Historical Biogeography - Lecture Slides | BOTANY 422, Study notes of Geography

Download Historical Biogeography - Lecture Slides | BOTANY 422 and more Study notes Geography in PDF only on Docsity! 1 " . . . 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 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 • We assume that the fundamental nature of the ecological processes has not changed over time, but certainly the surface of the earth and therefore the distribution of its organisms have changed dramatically over time We will see later how these geological changes have had major impact on the organisms inhabiting the areas 2 Historical Biogeography • This geological evolution (area evolution) is thus an important component of the “historical setting” or historical biogeography Historical Biogeography • It is also clear that the plants and animals inhabiting the changing environmental setting are not constant either. The flora and fauna comprising the vegetation biomes also have 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; species go extinct and are replaced by other perhaps more adapted species. The same holds true for larger lineages (genera, families) — or taxa. Historical Biogeography • This biological evolution (taxa evolution) is thus a second important component of the “historical setting” or historical biogeography 5 Evolution 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 the Greek “ladder of life” pattern. This confusion or mis-application is the basis of a lot of 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 the ladder metaphor, only few organisms occupy the top rung (Homo sapiens) and there is an implicit assumption about passing through one rung to get to the next rung. 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 Evolution The tree metaphor 6 Evolution http://tolweb.org/tree/phylogeny.html The tree metaphor today The tree or phylogeny is now the standard tool to describe and depict biodiversity at all taxonomic levels Evolution Although major religious denominations uphold the “two books of knowledge” view, the “evolution vs. creationist” debate continues — primarily in the United States and even in Wisconsin The “Evolution House” exhibit at Kew Royal Botanic Gardens was the inspiration of the Christian director (and biogeographer) Sir Ghillean Prance Evolution Evolution 7 Agrostis tenuis growing on a copper mine in Britain — natural selection for copper tolerance in 150 generations Evidence for Evolution Direct observation — anagenesis, speciation Direct observation of natural selection operating within a species to change genetic makeup of populations and their adaptation to a changing environment — anagenesis Direct observation — anagenesis, speciation Character displacement of floral color in zones of overlap of the geographic ranges of two similar colored species of phlox — anagenesis Although the two species can hybridize in this zone, the hybrids are sterile. The character displacement of floral color reduces interspecific pollen transfer by pollinators Phlox (Polemoniaceae) Evidence for Evolution Direct observation — anagenesis, speciation The splitting of a species into new species, speciation or cladogenesis, has been extensively studied in plants The speciation process has been studied at incipient stages as well as at recently occurring stages Evidence for Evolution Direct observation — anagenesis, speciation The splitting of a species into new species, speciation or cladogenesis, has been extensively studied in plants The speciation process has been studied at incipient stages as well as at recently occurring stages One of the best studied systems involves two western U.S. monkeyflowers Mimulus cardinalis (hummingbird pollinated) and M. lewisii (bee pollinated) — a pair of recently speciated species Evidence for Evolution 10 Evolution thus predicts that species coming from a common ancestor should share homologous characters — derived from the same structure(s) — but that they will show divergence in these characters through time Character divergence — homology vs. analogy The forelimb of all these mammals are homologous — it is composed of the same bones in the same position, but the individual parts have been greatly modified via selection for many different uses: grasping leaping flying swimming running Evidence for Evolution Evolution thus predicts that species coming from a common ancestor should share homologous characters — derived from the same structure(s) — but that they will show divergence in these characters through time Character divergence — homology vs. analogy In the same fashion, the homologous five petals of the monkeyflower show divergence in size, orientation, and color to facilitate the attraction of hummingbirds or bees Evidence for Evolution Vestigial structures — homology vs. analogy Evolution would also predict that species occupying very distinct environments from that of a common ancestor might show vestigial structures — structures obtained from a common ancestor but no longer needed for the original adaptive purpose. The pelvic girdle seen in reptiles and mammals as an adaptation for support in tetrapods, is vestigial in snakes and whales — it is a “fossil” footprint of their ancestry and serving no function today in crawling or swimming tetrapods. Evidence for Evolution Vestigial structures — homology vs. analogy Evolution would also predict that species occupying very distinct environments from that of a common ancestor might show vestigial structures — structures obtained from a common ancestor but no longer needed for the original adaptive purpose. In the same manner, the parasitic and non-green dodders retain “fossil” chloroplasts (photosynthetic organelles) in their cells as a vestigial structure inherited from a common ancestor with morning glories — although the plastid is very reduced and much of the plastid DNA has been lost Evidence for Evolution 11 Similar body shapes and structures have evolved in the North American desert cacti . . . and separately in the euphorbias in southern African deserts Biogeography and Comparative Biology — homology vs. analogy Our discussion of Vegetation vs. Flora has already provided numerous examples of unrelated organisms showing convergent (analogous) features as responses to similar environmental pressures Cactaceae Euphorbiaceae Evidence for Evolution Convergent structures in the ocotillo (left) from the North American deserts . . . and in the allauidia (right) from Madagascar. Biogeography and Comparative Biology — homology vs. analogy Foquieria - Foquieriaceae Allauidia - Didieriaceae Evidence for Evolution Biogeography and Comparative Biology — homology vs. analogy Convergent structures in bill and body shape in flower visiting birds from four different continents: North America, Australia, South America, and Africa hummingbird honeyeater sunbirdEcuadorian honeycreeper Evidence for Evolution Biogeography and Comparative Biology — homology vs. analogy European hare Patagonian hare Australian banded hare Convergent leg and ear features in three rabbit-like species of open woodland from three continents: one is a lagomorph, one is a rodent, one is a marsupial Evidence for Evolution 12 Biogeography and Comparative Biology The convergence of mammals (marsupials) in Australia vs. the placental mammals elsewhere in the world is one of the most spectacular examples of biogeographical based convergences in animals as well as divergences within each lineage Evidence for Evolution Molecular “fossil” record • DNA and the genes they encode are the new “fossil” characters . . . Human vs. chimpanzee chromosomes (23 vs. 24) 99.4% DNA identity (. . . and the resulting phenotype & behavior!) Evidence for Evolution Molecular “fossil” record • Francis Collins — evolution of DNA = language of God Evidence for Evolution Molecular “fossil” record — phylogenetic trees The use of DNA to produce (estimate) phylogenetic relationships among organisms has revolutionized our understanding of character evolution Evidence for Evolution