EVAPORATIVE WATER-LOSS IN 2 SYMPATRIC SPECIES OF VESPERTILIONID BAT, PLECOTUS-AURITUS AND MYOTIS-DAUBENTONI - RELATION TO FORAGING MODE ANDIMPLICATIONS FOR ROOST SITE SELECTION
Pi. Webb et al., EVAPORATIVE WATER-LOSS IN 2 SYMPATRIC SPECIES OF VESPERTILIONID BAT, PLECOTUS-AURITUS AND MYOTIS-DAUBENTONI - RELATION TO FORAGING MODE ANDIMPLICATIONS FOR ROOST SITE SELECTION, Journal of zoology, 235, 1995, pp. 269-278
Simultaneous measures of oxygen consumption and evaporative water loss
(EWL) were made in two species of temperate-zone vespertilionid bat (
Plecotus auritus and Myotis daubentoni; mean body mass 9 . 12 and 10 .
12g, respectively) at ambient temperatures (T-a) of 5, 15 and 25 degr
ees C and variable vapour pressure deficit. EWL was directly dependent
on vapour pressure deficit and oxygen consumption and inversely depen
dent on T-a. EWL was significantly greater in P. auritus than in M. da
ubentoni. A model for EWL in P. auritus under a variety of environment
al conditions (5-25 degrees C and 20-80% relative humidity) suggested
that EWL from bats in shallow summer torpor will be lowest at low T-a,
and that, except at low (< 50%) relative humidity, EWL from euthermic
bats will be lowest at high T-a. At low relative humidity (< 20%), re
sting bats could lose over 30% of body mass per day (24h) through evap
oration. At high T-a (> 25 degrees C), EWL from euthermic bats could b
e over 65% lower at high (> 80%) compared to low (< 20%) relative humi
dity. In bats in shallow summer torpor at low (5 degrees C) T-a the eq
uivalent saving was > 96%. At low relative humidity predicted EWL from
bats in shallow summer torpor was 34 to 81% of that from euthermic ba
ts, and at low T-a and high relative humidity was only 2%. In the wild
, M. daubentoni has freer access to drinking water than does P. auritu
s and yet EWL at rest was higher in the latter species. We suggest tha
t post-prandial dumping of urinary water by M. daubentoni leads to a l
imit in the amount of body water available to this species to cover ev
aporative losses once within the day roost, which in turn has led to a
n adaptation of physiology towards the minimization of EWL when at res
t.