Zoogeography
  1. I. Principles, definitions, processes
    1. Study of bio/zoogeography
      1. Two goals:
        1. Delineation and characterization of faunal areas
        2. Determine the evolutionary history of these faunas, in geographical context
      2. Distribution of taxa in space explained by:
        1. Historical factors: evolutionary origin of taxon on one part of planet, subsequent spread of that taxon over evolutionary time can be explored
        2. Ecological factors: distribution of abiotic (habitat variables: climate, etc) and biotic (predators, competitors) can explain distribution of organisms
        3. Will focus for today on historical zoogeography
    2. Types of distributions
      1. Endemic: found only in a particular region. Hawaii, Bermuda have many endemic fishes. Can be endemic to island, ocean, continent.
      2. Circumglobal, circumtropical: widely distributed across globe or throughout tropics. Particularly true of epipelagic fishes, e.g. many oceanic tuna, billfishes
      3. Antitropical: group absent from tropics but present at higher latitudes, both sides. Can be an individual species, e.g. Scomber japonicus; can refer to a higher taxon e.g. a genus, family
    3. Historical processes influencing distributions
      1. Dispersal
        1. Present or ancient distribution occurs in multiple places bkz group moved into areas it didn’t originally occur in.
        2. Center of origin of group; as group spreads, there is further cladogenesis
        3. Ancestral group in center or pushed out to edges?
        4. Freshwater fish may disperse:
          1. freshwater or overland dispersal:
            1. rivers change course
            2. stream capture, as headwater erosion cuts through watershed boundary
            3. primary freshwater fishes are groups strictly confined to fw
          2. dispersal via marine waters
            1. secondary freshwater fishes are usually limited to freshwater but occasional individuals or species may be estuarine or marine;
            2. peripheral fishes have evolved fw lifestyle from marine group, or migrate between (diadromy)
            3. Example: Plotosid catfishes; marine group that has secondarily invaded fw in Australia, new guinea. Secondary or peripheral?
          3. freshwater fishes on isolated oceanic islands are secondary or peripheral
        5. Marine fish can certainly disperse
        6. Dispersal involves random events, acting on individual taxa
      2. Vicariance
        1. barrier divides a distribution; division followed by allopatric speciation, perhaps to further cladogenesis.
        2. Present or ancient distribution occurs in multiple places because group was present before places were isolated.
        3. For terrestrial and freshwater organisms, continental drift is major vicariant event.
        4. for marine organisms,
          1. spreading of sea basin; isolation by distance
          2. formation of isthmus of Panama isolated w. atlantic from e. pacific, cutting species in two.
        5. Events likely to occur to many taxa
      3. Competing ideas
        1. These are two basic models for how distributions arise
        2. Both likely to be required for full explanation of any taxon; but lively debate on relative importance
        3. Classically, explanations were dispersalist
        4. Relatively modern evidence for continental drift gave life to vicariant hypotheses
    4. Modern methods used in analyzing processes:
      1. seek common patterns of distribution by comparing phylogenies and distributions for diverse taxa
      2. Determine distribution of taxon and subtaxa
      3. Determine phylogeny for group
      4. Repeat for other taxa in same areas
      5. If possible, also develop an 'area cladogram' based on known geological history: e.g., Australia, Africa and South America
      6. Fossils can be very useful; paleodistribution, and establishing a minimum age
  2. One example: the fishes of Africa and S. America
    1. Large number of shared taxa (table, Lundberg)
    2. Given a hypothetical clade, C, made up of C1 and C2, on different continents. Four possible models for this distribution (schematic)
      1. Simple drift/vicariance

        2. Drift followed by allopatric speciation

      2. Pre-drift intercontinental speciation

        3. divergence prior to drift

      3. Post drift dispersal

        4. divergence following dispersal

      4. Indirect dispersal

      common ancestor isn't present on either continent

    3. Geological evidence for split between continents

      4. Sometime between 106 and 84 Ma; mid-Cretaceous

    4. Lungfishes: support drift/vicariance model
      1. Well supported phylogeny (fig 8.2, Lundberg)
      2. fossil neoceratodontid from early Cretaceous; so ancestral lepidosirenid, as sister taxon, originated before drift.
        1. rules out model 3
      3. subsequent fossils of two genera limited to current continental ranges and earliest is late Cretaceous
        1. rules out model 2
      4. Marine dispersal for lungfishes out of the question
        1. rules out model 1
    5. Arapaimidae supports pre-drift speciation model

      6. Two fossils: Aptian (110 Ma) age of L. indicates that split between Arapaima and Heterotis occurred before drift

      1. indicates model 2 over vicariance
    6. Bottom line; diversification of freshwater fauna on these two continents cannot be explained by one geological event.
  3. North American freshwater fish zoogeography
    1. Relict fishes
      1. Several ancient fish families present here
      2. Pangaea (ca. 200 Ma) dominated by early actinopterygii (chondrosteans, holosteans) and sarcopterygii. (fig. 1.1, p 5 Hocutt and Wiley)
      3. Gars and bowfins: Jurassic in origin (check Nelson) and probably widespread, now present only here
      4. Polyodontidae, Hiodontidae: Asian-Namerican distribution. In late Cretaceous, one unified northern continent (fig 1.5 Hocutt and Wiley, p 7).
    2. Ostariophysans
      1. Gondwanaland, in Jurassic (prior to fig. 1.2, p 5 h&w) dominated by ostariophysans. Origin in western part, Africa/South America.
      2. Diversification of catfishes and characins in Jurassic and Cretaceous
      3. Ictaluridae (endemic family): catfishes invaded Eurasia and N America in Cretaceous. Ictalurid fossils from beginning of Cenozoic. Closely related to Asian African bagrids, so invasion from Asia.
      4. Catastomidae: (fig. 3-4, p. 607 bond): late arrival. N American fossils mid-Eocene.
      5. Cyprinidae (fig. 30-5, p. 609 bond). Earliest fossils in Asia, Eocene. Earliest fossils in Europe and N america are Oligocene. Persistent land bridge in Beringia may have permitted invasion, 32 ma. Even later invasion of Africa
    3. Zoogeography of the northeast
      1. Diversity in the area is pretty low; certainly relative to the Mississippi drainage basin
      2. Why? Pleistocene glaciation (fig 30-7, p. 611 Bond)
      3. Completely cleared the area of fish (fig 5.2 in Hocutt and Wiley 1986, p 142)
      4. Refugia

        5. There were several places that continued to have fish throughout. Obviously, down south; also some unlikely places, such as a spot off the Georges Banks.

      5. Dispersal

Once glaciers retreated, the fishes in the refugia recolonized our area.