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Ecology and comparative demography of the lizard Sceloporus grammicus: Life history of an altitudinal generalists on the eastern slope of the Iztaccihuatl Volcano, Puebla, Mexico
Abstract
Population studies on the high altitude lizard Sceloporus grammicus were conducted using mark-recapture methods on two study sites located at 3,700 m elevation (low altitude site) and 4,400 m elevation (high altitude site), on the eastern slope of the Iztaccihuatl Volcano, Puebla, Mexico, over a four year period to assess differences in thermal biology, growth rates, and demographic characteristics. Regardless of contrasting differences in environmental conditions between study sites, individual lizards maintained similar active body temperatures, growth rates, and population parameters. Active body temperatures at both study sites were approximately 32$\sp\circ$C. However, individual lizards at the low elevation site showed a greater resistance to high temperatures than individual lizards at the high elevation site. Acclimation to higher environmental temperatures at the low elevation site may explain the greater heat tolerance. Females in both populations grew slower and attained asymptotic sizes earlier in life than males (0.0025 mm per day and 49.7 mm snout-vent length for females vs 0.0027 mm per day and 53.2 mm snout-vent length for males). Growth rates of neonates were between 0.10 and 0.15 mm per day in both sexes and sites. Differential cost of thermoregulatory behavior, and differences in the number of predators and competitors between study sites are possible explanations for similar growth rates at both sites. Individual lizards at both study sites attained maturity at about 14-15 months of age. Females body size at this age was about 39-40 mm at both study sites. Females produced a single litter per year and litter size depended on female body size. Females at low elevation produced an average 3.64 $\pm$ 0.10 young per litter and at high altitude 3.31 $\pm$ 0.129 young per litter. Survivorship was slightly greater at the low elevation site, however, average survivorship for all years of data combined was not significantly different between study sites. Two different predation indices, percentage of broken tails and flushing distance, were greater at the low elevation site than at the high elevation site. Biotic factors reflected in higher syntopic competitors and higher predation indices appear to be responsible for population regulation at the low elevation site. Abiotic selective factors, especially low temperatures and shorter growing seasons, probably regulate population size at the high elevation site.
Subject Area
Ecology|Zoology
Recommended Citation
Lemos-Espinal, Julio A, "Ecology and comparative demography of the lizard Sceloporus grammicus: Life history of an altitudinal generalists on the eastern slope of the Iztaccihuatl Volcano, Puebla, Mexico" (1992). ETD collection for University of Nebraska-Lincoln. AAI9308186.
https://digitalcommons.unl.edu/dissertations/AAI9308186