Historical Biogeography - University of Wisconsin–Madison · 2011-02-22 · Historical...

" . . . that grand subject, that almost keystone of the laws of creation,Geographical Distribution"

[Charles Darwin, 1845, in a letter to Joseph Dalton Hooker,the Director of the Royal Botanic Garden, Kew]

Historical Biogeography

Once distributions of organismsare known (floristics), attempts toreconstruct the origin and subsequent historyof taxa and areas are possible (historical biogeography)

" . . . that grand subject, that almost keystone of the laws of creation,Geographical Distribution"

[Charles Darwin, 1845, in a letter to Joseph Dalton Hooker,the Director of the Royal Botanic Garden, Kew]

Historical biogeography requiresknowledge of the evolution of bothtaxa and areas — not surprising then thatDarwin considered “Geographical Distribution”such a keystone feature of natural history


• The environmental setting (climate, wind andocean currents, positions of landmasses,vegetation types) has not been constant orstatic over time — but dynamic

Plate tectonics showing major movements of Africa, India,and Australia


• This geological evolution (area evolution) isthus an important component of the “historicalsetting” or historical biogeography


Plate tectonics showing major movements of Africa, India,and Australia

• plants and animals inhabiting the changingenvironmental setting are not constant either

• flora and fauna comprising the vegetation biomes alsohave changed over time, often as a direct response to the“geological evolution”


• New species arise by immigration or directly from pre-existing species

• species accumulate variation, adapt, and further diversify


• species go extinct and are replaced by other perhapsmore adapted species

• the same holds true for larger lineages (genera, families)— or taxa.


• This biological evolution (taxa evolution) is thus asecond important component of the “historical setting” orhistorical biogeography


Example 1: Argyroxiphium sandwicense

The interplay of geological and biologicalevolution is critical in understanding why theHaleakala silversword is found in Maui, when andwhere it or its ancestors came from, and why it ishas specific features of morphology, chromosomenumber, and physiology.


Example 2: Clarkia franciscana

The interplay of geological and biologicalevolution is critical in understanding why, how,and when this clarkia became endemic toserpentine soils in the Golden Gate Park in SanFrancisco.


Philosophy and Basic Principles — a necessary digression

• Biogeography is not an experimental science, but mostly a comparativeobservational science


• Relationship between pattern and process — describes much of science, andespecially biogeography

• Common patterns often have common explanations

Evolution & BiogeographyBiogeography is central to the development of evolutionary theory.The extensive travels of Darwin and Wallace gave important examples ofbiogeographical distributions, associated variation, and evidence of evolutionarychange

Alfred Wallace and his travels inthe Malay archipelago

Charles Darwin and his travels inthe Galapagos Islands

Evolution & BiogeographyBiogeography is central to the development of evolutionary theory.The extensive travels of Darwin and Wallace gave important examples ofbiogeographical distributions, associated variation, and evidence of evolutionarychange Charles Darwin and his travels in

the Galapagos Islands

. . .werebiogeographical!

These biogeographical based examples played a pivotal role in the formulation ofboth Darwin’s and Wallace’s evolutionary theories jointly presented in 1858 inLondon and culminating in the publication of the Origin of Species in 1859.

Origin of Species

Darwin devoted two chaptersto biogeography in the Originof Species: Chapter 11 -Geographical Distribution;Chapter 12 - GeographicalDistribution continued

Charles Darwin

Two points about this book

Evolution & Biogeography

EvolutionWhat is it? a definition:

What is it? Evolution is often separated into:

anagenesis - evolution within a species lineage — modification (Darwin’s term)

cladogenesis - evolution to form new species lineages or speciation — descent

Evolution

What does it predict?

It is important to realize that evolution predicts a “tree”- like pattern to life; not theGreek “ladder of life” pattern. This confusion or mis-application is the basis of a lotof miscommunication in the “evolution-creationist” debate.

Evolution

What does it predict?

In the tree metaphor, all extant organisms occupy the tips of the branches; in theladder metaphor, only few organisms occupy the top rung (Homo sapiens) and thereis an implicit assumption about passing through one rung to get to the next rung.

Evolution

The affinities of all the beings of the same class have

sometimes been represented by a great tree . . . As

buds give rise by growth to fresh buds, and these if

vigorous, branch out and overtop on all sides many a

feebler branch, so by generation I believe it has been

with the great Tree of Life, which fills with its dead

and broken branches the crust of the earth, and covers the

surface with its ever branching and beautiful ramifications.

