final&exam&revie · 2019. 12. 3. · a&revolu1on&in&&...

Final Exam Review

A Revolu1on in Biogeographical Methods

Descrip(ve Biogeography

Evolu(onary Biogeography

Phylogene(c Biogeography

Humboldt Hooker Gray Darwin Wallace Hennig Brundin

Panbiogeography Croizat

Cladis(c Biogeography Nelson


•  Methods of biogeography are important and have changed through 1me

•  I want to go through the history of biogeographic methods up to this point and during the rest of the week we will read papers from the mid-‐20th century when there were rapid advancements in the methods of this field


•  Descrip)ve Biogeography

•  Early biogeographers were limited by a lack of understanding on process

•  The field was mostly descrip1ve, in that biogeographers were mostly concerned with describing the distribu1ons of organisms, looking for similarity and difference, and forming some hypotheses on how they got there

•  Focused on the what and the where


•  Evolu)onary Biogeography •  Darwin and Wallace gave order the idea of chao1c species change with natural selec1on

•  Many proponents of evolu1on, but few used it as a tool to explain biogeographic paOern (with the excep1on of Wallace)

•  There was however an emphasis on how a species changed as it spread out from a center of origin


•  Phylogene)c Biogeography

•  ShiS from sta1c species distribu1ons with a reliance on dispersal events to a more dynamic view

•  This was due to the acceptance of plate tectonics and improved systema1cs, the classifica1on of species

•  Willi Hennig was to systema1cs what Wegener was to a dynamic earth


•  Direc)on of evolu1onary change

•  “Close rela1ons between species and space.”

•  Use the two together to determine the direc1on in which certain transforma1ons needed to be read

•  Space is not limited to geographic space, but also ecological space (phenology changes, habitat shiSs)

Willi Hennig


1.  Study a group and determine derived characters

2.  Produce a phylogeny

3.  Examine the phylogeny of a monophyle1c group with respect to distribu1on of its members

4.  Reexamine the phylogeny using informa1on from the distribu1on and perhaps make changes in the previously determine derived characters

Willi Hennig Chorological Method


•  These vicarying reproduc1ve communi1es should be viewed as subspecies of a single species

•  Species groups belonging to a community of decent are restricted to unit areas that are unbroken

•  “Within the con)nuous range of a monophyle)c group it is also possible… under certain circumstances with certain transforma)on series of characters, to determine the direc)on in which it must be read.”

Willi Hennig


Willi Hennig

Rassenkreis “Ring Species”


•  The Panbiogeographical Method

1.  Map the ranges of the species of a given group

2.  Connect the ranges with a line to form a track, these would be minimum line, connec1ng all locali1es with the shortest possible path

3.  Do this over and over again for different taxa

Leon Croizat


•  The Panbiogeographical Method

4.  If tracks follow the same routes, they form a generalized track

5.  These generalized tracks are an empirical phenomenon

6.  Unite con1nental areas that together are an es1mate of the distribu1on of an ancestral biota

Leon Croizat


Leon Croizat


•  Phylogeny based on panbiogeography

Adrian Paterson


•  Phylogeny based on panbiogeography Actual phylogeny

Adrian Paterson

Alan Cooper


•  What is going on then?

•  Geographic neighbors aren’t necessarily evolu)onary neighbors

•  NZ Kiwi’s are more closely related to Australian emus and cassowaries than their (recently ex1nct) island neighbor the moa

•  In fact, not all Ra)tes are flightless, and the South American 1namou is the closest rela1ve to the moa

Adrian Paterson

Alan Cooper


•  What is going on then?

•  There is only one possible explana)on

•  The Ra)tes all evolved from small flying birds and independently lost the ability to fly on at least six separate occasions

•  An incredible example of convergent evolu1on

Adrian Paterson

Alan Cooper


•  “…there is no generally accepted methodology that enables biogeographers, when faced with the same data, to reach approximately the same answer to a given problem.”

•  “Frequently, external authori)es are called in to resolve problems biogeographers have ini)ally taken upon themselves.”

Gareth Nelson


•  Dispersal vs. vicariance models

•  Dispersal models explain disjunc1ons by dispersal across pre-‐exis1ng barriers

•  Vicariance models explain disjunc1ons by the appearance of barriers fragmen1ng the ranges of ancestral species

Gareth Nelson


•  Popper’s Criterion

•  Scien1fic explana1ons differ from non-‐scien1fic ones only be virtue of their falsifiability

•  We must be able to test and poten1ally reject any explana1on that is to be considered scien1fic

Gareth Nelson


•  Tes)ng Dispersal Hypotheses

•  If we can accept mul1ple parallel dispersal events, we can accept an almost infinite number of dispersal possibili1es made possible by a sufficient number of dispersal events

•  This means that this cannot be falsified, and under Popper’s Criterion it is unscien1fic

Gareth Nelson


•  Ockham’s (Occam) Razor

•  Among compe)ng hypotheses, the one with the fewest assump)ons should be selected.

