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SUMMARY:The evolutionary invention of food-webs: a palaeobiological and ma
 croecological approach - Nick Butterfield\, Department of Earth Sciences\,
  University of Cambridge
DTSTART:20130612T130000Z
DTEND:20130612T140000Z
UID:TALK45580@talks.cam.ac.uk
CONTACT:Christian Franzke
DESCRIPTION:Food webs are patterns of who eats whom\, and the associated c
 ycling of nutrients and biomass.   At the base of all food webs are primar
 y producers\, which are consumed and redistributed through a variety of he
 terotrophic organisms\, often arranged sequentially via trophic tiering.  
 The local expression of any particular food web is determined by the inter
 play of ‘bottom-up’ resources (competition) and ‘top-down’ consume
 rs (predation).  On a larger scale\, however\, they are dependent on the o
 verall diversity\, body sizes and connectivity of the constituent nodes\, 
 which in turn controls ecosystem function\, biogeochemical feedbacks and e
 volutionary potential.\n\nPrior to the evolution of ingestive multicellula
 r heterotrophs (animals)\, food-webs were presumably limited to few tiers 
 and microscopic size\, comparable to the bacteria-flagellate-ciliate micro
 bial loop that dominates modern oligotrophic oceans.  The small size and b
 illion-year stasis exhibited by early (pre-Cryogenian) fossil assemblages 
 attests to the absence of animal-based ecology and limited trophic innovat
 ion.\n\nThe Cryogenian-Ediacaran appearance of sponge-grade multicellulari
 ty allowed flagellate organisms to overcome the tyranny of viscous flow\, 
 introducing a fundamentally new process to food-web dynamics.  Macroscopic
 \, turbulent-flow suspension feeding would have had major effects on water
  column ventilation and nutrient cycling in shallow shelf settings.  Even 
 so\, the limited ability of sponges to consume larger particles or to move
 \, combined with their low palatability\, suggests that they contributed r
 elatively little to the expansion of trophic diversity.\n\nThe Ediacaran a
 ppearance of organ/cnidarian-grade multicellularity introduced both muscul
 ar motility and a potential for macrophagous ingestion into the trophic mi
 x.  Like sponges\, however\, jellies are largely a trophic dead-end\, and 
 their blind gut and limited brain-power would have had only modest\, prima
 rily indirect\, effects on early food-web dynamics.\n\nBy contrast\, the l
 ate Ediacaran evolution of cephalized bilaterians with a through gut revol
 utionized the structure\, function and evolutionary potential of food webs
 .  Bilaterians readily eat other bilaterians\, and have the neural\, locom
 otory and developmental capacity to derive sequentially higher-order troph
 ic tiers\, opening up fundamentally new regions of ecospace based on large
  body size and complex multi-trophic interactions.  Compounding counter-re
 sponses in underlying tiers further multiplied diversity and ecological re
 pertoires\, including escape into sediments and plankton.  These in turn h
 ad profound feedback effects on ecosystem function and evolutionary dynami
 cs\, ultimately giving rise to the modern marine.  The early exponential p
 hase of this planetary regime change is known as the Cambrian explosion. \
 n       \nButterfield\, N.J. 2011. Animals and the invention of the Phaner
 ozoic Earth system. Trends in Ecology & Evolution 26\, 81–87.
LOCATION:British Antarctic Survey\, Room 330B
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