TABLE 12--Food and Water Consumed by Young Mice in Litters, After Weaning. Consumption Is Calculated on the Basis of the Amount (Milliliters or Grams) Consumed per Gram of Litter Weight per Day; Total Amounts Are Shown and Can Be Divided by Litter Size for Average Individual Consumption. Litter Sizes Are as Follows: A=3; C=5; D=6. =====================+=======+=========+=====+=========+========+====== | Total | | | Average | ml. | Total Litter | water | Total | No. | total |H_{2}O/ | water | used |corrected|days | weight |gm./day | /day ---------------------+-------+---------+-----+---------+--------+------ _P. truei_ (A) | 1207 | 1120 | 57 | 58.30 | .337 | 19.64 _P. maniculatus_ (C) | 1427 | 1340 | 57 | 76.14 | .308 | 23.50 _P. maniculatus_ (D) | 700 | 670 | 31 | 58.80 | .367 | 21.61 ---------------------+-------+---------+-----+---------+--------+------ | Total | | Average | Gms./ | Total Litter | food | No. | total |gms. wt.| food | used |days | weight | /day | /day -----------------------------+---------+-----+---------+--------+------ _P. truei_ (A) | 651.2 | 50 | 58.30 | .223 | 13.02 _P. maniculatus_ (C) | 743.8 | 57 | 76.14 | .171 | 13.04 _P. maniculatus_ (D) | 471.1 | 31 | 58.80 | .258 | 15.19 -----------------------------+---------+-----+---------+--------+------ The young of pregnant and lactating females are the animals in the population most likely to be affected by a deficient supply of water. Drought could reduce the water content of the vegetation to such a level that pregnant or lactating females might find it difficult, if not impossible, to raise litters successfully. If such a drought persisted throughout an entire breeding season, the next year's population would be reduced in numbers, for even under normal climatic conditions it is almost exclusively the juveniles that survive from one breeding season to the next. If such a hypothetical drought occurred, lactating females of _P. truei_ would be in a more critical position than lactating females of _P. maniculatus_.