Annual Variation in the Population Ecology of the Endangered Gopher Frog, Rana sevosa Goin and Netting

We studied variation in the population ecology of dusky gopher frogs, Rana sevosa Goin and Netting, in southern Mississippi from 1996–2001. Specifically, we measured adult size structure, adult survivorship, residency length within the pond, and juvenile recruitment using a drift fence that completely enclosed the study pond. Population size structure shifted among years because of lack of recruitment in previous years, adult mortality, and differential age at maturity. Age at maturity was 6–8 months for males and 24–36 months for females. Annual survival ranged from 65 to 92%; however, the rate at which adults returned to breed among years was low (16–22%). The average number of seasons that adults bred was 1.2, although nine individuals bred in 3–5 seasons. Our data suggest that R. sevosa has high population turnover among years and that most adults live less than 7 yr. Because of the low rate of return of adults among years and complete isolation of the population, the viability of the population is contingent on consistent recruitment of juveniles with minimal years of reproductive failure.

Fig. 1.

Adult Rana sevosa movement patterns and associated rainfall as determined by drift fence captures of frogs entering and exiting Glen's Pond during 1996, 1997, and 1998

Fig. 2.

Pattern of emergence of adult and metamorphic Rana sevosa captured exiting Glen's Pond during 1997, 1998, and 2001. The circle with numbers represents the orientation of the drift fence (circle) and pitfall traps (numbers). See Richter et al. (2001:fig. 1) for habitat features

Fig. 3.

Average (± 1 SE) SVL, body mass, and residency length of male and female Rana sevosa during 1996, 1997, and 1998. Letters and asterisks depict differences found using Games-Howell multiple comparisons following AN(C)OVA analyses (see Table 2 and Materials and Methods for details). An asterisk indicates a significant within-year difference between the sexes. Upper case letters represent among-year comparisons for males, and lower case letters represent among-year comparisons for females. In both cases, a different letter indicates a significant difference among years