332 
Discussion 
DISCUSSION 
RUIBAL to RAND: You will have a hard 
time defending the position that a lunge 
and a huff take less energy than a single 
bite. 
RAND: Yes, if by bite you mean a single 
nip and release. But an iguana usually bites 
and holds on despite the struggles of the 
bitten individual and this appears to take 
a lot of energy. Still, I would like very much 
to have real measurements of the costs of 
these activities. 
RUIBAL: If 99 percent of the energy is 
in digging the hole, then the energy involved 
in display is meaningless in the economy of 
the animal anyway. 
RAND: That is possible, but we are sug- 
gesting the contrary. We suggest that the 
energy used in display is important to these 
animals. The close correlation between energy 
and effectiveness of displays, for example, 
argues that energy costs are important. In 
this lizards differ from birds and mammals. 
The much lower maintenance energy budget 
of an ectotherm means that any action, even 
a fairly simple one, costs a much larger 
fraction of the energy the animal will use in 
the course of its day than would be the case 
of a homeotherm with its much higher main- 
tenance energy budget. 
CREWS to MARCELLINI: Did you ever 
follow one or several animals through the 
night to determine calling periodicity? 
MARCELLINI: No, I didn’t, but in cap- 
tivity animals tend to call more females in 
the evening and morning hours. 
CREWS: Did courting males call from 
near females or distantly; and did females 
stand for males after calling or did they move 
away? 
MARCELLINI: Calls varied in distance 
from a few centimeters to as much as several 
meters. Females frequently moved away frofn 
calling males but males pursued them. There 
was little, if any, courtship; males simply 
rushed females, took a neck grip, and copu- 
lated. 
JENSSEN : Before man built habitable 
buildings for dense populations of geckos to 
live in, how do you think the calls functioned 
in sparse natural populations of geckos? 
MARCELLINI : Many populations of 
geckos are naturally dense, even in habitats 
such as trees or rock cliffs. The calls function 
in these situations just as in my study. 
JENSSEN to FERGUSON: Did you run 
your density dependence analysis between 
years as well as between sectors within a 
year? 
G. FERGUSON : Yes, and we did not detect 
density dependence. The densities between 
the 2 years were quite different, yet “appar- 
ent” competition was greater in the low- 
density year. Variation between years in 
carrying capacity was probably masking den- 
sity dependent effects. 
CREWS: Could you compare growth rates 
of early and late clutch hatchlings and relate 
differences to differences in food availability ? 
G. FERGUSON : Later hatchlings did grow 
slower. However, the temperature was lower 
and cloud cover was greater later in the 
hatching season. So, even if food were equally 
available to early and late hatchlings, the 
later ones might have grown slower due to 
fewer favorable growth periods per unit 
time. 
BR ATTSTROM : Have the first clutch 
hatchlings attained a larger size by the next 
spring ? 
G. FERGUSON: Yes, and we did not detect 
may have a fitness advantage over younger 
siblings due to dominance advantage or 
larger clutches, but within a size-peer group 
of younger (hatched later) lizards there is 
a definite fitness advantage of the larger ones. 
RAND : In your proposed test of the preda- 
tor avoidance model for the evolution of Uta 
displays, how are you going to distinguish 
between a lizard that gives a long display 
less frequently and one that gives a short 
display more frequently so that the total time 
of display for the two lizards is the same? 
G. FERGUSON: One must measure fre- 
quency of display. The model assumes that 
display frequency is not different, but only 
the display complexity. 
GREENBERG: The real selection in such 
