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Design of occupancy studies with imperfect detection
Article first published online: 9 MAR 2010
© 2010 The Authors. Journal compilation © 2010 British Ecological Society
Methods in Ecology and Evolution
Volume 1, Issue 2, pages 131–139, June 2010
How to Cite
Guillera-Arroita, G., Ridout, M. S. and Morgan, B. J. T. (2010), Design of occupancy studies with imperfect detection. Methods in Ecology and Evolution, 1: 131–139. doi: 10.1111/j.2041-210X.2010.00017.x
- Issue published online: 4 MAY 2010
- Article first published online: 9 MAR 2010
- Received 7 December 2009; accepted 2 February 2010 Handling Editor: Robert P. Freckleton
- imperfect detection;
- small sample size;
- study design
1. Occupancy is an important concept in ecology. To obtain an unbiased estimator of occupancy it is necessary to address the issue of imperfect detection, which requires conducting replicate surveys at the sites being sampled. As the allocation of total effort can be done in different ways, occupancy studies should be designed carefully to ensure an efficient use of available resources.
2. In this paper we address the design of single-season single-species occupancy studies with a focus on: (1) issues relating to small sample sizes and (2) the potential relevance of including the precision of the detectability estimator as a criterion for design. We explore analytically the model with constant probabilities and examine how bias and precision are affected by the numbers of sites and replicates used.
3. We show how, for small sample sizes, the estimator properties depart from those predicted by large sample approximations, emphasize the need to use simulations when designing for small sample sizes and provide a new software tool that can assist in this process.
4. We offer advice on the amount of replication needed when the probability of detection is a quantity of interest and show that, in this case, it is more efficient to reduce the number of sites and increase the amount of replication per site compared with situations where only occupancy is of concern.
5. Synthesis and applications. It is essential to have clearly stated objectives before starting a study and to design the sampling accordingly. As the allocation of effort into replication and sites can be done in different ways, occupancy studies should be designed carefully to ensure an efficient use of available resources. To avoid waste, it is crucial to anticipate the quality of the estimates that can be expected from a particular study design. The discussion and guidance provided here is of special interest for those designing occupancy studies with small sample sizes, something not uncommon in the context of ecology and conservation.