Posted: Jun 19, 2010 3:03 pm
@susu.exp
I realize that mass extinctions, by definition, global. However, it seems that some palaeontologists in the past have talked about a "reef gap", where in fact there existed extensive reefs in some areas, and not in others(1). For sure, the diversity of surviving taxa is measure of recovery, but if and only if the population numbers are sustainable in each species. As I said before, some groups made it though a bad extinction, and petered out soon after. A thousand Koalas without Eucalyptus leaves are dead Koalas. A thousand Koalas of post-reproductive age means the species is doomed to extinction. Exaggerated small numbers in my example, but you get my point.
And if they are in low numbers, then the fossil record might not record them. So, the record may look like a PE event, in that they might look extinct locally, or another population may re-invade the extinct populations area from some refuge.
A citation please? I did not see much in Gould's "Structure of Evolutionary Theory"
Perhaps you have not seen papers like the one by Hinman & Davidson (2007)? (2). They compare the Genes Regulatory Networks [GRN's] of Sea Stars and SeaUrchins, who shared a common ancestor some 500 myo in the Cambrian. Thus the LUCA of these clades must have had the same GRN as well, where the CORE is conserved and different organisms innovate and co-opt less conserved parts to satisfy their own evolutionary challenges. All methodologies have their problems of course, but palaeontologists can usable only resolve down to families or perhaps genus level, and can only work on morphologies, which is a rather crude and unreliable indicator of diversity.
In any case, real recovery seems to depend on ecological balance after the perturbations have ceased, or at least, the ecosystem can buffer those disturbances. A crude bunch of refugee species with large populations is still not out of the woods until autotrophic production is back ot capacity and there is depth to the trophic levels. Just counting mere species, or mere population numbers, is not in itself a robust measure of recovery. It depends very much who those species are, although there are sometimes gaps in niches after a recovery is said to be complete and at carrying capacity.
(1) Erwin (2008): "Extinction as the loss of evolutionary history" PNAS Vol 105, Aug 12, Supp 1. pp. 11,520-11527. See also Erwin's 2001 paper in PNAS, Vol. 98, No. 10, pp. 5399-5403.
(2) Hinman, V.F & Davidson, E.H. (2007): "Evolutionary Plasticity of Developmental Gene Regulatory Network Architecture" in PNAS, Vol 104, No 49, pp. 19404-19409.
??? What does that have to do with punctuated equilibrium? There are some point you raise that have answers: Diversity rather than abundance is the criterion for extinction and recovery. There are some species that become very abundant in mass extinctions - disaster taxa - so abundance is no criterion. Regional vs. global: Global, if we´re looking at mass extinctions.
I realize that mass extinctions, by definition, global. However, it seems that some palaeontologists in the past have talked about a "reef gap", where in fact there existed extensive reefs in some areas, and not in others(1). For sure, the diversity of surviving taxa is measure of recovery, but if and only if the population numbers are sustainable in each species. As I said before, some groups made it though a bad extinction, and petered out soon after. A thousand Koalas without Eucalyptus leaves are dead Koalas. A thousand Koalas of post-reproductive age means the species is doomed to extinction. Exaggerated small numbers in my example, but you get my point.
And if they are in low numbers, then the fossil record might not record them. So, the record may look like a PE event, in that they might look extinct locally, or another population may re-invade the extinct populations area from some refuge.
Gould co-authored the MBL papers which introduced some of the most important mathematical models of morphological evolution in deep time. There´s also a longish section on regulatory networks in his structure. But then again Gould was a paleontologist, not a geneticist and thus not focussed on them.
A citation please? I did not see much in Gould's "Structure of Evolutionary Theory"
I don´t think they will.
Perhaps you have not seen papers like the one by Hinman & Davidson (2007)? (2). They compare the Genes Regulatory Networks [GRN's] of Sea Stars and SeaUrchins, who shared a common ancestor some 500 myo in the Cambrian. Thus the LUCA of these clades must have had the same GRN as well, where the CORE is conserved and different organisms innovate and co-opt less conserved parts to satisfy their own evolutionary challenges. All methodologies have their problems of course, but palaeontologists can usable only resolve down to families or perhaps genus level, and can only work on morphologies, which is a rather crude and unreliable indicator of diversity.
In any case, real recovery seems to depend on ecological balance after the perturbations have ceased, or at least, the ecosystem can buffer those disturbances. A crude bunch of refugee species with large populations is still not out of the woods until autotrophic production is back ot capacity and there is depth to the trophic levels. Just counting mere species, or mere population numbers, is not in itself a robust measure of recovery. It depends very much who those species are, although there are sometimes gaps in niches after a recovery is said to be complete and at carrying capacity.
(1) Erwin (2008): "Extinction as the loss of evolutionary history" PNAS Vol 105, Aug 12, Supp 1. pp. 11,520-11527. See also Erwin's 2001 paper in PNAS, Vol. 98, No. 10, pp. 5399-5403.
(2) Hinman, V.F & Davidson, E.H. (2007): "Evolutionary Plasticity of Developmental Gene Regulatory Network Architecture" in PNAS, Vol 104, No 49, pp. 19404-19409.