GEOS 26400/36400/BIOS 23255/EVOL 32300: Principles of Paleontology

Evolutionary Paleoecology

I. Relationships between evolutionary patterns and ecological factors
 A. global diversity increase
  *To what extent is diversity accommodated by increase in occupied "ecological space," and to what extent by packing into existing ecospace?
   --evidence for expansion of ecospace
      --increase in bioturbation
      --increase in tiering of suspension feeders
      --increase in number of guilds (Bambach 1983, 1985) [recent, more refined analyses by Bush et al. (Paleobiology vol. 31; Palaeontology vol. 50) consistent with Bambach's results]
      --Novak-Gottshall's theoretical ecospace (Paleobiology 33:273) shows greater ecological diversity and disparity in modern communities	
   --evidence for increased packing in ecospace
      --Cenozoic increase in diversity not matched by tiering
      --increase in number of higher taxa within guilds
      --increase in within-habitat species richness

 B. Clade replacement
   *Agreement between global diversity pattern and LOGISTIC GROWTH MODEL provides prima facie evidence for POSSIBLE clade interactions.
   *Is replacement of one clade by another mediated by competition?
   1. Extinction-mediated replacement
      --Long coexistence of clades with one dominant
      --Extinction of dominant clade
      --Subsequent radiation of formerly small clade
      --Pattern suggests advantages of incumbency
      --Example: dinosaurs and mammals

    2. "Double wedge"
       --Problem: independent time series often show correlations
       --Evidence needed to argue for interaction
         --species in two clades have common resource need
         --geographic coexistence
         --direct evidence for interaction
           *possible example: cheilostome and cyclostome bryozoans
            -coupled logistic equations
            -overgrowth evidence; relation to frontal budding
            -mechanism unclear (How exactly does greater ability to overgrow yield higher diversity?)

II. Geography of evolutionary innovation
 A. Onshore-offshore patterns
   -Basic observation: Many higher taxa and communities show differential
origin nearshore, subsequent expansion or retreat into offshore habitats.
   -Aspects of data and analysis
    -taxonomic lists with lithologic descriptions
    -environmental interpretations on physical, not biologic, criteria
    -taphonomic controls (not all studies)
    -attempts to determine patterns attributable to preservation and sampling intensity
	*unresolved question: Exactly what pattern is expected to result as artifact of sampling?  				 -pattern of first appearance depends on:
	   -true probability of origination in given environment
	   -probability of "migration" between environments
	   -relative sampling probability of environments
   -Potential explanations
    1. greater diversity nearshore (more novelties generated)
    2. greater per-taxon orig. rate nearshore (more noveltiess generated)
       -some data show this differential rate, others don't
    3. lower per-taxon extinction rate nearshore (more noveltiess survive)
       -some data show this differential rate, others don't 
	(in fact, comprehensive data for Paleozoic genera show the opposite)
    4. Extinction gradients (Sepkoski model)
       a. higher extinction rate nearshore (works in Paleozoic)
       b. successive faunas have progressively lower rates of origination and extinction
       c. Model predicts expansion of new group and retreat of old group regardless of where new group originates. 

 B. Latitudinal patterns: lower taxa
  --Background: High diversity in tropics: "cradle or museum?"
  --Analysis by Jablonski et al. (2006, Science) suggests cradle AND museum
    --data: marine bivalve genera
    --higher rate of origination of new genera in tropics
    --spread of genera to higher latitudes ("Out of the Tropics" model)
  --For living bivalve genera anchored in tropics, geographic range is correlated with species richness
    --This suggests increase in geographic range and accumulation of species go hand-in-hand
	(Krug et al. 2008, Proc. Roy. Soc. Lond. B. 275:1117)

 C. Latitudinal patterns: higher taxa
  --Basic observation: disproportionate origin of marine orders in tropics (Jablonski 1993)
    --Aspects of data and analysis
      --origin of orders as proxy for evolutionary novelties
      --pattern in poorly preserved groups used to show expectation of sampling alone (see "unresolved question" under Onshore-offshore patterns, above)
      --Possible explanation: opportunities in the wake of extinction events

III. Age and Area
 --Willis (1922, "Age and Area") proposed that taxa expand geographically as they age.
  -some evidence based on living organisms
  -Willis's idea was summarily dismissed
 --Miller 1997 (Paleobiology) showed that, in Ordovician, genera tend to expand geographically with age.
 --Several recent studies show, on average, gradual expansion and contraction over lifetime of species and genera (Jernvall & Fortelius, 2004, American Naturalist; Foote 2007, Paleobiology; Foote et al. 2007, Science; Liow & Stenseth 2004, Proc. Roy. Soc. B.)
 --Correlation between geographic range and taxonomic duration found in many groups.  What is direction of cause and effect?
    --Recent analysis by Foote et al. (2008, Paleobiology) shows effect of duration on range and of range on duration are about equally strong