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Dispersal and vicariance

Dispersal and vicariance. Explanations for colonization and disjunct ranges Dispersalist concepts Dispersal mechanisms Centres-of-origin Vicariance concepts Cladistic analysis Fragmentation mechanisms. Dispersal. A function of:. Species-specific dispersal mechanisms; and

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Dispersal and vicariance

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  1. Dispersal and vicariance Explanations for colonization and disjunct rangesDispersalist conceptsDispersal mechanisms Centres-of-origin Vicariance concepts Cladistic analysis Fragmentation mechanisms

  2. Dispersal A function of: Species-specific dispersal mechanisms; and Availability of dispersal agents; and Suitability of new habitat Stepping- stone Phalanx Jump Sweepstakes

  3. Reconstruction of the spread of Argentine ants throughout the United States from first detection in 1891 in New Orleans to the present. Average maximum distance of daughter colonies from parent: 150 m/yr. This is one example (of many)of multi-modal dispersal native range Suarez A. V. et.al. PNAS 2001;98:1095-1100 ©2001 by The National Academy of Sciences

  4. Dispersal agents Wind Ocean currents Rivers Animal vectors (internal, external) including humans Vehicles

  5. e.g. forest trees, Cameroon, Africa “Seed-shadows”how far do propagules or progeny disperse away from the parent(s)? C. J. Clark, et al., 2005 Ecology: 86, 2684-2694.

  6. Dispersal of seeds by ocean currents:from the Caribbean to Ireland “Tropical” seeds found on Irish beaches

  7. Dispersal of seeds by animals N. American flora Hawai’ian flora Seeds with wings: transported by wind Barbed seeds: transported in animal fur Fleshy fruits: transported in animal gut Seeds catapulted by explosions

  8. Dispersal of seeds by animals e.g. germinable seeds in horse dung* (Shetland Islands, Scotland) Median density: 700 seeds/pat Median number of plant species: 27 Total number of plant species: 67 *14 samples Cosyns, E. and Hoffmann, M. 2005. Basic & Applied Ecol., 6, 11-24.

  9. Stepping-stone? dispersal e.g. giant tortoises (Dipsochelys); Aldabra extant; populationson Seychelles ( ) and Malagasy now extinct 400 km

  10. Island flightlessness Why are ALL the endemic crickets on the Hawai’ian islands flightless (they only have rudimentary wings)?, and Why are the seeds of many plants in the sunflower family in Hawai’i barbless (e.g. Bidens spp.) ? Mainland Hawaii

  11. Heteroblasty (“blast” = bud/sprout) (a.k.a. “Don’t put all your eggs in one blastket”) Crepis sancta, a dandelion-like weed,commonly produces two kinds of seeds. In urban environments theheavier, non wind-dispersed formis dominant*. Why? *3 March 2008 | Nature | doi:10.1038/news.2008.639

  12. Dispersal:overcoming barriers e.g. desert barrier corridor A to B habitatsdispersal dispersal corridor dispersal filter sweepstakes dispersal wide variety easy A B difficult; only certain organisms make it limited array (oases) A B occasional migrants none A B

  13. Land bridges as terrestrial corridors Real: e.g. Beringia (later lecture) or Panama Hypothetical: e.g. Lemuria (proposed by Sclater and others in 19thC to explain presence of fossil lemurs in India and Pakistan Lemuria?

  14. Stopped by filter Now stopped in filter Crossing filter Panama land bridge: the corridor as filter Northern ancestry Rabbits Squirrels Field mice Raccoons Weasels Otters Skunks Pumas Deer Shrews Pocket mice Pocket gophers Beavers Bobcats Pronghorns Bison Sheep Southern ancestry Coatis Kinkajous many Cats Tapirs PeccariesCamels most Armadillos Anteaters Sloths Guinea pigs capybaras Porcupines Seaway closed ~ 4.5 Ma BP

  15. Vicariance biogeography • Based on the precept that regional biotas are remnants of more extensive grouping that have been fragmented by vicariant events. • Vicariant events include such processes as continental fragmentation, mountain building, desertification. • Emphasizes the role of allopatric speciation in populations isolated by vicariant barriers.

