" . . . 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 organisms are known (floristics), attempts to reconstruct the origin and subsequent history of 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 requires knowledge of the evolution of both taxa and areas — not surprising then that Darwin considered “Geographical Distribution” such a keystone feature of natural history Historical Biogeography • The environmental setting (climate, wind and ocean currents, positions of landmasses, vegetation types) has not been constant or static over time — but dynamic Plate tectonics showing major movements of Africa, India, and Australia Historical Biogeography • This geological evolution (area evolution) is thus an important component of the “historical setting” or historical biogeography Historical Biogeography Plate tectonics showing major movements of Africa, India, and Australia
Transcript
" . . . 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
Historical Biogeography
• 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
Historical Biogeography• This geological evolution (area evolution) isthus an important component of the “historicalsetting” or historical biogeography
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”
Historical Biogeography• New species arise by immigration or directly from pre-existing species
• species accumulate variation, adapt, and further diversify
Historical Biogeography
• species go extinct and are replaced by other perhapsmore adapted species
• the same holds true for larger lineages (genera, families)— or taxa.
Historical Biogeography• This biological evolution (taxa evolution) is thus asecond important component of the “historical setting” orhistorical biogeography
Historical 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.
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.
Historical Biogeography
Philosophy and Basic Principles — a necessary digression
• Biogeography is not an experimental science, but mostly a comparativeobservational science
Historical Biogeography
• 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.
EvolutionWhat 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 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
Evidence for EvolutionDirect 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
One of the best studied systemsinvolves two western U.S.monkeyflowers Mimuluscardinalis (hummingbirdpollinated) and M. lewisii (beepollinated) — a pair of recentlyspeciated species
Evidence for Evolution
Direct observation — anagenesis, speciation
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.
Evidence for EvolutionTaxonomic 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.
Evidence for Evolution
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.
Evidence for EvolutionFossil 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.
Evidence for Evolution
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
Evidence for EvolutionVestigial 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.
Evidence for Evolution
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
Evidence for Evolution
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
Evidence for Evolution
Convergent structures in theocotillo (left) from the NorthAmerican deserts . . .
and in the allauidia (right)from Madagascar.
Biogeography and Comparative Biology — homology vs. analogy
Evidence for EvolutionBiogeography 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
Evidence for Evolution
Molecular “fossil” record — phylogenetic trees
The use of DNA to produce (estimate) phylogenetic relationships amongorganisms has revolutionized our understanding of character evolution
Evidence for Evolution
The Brodiaea complex (Themidaceae) inCalifornia and Madrean Region of SWN. Amer.
(Pires and Sytsma 2002)
Brodiaeaterrestris
Besseraelegans
Molecular “fossil” record — phylogenetic trees
Evidence for Evolution
Fossil fixedages of 71.5and 70.5 mya
Molecular “fossil” record — phylogenetic trees
Chronogram of Themidaceae andHyacinthaceae
• origins of CaliforniaFloristic Province lineages (2or 3) are Miocene
(Sytsma et al. 2006)
Evidence for EvolutionMolecular “fossil” record — phylogenetic trees
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
Evidence for Evolution
Molecular “fossil” record — phylogenetic trees
As we will see, molecularphylogenetics will be critical inunraveling “adaptive radiations” inisland biogeographic settings
