SREL Reprint #2160
EFFECTS OF LARVAL DENSITY DEPENDENCE ON
POPULATION DYNAMICS OF AMBYSTOMA OPACUM
BARBARA E. TAYLOR AND DAVID E. SCOTT
Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA
ABSTRACT: Using data and insights derived from laboratory experiments, 9
yr of field experiments, and numerous observations of natural populations of the
marbled salamander, Ambystoma opacum, we constructed a model to study
the effects of larval density dependence on population dynamics. The model
includes density-dependent larval survival and size at metamorphosis, density
independent survival in other stages, and size- and age-dependent terrestrial
growth and reproduction. Terrestrial females are tracked individually. When
survival in non-larval stages is high, equilibria are unstable, and high reproductive
potential at low population densities leads to population dynamics with wide
fluctuations. Density-dependent larval regulation, which decreases in intensity
with decreasing survival in other stages, is much more sensitive to terrestrial
survival than to egg survival. Density-dependent size at metamorphosis delays
reproduction by as much as 3 yr and reduces average clutch size by as much as
70%. Applied to a natural population with low annual recruitment (range 0.7-7.9
metamorphs per breeding female over 9 yr), model results indicate that either
high terrestrial survival (>O.7 yr-1) or immigration is required to maintain the
population. The general sensitivity of the model population to terrestrial
parameters underscores the importance of additional data on the demography of
the terrestrial stages, as well as on processes controlling year-to-year variation in
recruitment of larvae. This information is critical to understanding population
regulation and to developing an adequate basis for conservation or management
plans.
Key words: Ambystoma opacum; Amphibians; Complex life cycle;
Density-dependence; Model; Population dynamics; Salamander
SREL Reprint #2160
Taylor, B.E. and D.E. Scott. 1997. Effects of larval density dependence on
population dynamics of Ambystoma opacum. Herpetologica 53:132-145.
