RELATIONS AMONG SPECIES 



353 



Figure 19.1 The sources ot community variation. 



only seeds in annual plants. In animal dormancy, in- 

 activity is characterized by comalike states, es- 

 pecially summer aestivation or winter hibernation. 



MOVEMENTS 



Movements of all kinds can be used to classify the 

 occurrence of individuals or populations within a 

 community. .Nomads are wanderers that are irregular 

 occupants; residents are present at all times; transients 

 are predictable seasonal migrants through the com- 

 munity; and visitants are seasonal occupants dis- 

 tinguished on the basis of their time of presence, 

 usually summer or winter. 



Travel, like activity, can be both daily and sea- 

 sonal; and also like seasonal activity or dormancy, 



movement causes alteration of community composi- 

 tion and structure. Daily animal motility is within 

 the home range, but can be vertical or horizontal. 

 For example, vertical movements are common in the 

 soil or in water, and horizontal ones are within or 

 between surface communities. All of these journeys 

 contribute to changes in spatial relations, and some 

 contribute to changes in composition and structure 

 of a community during any twenty-four hour cycle. 

 Seasonal movements can be vertical or horizontal, 

 local or distant. When they involve some distance, 

 they may be permanent departures {emigrations) or 

 involve later return (migralwns). 



Daily and seasonal movements are not the only 

 possibilities. In addition, movements can be related 

 to cyclic increase of a species or years of peculiar 



