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Freshwater



Dear list

I have enjoyed reading the posts about the K-T extinction. Would anyone
like to comment on the following about why freshwater ecosystems might have
been less affected than terrestrial ones.

1) Under the impact scenario, photosynthesis stopped and plants died. This
devastated terrestrial food chains and hit large animals with big appetites
arranged in simple feeding heirarchies hardest (lots of greenstuff for
large herbivores, lots of herbivore for large carnivores).
2) Small animals with large populations, high fecundity and low absolute
food requirements were less at risk. Enough food could be found in the
nooks and crannies of the environment. Insectivores in particular subsisted
on a virtually indestructible food resource largely grounded in detritus
feeding.
3) Rivers receive organic detritus from the land and many food chains are
partly built on this material (detritus - invertebrate - small fish - big
fish - turtle/croc). The flow of detritus persisted long after edible
material firther out on the watershed had been exhausted so the food chain
persisted also.
4) Animals at the top of freshwater food chains were ectotherms with low
food requirements and the ability to fast for long periods.

Keep writing
Chris Lavers, Nottingham University.