576 



INTERRELATIONSHIPS OF ORGANISMS 



populations of "base-industry" animals and contribute large quantities 

 of dead plant tissues to the detritus on the bottom. The latter supports a 

 tremendous biota of bacteria, fungi, algae, protozoa, and minute Crus- 

 tacea; these organisms add one or two links, not indicated in the diagram, 

 to the "detritus food chain." The arrows lead from supply to user and 





i-: ; \;.i?>;»'. ,.','..' «, i i,i{ :. »• 





i—LL. 



Fig. 33.10. The filling of a lake with peat deposits, and the succession of land plants on its 

 margins. (From Skull, Principles of Animal Biology.) 



indicate by the various thicknesses of line the approximate importance 

 of the relation. 



Another type of food chain is found in host-parasite relationships. Here 

 the progression from link to link in size, numbers, and biotic potential 

 is just the reverse of that shown in prey and predator relationships. The 

 parasites of the fox are smaller, more numerous, and have a higher biotic 

 potential than the fox, and they, in turn, are hosts for still smaller, more 



