The Metapopulation Ecology of the Red‐Spotted Newt, Notophthalmus viridescens (Rafinesque)

Abstract

The population dynamics and ecology of the red—spotted newt were studied from 1974 to the present in a series of mountain ponds in the Shenandoah Mountains, Virginia. Adult and juvenile newts were censused using a combination of methods, including drift fences and dip—netting. A technique of individual recognition was developed utilizing the number and pattern of dorsal red spots. Assisted by a simple system of toeclips, designating pond and year of first capture, these methods provided records of age, survival, and movements of >8,500 individuals. The results revealed 2 migratory peaks of adults each year: a breeding migration to ponds in March, and an August—September emigration to terrestrial hibernacula. Breeding population size, ranging from 6 to >2,600 adults per pond was stationary during the study but was significantly correlated with pond age. Annual turnover of breeding populations to new adults exceeded 50%. Sex ratios were consistently 2 ♂ ♂: 1 ♀ in the breeding populations but tended toward 1:1 in the cohorts of new recruits. Annual adult ♀ survival was density dependent and significantly less than that of♂ ♂. The average ♀ expected to breed only 1.3 times, whereas ♂ ♂ had an expectancy of 1.9 breeding seasons. Faithfully homing to the same pond year after year, adults never migrated to new ponds between breeding seasons. Juvenile production at most ponds was poor over the 3 yr. Only 1 pond had a reproductive output consistently above a calculated replacement rate. It is inferred from the combination of poor reproduction and high immigration rates that breeding adults were not replaced by their own progeny but rather by foreign—born individuals. The red—spotted newt is basically a colonizing species responding to pond habitats that rapidly shift in time and space. It is suggested that beaver ponds have the necessary attributes of small size and temporal instability to which the life—history patterns of newts seems adapted. The majority of ponds in this area functioned as reproductive sinks in a larger, metapopulational structure. Adults in such ponds were reproductive failures or most of their lives. Only a small number of adults accounted for the regional reproduction in 1974 and 1975, but I very populous pond produced >91% of the young in 1976. Because reproductive success is pond dependent, interdemal selection may play an important role in newt evolution. It is hypothesized that homing behavior evolved as a consequence of natural selection within metapopulation centers and that the eft stage is the mechanism of dispersibility to new ponds. A new model of metapopulational dynamics is presented.