DEMOGRAPHY OF A BIMODAL REPRODUCTIVE SPECIES OF LIZARD (LACERTA VIVIPARA): SURVIVAL AND DENSITY CHARACTERISTICS OF OVIPAROUS POPULATIONS

Lacerta vivipara is a bimodal reproductive species of lizard with allopatric oviparous (egg-laying) and viviparous (live-bearing) populations. The demography of this species has previously been studied in several viviparous populations but has never been studied in oviparous populations. We present a four-year mark-recapture study, including estimates of survival rates and densities for two oviparous populations in the French Pyr6nees. Densities fluctuated between 513 and 709 in- dividuals/ha in the mountain population at Gabas and between 920 and 1830 individuals/ha in the lowland population at Louvie. Survival rates of juveniles from first clutches, subadults, and adults were generally higher at Louvie than at Gabas. These demographic characteristics are very likely responsible for the difference in density. Earlier maturity and higher annual fecundity (due to the ability to lay two clucthes/year) could also account for the higher density observed at Louvie. A comparison of demographic (density, survival) and reproductive (birth dates, maturity, reproductive frequency) characteristics of oviparous and viviparous natural populations reveal that oviparous pop- ulations occur under ecological conditions that allow (1) birth dates and age at first reproduction to be similar to those observed in viviparous populations and (2) density levels and annual fecundities to be at least comparable to (Gabas), or even greater than (Louvie), those observed in viviparous populations. Differences in survival rates between oviparous and viviparous populations were gen- erally not clear-cut. Although these comparisons between allopatric oviparous and viviparous populations cannot be regarded as direct tests of the theories of the evolution of viviparity in reptiles, they yield data for future research (transplant experiments) designed to test these theories.