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UW-Madison BOTANY 422 - Historical Biogeography

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" . . . 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 BiogeographyOnce 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 historyHistorical Biogeography• The environmental setting (climate, wind andocean currents, positions of landmasses,vegetation types) has not been constant orstatic over time — but dynamicPlate tectonics showing major movements of Africa, India,and AustraliaHistorical Biogeography• This geological evolution (area evolution) isthus an important component of the “historicalsetting” or historical biogeographyHistorical BiogeographyPlate 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 diversifyHistorical 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 biogeographyHistorical BiogeographyExample 1: Argyroxiphium sandwicenseThe 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.Historical BiogeographyExample 2: Clarkia franciscanaThe 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 BiogeographyPhilosophy and Basic Principles — a necessary digression• Biogeography is not an experimental science, but mostly a comparativeobservational scienceHistorical Biogeography• Relationship between pattern and process — describes much of science, andespecially biogeography• Common patterns often have common explanationsEvolution & 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 evolutionarychangeAlfred Wallace and his travels inthe Malay archipelagoCharles Darwin and his travels inthe Galapagos IslandsEvolution & 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 evolutionarychangeCharles Darwin and his travels inthe 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 SpeciesDarwin devoted two chaptersto biogeography in the Originof Species: Chapter 11 -Geographical Distribution;Chapter 12 - GeographicalDistribution continuedCharles DarwinTwo points about this bookEvolution & BiogeographyEvolutionWhat 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 — descentEvolutionWhat 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.EvolutionThe affinities of all the beings of the same class havesometimes been represented by a great tree . . . Asbuds give rise by growth to fresh buds, and these ifvigorous, branch out and overtop on all sides many afeebler branch, so by generation I believe it has beenwith the great Tree of Life, which fills with its deadand broken branches the crust of the earth, and covers thesurface with its ever branching and beautiful ramifications.Charles Darwin, 1859The tree metaphorEvolutionhttp://tolweb.org/tree/phylogeny.htmlThe tree metaphor todayThe tree or phylogeny is now thestandard tool to describe and depictbiodiversity at all taxonomic levelsEvolutionEvidence for EvolutionEvidence for EvolutionDirect observation — anagenesis, speciationThe splitting of a species intonew species, speciation orcladogenesis, has beenextensively studied in plantsThe speciation process has beenstudied at incipient stages aswell as at recently occurringstagesEvidence for EvolutionDirect observation — anagenesis, speciationThe splitting of a species intonew species, speciation orcladogenesis, has beenextensively studied in plantsThe speciation process has beenstudied at incipient stages aswell as at recently occurringstagesOne of the best studied systemsinvolves two western U.S.monkeyflowers Mimuluscardinalis (hummingbirdpollinated) and M. lewisii (beepollinated) — a pair of recentlyspeciated speciesEvidence for EvolutionDirect observation — anagenesis, speciationThese two species and theirorigin have been studied bylooking at their DNA,ecological niches, and naturalselection via


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