Sandra Raup, R.D., J.D., M.P.H. TCDDA Meeting April 10, 2012.
Equilibrium)and)Non/Equilibrium) Diversity:)Valen8ne)vs.)Raup · Diversificaon) –or!–!...
Transcript of Equilibrium)and)Non/Equilibrium) Diversity:)Valen8ne)vs.)Raup · Diversificaon) –or!–!...
Equilibrium and Non-‐Equilibrium Diversity: Valen8ne vs. Raup
Reading: David Raup
Diversifica8on – or – Why are there so many species?
Lecture 15 Recap
David Lack
Diversifica8on – or – Why are there so many species?
• What is diversifica-on?
• Increase in species richness within biological lineages through 8me
Diversifica8on – or – Why are there so many species?
• Biological species concept
• “(Popula-ons) …have risen to species rank (that) have become so different from each other physiologically that they… can come together again without interbreeding.”
-‐Ernst Mayr
Diversifica8on – or – Why are there so many species?
Diversifica8on – or – Why are there so many species?
David Lack
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Degree of Isolation
% E
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Diversifica8on – or – Why are there so many species?
David Lack
C. pauper C. affinis C. psiEacula C. habeli
Diversifica8on – or – Why are there so many species?
David Lack
C. pauper C. affinis C. psiEacula C. habeli
Diversifica8on – or – Why are there so many species?
David Lack
C. pauper C. affinis C. psiEacula C. habeli
Diversifica8on – or – Why are there so many species?
David Lack
C. pauper C. affinis C. psiEacula C. habeli
Diversifica8on – or – Why are there so many species?
David Lack
C. pauper C. affinis C. psiEacula C. habeli
Diversifica8on – or – Why are there so many species?
• As we have learned throughout the class, what we observe today is merely the latest layer of an ever evolving series of specia8on
• What if we wanted to examine long-‐term diversifica8on through 8me?
• Have to look to the fossil record for answers
Diversifica8on – or – Why are there so many species?
• By the late 1960’s science had amassed a large collec8on of marine shelf sediments from many depths containing fossil remains of benthic invertebrates
• James Valen8ne set out to assess the global diversity of these well-‐skeletonized marine shelf invertebrates, and track diversity through 8me
James Valen8ne
Diversifica8on – or – Why are there so many species?
• Valen8ne found that early Paleozoic fauna contained rela8vely few species represen8ng many higher taxa (generalized ecosystems)
• As 8me progressed and higher taxonomic levels went ex8nct, they were replaced by lower, more specialized taxa
James Valen8ne
Diversifica8on – or – Why are there so many species?
James Valen8ne
Diversifica8on – or – Why are there so many species?
• This rela8ve difference between higher and low taxa led to substan8al varia8on in diversity through 8me
• Valen8ne observed periods of rapid diversifica8on followed rapid decline and then rapid diversifica8on
James Valen8ne
Diversifica8on – or – Why are there so many species?
James Valen8ne
Diversifica8on – or – Why are there so many species?
• Evidence for Permian ex8nc8on event with rapid diversity aZer and con8nuing un8l present
James Valen8ne
Diversifica8on – or – Why are there so many species?
James Valen8ne
Diversifica8on – or – Why are there so many species?
• Valen8ne postulated that this increasing trend in diversity was due to three main reasons
1. Increasing specializa8on of species through 8me
2. Increasing number of centers of endemism associated with intensifying la8tudinal temperature gradients
3. Fragmenta8on of shelf environments due to con8nental driZ
James Valen8ne
Diversifica8on – or – Why are there so many species?
• Advocated for a non-‐equilibrium model of diversity
• This means that diversity was not stable through -me, shiZs between many higher taxonomic groups with a few generalist species to rela8vely few higher taxonomic groups with many specialized species
James Valen8ne
Diversifica8on – or – Why are there so many species?
• Taxonomic Diversity during the Phanerozoic
• Directly refutes Valen8ne’s methods and conclusions about non-‐equilibrium diversity
• Advocates for an equilibrium model of diversity where diversity changes but will fluctuate around a stable level through 8me
David Raup
Diversifica8on – or – Why are there so many species?
• Tradi-onal view of diversity through -me (Valen8ne)
1. A rapid rise during the Cambrian
2. Maximum in the Devonian
3. Persistent decline in the Permian
4. Rapid increase to an all 8me high in the Ter8ary
David Raup
Diversifica8on – or – Why are there so many species?
David Raup
Diversifica8on – or – Why are there so many species?
David Raup
A rapid rise during the Cambrian
Diversifica8on – or – Why are there so many species?
David Raup
Maximum in the Devonian
Diversifica8on – or – Why are there so many species?
David Raup
Persistent decline in the Permian
Diversifica8on – or – Why are there so many species?
David Raup
Rapid increase to an all 8me high in the Ter8ary
Diversifica8on – or – Why are there so many species?
• Both Valen8ne and Raup used the same fossil data of benthic shelf invertebrates
• How did they come to such different conclusions?
David Raup
Diversifica8on – or – Why are there so many species?
