To further our understanding of population dynamics, we have recently begun to age individual frogs using skeletochronology. Bullfrogs are of particular concern because they have been reported to be declining in many parts of their range. This decline has been attributed, in part, to extensive commercial harvest. In 1996, we hope to compare the age-structure in our population with that of harvested populations. Other future research will examine longevity, sex ratio dynamics, distribution of reproductive success, and growth rates.
Fluctuations is mean size and in age structure also occured.
This evidence of fewer but larger and older toads in 1994 and 1995, especially, implies that poor summer growth rates in 1993 and 1994 may have determined the decline in calling male numbers simply by diminishing the early recruitment of yearling males into the adult chorus without correlation to the total abundance of postmetamorphic toads. Because age structure among adults is evidently variable and chorus behaviour is weather-dependant, chorus size is highly stochastic. Since there is no stable age structure, simple population growth models cannot be applied. Furthermore, neither the spring field studies nor reference to weather records could identify consistent factors correlated with either the increase in adult males beginning in 1990-91 or the declines of 1994 and 1995. All of this underscores the extreme difficulty of predicting population numbers, much less trends, in randomly fluctuating, short-lived species.