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Re: pineal gland notes (large body mass)



Drawbacks of large body size when the going gets rough:

1) High trophic position. Large theropods, for example, were at the  
very top of any food chain you might want to construct. This has  
immediate effects (e.g., concentration of toxins) as well as indirect  
effects due to the loss of energy going up the food chain, namely,

2) Smaller slice of the energy "pie," translating into lower total  
body mass, translating into lower population sizes, translating into  
greater risk of extinction for stochastic reasons. Note that smaller  
population sizes are a side-effect of large body size even if you get  
an EVEN share of the pie, just because each big dinosaur needs more  
energy. Here's an example of stochasticity: if there are ten  
dinosaurs on an island, a disaster occurs, and the chance of dying  
immediately goes to 50%, there is a fairly large chance that all the  
dinosaurs (or at least all the ones of one sex or another) will die.  
But if there are 100 dinosaurs that chance is much, much, much lower.

3) Lower intrinsic rate of population increase. This is familiar to  
everyone: if you wipe out 99% of the little tiny roaches in an  
apartment, it will take them no time at all to recover to "normal"  
population sizes before the next catastrophe occurs. If you do this  
to a population of dinosaurs, it could take hundreds or thousands of  
years to recover EVEN if the environment is temporarily "friendly."  
If the K-T was marked by waves of environmental disturbance (say,  
wildfires and then a collapse of the food chain and then a sudden  
climate change due to changes in ocean circulation patterns, not  
necessarily in that order and surely involving many other things),  
little guys like birds may have had time to build back their  
populations inbetween "rounds" of disturbance, and dinosaurs may not  
have.

There's more to this, but there's a LOT more of my thesis to get  
written in the next 72 hours (thank god I write fast), so enough for  
now...