Reduced-effort schemes for monitoring butterfly populations
Article first published online: 12 JUN 2007
Journal of Applied Ecology
Volume 44, Issue 5, pages 993–1000, October 2007
How to Cite
ROY, D. B., ROTHERY, P. and BRERETON, T. (2007), Reduced-effort schemes for monitoring butterfly populations. Journal of Applied Ecology, 44: 993–1000. doi: 10.1111/j.1365-2664.2007.01340.x
- Issue published online: 23 JUL 2007
- Article first published online: 12 JUN 2007
- Received 16 November 2006; final copy received 10 April 2007Editor: Davy McCracken
- log-linear model;
- statistical power;
- UK butterfly monitoring scheme;
- wider countryside
- 1Butterflies are one of the few insect groups that can be monitored effectively and have the potential to develop national and Europe-wide trends in abundance.
- 2For 20 widespread butterfly species, we assess the relative efficiency of reduced-effort schemes compared to the existing design and estimate the number of sites required to detect changes of given magnitudes over specified periods of time.
- 3A scheme restricted to three counts during July and August requires twice as many monitored sites on average to achieve comparable precision to the existing 26-week scheme in the United Kingdom. Such a scheme requires 430 monitoring sites on average to achieve 80% power (5% significance level) for detecting a 25% decline in abundance over 10 years.
- 4Such a reduced-effort scheme may also mean that volunteers are more willing to record in areas where they are likely to see only a few individuals of a few common species (such as on intensively farmed areas). This could potentially help to ensure that butterfly monitoring schemes achieve a more even geographical coverage and less of a bias towards areas rich in butterflies.
- 5Synthesis and applications. Schemes with few sampling visits per year are cost-effective for expanding butterfly monitoring across Europe, and can be applied to national monitoring programmes and lead to effective assessment of continent-wide trends in populations.