Panama and the Great American Interchange. Reading: Marshall et al. 1982

Transcription

1 Panama and the Great American Interchange Reading: Marshall et al. 1982

2 Lecture 6 Recap Lars Brundin

3 Lars Brundin What about the general suitability of chironomid midges as indicators in biogeography? In the possession of a developmental cycle comprising larva, pupa, and imago these orders offer three quite different types of organiza4on and adapta4on within the limits of a species. We thus have the great advantage of being able to cross- check the phylogene4c conclusions drawn from one stage with the others, thus a>aining a high degree of reliability by the establishment of monophyle?c sister groups.

4 Earth History, Vicariance, and Dispersal Lars Brundin NZ S. America S. Af Aus

5 Lars Brundin Major observa+ons from phylogeny The sister group of a NZ group lives always in S. America, or in S. America and Tasmania- Aus. There are no direct connecpons between a group of Tasmania- Aus. and group of NZ A group of Tasmania- Aus. Is always an apomorph (morphological advance) offshoot of the S. American fauna.

6 Lars Brundin

7 Joseph Dalton Hooker the botanical rela?onship [of the three great areas of land in the southern la?tudes] is as strong as that which prevails throughout the lands within the Arc?c and Northern Temperature zones, and which is not to be accounted for by any theory of transport or varia?on, but which is agreeable to the hypothesis of all being members of a once more extensive flora, which has been broken up by geological and clima?c causes.

8 Lars Brundin Note on the amphitropical movement of midges the search for the sister group of an austral group leads sooner or later to a group in the northern con?nents. Ones seen are all apomorphs of austral groups, consequence of transtropic dispersal north There are warm- adapted sister groups which allow for tropical habitapon, which can then spread out of the tropics again into cool running streams

9 Dispersal and Centers of Origin Dispersal includes all types of geographic translocapon of individuals leading to changes in the distribupon of populapons and species across a range of spapal scales Two main processes: - Range Expansion - Jump Dispersal

10 Range Expansion Movement away from parents as a normal part of the life cycle (small scale) Gradual expansion of geographical ranges through the spread into areas beyond the boundaries of the inipal range in response to: - Habitat modificapons - ClimaPc shi\s - AdaptaPons

11 Range Contrac+on This can lead to disjunct distribupons and isolapon of closely related taxa in refugia This has been studied extensively in light of North American Pleistocene (2.6 million to 11K years ago) glaciapon events

12 Range Contrac+ons + Expansions Walker et al Looked at a widely distributed millipede Northern animal populapons tend to show lower genepc diversity than southern populapons Looked at millipede genepcs and paleoclimate niche- based distribupon models to invespgate populapons in refugia and post- glacial populapon expansions

13 Range Contrac+ons + Expansions Look at how far we have come since Brundin!

14 Range Contrac+ons + Expansions Present Last Glacial Maximum

15 Range Contrac+ons + Expansions Results show that there is evidence for refuge populapons in the S. Appalachian Mountains and coastal plains Range expansions radiated from two separate areas Strong correlapon between zones of ecological suitability and levels of genepc diversity

16 Jump Dispersal Species level process, carried out by individuals, that involves crossing some kind of barrier through some chance or otherwise rare event Considered very important by some biogeographers, and important in some systems (oceanic islands)

17 Center of Origin First postulated by Linnaeus, life spread outward from a single point as more land emerged from the sea If this theory explained everything (a world with no barriers) we would have mostly pan- tropical and pan- temperate species, with conpnental species reaching every island - This is obviously not the case

18 Effec+veness of Barriers The fact that most species occupy only a limited part of their potenpal range demonstrates the existence and effecpveness of barriers The existence of endemic species requires that geographic areas remain isolated long enough for these species to evolve in the first place

19 Barriers are less effec+ve for certain species Some species can achieve a cosmopolitan distribupon, either because the barriers are ineffecpve or they have good powers of jump dispersal

20 Earth History, Vicariance, and Dispersal Barriers are less effec+ve for certain species Some species can achieve a cosmopolitan distribupon, either because the barriers are ineffecpve or they have good powers of jump dispersal Pan- tropical distribupon

21 Earth History, Vicariance, and Dispersal Barriers are less effec+ve for certain species Some species can achieve a cosmopolitan distribupon, either because the barriers are ineffecpve or they have good powers of jump dispersal Supertramp Strategy Pan- tropical distribupon Jared Diamond

22 Larry Marshall Great American Interchange History Advances in technology Theories of immigrapon and expncpon rates Because you will be discussing this today, I wanted to give you some background on some of the technical parts of the reading

23 Central American Seaway

24 Changes to Ocean Circula+on

25 Changes to Ocean Circula+on

26 Allowed for Exchange of Fauna

27 Radioisotopes We know this because of: - Beder sampling methods (esp. of small mammals) - Improved taxonomies - Radioisotopic- based dates on mammal- bearing strata 40 K - > 40 Ar dapng

28 Radioisotopes

29 Rarefac+on Rarefac+on Analysis Assess species richness from the results of random sampling In the case of the paper, they are assessing familial richness from the results of randomly sampled genera i. Is the nature of sampling and taxonomic treatment consistent? ii. Did familial diversity differ significantly among the Pme intervals sampled

30 Robert MacArthur E.O. Wilson Equilibrium Theory of Island Biogeography Larger areas can support more species Islands closer to the mainland will have more immigrapon Increased immigrapon will increase compeppon and increase expncpon rates Species richness is a funcpon of immigrapon and expncpon Species composi?on is constantly changing, but species richness will stay constant

31 Earth History, Vicariance, and Dispersal Larry Marshall

32 Larry Marshall

33 Larry Marshall

34 Larry Marshall ~130 Higher # of na+ve genera in N. America ~70

35 Larry Marshall ~130 Higher # of immigrants from N. America ~70 ~15 ~25 The number of primary immigrants appears proporponal to the size of the respecpve source faunas.

36 Larry Marshall ~130 Higher ex+nc+on rate of na+ve S. American genera ~70 ~15 ~25 Consistent with paderns expected for a supersaturated biogeographic system.

37 Larry Marshall Higher diversifica+on rate for N. American immigrants ~130 ~70 ~15 ~25 Not predicted from equilibrium theory.

38 Main Points Dispersal processes include range expansion and jump dispersal Range Expansion - Gradual expansion of geographical ranges through the spread into areas beyond the boundaries of the inipal range in response to habitat modificapons, climapc shi\s, adaptapons Jump Dispersal - Species level process, carried out by individuals, that involves crossing some kind of barrier through some chance or otherwise rare event Organisms spread from a center or origin, but are kept from global movement due to barriers, which are more or less effecpve depending on species

39 QuesPons on the reading?