170 



Increase in Number of Species 



both species evolved on the island from a parent which colonized 

 the island before them and that one of the insular species so 

 produced subsequently colonized the mainland. This latter course 

 is a possibility for a number of insular West Indian species of both 

 plants and animals which have become established successfully in 

 Florida (Neill, 1957). 



Possibilities of species fission by colonization. The possibilities 

 for increase in number of species by colonization are manifold, 

 essentially a product of the multiplication of dispersal possibilities 

 by the number of barriers to species range extension. The manner 

 by which plants and animals become dispersed across inimical 

 ecological areas is extremely varied and has been discussed at 

 length by Hesse, Alice, and Schmidt (1951), Alice, Emerson, Park, 

 Park, and Schmidt (1950), Savile (1956), and Darlington (1957). 

 By far the greatest amount of dispersal which might lead to coloniza- 

 tion is passive: by rafting following floods, by wind, or by other 

 agents. Some animals may cross barriers actively. Flying birds may 

 wander or be blown over mountains or water barriers, or wander 

 far from their normal range (Fig. 71), fish occasionally may swim 



Fig. 71. Unusual wandering of a neotropical bird, the groo\'e-billed ani 

 Crofophaga sulciioslris sitlcirostiis. The "x's" indicate unusual northern or east- 

 ern records; those indicated also with an arrow represent the unusually 

 numerous dispersals noted in 1952. (Adapted from Tordoff 1952, and other 

 sources.) 



