BIOLOGY OF RODENTS 



209 



TABLE 3 



Summary of Enewetak Atoll (All Islets. 1978) 



Wounding and Adrenal Weight Data for 



Roof and Polynesian Rats 



2 4 6 8 10 12 14 16 

 RATS/TRAP HOUR 



Fig. 4 Rats per trap iiour (X 100) and mean wounds per rat 

 (roof and Polynesian rats combined) for eacii islet (1978); f = 

 female, m = males. 



colonies and direct field observations and the incidence of 

 wounding, possibly these fights are not as severe or stress- 

 ful as with the roof rats. 



Although it is likely that food sets the upper limit to 

 density on these islets, with the absence of dispersal and 

 predation as regulatory mechanisms, it also seems likely 

 that physiological changes associated with crowding act to 

 adjust birth and death rates to keep numbers below the 

 point where starvation occurs. 



Stomach Parasite Loads 



The stomach nematode (Protospiura muricola) was not 

 uniform in distribution. Although present in all Polynesian 



*Aomen Islet, Enewetak Atoll. 



rat populations studied by P. C. Rabalais at Enewetak 

 (average prevalence = 0.32; Table 5), it was not found at 

 Bikini Atoll and Mejit Island In the Northern Marshalls sur- 

 vey (Temme, 1979). The parasite load was small in both 

 studies, about two parasites f>er rat. 



In contrast, this parasite was not found in all roof rat 

 populations at Enewetak Atoll; Ananij and Enewetak rats 

 lacked the worm (Table 5). However, the average 

 prevalence on the other islets was 0.56. The average 

 parasite load was 10 times that in the Polynesian rat. 



A second stomach nematode (Gong\ilonema neoplasti- 

 cum) was found by Temme (1979). Because it is imbedded 

 in the mucosal lining. It Is not often recorded. It was found 

 In nearly half the rats In all populations studied (Table 5). 

 However, the parasite load averaged 1.7 worms per rat. 

 About half the rats were Infested with both nematodes. 



In the case of both host species, the larger animals 

 tended to have more parasites. Some roof rats had in 

 excess of 75 Protospiura. Even so, these parasites did not 

 appear to be a serious stress factor. 