Charles Darwin, 1859

The tree metaphor

Evolution

http://tolweb.org/tree/phylogeny.html

The tree metaphor today

The tree or phylogeny is now thestandard tool to describe and depictbiodiversity at all taxonomic levels

Evolution

Evidence for Evolution

Direct observation — anagenesis, speciation

The splitting of a species intonew species, speciation orcladogenesis, has beenextensively studied in plants

The speciation process has beenstudied at incipient stages aswell as at recently occurringstages



The splitting of a species intonew species, speciation orcladogenesis, has beenextensively studied in plants

The speciation process has beenstudied at incipient stages aswell as at recently occurringstages

One of the best studied systemsinvolves two western U.S.monkeyflowers Mimuluscardinalis (hummingbirdpollinated) and M. lewisii (beepollinated) — a pair of recentlyspeciated species



These two species and theirorigin have been studied bylooking at their DNA,ecological niches, and naturalselection via pollinatorpressures.

Importantly, using crosses anddetailed genetic analyses, thequite different floralmorphologies (bird vs. beepollinated syndromes) havebeen shown to be due to just afew genes — do not haveinvoke long periods of time ormany, small incrementalchanges.


Taxonomic pattern of relationships — hierarchical nature

• Species do not vary in arandom manner . . .

. . . but exhibitcharacteristics that allowthem to be placed in largergroups (taxa) sharingsubsets of these characters.


Taxonomic pattern of relationships — hierarchical nature

• Species do not vary in arandom manner . . .

. . . but exhibitcharacteristics that allowthem to be placed in largergroups (taxa) all sharingthese characters.

• This pattern ofhierarchical structure ispredicted by evolution.


Fossil record — transitional forms, “missing links”

Fossil record provides amazing detail thatsupports evolutionary interpretations – e.g., horselineage and the whale lineage.

A major misconception in the “evolution vs.creationist” debate is the idea that there has to bedirect links between forms.

This misconception generates the accusation of“missing links”. These “missing links” are indeedthere but not necessarily of the form looked forbecause of naïve assumptions.


Evolution thus predicts that species coming froma common ancestor should share homologouscharacters — derived from the same structure(s)— but that they will show divergence in thesecharacters through time

Character divergence — homology vs. analogygrasping

leaping

flying

swimming

running


Vestigial structures — homology vs. analogy

Evolution would also predict that speciesoccupying very distinct environments from that ofa common ancestor might show vestigialstructures — structures obtained from a commonancestor but no longer needed for the originaladaptive purpose.

The pelvic girdle seen in reptilesand mammals as an adaptation forsupport in tetrapods, is vestigial insnakes and whales — it is a“fossil” footprint of their ancestryand serving no function today incrawling or swimming tetrapods.


Vestigial structures — homology vs. analogy

Evolution would also predict that speciesoccupying very distinct environments from that ofa common ancestor might show vestigialstructures — structures obtained from a commonancestor but no longer needed for the originaladaptive purpose.

In the same manner, the parasiticand non-green dodders retain“fossil” chloroplasts(photosynthetic organelles) intheir cells as a vestigial structureinherited from a common ancestorwith morning glories — althoughthe plastid is very reduced andmuch of the plastid DNA has beenlost


Similar body shapes and structureshave evolved in the NorthAmerican desert cacti . . .

and separately in the euphorbias insouthern African deserts

Biogeography and Comparative Biology — homology vs. analogy

Our discussion of Vegetation vs.Flora has already providednumerous examples of unrelatedorganisms showing convergent(analogous) features as responses tosimilar environmental pressures

Cactaceae

Euphorbiaceae


Convergent structures in theocotillo (left) from the NorthAmerican deserts . . .

and in the allauidia (right)from Madagascar.

Biogeography and Comparative Biology — homology vs. analogy

Foquieria - Foquieriaceae Allauidia - Didieriaceae


Biogeography and Comparative Biology

The convergence of mammals(marsupials) in Australia vs. theplacental mammals elsewhere in theworld is one of the most spectacularexamples of biogeographical basedconvergences in animals as well asdivergences within each lineage


Molecular “fossil” record — phylogenetic trees

The use of DNA to produce (estimate) phylogenetic relationships amongorganisms has revolutionized our understanding of character evolution


The Brodiaea complex (Themidaceae) inCalifornia and Madrean Region of SWN. Amer.

(Pires and Sytsma 2002)

Brodiaeaterrestris

Besseraelegans



Fossil fixedages of 71.5and 70.5 mya


Chronogram of Themidaceae andHyacinthaceae

• origins of CaliforniaFloristic Province lineages (2or 3) are Miocene

(Sytsma et al. 2006)



The use of DNA to estimatephylogenetic relationshipsamong organisms has alsorevolutionized biogeography

Phylogenetic trees not onlyprovide strong hypotheses ofbiological relationships but theycan also give estimates ofrelationships of the areas whichthe taxa occupy



As we will see, molecularphylogenetics will be critical inunraveling “adaptive radiations” inisland biogeographic settings

Hawaiian silversword alliance

Hawaiian honeycreeper alliance


Historical Biogeography - University of Wisconsin–Madison · 2011-02-22 · Historical...

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