46 ANIMAL ECOLOGY 



was below 4-6. But when the pH was allowed to rise, the 

 larvae died or suspended their development. This was also 

 the case with another tree-hole mosquito {Anopheles plumbeus) 

 which flourished in acid and not in alkaline water. On the 

 other hand, two species of mosquitoes {Anopheles hifurcatus 

 and maculipennis) normally found in alkaline ponds with a 

 pH of about 8*4, died when brought up in acid water of 4-4. 

 The death was partly due to the fact that the water fungus 

 Saprolegnia, which is one of the greatest potential enemies of 

 mosquito larvae, flourishes in acid but not in alkaline water, so 

 that A. hifurcatus and maculipennis are not normally attacked 

 by it in their alkaline ponds. As soon as the water is made 

 acid Saprolegnia can grow and attack the larvae. Finlaya does 

 not normally get attacked by Saprolegnia ^ but when the water 

 is made slightly more alkaline than usual the lowered resistance 

 of the larvae gives the Saprolegnia an advantage and causes it 

 to become dangerous to the mosquito. 



15. In tropical countries, water-supply is often the chief 

 limiting factor in the ranges of many wild birds and mammals. 

 In the Burmese forests the occurrence of elephants, buffalo, 

 tiger, panther, sambur, barking deer, pig, wild cat, monkeys, 

 etc., is determined in the dry season by the proximity of 

 water-holes, or, in the case of rooting and digging animals, 

 such as pigs and moles, by the softness of the ground, which 

 in turn depends on the water-supply.* In Mesopotamia the 

 black partridge {Francolinus vulgaris) is never found more than 

 a hundred yards from water (which it requires for drinking 

 purposes). ^^ The desert quail {Lophortyx gambeli) of Cali- 

 fornia is similarly limited by water-supply to areas of scrub 

 by rivers."^ 



Shelter is sometimes the determining factor in distribution. 

 In North America the round-tailed ground squirrel {Citellus 

 tereticaudus), which inhabits deserts, is confined to sandy 

 places which have bushes, since it is diurnal and therefore 

 exposed to the rigours of the hot sun, which it avoids by running 

 from one bush to the next. The big desert kangaroo-rat 

 {Dipodomys deserti), which inhabits similar sandy places, is not 



* This information was supplied by Capt. C. R. Robbins. 



