UNIVERSITY GRADUATE SCHOOL BULLETIN

ANNOUNCEMENT

Florida International University

Division of Graduate Studies

Master’s Thesis Defense

Abstract

Population dynamics of two fishes, Heterandria formosa and Poecilia latipinna, across a hydroperiod gradient in the Florida Everglades

by

Timothy J. Konnert

The purpose of this study was to determine if spatial and temporal variation in hydrological regime (especially frequency of marsh drying) of the Florida Everglades yields a gradient of stressfulness reflected in life-history parameters of two of its resident fish, Poecilia latipinna and Heterandria formosa. Samples collected over a two-year period were combined with historical data from the years 1997 through 1999 to calculate demographic rates (growth of individuals, age-specific reproduction, and age-specific survival) for fish from six populations of each species. Specimens were collected from two sites characterized by short, medium, or long hydroperiod (six study sites total). These demographic rates were then combined to produce life tables used to illustrate idealized dynamics of each population. The life table predictions were compared to population dynamics measured in the field.

I used analysis of otoliths to estimate age-length relations for fish from each of the six study populations of P. latipinna. Although there were inter-site differences in growth rates of P. latipinna, none were attributed to hydroperiod. The age-specific fecundity estimates of P. latipinna were also similar across hydroperiod. Hydroperiod was linked to fecundity in H. formosa; the short-hydroperiod populations exhibited greater fecundity than those collected at long-hydroperiod sites. Growth curves calculated by Haake and Dean (1983) for H. formosa were used to construct the life tables of this species, however since they were not specific to hydroperiod they did not provide information on spatial or temporal patterns of growth rates. Hydroperiod did not have a significant effect on survivorship curves of either species. The life-table analysis showed that the intrinsic rate of increase became greater with decreasing hydroperiod in both species. These findings illustrate that simple characterizations of “stressful” conditions based on frequency of dry-down events may not be reflected in demographic rates of fish.

Date: August 21, 2002 Department: Biological Sciences

Time: 2:00 p.m. Major Professor: Dr. Joel Trexler

Place: Wertheim Conservatory