Age structure dynamics in an eastern collared lizard population from founding to demographic stability

The global decline of reptile species has raised much concern, and many translocation programs have been implemented in response to this decline. Most of these programs have not been successful, but one exception is the translocation program for eastern collared lizards that had experienced massive local extinction on glades in the Ozarks in central North America. Translocation coupled with glade restoration was initiated in the 1980s, including reintroductions starting in 1984 on Stegall Mountain in southern Missouri. The translocated populations underwent three distinct demographic phases: (1) an isolate phase with no net growth in population size, no colonization of nearby glades and almost no dispersal among populations, (2) a colonizing phase of high dispersal, colonization of new glades and population growth that started with the onset of prescribed woodland burning and (3) a stable metapopulation phase established by 2000 on Stegall Mountain in which the number of occupied glades, total population size and measures of genetic variation were roughly constant. This study uses distinct color phases to infer the age of 1162 marked individuals. Age probabilities were assigned to 391 individuals based on time-of-capture within the field season and snout-vent length, as calibrated from following 529 individuals first captured as hatchlings. Age structure differed significantly between phases. The isolate phase was characterized by an old age structure. The colonization phase had a younger age structure and much more recruitment. The stable metapopulation phase had an intermediate age structure. These dynamic age structure attributes show that species cannot be regarded as static units, and ignoring this dynamism can result in poor conservation practice. These results also validate age-structure as a monitoring device for a conservation program and a tool to identify significant shifts in the environment or management that have a conservation impact, in this case prescribed woodland burning.

Automated summary

This study examines the translocation program for eastern collared lizards and its effects on the demographic phases and age structure of the populations. The results show that the populations went through isolate, colonizing, and stable metapopulation phases, with distinct age structure attributes. Ignoring the dynamic nature of species can have negative impacts on conservation efforts.