Development and assessment of population dynamics models for Ash Meadows fishes

Authors: Gene R. Wilde

Year: 2009 (xli)

Abstract

Mark and recapture estimates of population sizes of several Ash Meadows fishes have made since 1989. I used estimates made during 1989-2004, which were made annually to biennially, to parameterize population dynamics models for three species of Ash Meadows endangered fishes, including seven populations of Ash Meadows Amargosa pupfish, Cyprinodon nevadensis mionectes, two populations of Warm Springs pupfish, Cyprinodon nevadensis pectoralis, and one population of Ash Meadows speckled dace, Rhinichthys osculus nevadensis. Population dynamics models were based on a modification of the age-structured Leslie matrix population model and assumed a birth-pulse population with post-breeding census. In this instance, the Leslie matrix model was modified so that fecundity was modeled as a function of a fitted constant multiplied by the adult-juvenile ratio from the previous year. The models accurately predicted population dynamics of most species and populations studied. The correspondence between predicted and estimated population sizes was closest between 1989 and 2000, when adult-juvenile ratio ratios were measured annually. In general, the greatest discrepancy between predicted and estimated population sizes occurred around 2000, when estimated population sizes began to decline in several springs. Thus, the models may provide early warning of the need for management intervention.