76 



body temperature values recorded of any lizard genus. Species varia- 

 tion in thermal characteristics reported is due to recently evolved 

 differences in habitat niches, individual seasonal differences asso- 

 ciated with reproductive and nutritional state, and behavioral trade- 

 offs between maintaining the optimal body temperature and maintenance 

 activities such as foraging. 



200. — . 1978. Reproductive strategies in sympatric Whiptail lizards 

 (Cnemidophorus ): 2 parthenogenetic and 3 bisexual species. COPEIA 

 1978(1): 108-116. 



Cnemidophorus exsanguis , _C. gularis , _C. inornatus , C. tesselatus 

 and _C. tigris were studied in southwest Texas. If the unisexual species 

 are animal weeds, they should possess relatively ^-selected reproductive 

 traits compared to sympatric bisexual forms. Reproductive effort (RE) 

 was estimated by clutch weight to body weight ratios. RE varies inter- 

 specifically, partly as a result of differential habitat preference and 

 productivity. Clutch size and egg weight is partially correlated with 

 female body size. A minimum egg size is suggested; too small and young 

 cannot compete successfully. No differences in RE were observed between 

 the bisexual and unisexual species studied here, except for the higher 

 intrinsic rate of increase for the parthenoforms. Reproductive strategy 

 of a particular species of Cnemidophorus is probably related to its eco- 

 logical position. Any differential selective factors operating on 

 static reproductive characteristics may be overshadowed by constraints 

 imposed by body form, size, and foraging techniques. 



201. — . and E. R. Pianka. 1980. Evolution of escape behavior diver- 

 sity. AMERICAN NATURALIST l[5W: 551-566. 



This paper examines the hypothesis that escape tactic diversities 

 should vary positively with predation pressure among conspecific prey 

 populations and escape tactics should diverge among similar sympatric 

 species that share predators. Escape behavior was quantified for 

 Cnemidophorus tigris at many sites where it occurs alone and for an 

 assemblage of Cnemidophorus species ( exsanguis , gularis , inornatus , 

 tesselatus and tigris ) in southwest Texas. Predation pressure was es- 

 timated by tail-break frequencies. Escape behaviors are described for 

 species. Sympatric whiptail species differ significantly in escape 

 behavior; escape behaviors are more divergent than if each species 

 evolved escape tactics independently of other species in a random fash- 

 ion. Cnemidophorus tigris exhibits a reduced tail-break frequency in 

 southwest Texas than at more westerly sites where it occurs alone but 

 with presumed similar predation pressures, perhaps as a result of in- 

 creased protection offered by a species assemblage with diverse escape 

 behaviors. 



