Herpetologica, 53(1), 1997, 132-145
©1997 by The Herpetologists' League, Inc.
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 (>0.7 yr ) 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