Reptile species are declining on a global scale. Six significant threats to reptile populations are habitat loss and degradation, introduced invasive species, environmental pollution, disease, unsustainable use, and global climate change

The relationships among timing of metamorphosis, size at metamorphosis, and traits related to adult fitness were studied for 8 yr in the salamander Ambystoma talpoideum at a temporary pond. Among years, the modal time of metamorphosis and mean body size at metamorphosis were positively correlated with the date the pond dried. In years that the pond dried late, one group of larvae metamorphosed well before the pond dried, whereas the other group metamorphosed just before pond drying. Mean body size of late—metamorphosing individuals was not greater than that of individuals metamorphosing early. Early—metamorphosing males and females were larger at first and second reproduction than were late—metamorphosing individuals. Independent of timing of metamorphosis, larger juveniles at metamorphosis were also larger adults at first reproduction. Age at first reproduction for males was not associated with timing of or size at metamorphosis but large early—metamorphosing females reproduced at a younger age than did small early—metamorphosing females. Neither time of metamorphosis nor size at metamorphosis was associated with survival to first reproduction. These results demonstrate a direct relationship between phenotypic variation generated in the larval stage and adult traits closely associated with an individual's fitness.

Reports of declining amphibian populations in many parts of the world are numerous, but supporting long-term census data are generally unavailable. Census data from 1979 to 1990 for three salamander species and one frog species at a breeding pond in South Carolina showed fluctuations of substantial magnitude in both the size of breeding populations and in recruitment of juveniles. Breeding population sizes exhibited no overall trend in three species and increased in the fourth. Recent droughts account satisfactorily for an increase in recruitment failures. These data illustrate that to distinguish between natural population fluctuations and declines with anthropogenic causes may require long-term studies.

Factors that affect traits of aquatic larvae of amphibians may have long—lasting effects on terrestrial juveniles and adults. I manipulated larval densities of marbled salamanders, Ambystoma opacum, in large—scale field enclosures during 2 yr, released the juveniles that metamorphosed from these enclosures, and tested for effects on adults that returned to the pond during 6—7 subsequent breeding seasons. Individuals from low larval density treatments tended to have greater lipid stores at metamorphosis than those from high densities and survived longer in a laboratory inanition study. In the field, individuals that experienced low larval density returned for their first reproductive bout as larger adults than those from high—density treatments. For 5—yr—old females released in 1986, low larval density was linked to greater clutch size; clutch size in 4—yr—old animals from the 1987 cohort did not differ between larval treatment groups. Larval density also influenced age at first reproduction, as animals reared at low densities returned to breed at younger ages. Averaged across both cohorts, the proportion of animals that returned to breed at least once was 21% for low—density groups compared to 6% for the high—density groups. The larval environment exerted a strong influence on postmetamorphic traits, and thus larval density likely plays an important role in population regulation in both the aquatic and terrestrial phase of the life cycle.