Alpha, beta, or gamma: where does all the diversity go?
Blurb Author: Peter Wagner
When you look up Peter Wagner you get some idiotic author of
Christian fan fiction. The REAL PW is a malacologist and a curator of Paleozoic
malacology at the Smithsonian. I really wish I shared a name with a famous
moron. The real one is actually kind of young for a curator. I envy him his
position, I hope to be a curator at the Natural History Museum someday - that
is, if our governor doesn't shut it down first. I digress. Wagner got his PhD,
surprise surprise, at Chicago
Paper Author: Jack Sepkoski
Jack is worse than Wagner! It’s the most insulting thing,
whenever I search 'Jack Sepkoski' Google says, "Did you mean Jack Septiceye?" NO GOOGLE, I wanted a
scientist, not an LPer. All that being neither here nor there, Jack was the
archetypal prodigy who died young and left people wondering what else he would
have contributed if he hadn't left so early. I think Wagner makes a musical
analogy, comparing Jack to the Beatles and Elvis, but I'd say Mozart makes a
more apt comparison when it comes to premature death. I think we're probably
all pretty familiar with Jack at this point, so I won't belabor it beyond
saying he made the Sepkoski curve, was the student of Gould, etc.
Cliff notes for the paper:
The paper deals with the perplexing discrepancy between the
different measures of marine diversity during the Paleozoic. To recap, alpha
diversity is the total number of species at a locality, beta diversity is the
difference in diversity between two localities, and gamma diversity is the
diversity within regions.
Jack notes that while generic alpha diversity increases on
average about 50~70% during the Ordovician radiation, the global genera-level
diversity perplexingly increases by about 300%. That's odd. Where did that 300%
come from, where did it go? Where did it come from Cotton Eyed Joe?
In order to deal with this quandary (I think it had been a
problem ever since Bambach published a somewhat similar work in 1977) Jack did
what Jack was famous for: he compiled a gigantic database and split it into
twice as many environmental zones as had ever been done before. "Trends
found for between-zone beta diversity are very similar to those seen within
adjacent environmental zones are not of precisely the same age." On pg.
621-622. Is that a typo or am I an idiot? I'm more inclined to think the
latter.
Ultimately, the conclusion is that during the Paleozoic, and
the Ordovician particularly, environments became more segregated and, as a
result, the diversity within all the environments could increase without the
diversity greatly changing in one individual environment.
The way I imagined it is this: I've got bins, and in each
bin there are ten object, five of which are unique to each bin. The other five
objects occur, to one degree or another, in the other bins. If I have five
bins, then the maximum global number of unique objects is 50, and the minimum
global number of unique objects is 25. If I have 15 bins instead of five
though, then the maximum global number of unique objects is 150, and the
minimum global number of unique objects is 75. BUT, in both instances (5 bins
and 15 bins) the average number of objects in each bin is still exactly 10.
Thus, without increasing alpha diversity at all, we can still increase beta
diversity by segregating up the shelf and letting things diverge. At least,
that's the impression I got, but
maybe I read it wrong. I was a bit confused, to be perfectly honest.
https://youtu.be/By2y8VkvyJI
https://www.youtube.com/watch?v=By2y8VkvyJI
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