I- 115 



o 

 ^100 



85 



75 



70 



INCHES OF RAINFALL 

 14 16 

 I \ 



.^''^-' .-b' 



35 40 



CENTIMETERS OF RAINFALL 



FIG. 8-2 An ultraviolet-hydrogram for February populations of 

 pronghorn antelope In Yellowstone Park for the years indicated 

 In italic numerals. It appears that the number of young produced 

 in any year has been determined in a sensitive period two 



Septembers earlier; hence, the ultraviolet data given for each 

 year Is for the second preceding September, and rainfall Is 

 for that September through the August following. Inclusive 

 (modified from Shelford 1954). 



be arhythmic ; cave crayfish, log-inhabiting beetles, 

 moles, shrews, and some ants, for instances. The 

 microfauna of the soil is probably arhythmic. About 

 two-thirds of the mammal species occurring in both 

 temperate deciduous and tropical rain forests are 

 nocturnal. Birds are predominantly diurnal, except 

 that owls are nocturnal and goatsuckers crepuscular. 

 The majority of amphibian and reptile species are 

 nocturnal ; some frogs and lizards are diurnal. 



Among invertebrates, there is considerable vari- 

 ation. The drosophilid flies are crepuscular, having 

 pronounced peaks of activity at dawn and dusk 

 (Taylor and Kalmus 1954). The major period of 

 activity of many nocturnal animals occurs during the 

 first half of the night period, although they often 

 possess a secondary pre-dawn period of activity. 

 With diurnal animals, the major period of activity 

 usually comes during the first portion of the day, al- 



100 Habitats, communities, 



succession 



