sharon sanders
Editor-in-Chief & President
Devonian die-off teaches grim lesson
snip
Many scientists say that we are in the throes of a sixth great mass-extinction event. The two main reasons are habitat loss ? land converted to human use is less available to other critters ? and the fact that we are moving species around the planet.
"What we can expect in the long term is that because we have this global movement of invasions, we can expect speciation rates to be very low, but we also know that because of habitat loss, the extinction rate is very high. So we are really looking at a very bad combined effect," Stigall said.
more...
http://cosmiclog.msnbc.msn.com/_news/2010/12/30/5738534-devonian-die-off-teaches-grim-lesson
Invasive Species and Biodiversity Crises: Testing the Link in the Late Devonian
Abstract
During the Late Devonian Biodiversity Crisis, the primary driver of biodiversity decline was the dramatic reduction in speciation rates, not elevated extinction rates; however, the causes of speciation decline have been previously unstudied. Speciation, the formation of new species from ancestral populations, occurs by two primary allopatric mechanisms: vicariance, where the ancestral population is passively divided into two large subpopulations that later diverge and form two daughter species, and dispersal, in which a small subset of the ancestral population actively migrates then diverges to form a new species. Studies of modern and fossil clades typically document speciation by vicariance in much higher frequencies than speciation by dispersal. To assess the mechanism behind Late Devonian speciation reduction, speciation rates were calculated within stratigraphically constrained species-level phylogenetic hypotheses for three representative clades and mode of speciation at cladogenetic events was assessed across four clades in three phyla: Arthropoda, Brachiopoda, and Mollusca. In all cases, Devonian taxa exhibited a congruent reduction in speciation rate between the Middle Devonian pre-crisis interval and the Late Devonian crisis interval. Furthermore, speciation via vicariance is almost entirely absent during the crisis interval; most episodes of speciation during this time were due to dispersal. The shutdown of speciation by vicariance during this interval was related to widespread interbasinal species invasions. The lack of Late Devonian vicariance is diametrically opposed to the pattern observed in other geologic intervals, which suggests the loss of vicariant speciation attributable to species invasions during the Late Devonian was a causal factor in the biodiversity crisis. Similarly, modern ecosystems, in which invasive species are rampant, may be expected to exhibit similar shutdown of speciation by vicariance as an outcome of the modern biodiversity crisis.
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0015584
snip
Many scientists say that we are in the throes of a sixth great mass-extinction event. The two main reasons are habitat loss ? land converted to human use is less available to other critters ? and the fact that we are moving species around the planet.
"What we can expect in the long term is that because we have this global movement of invasions, we can expect speciation rates to be very low, but we also know that because of habitat loss, the extinction rate is very high. So we are really looking at a very bad combined effect," Stigall said.
more...
http://cosmiclog.msnbc.msn.com/_news/2010/12/30/5738534-devonian-die-off-teaches-grim-lesson
Invasive Species and Biodiversity Crises: Testing the Link in the Late Devonian
Abstract
During the Late Devonian Biodiversity Crisis, the primary driver of biodiversity decline was the dramatic reduction in speciation rates, not elevated extinction rates; however, the causes of speciation decline have been previously unstudied. Speciation, the formation of new species from ancestral populations, occurs by two primary allopatric mechanisms: vicariance, where the ancestral population is passively divided into two large subpopulations that later diverge and form two daughter species, and dispersal, in which a small subset of the ancestral population actively migrates then diverges to form a new species. Studies of modern and fossil clades typically document speciation by vicariance in much higher frequencies than speciation by dispersal. To assess the mechanism behind Late Devonian speciation reduction, speciation rates were calculated within stratigraphically constrained species-level phylogenetic hypotheses for three representative clades and mode of speciation at cladogenetic events was assessed across four clades in three phyla: Arthropoda, Brachiopoda, and Mollusca. In all cases, Devonian taxa exhibited a congruent reduction in speciation rate between the Middle Devonian pre-crisis interval and the Late Devonian crisis interval. Furthermore, speciation via vicariance is almost entirely absent during the crisis interval; most episodes of speciation during this time were due to dispersal. The shutdown of speciation by vicariance during this interval was related to widespread interbasinal species invasions. The lack of Late Devonian vicariance is diametrically opposed to the pattern observed in other geologic intervals, which suggests the loss of vicariant speciation attributable to species invasions during the Late Devonian was a causal factor in the biodiversity crisis. Similarly, modern ecosystems, in which invasive species are rampant, may be expected to exhibit similar shutdown of speciation by vicariance as an outcome of the modern biodiversity crisis.
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0015584