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When Is a Species Declining? Optimizing Survey Effort to Detect Population Changes in Reptiles

Sewell, David, Guillera-Arroita, Gurutzeta, Griffiths, Richard A., Beebee, Trevor J. C. (2012) When Is a Species Declining? Optimizing Survey Effort to Detect Population Changes in Reptiles. PLoS ONE, 7 (8). ISSN 1932-6203. (doi:10.1371/journal.pone.0043387) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided. (Contact us about this Publication)
Official URL
http://dx.doi.org/10.1371/journal.pone.0043387

Abstract

Biodiversity monitoring programs need to be designed so that population changes can be detected reliably. This can be problematical for species that are cryptic and have imperfect detection. We used occupancy modeling and power analysis to optimize the survey design for reptile monitoring programs in the UK. Surveys were carried out six times a year in 2009–2010 at multiple sites. Four out of the six species – grass snake, adder, common lizard, slow-worm –were encountered during every survey from March-September. The exceptions were the two rarest species ­– sand lizard and smooth snake – which were not encountered in July 2009 and March 2010 respectively. The most frequently encountered and most easily detected species was the slow-worm. For the four widespread reptile species in the UK, three to four survey visits that used a combination of directed transect walks and artificial cover objects resulted in 95% certainty that a species would be detected if present. Using artificial cover objects was an effective detection method for most species, considerably increased the detection rate of some, and reduced misidentifications. To achieve an 85% power to detect a decline in any of the four widespread species when the true decline is 15%, three surveys at a total of 886 sampling sites, or four surveys at a total of 688 sites would be required. The sampling effort needed reduces to 212 sites surveyed three times, or 167 sites surveyed four times, if the target is to detect a true decline of 30% with the same power. The results obtained can be used to refine reptile survey protocols in the UK and elsewhere. On a wider scale, the occupancy study design approach can be used to optimize survey effort and help set targets for conservation outcomes for regional or national biodiversity assessments.

Item Type: Article
DOI/Identification number: 10.1371/journal.pone.0043387
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Q Science > QH Natural history > QH75 Conservation (Biology)
Divisions: Faculties > Social Sciences > School of Anthropology and Conservation
Depositing User: Richard Griffiths
Date Deposited: 29 Aug 2014 15:14 UTC
Last Modified: 29 May 2019 13:02 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/42782 (The current URI for this page, for reference purposes)
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