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Article << Previous     |     Next >>   Contents Vol 39(4)

Estimates of sex ratio require the incorporation of unequal catchability between sexes

Evan J. Pickett A B, Michelle P. Stockwell A, Carla J. Pollard A, James I. Garnham A, John Clulow A and Michael J. Mahony A

A School of Environmental and Life Sciences, University of Newcastle, University Drive, Callaghan, NSW 2300, Australia.
B Corresponding author. Email: evan.pickett@uon.edu.au

Wildlife Research 39(4) 350-354 http://dx.doi.org/10.1071/WR11193
Submitted: 24 November 2011  Accepted: 21 March 2012   Published: 26 April 2012


 
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Abstract

Context: Estimates of the sex ratio of a population are a common summary statistic used for ecological studies and conservation planning. However, methods to determine the sex ratio often ignore capture probability, which can lead to a perceived bias in the sex ratio when the sexes are detected at different rates.

Aims: To illustrate the bias from conventional count-based analysis methods for determining sex ratio by comparison with analytical methods that include capture probability.

Methods: Closed-population mark–recapture analysis was used to determine the population size of each sex within a population of green and golden bell frogs (Litoria aurea). This was then compared with the traditional count-based methods of estimating sex ratio to determine the effect of incorporating capture probability on the sex ratio estimate.

Key results: More males than females were detected during surveys, producing a male-biased sex ratio when there was no incorporation of capture probability. Mark–recapture results indicated a similar population size between the two sexes, suggesting that the sex ratio is closer to even.

Conclusions: Methods to estimate sex ratio that incorporate capture probability can significantly reduce the bias obtained from count data.

Implications: We suggest that population studies must incorporate capture probability to determine the sex ratio of a population.

Additional keywords: Anuran, conservation, frog, Litoria aurea, mark–recapture, population ecology.


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