of food
sources and in new climates became dominant, wiping out more locally adapted
species. The invasive species were so prolific at this time that it became
difficult for many new species to arise.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>"The
main mode of speciation that occurs in the geological record is shut down
during the Devonian," said Stigall. "It just stops in its tracks."<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Of the
species Stigall studied, most lost substantial diversity during the Late
Devonian, and one, <em><i><font face="Times New Roman">Floweria</font></i></em>,
became extinct. The entire marine ecosystem suffered a major collapse.
Reef-forming corals were decimated and reefs did not appear on Earth again for
100 million years. The giant fishes, trilobites, sponges and brachiopods also
declined dramatically, while organisms on land had much higher survival rates.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The study
is relevant for the current biodiversity crisis, Stigall said, as human activity
has introduced a high number of invasive species into new ecosystems.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>In
addition, the modern extinction rate exceeds the rate of ancient extinction
events, including the event that wiped out the dinosaurs 65 million years ago.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>"Even
if you can stop habitat loss, the fact that we've moved all these invasive
species around the planet will take a long time to recover from because the
high level of invasions has suppressed the speciation rate substantially,"
Stigall said.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Maintaining
Earth's ecosystems, she suggests, would be helped by focusing efforts and
resources on protection of new species generation. "The more we know about
this process," Stigall said, "the more we will understand how to best
preserve biodiversity."<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The
research was also funded by the American Chemical Society and <st1:place w:st="on"><st1:PlaceName
w:st="on">Ohio</st1:PlaceName> <st1:PlaceType w:st="on">University</st1:PlaceType></st1:place>.<o:p></o:p></span></font></p>
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<p><strong><b><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Story
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>The above story is reprinted (with editorial adaptations by Science<em><i><font
face="Times New Roman">Daily</font></i></em> staff) from materials provided by <a
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<p><strong><b><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Journal
Reference</span></font></b></strong>:<o:p></o:p></p>
<p style='background:#EEEEEE'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>Anna Stepanova, Alycia L. Stigall. <strong><b><font
face="Times New Roman">Invasive Species and Biodiversity Crises: Testing the
Link in the Late Devonian</font></b></strong>. <em><i><font
face="Times New Roman">PLoS ONE</font></i></em>, 2010; 5 (12): e15584 DOI: <o:p></o:p></span></font></p>
<p><strong><b><i><font size=3 face="Times New Roman"><span style='font-size:
12.0pt;font-style:italic'>Disclaimer</span></font></i></b></strong><em><i><font
face="Times New Roman">: Views expressed in this article do not necessarily
reflect those of ScienceDaily or its staff.</font></i></em><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><!-- end story --><img border=0 width=300 height=188 id="_x0000_i1029"
src="cid:image001.jpg@01CBAB38.77B41540"><o:p></o:p></span></font></p>
<p class=MsoNormal><em><i><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>The ocean in Devonian times. A study of the collapse
of Earth's marine life 378 to 375 million years ago suggests that the planet's
current ecosystems, which are struggling with biodiversity loss, could meet a
similar fate. (Credit: <st1:PlaceType w:st="on">University</st1:PlaceType> of <st1:PlaceName
w:st="on">Michigan</st1:PlaceName> <st1:place w:st="on"><st1:PlaceType w:st="on">Museum</st1:PlaceType>
of <st1:PlaceName w:st="on">Paleontology</st1:PlaceName></st1:place>)</span></font></i></em><o:p></o:p></p>
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