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Extinction is key to vertebrate terrestrial diversity?

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We don’t think the World Wildlife Fund would welcome the news, put that way.

Anyway, from ScienceDaily:

Periods of high extinction on Earth, rather than evolutionary adaptations, may have been a key driver in the diversification of amniotes (today’s dominant land vertebrates, including reptiles, birds, and mammals), according to new research.

The new study examined the issue of adaptive radiations among early amniotes, from 315 to 200 million years ago. This time period witnessed some of the most profound climate changes on a global scale, including the dramatic shrinking of the southern polar icecap, the disappearance of equatorial rainforests, a substantial increase in temperature, and prolonged drought conditions. The time period under study also included the largest mass extinction in Earth’s history, about 252 million years ago.

A key finding of the research is that even the appearance of an important innovation in the larger group does not trigger a large proliferation of species until a major new extinction takes place.

Dr Neil Brocklehurst, a postdoc at the Museum für Naturkunde in Berlin, is the lead author of the paper. He said: “It appears that these ‘key innovations’ do not promote massive increases in species richness, but instead buffer against extinction when times get tough.” More.

See also: New findings support rethink of mass extinction?

Do mass extinctions happen every 26 million years or so?


Are mass extinctions driven by mineral deficiency?

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Here’s the abstract:

Tree shape analyses are frequently used to infer the location of shifts in diversification rate within the Tree of Life. Many studies have supported a causal relationship between shifts and temporally coincident events such as the evolution of “key innovations”. However, the evidence for such relationships is circumstantial. We investigated patterns of diversification during the early evolution of Amniota from the Carboniferous to the Triassic, subjecting a new supertree to analyses of tree balance in order to infer the timing and location of diversification shifts. We investigated how uneven origination and extinction rates drive diversification shifts, and use two case studies (herbivory and an aquatic lifestyle) to examine whether shifts tend to be contemporaneous with evolutionary novelties. Shifts within amniotes tend to occur during periods of elevated extinction, with mass extinctions coinciding with numerous and larger shifts. Diversification shifts occurring in clades that possess evolutionary innovations do not coincide temporally with the appearance of those innovations, but are instead deferred to periods of high extinction rate. We suggest such innovations did not cause increases in the rate of cladogenesis, but allowed clades to survive extinction events. We highlight the importance of examining general patterns of diversification before interpreting specific shifts. (Public access) – Neil Brocklehurst, Marcello Ruta, Johannes Müller, Jörg Fröbisch. Elevated Extinction Rates as a Trigger for Diversification Rate Shifts: Early Amniotes as a Case Study. Scientific Reports, 2015; 5: 17104 DOI: 10.1038/srep17104

From the "Results and Discussion": (beginning paragraph)
Based on the Akaike Weights criterion for model selection (Table 1), extinction is found to provide the best fit for the ?2 values of amniotes, substantially better than a multivariate model that incorporates both origination and extinction. This suggests that many of the largest diversification rate shifts tend to occur preferentially during periods of elevated extinction rates, rather than periods of high origination rates.
NS "conserves," it doesn't "create." PaV
So maybe the approaching mini ice age has a silver lining? http://www.telegraph.co.uk/news/science/11733369/Earth-heading-for-mini-ice-age-within-15-years.html ppolish

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