Interesting explanation as to why evolution proceeds in spurts.
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Predators stifle rapid evolution of prey
Studies suggest predator-prey system affects speed of branching process
By Ker Than
Staff Writer
LiveScience
Updated: 11:34 a.m. PT March 21, 2007
Evolution, normally viewed as a slow, steady process, can occur in rapid
fits and starts with one species splitting into several lineages in a
relatively short period of time. Now scientists have identified two
factors that influence these bursts of new species.
Called adaptive radiation, the relatively swift emergence of new species
is known to occur in isolated ecosystems, such as remote islands, or
following mass extinctions. But details about what drives this process
have remained murky.
Two new studies, detailed in the March 22 issue of the journal Nature,
suggest predator-prey relationships, as well as the timing and relative
order of a species' arrival into a new environment, can greatly affect
how rapidly this branching process occurs.
The studies involved microbes, in part because they can be easily
manipulated in the lab and, with such short life cycles, they evolve
quickly over time.
Justin Meyer and Rees Kassen of the University of Ottawa in Canada
looked at the effects of a predator, a single-celled microbe called
Tetrahymena thermophila, on the diversification of the soil bacterium
Pseudomonas fluorescens.
They found that under some circumstances, the predators helped cull the
bacteria population. This prevented overcrowding, which, in turn,
reduced bacterial competition for food resources. With less interspecies
competition, the bacteria were less inclined to spread out and fill new
niches or experiment with new foods. Thus, predators appear to stifle
speciation under some circumstances.
³There¹s less need for prey to evolve into different types because the
environment¹s not saturated,² Meyer explained.
The findings suggest predation plays a prominent, yet often overlooked,
role in the evolutionary histories of many species. It also helps
explain why organisms that find their way to remote islands often
undergo a speciation explosion and branch rapidly into different
lineages. A classic example is Darwin¹s finches in the Galapagos.
Scientists think these 13 finches evolved from a common ancestor that
found its way to the islands about 3 million years ago.
On an island with plentiful resources, few competitors and no predators,
the ancestral finch was in evolutionary paradise and diversified to fill
available niches. The ancestral finch ate seeds and spent most of its
time on the ground; today, the Galapagos finches eat insects, grubs,
seeds, fruit and even blood. There¹s even a finch that uses small twigs
as tools.
The birds are named after Charles Darwin, who at age 26 visited the
islands and collected the birds. The finches were one of the
inspirations for Darwin¹s theory of evolution by natural selection.
Immigration history
Another study, by Tadashi Fukami at the University of Hawaii and
colleagues, found that the order and timing of a species arrival into an
isolated habitat can have a large influence on whether a species
diversifies at all.
Also using P. fluorescens as a model, Fukami¹s team showed that if two
variants of the bacteria are introduced into an environment at different
times, the first to arrive has a huge resource advantage.
³You can preempt resources like nutrients and oxygen, and by doing that,
you can suppress others,² Fukami told LiveScience.
The team also showed that under some circumstances, the opposite can
also be true, and it actually pays to arrive last. For example, if
species A and B are already living in an environment and busy competing
with each other, a third species C could sneak in and establish itself
while the other two species duke it out.
Rosemary Gillespie, a biologist at the University of California,
Berkeley who was not involved in the studies, says the results could
help explain some findings that have puzzled biologists. One ecological
conundrum involves the existence of empty niches that never get filled
by species.
The results of Fukami¹s team ³raise the possibility that inconsistencies
are partly due to immigration history,² Gillespie wrote in an
accompanying Nature commentary article.
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http://www.msnbc.msn.com/id/17723198/
--
John #1782
"We should always be disposed to believe that which appears to us to be
white is really black, if the hierarchy of the church so decides."
- Saint Ignatius Loyola (1491-1556) Founder of the Jesuit Order.
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