MORBISON 



A small scattering of points below the main body have not been 

 included in the heavy average because they represent a distinct 

 population, but their inclusion as shown by the dotted curve does 

 not change the picture appreciably. Figure 11 presents the thermo- 

 regulatory response to cold in this species and shows it to be an 

 adequate regulator since the slope is a modest one, comparable 

 to that in many other mammals. Under heat stress, however, there 

 is almost no regulation, the slope being little less than the value 

 of 1.0 characteristic of a poikilo therm. 



Figure 12 shows a somewhat different T response in a smaller 

 species. At modest T^ values of 15-20 cf, the T falls subs tan- 



^ ^/::..:-:.-:r--B 



tially. But when the T is cooled further, the animal seizes hold 

 and regulates its temperature quite effectively. Thus, the reduced 

 T did not represent a deficit in capacity or ability to regulate, 

 Since the animal regulated well at an even lower T . It can be con- 

 sidered as representing a kind of deficiency — careless thermo- 

 regulation — but there may be functional implications. This type 

 of response may be seen in other mammals. The jumping mouse 

 (Zapus), for example, may cool appreciably at intermediate T 

 values, but regulates well at or below . Again, there is no deficit 

 in the capacity or ability to regulate, but the animal retains an 

 option as to its use. 



Figure 13 shows the daily cycle in a larger bat (P hyllostomus) 

 which differs somewhat. The two peaks are characteristic of a 

 crepuscular animal which feeds at dawn and dusk. Again, there 

 are a number of points which exceed the dispersion of the bulk 

 of the values (d 3 S. D.), and we have in addition some very low 

 points which approach the T . This polydispersity (seen also in 

 Artibeus, Fig. 10) suggests that we may be dealing with several 

 conditions or activity levels, a situation already indicated in the 

 insectivorous bat Miniopterus (Morrison, 1959). This suggestion 

 appears to be confirmed in Figure 14 which shows the more com- 

 plicated response of Phyllostomus to cold. Now in Figure 13 this 

 bat could be thought of as operating under different conditions — 

 perhaps "active," "quiet," "sleeping" and "torpid." It was ordi- 

 narily resting during the daytime but even then could become active 



with a higher T . Occasionally it showed a torpid, poikilo thermic 

 B 



400 



