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
+ Author Affiliations
- Author Affiliations
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 https://doi.org/10.1071/WR11193
Submitted: 24 November 2011 Accepted: 21 March 2012 Published: 26 April 2012
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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