• Raup iden8fied several methodological errors in Valen8ne’s (and others) assessment of the raw data
1. Sediment Record
2. Sampling Problems
David Raup
Diversifica8on – or – Why are there so many species?
David Raup
Diversifica8on – or – Why are there so many species?
David Raup
Survival Rate of Marine Sediments
Diversifica8on – or – Why are there so many species?
David Raup
Survival Rate of Marine Sediments
Diversifica8on – or – Why are there so many species?
David Raup
Diversifica8on – or – Why are there so many species?
• Sampling Problems
• There are many more taxa than those that are discovered in the fossil record
• Approximate rates of discovery can be explored using probability models
David Raup
Diversifica8on – or – Why are there so many species?
David Raup
10 Cups
10% chance of ending up in any 1 cup
Infinite turns, no drinking
10/10 chance of filling a cup
Diversifica8on – or – Why are there so many species?
David Raup
10 Cups
10% chance of ending up in any 1 cup
Infinite turns, no drinking
9/10 chance of filling a cup
Diversifica8on – or – Why are there so many species?
David Raup
10 Cups
10% chance of ending up in any 1 cup
Infinite turns, no drinking
8/10 chance of filling a cup
Diversifica8on – or – Why are there so many species?
David Raup
10 Cups
10% chance of ending up in any 1 cup
Infinite turns, no drinking
8/10 chance of filling a cup
Diversifica8on – or – Why are there so many species?
• As the number of balls thrown increases, the likelihood of making it in an unoccupied cup decreases
• The creates a func8on that resembles this
David Raup
% of cup
s filled
Ball throws
Diversifica8on – or – Why are there so many species?
David Raup
10 Cups
This may represent the Order level
Diversifica8on – or – Why are there so many species?
David Raup
36 Cups
This may represent the Family level
36/36 chance of filling a cup
Diversifica8on – or – Why are there so many species?
David Raup
36 Cups
This may represent the Family level
35/36 chance of filling a cup
Diversifica8on – or – Why are there so many species?
David Raup
36 Cups
This may represent the Family level
34/36 chance of filling a cup
Diversifica8on – or – Why are there so many species?
David Raup
36 Cups
This may represent the Family level
33/36 chance of filling a cup
Diversifica8on – or – Why are there so many species?
David Raup
36 Cups
This may represent the Family level
33/36 chance of filling a cup
Diversifica8on – or – Why are there so many species?
• As the number of balls thrown increases, the likelihood of making it in an unoccupied cup decreases
• The creates a func8on that resembles this
David Raup
% of cup
s filled
Ball throws
36 cups 10 cups
Diversifica8on – or – Why are there so many species?
• As the number of balls thrown increases, the likelihood of making it in an unoccupied cup decreases
• The creates a func8on that resembles this
David Raup
% of cup
s filled
Ball throws
10 cups 36 cups
3 cups
Diversifica8on – or – Why are there so many species?
• At any given number of geographic areas studied you will tend to find a higher propor8on of higher taxonomic ranks than lower taxonomic ranks
David Raup
% of cup
s filled
Ball throws
10 cups 36 cups
3 cups
Diversifica8on – or – Why are there so many species?
• At any given number of geographic areas studied you will tend to find a higher propor8on of higher taxonomic ranks than lower taxonomic ranks
• Given that more recent sediments are more likely to contain more examples of lower ranks (species, genus, family) because there is an inherent increase in quality and quan8ty of sampling in more recent sediments
David Raup
Diversifica8on – or – Why are there so many species?
• With repeated sampling, you will find the higher ranks first a more completely find all of the examples
• While you will con8nue to find lower ranks, and these tend to be overrepresented in more recent sediments
David Raup
Diversifica8on – or – Why are there so many species?
David Raup
Tradi8onal View Hypothesized diversity and preserva8on with added temporal biases
Diversifica8on – or – Why are there so many species?
• Raup advocated that Valen8ne’s non-‐equilibrium model could be ini8al period of diversity and overshoot followed by a decline to an equilibrium state
• The diversity trends were simply ar8facts of the temporal biases and sediment volumes of the raw data
David Raup
Diversifica8on – or – Why are there so many species?
• S8mulated a debate that went on for 15+ years
• Raup and Valen8ne eventually published a paper together that corrected for sampling biases while acknowledging that there was substan8al varia8on in diversity over this 8me period
• There may be the existence of ‘mul8ple equilibria’
David Raup
Diversifica8on – or – Why are there so many species?
Main Points • Valen8ne’s work showed that the rela8ve propor8ons of higher to lower taxa changed over the Phanerozoic
• This lead to the idea that diversity changes drama8cally through 8me, a non-‐equilibrium model
• Raup used the same data and found poten8al biases in sediment survival/volume and sampling of taxonomic rank
• He advocated for an equilibrium model with changes that fluctuated around an equilibrium diversity through 8me
David Raup
Ques8ons on the reading?
Discussion Point
• What was your impression of Raup from the reading?
David Raup
Discussion Point
• There have obviously been several mass ex8nc8on events, with massive losses of diversity. What evidence is there that there are a defined and stable number of niches for equilibrium diversity?
David Raup
Discussion Point
• What do you think the most probable solu8on is to this issue?
David Raup