  16. Continental fragmentation and biogeography “the breakup of a large landmass into smaller units would necessarily lead to the extinction or local extermination of one or more species and the differential preservation of others” Alphonse de Candolle, 1855 Biogeographic realms are continental rafts; their boundaries reflect tectonic divergences and convergences

  17. Vicariant events: ratites andthe Gondwana breakup

  18. T Dinosaurs Bird evolution in mid-Jurassic(from theropod dinosaurs?) Birds K J T R Struthiomimus

  19. 8 7 6 5 2 1 Living ratites and tinamous (large, mainly flightless birds) 1. Tinamous: SAm 2. Kiwis: NZ 3. (Moas: NZ) 4. (Elephant birds: Africa) 5. Cassowaries: Aus-NG 6. Emus: Aus 7. Ostrich: Af-EurA 8. Rheas: SAm (extinct groups)

  20. Cladistics of the ratites (and their close relatives, the tinamous) Taxon: 1 2 3 4 5 6 7 8 Area: S.Am NZ NZ Ma Au,NG Au Af S.Am

  21. Distribution of the ratites [and close relations]prior to human-induced extinctions 7 1 5 4 6 8 2,3

  22. Distribution of the ratites [and close relations]prior to human-induced extinctions 7 1 5 4 6 8 2,3 Inter-continental dispersal?

  23. Vicariance hypothesis:fragmentation of Gondwana 7 1 4 2,3 8 5,6 Gondwana

  24. Europe Europe North America North America South America South America Australia Australia Similar area cladograms = similar vicariant histories Ratite birds Chelid turtles South America South America New Zealand Australia Madagascar New Guinea Australia New Guinea Hylid frogs Galliform birds New Guinea New Guinea

  25. Extinctions and radiations • why is evolutionary history marked by catastrophes? • what causes mass extinctions? • what controls survival? • what controls post-catastrophe success? • are there biogeographic lessons?

  26. Biotic/evolutionary metaphors “Great Chain of Being” “The cone of diversity” “The ultimate lottery” “The ladder”

  27. The ladder of progress: evolution of horses

  28. The ladder of progress

  29. The tree of life or cone of diversity Haeckel, 1866

  30. The cone of diversity:arthropod evolution (1986)

  31. Punctuated equilibrium Proposed by Niles Eldredge and Stephen Jay Gould (in 1972) Evolution tends to be characterized by long periods of virtual standstill punctuated by episodes of rapid diversification (mass extinction events are simply megascale examples of this), rather than the “gradualism” proposed by Darwin .

  32. recent middle “visible life” ancient “prior life”

  33. The geological time scale is subdivided by events of mass extinction which are followed by phases of rapid evolution. Were these extinction events a product of catastrophes?

  34. The evolutionary roller-coaster after Phillips (1860) Radiation Diversity Cenozoic Radiation Mesozoic Radiation Palaeozoic E E PD Time

  35. Marine invertebrates: extinctions and radiations

  36. Survivals and radiations

  37. Extinction events • potential catastrophic causes: • Glaciation • Continental collision • Mountain building and climate change • Volcanism • Asteroid/comet impacts • Gamma-ray outbursts

  38. Terrestrial animals through time The K/Tboundary

  39. The Cretaceous/Tertiary (K/T) extinction • Time: 65 Ma • Magnitude: 11% of marine families • Victims: dinosaurs • Inferred cause:asteroid impact, (and associated vulcanism?) • Beneficiaries:mammals, birds, etc.

  40. K/T “smoking guns”

  41. Helen Frank Walter LuisMichaels Asaro Alvarez Alvarez The K/T impactor theory

  42. Cretaceous - Tertiary boundary rocks, Los Brazos, SW Texas v. dark clays: soot & rare elements (e.g. Ir) broken sandstone=tsunami deposit? sandstone

  43. Post-K/T radiation Diversification in aftermath of extinction event (highly “punctuated”) Diversification within orders after extinction, but orders predate event Diversification primarily prior to extinction event (“gradualism”) Source: Springer et al., 2003. PNAS 100:1056-1061

  44. Bird radiation(chronology based on molecular clock) K-T boundary Source: Slack, K.E. 2006. Mol. Bol. & Evol. 23, 1144-1155.

  45. Mammal radiation Source: Springer et al., 2003. PNAS 100:1056-1061

  46. Biogeographic implications • Surviving a mass extinction or major vicariant event is a product of luck, genes and geography. • Organisms that opportunistically disperse into devastated habitats win the lottery. • In the aftermath of the catastrophe distributions may be fragmented, leading to rapid adaptive radiation.

  47. Plant diversity through time: radiation in the Tertiary resulting from continental fragmentation?

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