Population structure of the rare damselfly, Ischnura gemina (Kennedy) (Odonata: Coenagrionidae)

Abstract

The population structure of the endemic San Francisco Bay Area damselfly, Ischnura gemina, is examined using mark-recapture methods. Average daily movements, sex ratios, population size, maturation times, survivorship, and dispersion patterns, were recorded and calculated from two small (each less than one hectare) sites 150 m apart in Glen Canyon, San Francisco. Of 563 adults marked over 36 days, 412 (73%) were recaptured at least once. Average daily movements for males and females were less than 6 m, suggesting local movements. However, directional movements of 150 m were observed from one site to the other, indicating dispersal potential. One of the populations was a satellite composed entirely, of emigrating individuals from the other site; no larvae or teneral adults were found at the satellite area. Males were more aggregated than females at both sites. Both sexes were highly clumped at one site but were nearly randomly dispersed at the other site. Total population size for both sexes tended to be constant throughout the sampling period, at about 250. Adult population estimates showed more males were present than, females, but larval counts at one site indicated only a slight excess of males. Average life span estimates ranged from 6.5 days (females) to 23.3 days (males). One male lived at least 36 days. Maturation time for males was about 5-7 days, 7-10 days for females. A long life span and long flight season (March to November) are probably adaptations to the foggy San Francisco climate. All populations of I. gemina located to date are small, possibly originating from founders from nearby demes, and may be subject to different selection pressures. The dispersal potential of I. gemina may increase its chance of survival should small urban demes be threatened with destruction.

A review of odonatology in freshwater applied ecology and conservation science

“…Here we provide an overview. The first clear records of applied ecology or conservation science (Moore 1980, Garrison andHafernik 1981) focused on population ecology, habitat requirements, and threat factors of 2 rare damselfly species, and were followed by 6 more papers during the 1980s (Fig. 1).…”

Estructura poblacional de Polythore gigantea (Odonata: Polythoridae) en sistemas lóticos con diferentes estados de conservación en Antioquia, Colombia

“…En el caso de P. gigantea, los machos se observaron la mayor parte del tiempo posados en la vegetación adyacente a la zona ribereña de estos ecosistemas lóticos. De manera similar, Garrison 1978, Garrison & Hafernik 1981, Córdoba 1993, Angelibert & Giani 2003, lo han reportado también para otras especies de odonatos y Sánchez & Realpe (2010), en particular, lo reportan para Polythore procera (Selys 1869).…”

“…El promedio de supervivencia diaria y la esperanza de vida en días, se calcularon como lo describen Garrison & Hafernik (1981). La tasa de supervivencia diaria se convirtió en Esperanza de Vida Diaria por el método de Cook et al 1967(Garrison & Hafernik 1981, Córdoba 1994.…”

“…La tasa de supervivencia diaria se convirtió en Esperanza de Vida Diaria por el método de Cook et al 1967(Garrison & Hafernik 1981, Córdoba 1994.…”

“…Si los estudios de campo son intensivos, los datos no sólo permitirán determinar el papel de las especies en su ambiente, sino que también, podrían permitir la elaboración de modelos para el análisis de poblaciones localizadas de la misma especie, bajo condiciones ambientales diferentes. Asimismo, los estudios comparativos entre dos o más poblaciones son especialmente valiosos porque el resultado puede ilustrar las diferencias y la flexibilidad en los patrones de comportamiento de una especie en diferentes ambientes (Garrison & Hafernik 1981).…”