INSECT ECOLOGY 



397 



no plus strumosus. On bare or lichen-crusted rock occurs Trimerotropis 

 saxatilis (see page 197), which occupied that station before the forest 

 came. 



Adaptations. "Brachypterism (the short-winged condition) in 

 locusts is a more complete adaptation to a leaping mode of progression 

 brought about by life in situations where flight is difficult or impracti- 

 cable, and consequently disadvantageous. That this is the true ex- 

 planation is indicated by the habits and haunts of the majority of the 

 flightless species (sylvan surroundings or tangled undergrowth wherever 

 found); by their distribution locally, horizontally, and vertically; and 

 by the equally characteristic habits, haunts, and distribution of macrop- 

 terous (long-winged) species as inhabitants of the open field, desert, or 

 savanna. 



"The advantages of progression by flight dispersal widely and 

 easily effected, often aided by the wind, ease of escape from many ene- 

 mies, etc., and the superiority of this mode in open lands are evident 

 to all. On the other hand, long wings and locomotion by flight are 

 disadvantageous amid dense underbrush, where a leaping mode of 

 progression has decided advantages. Organs unused or disadvanta- 

 geous tend to dwindle and disappear; hence the loss of wings. 



"It is found that Orthoptera frequenting habitats involving passage 

 over open spaces of considerable extent, such as fields, between trees in 

 forests, and bushes or thickets in deserts, are usually long-winged, flying 

 species; and others dwelling in an environment of more or less dense, 

 intricate, interlacing vegetal growth, be it sub-alpine or sub-tropical, 

 in forest or swamp or in burrows, crevices, etc., in short, in stations 

 where wings are not needed or are at a disadvantage, are very generally 

 apterous (wingless) or brachypterous (short- winged) . 



" Brachypterism, therefore, appears to be largely not so much a case 

 of natural selection through the agency of the wind as an adaptation in 

 structure to habits. The fact that the heavier-bodied female is more 

 frequently or completely brachypterous than the male and that the teg- 

 mina in the latter sex when used as musical organs are retained in a 

 less degenerate condition (even when entirely useless in flight) , confirms 

 this explanation of brachypterism." (A. P. Morse.) 



COMMUNITIES OF STREAMS 



From Shelf ord's notable volume, Animal Communities in Temperate 

 North America, we may take, from the wealth of data given, examples of 

 common insects representing the various communities of streams. 



