284 



Origin of Biomes and Succession 



124). A remarkable set of behavior patterns have evolved parallel 

 with this set of successional events. In the first stage there is a 

 remarkably timed succession of ovipositing flies, starting at the 

 very instant that the dung is dropped. The first fly species is on 



INSECT 



DAYS 



I 2 3 4 b e 7 9 10 II 12 13 14 15 le 17 18 19 20 21 22 23 24 2b 26 27 28 



Haematobia 



Sarcophaga 



Paregle 



Cryptolucilia 



Sepsis 



Leptocera 



Geosargus 



"T — I — I r — I — I r- 



"T — I 1 — r- 



ECC AND LARVAL STAGE 



PUPAL STAGE 



_i I 1 1 1 i_ 



_l I I I I L- 



_1 I I 1 l_ 



Fig. 124. Predominant fly maggots of the first two microcommunities in 

 freshly dropped cattle droppings. The upper four species belong to the first 

 stage of succession. (From Mohr.) 



the cake only one or two minutes, the next set less than an hour, 

 and the others up to six hours (Fig. 125). 



The key species of the first microcommunity and many of those 

 in the second occur only in this microhabitat. The various species, 

 however, are related not to each other but to species with other 

 habits. The various species therefore colonized the microhabitat 

 independently, then, after forming a species mixture, evolved habits 

 which resulted in the present community structure. Although this 

 example is not an exact replica of successional communities in 

 plants, there is considerable indication that the members of the 

 first dung microcommunity bring about changes in the medium 

 making it more readily available to invaders of the second micro- 

 community. 



After a series of subclimax stages have evolved, it is always 

 theoretically possible for new species to colonize the system or old 

 species to evolve new properties, and to bring about a modification 

 of successional relationships. 



