Population trend inferred from aural surveys for calling anurans in Korea.

Desiree Andersen,Amaël Borzée,Yikweon Jang

doi:10.7717/peerj.5568

Desiree Andersen, Amaël Borzée + Show 1 more

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https://doi.org/10.7717/peerj.5568

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Abstract

Amphibian populations fluctuate naturally in size and range and large datasets are required to establish trends in species dynamics. To determine population trends for the endangered Suweon Treefrog (Dryophytes suweonensis), we conducted aural surveys in 2015, 2016, and 2017 at each of 122 sites where the species was known to occur in the Republic of Korea. Despite being based on individual counts, the focus of this study was to establish population trends rather than population size estimates, and we found both environmental and landscape variables to be significant factors. Encroachment was also a key factor that influenced both the decreasing number of calling individuals and the negative population dynamics, represented here by the difference in the number of calling individuals between years. Generally, most sites displayed minimal differences in the number of calling males between years, although there was a large fluctuation in the number of individuals at some sites. Finally, when adjusted for the overall population size difference between years, we found the population size to be decreasing between 2015 and 2017, with a significant decrease in the number of calling individuals at specific sites. High rate of encroachment was the principal explanatory factor behind these marked negative peaks in population dynamics.

Highlights

The current population decline in most organisms is so widespread that it has been termed the sixth mass extinction (Wake & Vredenburg, 2008)
It is interesting to note that the likelihood ratio for encroachment ranked fifth, following site, date, time and calling indices (CI) of P. chosenicus
We determined population trends for the endangered Suweon Treefrog (D. suweonensis) through aural surveys in 2015, 2016, and 2017 at most of 122 sites where the species was known to occur in the Republic of Korea

Summary

Introduction

The current population decline in most organisms is so widespread that it has been termed the sixth mass extinction (Wake & Vredenburg, 2008). It is difficult to ascertain the causes of population decline (Loehle & Weatherford, 2017), mainly due to a general low detectability of individuals, non-recurrent breeding, breeding at different sites over years, and highly variable populations sizes (Semlitsch et al, 1996; Taylor, Scott & Gibbons, 2006; Bevelhimer et al, 2008; McCain, Szewczyk & Bracy Knight, 2016). Abundant species at a site have a higher probability of being detected than species with low population size (MacKenzie, 2006; Tanadini & Schmidt, 2011), and the experience of observers has a direct impact on the detection probability (Fitzpatrick et al, 2009). All amphibian population estimates may suffer from biases and inaccuracies that may not all be accounted in population dynamics models (MacKenzie, 2006; MacKenzie et al, 2009)

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