•  This leads us to the idea of parsimony

William of Ockham


•  Parsimony

•  Methodological rule that requires us to minimize the number of parallel dispersals

•  In the last example, it would require parallel dispersal from a to b, and possibly to c as well

•  We must abandon the dispersal hypothesis in favor of a vicariance hypothesis

Gareth Nelson


•  The cladis1c method of biogeography is the most rigorous, but this model of dispersal followed by a model of vicariance cannot explain all distribu1ons

•  …but, we have a beOer chance of understanding biogeographical paOerns when we have a phylogeny because it allows us to select a method that works best for the group

Gareth Nelson


Descrip(ve Biogeography

Evolu(onary Biogeography

Phylogene(c Biogeography

Humboldt Hooker Gray Darwin Wallace Hennig Brundin

Panbiogeography Croizat

Cladis(c Biogeography Nelson

Diversifica1on – or – Why are there so many species?

•  One of the most fundamental ques1ons in biology…

How, when, and under what circumstances does species prolifera1on take place?


•  “The diversity of organisms which live in a given territory is a func)on of the variety of available habitats. The richer and more diversified the environment becomes, the greater should be the mul)formity of the inhabitants. And vice versa: diversity of the inhabitants signifies that the environment is rich in adap)ve opportuni)es.”

-‐Dobzhansky


•  Much of the diversifica1on literature documents paOerns of diversity across space

•  Treats geography as playing an integral role in the evolu1on in biological diversity

•  Even in cases where specia1on occurs in the same area, highly localized geographic circumstances are oSen said to play a role


•  What is diversifica)on?

•  Increase in species richness within biological lineages through 1me


•  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


•  How did so many finch species come to be on this small, isolated archipelago?

David Lack


•  “…the most isolated islands, namely Cocos, Culpepper, Wenman, Tower and Hood, have a much higher propor)on of peculiar forms than have the central Galapagos islands, while on moderately isolated islands, …, there is an intermediate condi)on, with propor)onately fewer endemic forms than on the remote islands, but propor)onally more than on the central islands.”

David Lack


David Lack

1 2 3 4 5 60

20

40

60

80

100

Degree of Isolation

% E

ndem

ic


David Lack

C. pauper C. affinis C. psiWacula C. habeli


•  “The only type of incipient differen)a)on found in Darwin’s finches is that shown by geographical races, and there is nothing to suggest that geographic isola)on is not the essen)al preliminary to species-‐forma)on in this group.”

David Lack


James Valen1ne


•  Valen1ne postulated that this increasing trend in diversity was due to three main reasons

1.  Increasing specializa1on of species through 1me

2.  Increasing number of centers of endemism associated with intensifying la1tudinal temperature gradients

3.  Fragmenta1on of shelf environments due to con1nental driS

James Valen1ne


•  Advocated for a non-‐equilibrium model of diversity

•  This means that diversity was not stable through )me, shiSs between many higher taxonomic groups with a few generalist species to rela1vely few higher taxonomic groups with many specialized species

James Valen1ne


•  Taxonomic Diversity during the Phanerozoic

•  Directly refutes Valen1ne’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 1me

David Raup


David Raup

Survival Rate of Marine Sediments


David Raup


•  At any given number of geographic areas studied you will tend to find a higher propor1on of higher taxonomic ranks than lower taxonomic ranks

David Raup

% of cup

s filled

Ball throws

10 cups 36 cups

3 cups


•  Raup advocated that Valen1ne’s non-‐equilibrium model could be ini1al period of diversity and overshoot followed by a decline to an equilibrium state

•  The diversity trends were simply ar1facts of the temporal biases and sediment volumes of the raw data

David Raup


•  “Any organism which lives in a temperate or a cold climate is exposed at different periods of its life cycle or in different genera)ons to sharply different environments. The evolu)onary implica)ons of nature's annually recurrent drama of life, death, and resurrec)on have not been sufficiently appreciated. In order to survive and reproduce, any species must be at least tolerably well adapted to every one of the environments which it regularly meets. No maWer how favored a strain may be in summer, it will be eliminated if it is unable to survive winters, and vice versa. Faced with the need of being adapted to diverse environments, the organism may be unable to aWain maximum efficiency in any one of them. Changeable environments put the highest premium on versa)lity rather than on perfec)on in adapta)on.”

