What Triggers Mass Extinctions? Study Shows How Invasive Species Stop New Life
ScienceDaily (Dec. 30, 2010) — 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 PLoS ONE. 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.
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: University of Michigan Museum of Paleontology)
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.
"We refer to the Late Devonian as a mass extinction, but it was actually a biodiversity crisis," said Alycia Stigall, a scientist at Ohio University and author of the PLoS ONE paper.
"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.
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Invasive Species and Biodiversity Crises: Testing the Link in the Late Devonian
Alycia L. Stigall*
Department of Geological Sciences and OHIO Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, United States of America
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.
Citation: Stigall AL (2010) Invasive Species and Biodiversity Crises: Testing the Link in the Late Devonian. PLoS ONE 5(12): e15584.
doi:10.1371/journal.pone.0015584
Editor: Anna Stepanova, Paleontological Institute RAS, United States of America
Received: August 22, 2010; Accepted: November 15, 2010; Published: December 29, 2010
Copyright: © 2010 Alycia L. Stigall. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: Funding was provided by the National Science Foundation (NSF) EAR-0922067, a grant from the American Chemical Society's Petroleum Research Fund, and Ohio University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The author has declared that no competing interests exist.
* E-mail: stigall@ohio.edu
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