Intraspecific Variation in demography and Life History of the Lizard, Sceloporus Jarrovi, Along an Altitudinal Gradient in Southeastern Arizona

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Abstract
Mark—recapture studies were conducted on a low (1675 m) and high (2542 m) altitude population of Sceloporus jarrovi in southeastern Arizona, USA from 1973 through 1976. Average age—specific mortality rates differed between altitudes only in the 0—1 yr age class. The increased mortality of neonates are low altitude was correlated with an increased number of potential predators and a significantly greater frequency of natural tail—breaks. Tail—break frequency did not differ between sites for older age classes. Survivorship and age at maturity were greater at high altitude. Low—altitude females mature in their first reproductive season. Transfer of neonates between altitudes indicate that high—altitude females do not mature in their first season even if raised at low altitude. Age at maturity appears to be adaptively adjusted by the demographic environment. Fertility schedules indicate that °40% of the replacement of low—altitude populations results from reproduction by 1st yr animals. There was a greater variation in replacement rate and population size at low than at high altitude.