-‐Dobzhansky

Theodosius Dobzhansky

The Importance of Islands – Islands as Natural Laboratories

•  Natural Laboratories

•  Natural systems where key factors vary so that their effects can be isolated


•  Islands serve as perfect natural laboratories for biogeography

1.  Numerous

2.  Varied geographical circumstances -‐  Distance from mainland -‐  Age -‐ Size

3.  Tractable biotas


•  Species vs. Area Rela)onship •  As area increases there tends to be more species •  Satura1ng func1on can be transformed to a first order func1on (linear) using Arrhenius plots (log-‐log)

•  No1ced that the slope of the line appeared to differ systema1cally between islands and non-‐isolated areas on con1nents

Olof Arrhenius


•  In oceanic islands, species richness declines with distance from a mainland source

•  Tradi1onal explana1on was impoverishment with distance, which held that 1me had been insufficient for remote islands to fill up

•  Implica1on that over 1me the species richness of these islands would increase further

•  This is a non-‐equilibrium explana1on


•  An Equilibrium Theory of Insular Zoogeography

•  The authors argued for an equilibrium model of species richness along a distance gradient from the mainland sources, and that this was also a func1on of island size

•  This theory represents a dynamic steady state due to the offsemng effects of immigra1on (influenced by distance) and ex1nc1on (influenced by area)

Wilson & MacArthur


•  Much less likely that an organism from the mainland source popula1on is going to reach a remote island rela1ve to a near island

•  Also the rela1onship between the number of species and new immigrant species – the more species an island has, the less likely a new immigrant is going to represent a novel species that does not already exist on that island

Wilson & MacArthur


Wilson & MacArthur

Immigra1o

n Ra

te

Number of Species Present

The rela1onship between the number of species and new immigrant species – the more species an island has, the less likely a new immigrant is going to represent a novel species that does not already exist on that island


Wilson & MacArthur

Immigra1o

n Ra

te


Near Island

Far Island

Much less likely that an organism is going to reach a remote island rela1ve to a close island from the mainland with the source popula1on


•  As the number of species on an island increases, the rate of ex1nc1on will also increase, as there are more species to possibly go ex1nct (given that all species are equally likely to die out), there is also less space overall for each species which means smaller popula1ons

•  A smaller island will have greater ex1nc1on rates than a larger island for the same number of species as there is less space and can support a small popula1on sizes

Wilson & MacArthur


Wilson & MacArthur

Ex1n

c1on

Rate


As the number of species on an island increases, the rate of ex1nc1on will also increase, as there are more species to possibly go ex1nct (given that all species are equally likely to die out), there is also less space overall for each species which means smaller popula1ons


Wilson & MacArthur

Ex1n

c1on

Rate


A smaller island will have greater ex1nc1on rates than a larger island for the same number of species as there is less space and can support a small popula1on sizes

Small Island

Large Island


Wilson & MacArthur

Ex1n

c1on

Rate


Small Island

Large Island

Near Island

Far Island

Immigra1o

n Ra

te


1.  An island which is farther away from the source of coloniza1on will have fewer species, because the immigra1on curve will be lower and hence intersect the ex1nc1on curve farther to the leS

2.  Reduc1on of the species pool of immigrants will reduce the number of species on the island

3.  If an island has a smaller area, or more severe climate, the ex1nc1on curve will rise and the number of species will decrease

Wilson & MacArthur


4.  If you have two islands with the same immigra1on curve but different ex1nc1on curves, any given species on the island with the higher ex1nc1on curve is more likely to die out

5.  The # of species on an island far from the source will grow more rapidly with island area than will near islands

6.  The # of species on large islands decreases with distance form the source of coloniza1on faster than does the number of species on small islands

Wilson & MacArthur


Simberloff & Wilson


•  Results demonstrated a return to an equilibrium state and then a balanced turnover due to offsemng coloniza1on and ex1nc1on

•  Provided strong support for the theory

•  Interes1ngly, most islands showed a slight overshot of the equilibrium state, then a fall, and then another rise to a new equilibrium point (assorta1ve equilibrium)

Simberloff & Wilson


•  This new equilibrium suggested a convergence toward the original species composi1on

•  There appeared to be some structure in the recoloniza1on process, whereby “more highly co-‐adapted species sets find themselves by chance on an island and persist longer as sets.”

Simberloff & Wilson


•  One of the main issues with the equilibrium theory is that it treats the dominant ecological processes determining species composi1on on islands as stochas1c and equivalent across species

•  The theory does not account for any observed regulari1es in community organiza1on; the role of compe11on, preda1on, and evolu1on in structuring island communi1es

•  The major focus of contemporary studies in biogeography is the search for those processes, in addi1on to immigra1on and ex1nc1on, that account for overall community organiza1on

Simberloff & Wilson

final&exam&revie · 2019. 12. 3. · a&revolu1on&in&&...

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