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Sex ratio estimation and survival analysis for Orthetrum coerulescens (Odonata, Libellulidae)

Canadian Journal of Zoology

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Abstract

There is controversy over whether uneven sex ratios observed in mature dragonfly populations are a mere artifact resulting from the higher observability of males. Previous studies have at best made indirect inference about sex ratios by analysis of survival or recapture rates. Here, we obtain direct estimates of sex ratio from capture?recapture data based on the Cormack?Jolly?Seber model. We studied Orthetrum coerulescens (Fabricius, 1798) at three sites in the Swiss Jura Mountains over an entire activity period. Recapture rates per 5-day interval were 3.5 times greater for males (0.67, SE 0.02) than for females (0.19, SE 0.02). At two sites, recapture rate increased over the season for males and was constant for females, and at one site it decreased with precipitation for both sexes. In addition, recapture rate was higher with higher temperature for males only. We found no evidence for higher male survival rates in any population. Survival per 5-day interval for both sexes was estimated to be 0.77 (95% CI 0.75?0.79) without significant site or time-specific variation. There were clear effects of temperature (positive) and precipitation (negative) on survival rate at two sites. Direct estimates of sex ratios were not significantly different from 1 for any time interval. Hence, the observed male-biased sex ratio in adult O. coerulescens was an artifact resulting from the better observability of males. The method presented in this paper is applicable to sex ratio estimation in any kind of animal.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Sex ratio estimation and survival analysis for Orthetrum coerulescens (Odonata, Libellulidae)
Series title:
Canadian Journal of Zoology
Volume
82
Issue:
3
Year Published:
2004
Language:
English
Contributing office(s):
Patuxent Wildlife Research Center
Description:
399-406
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Canadian Journal of Zoology
First page:
399
Last page:
406
Number of Pages:
8