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

Abstract

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 (Crotophytus collaris collaris) 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.

Life history changes in the eastern collared lizard in response to varying demographic phases and management policies

“…In this study, females show greater life history plasticity than males for the most part. This is also reflected by the significant changes in female age structure at each demographic transition in contrast to no significant changes in male age structure throughout the entire study period (Templeton et al, 2022). Female plasticity is most pronounced in the transition from the isolate phase to the colonizing phase.…”

“…Female plasticity is most pronounced in the transition from the isolate phase to the colonizing phase. The average age of a female plummeted in this transition from 2.78 years during the isolate phase to 1.75 years in the colonizing phase while male average age stayed relatively constant (Templeton et al, 2022). The demographic transitions monitored in this study were all marked by changes in reproductive opportunities, and given the asymmetrical energy demands of reproduction in females versus males, it is not surprising that females show more plasticity to changes in reproductive opportunities.…”

“…Telemeco and Baird (2011) found that the size of a female was highly predictive of their reproductive capacity, and Sexton et al (1992) found that there was a large increase in reproductive potential in females that passed a threshold of a snout-vent length of 77 mm in Ozark collared lizards. Figure 2 in Templeton et al (2022) shows that by the beginning of June (the month in which the first clutch is normally laid), most yearling females have already passed this size threshold in this population. Perhaps yearling females on newly occupied glades reach this size threshold earlier or in a greater proportion, which could lead to higher reproductive capacities.…”

“…Collared lizards have distinct color patterns for hatchlings, yearlings, adult females, and adult males (Templeton et al, 2022). One thousand one hundred sixty-two lizards with hatchling or yearling coloration were of known age upon capture.…”

“…The transition to adult coloration occurs during the yearling summer activity period, so 391 lizards with adult coloration upon first capture could be 1 or more years of age. By following 529 hatchlings over subsequent recaptures, Templeton et al (2022) assigned age probabilities to lizards first captured with adult coloration as a function of their size and date of first capture. It was unlikely for any animal to be more than 3 years of age in this study at the time of first capture.…”