Just Accepted

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Power and the passion: assessing statistical power with simulations to optimise monitoring of a threatened lizard

Jack Bilby , Joshua Martin , Kelly Arbon, Ryan Baring, Jess Clayton, Lucy Clive

Abstract

Context. Effective ecological surveying is a crucial component of the conservation management of cryptic and threatened species. Ensuring that a survey design has adequate statistical power to confidently detect changes is often overlooked. The pygmy bluetongue (Tiliqua adelaidensis) is an endangered species likely to benefit from increased survey optimisation and structured monitoring efforts across its fragmented and limited distribution. Aims. We compared multiple quadrat sizes on simulated populations of T. adelaidensis at varying densities to evaluate sample sizes and detection rates required to achieve optimal statistical power and assess the ideal quadrat size and number for detecting population changes at Tiliqua Nature Reserve, South Australia. Methods. We employed power analyses to assess the number of 30×30, 50×50, and 100×100-m quadrats required to detect 10%, 25%, and 50% declines in a simulated population of T. adelaidensis. Based on these analyses, we conducted the first site-wide monitoring survey for this species at Tiliqua Nature Reserve and, with the assistance of volunteer citizen scientists, surveyed twenty-five 50×50-m quadrats over five days, achieving the expected sample size required to detect changes in the population size and estimate population densities for the site. Key results. Our results suggest that 50×50-m quadrats were comparable or had significantly higher statistical power than other quadrat sizes within the survey area and during the sampling period. Conclusions. This study demonstrated that 50×50-m quadrats were the most effective survey strategy for detecting significant population declines of the endangered T. adelaidensis at Tiliqua Nature Reserve. This quadrat size balances survey effort and statistical power, providing a reliable method for long-term monitoring. Implications. The optimised survey design using 50×50-m quadrats provides a robust framework for annual monitoring at Tiliqua Nature Reserve and is likely a viable method for other properties. This approach to determining survey effort can be applied to similar conservation efforts for other cryptic and threatened species, ensuring more effective use of resources and timely detection of population changes to inform conservation actions.

WR24159  Accepted 17 April 2025

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