How do we reconstruct the origin, dispersal, and extinction of taxa?

1. How do we reconstruct the origin, dispersal, and extinction of taxa?

2. Taphonomy--study of the process of fossilization and the interpretation of the fossil record

3. Potential problems arise trying to interpret fossil record • Some taxa are more likely to be preserved than others

4. Potential problems arise trying to interpret fossil record • Location of fossils may not match organism's original environment • Example, bones brought into caves in owl pellets

5. La Brea Tar Pits, California 1910, located in Los Angeles. “Tar” seeps up from below, pooling to trap animals.

6. Most common fossil mammal from La Brea, Smilodon, saber-tooth cat.

7. 90% of the mammal fossils from La Brea are of carnivores or scavengers Many bird fossils are also predators or scavengers Does this reflect actual abundances of carnivores in the environment? Or is there some bias as to which animals were trapped in the tar pits? Smilodon may have hunted in packs

8. Even with these biases, the fossil record is invaluable for biogeographers because it provides information on the characteristics of past organisms, areas where they existed, and when they existed.

9. Fossil distributions may provide information to explain disjunct distributions Camels in Old world, vicunas and guanacos in South America

10. Fossil distributions may show how the distribution of a group has changed over time. For example the lungfishes (Lepidoseriiformes) have fossils from sites throughout most of the world but are today only found in tropical regions of the world. • Lungfishes breathe air, have unique dentition

11. Fossils also provide information about past environments. For example, the limestone left behind by coral reefs tells us where there were shallow, warm seas in the past.

12. Fossils may also provide information about past interactions between organisms. For example, carnivorous snails have left drill holes in the fossilized shells of herbivorous snails that they ate.

13. Systematics—the study of the evolutionary relationships among organisms through the comparison of fossils, and the examination of the morphology, behavior, physiology, and molecular characteristics of living organisms

14. Classification of organisms • Kingdom—Animal • Phylum—Chordata • Class—Mammalia • Order—Primates • Family—Hominidae, no other living members of this family • Genus—Homo, no other living members of the genus • Species—sapiens

15. Cladistics is a method of generating hypotheses as to the evolutionary relationships among organisms based on the derived (advanced, apomorphic) characters that groups of organisms share.

16. Characters that are used in cladograms may be morphological, behavioral, physiological, or molecular

17. Cladistics uses the assumption of parsimony to create trees of evolutionary relationships. • Parsimony--rule that the least number of evolutionary changes is assumed to have resulted in patterns we see today. This assumption is likely usually correct but it may not always be

18. Limitations of cladistic classifications • Cladograms are hypotheses which may contain some errors • Cladistic methods assume branching patterns whereas organisms may sometimes hybridize (plants particularly) or share DNA (for example some microbes) • Cladograms usually use only information from living forms, not fossil forms

19. Approaches to investigating historical biogeographic patterns • Determining centers of origin and subsequent dispersal patterns

20. Criteria for centers of origin determination (Cain 1994) • Greatest number of species • Greatest number of individuals • Primitive forms • Maximum size of individuals • Greatest productivity and relative stability • Lines of migration that converge on a single point • Generalists

21. Criteria for centers of origin determination (Cain 1994) • Continuity and directness of clines • Direction indicated by geographic affinities • Direction indicated by migration routes • Direction indicated by seasonal appearance • Greatest number of dominant genes • Concentricity of progressive equiformal areas

22. Approaches to investigating historical biogeographic patterns • Panbiogeography • Disjunct distributions

23. Panbiogeography • A track is a line connecting known areas of distribution for a taxon. When many organisms had similar disjunct distributions and so similar tracks, Croizat called this a generalized track. Croizat inferred that the tracks represented pathways used by organisms that now had disjunct distributions

24. Where different taxonomic entities are involved the minimum spanning tree method provides for the following principal steps (after Craw et al. 1999):--Minimum spanning tree method essentially involves connecting the dots in the simplest way • Plot the locality records of each taxon on a map • Connect all localities of each taxon by a minimal spanning tree. • Connect each minimal spanning tree for all taxa by further minimal spanning links.

25. Croizat believed in vicariance events, landbridges, for example, to explain distributions, and didn’t think dispersal could account for many present-day distributions

26. Croizat’s contribution was in advocating a rigorous methodology for biogeographers

27. More well-accepted today are the development of tracks for monophyletic groups. Monophyletic means that all members of the group are descended from a common ancestor. These tracks can then be used with geological data to try to determine the biogeographical history of an area.

28. Dispersal and vicariance • Dispersal—migration by a taxon across a barrier from place A to place B • Vicariance—development of a barrier between place A and place B, both of which were already occupied by a taxon

30. Approaches to investigating historical biogeographic patterns • Cladistic biogeography--Brundin, in 1966, an entomologist, had the idea of linking phylogenies to the analysis of biogeographic patterns. He worked with midges

31. Brundin devised a cladogram of the midges and then put the continents where the species were found on the cladogram. A cladogram in this state is known as a taxon-area cladogram

32. Brundin’s simplified midge taxon-area cladogram. Phylogeny based on morphology of midges and current distributions of midges then mapped on phylogeny.

33. Phylogenies (cladograms) provide hypotheses about both the evolutionary relationships among organisms and the historical relationships among geographic areas.

34. Brundin’s simplified midge taxon-area cladogram. Phylogeny based on morphology of midges and current distributions of midges then mapped on phylogeny.

35. If the successive splits in the phylogeny were driven by successive break-ups of the land), the phylogeny implies a definable sequence of vicariance events. The common ancestor of the modern forms would have occupied a large area that includes the areas the species currently inhabit, Gondwanaland.

36. Gondwanaland would then, Brundin's analysis predicts, have split in the following order: • Africa splits from a combination of Australia, New Zealand, and South America; • then New Zealand splits from South America and Australia; • and finally Australia splits from South America.

37. This prediction of the sequence of vicariance events can be tested against the geological evidence, which was accumulating during and after Brundin's work. Evidence indicates vicariance was important but not the whole answer Dispersal may have been important in some situations, as in dispersal through Antarctica between South America and the Australia region

38. Cladistic biogeography is dependent upon how good the cladogram is

39. Approaches to investigating historical biogeographic patterns • Vicariance biogeography--Practitioners starting using data from as many taxonomic groups as possible to see whether the patterns of divergence were similar

40. Numerous studies have been conducted with taxonomic groups from those continents of Gondwanaland. Although they show some similar general patterns, the details are often different from group to group

41. Antarctica likely was a dispersal route between South America and the Australian/New Zealand region at points in the past

42. Patterns of speciation among hosts and their parasites • Most investigations show high degrees of congruence • Indicates biogeographic history is similar for hosts and parasites

43. Difficulties with vicariance biogeography • Dismissal of dispersal • Assumption that past geographic patterns that produced speciation are still evident in today's geographic patterns.

44. Approaches to investigating historical biogeographic patterns Phylogeography or historical biogeography 1. Emphasizes hypothesis testing 2. Uses phylogenies (many of which are developed with molecular data) • Uses area cladograms • Uses fossil and geological data

45. Use of molecular data • Riddle et al. and subspecies of mice and lizards in southwestern U.S. • Species and subspecies have been distinct for millions, rather than thousands of year, indicating reasons for speciation have to do with environmental changes millions, rather than thousands of years ago