ECOLOGICAL SUCCESSION 29 



theory of succession are probably just as valuable. In any 

 case, it is desirable that botanists and animal ecologists should 

 cooperate in such studies, and in most cases a team of several 

 people is required for the proper working out of the animals. 

 It is probable, however, that in the simpler cases one man could 

 do very valuable work. 



15. We have not spoken so far of succession in the sea. 

 Owing to the peculiar importance of sessile animals on the 

 shores and slopes of the sea, it is not uncommon to find plant 

 and animal succession becoming rather closely related. 

 Wilson ^2 watched the succession on bare areas on the shores 

 of California at La Jolla, and found that the pioneers were 

 colonial diatoms which formed the first community. These 

 were followed by an association of colonial hydroids (mostly 

 Obelia)y and the latter were then replaced by a seaweed (Ecto- 

 carpus), which became dominant after some four months. 

 Further stages were foreshadowed, and it appeared that the 

 whole would ultimately develop into a cHmax association of 

 other seaweeds (chiefly kelp). The interesting thing about 

 this sere is the fact that the second stage in succession is 

 formed by sessile animals, and is sandwiched between two 

 plant stages. The zonation of animals and plants in the inter- 

 tidal zone in other regions is often an alternation of animal 

 and plant dominance, e.g. Balanus or Mytilus and seaweeds, 

 in the temperate regions. On coral islands succession may 

 consist almost entirely of a series of animal zones with only an 

 occasional plant zone formed of calcareous algae.io* In such 

 cases it is perfectly legitimate to refer to the most abundant 

 animal as the " dominant " species, but in most animal com- 

 munities the term has little meaning owing to the different 

 methods of feeding adopted by animals and plants. It is 

 perhaps better to avoid the use of the term " dominant " in 

 the cases of animals except for sessile aquatic species, since 

 dominance implies occupying more space or getting more light 

 than other species. 



16. We have just pointed out that animals play an important 

 part in ecological succession in the sea ; but it should also be 

 realised that they also have very important effects in a different 



