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For terrestrial animals breathing air there is usually no problem in gaining access to a sufficient supply of oxygen; 21 per cent of air is oxygen and the rapidity of gaseous diffusion makes the occurrence of significant oxygen gradients highly unlikely. In any case, even in a confined body of air such as that within a nest or burrow, rising carbon dioxide levels are likely to affect animals long before oxygen tensions become limiting. Animals living in extensive burrow systems are faced with a problem of the removal of stagnant, CO2 - laden air, and this tends to be solved by appropriate burrow architecture, reaching its culmination in the intricate ‘cities’ of the prairie dogs (Cynomys). Prairie dogs live in burrow systems which extend for miles, and were even larger in the last century, before burgeoning agriculture came into conflict with their habitat. The burrow entrances invariably have lips to prevent flooding, are usually constructed on eminences to give ‘watchdogs’ a good view, and apparently produce adequate air conditioning by virtue of the Bernoulli effect acting upon the raised openings.
KeywordsOxygen Tension Ventral Sucker Rock Pool Mantle Cavity Shell Valve
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