Elsevier

Biological Conservation

Volume 143, Issue 9, September 2010, Pages 2102-2110
Biological Conservation

Optimising biodiversity assessments by volunteers: The application of occupancy modelling to large-scale amphibian surveys

https://doi.org/10.1016/j.biocon.2010.05.019Get rights and content

Abstract

Mobilising volunteers to carry out biodiversity assessments can help to identify priorities for conservation across broad geographical scales. However, even when volunteers carry out simple presence–absence surveys, there can be significant issues over false absences and subsequent data interpretation. Simple but scientifically robust protocols are therefore required for these programmes. Here we evaluate amphibian survey protocols for the National Amphibian and Reptile Recording Scheme (NARRS) in Britain, which aims to assess the status of five widespread amphibian species. Surveys were undertaken by trained volunteers and researchers in two contrasting landscapes over 2 years, and occupancy modelling was used to determine covariates of detection, and to optimise the number of surveys and number of methods required. Although surveys need to take into account seasonal and annual changes in the detectability of different species, there were also landscape effects. Frogs and toads were generally harder to detect in ponds in Kent than in Wales, while the converse was true of newts. Adding bottle-trapping to the suite of methods increased the detection of smooth and palmate newts in both areas, and of great crested newts in Wales. Overall, reliable assessment of the presence or absence of all five species at a site required four separate surveys, each using four different methods (visual encounter surveys during both day and night, dip netting and bottle-trapping). Our approach may prove useful for finding the best compromises between rigor and simplicity when volunteers are used in large-scale surveys.

Introduction

The use of volunteers in biodiversity monitoring schemes overcomes constraints caused by a lack of funding for professional researchers and increases public perception and involvement (Schmeller et al., 2009). In the USA at least 200 volunteer-based survey programmes exist (Cohn, 2008), whilst in the UK the Royal Society for the Protection of Birds mobilised in excess of half a million volunteers for its Big Garden Birdwatch in 2010 alone (http://www.rspb.org.uk/birdwatch/results/ accessed 10th May 2010). In the developing world long term biodiversity monitoring schemes may only be sustainable if volunteers are used (Holck, 2008). On the other hand, there are significant concerns over the reliability of data collected by volunteers (e.g. Engell and Voshell, 2002, Lotz and Allen, 2007, Schmeller et al., 2009). Even when simple presence–absence surveys are carried out, there may be a tendency to miss small populations, resulting in false absences. This problem may be compounded by the misidentification of some species (Genet and Sargent, 2003, Fitzpatrick et al., 2009).

Renewed interest in the global status of amphibians has precipitated coordinated volunteer surveys in a range of countries. However, detection probabilities for amphibian species are highly variable and often low (MacKenzie et al., 2002, MacKenzie et al., 2003). Failing to allow for variation in detectability generates unreliable data, especially with respect to false negatives (MacKenzie et al., 2002, Schmidt, 2003). Many volunteer amphibian survey schemes reported so far have relied on a single detection method, usually vocalisation by breeding males (Genet and Sargent, 2003, de Solla et al., 2005, Pellet and Schmidt, 2005, Pierce and Gutzwiller, 2007). Surprisingly little attention has been paid to the efficiency and variation between the methods used by volunteers for detecting amphibians, and how these fare in different landscapes and between different species.

In Britain, a National Amphibian and Reptile Recording Scheme (NARRS) was instituted in 2007 with a view to assessing future status changes of the herpetofauna of the UK, including the five widespread native amphibian species, common frog (Rana temporaria), common toad (Bufo bufo), smooth newt (Lissotriton vulgaris), palmate newt (L. helveticus) and great crested newt (Triturus cristatus). NARRS primarily uses trained volunteer surveyors who carry out presence–absence surveys using a standard protocol. In this study, we applied occupancy modelling to the current NARRS survey protocol. Occupancy modelling is based on the patterns of detection and non-detection of species at a range of sites over multiple visits, and estimates both site occupancy and detection probability (Mackenzie et al., 2002). There have been previous attempts to use this methodology to determine the survey effort required for the reliable inference of absence, rather than non-detection, of amphibian species (e.g. Pellet and Schmidt, 2005), but they have not yet been applied to a large-scale national survey programme using multiple detection methods. We used this approach to determine: (1) whether the range of methods recommended to volunteers can reliably detect presence and absence; (2) the number of surveys required to minimise the risk of false absences; and (3) covariates of detectability that may assist volunteers with the timing of surveys.

Section snippets

Study areas and field work

Two contrasting landscapes in Britain were chosen for comparison. A lowland area in east Kent, (Lat. 51°20′N, Long. 1°05′E) was compared with an upland area of central Wales approximately centred at Lat. 52°06′N; Long. 3°20′W. Land uses in the Kent study area were primarily woodland, arable and fruit growing, with extensive urban areas. In contrast, the study area in Wales had lower levels of human occupation with grazing predominant in the lower areas and open moorland with rough grazing on

Differences between study areas

Differences between the two study areas were confirmed in five variables (elevation, pond area, pond density, shade and macrophyte cover) by means of a MANOVA (Wilks lambda = 0.155, F5,42 = 45.7, P < 0.001). Comparison of individual variables showed that the ponds sampled in Wales were at higher altitude (means ± SD: Kent 72 ± 12 m, Wales 274 ± 81 m, F1,46 = 138.6, P < 0.001), larger (Kent 143 ± 154 m2, Wales 1185 ± 1199 m2, F1,46 = 17.1, P < 0.001), less-shady (Kent 50 ± 27%, Wales 15 ± 19% shading, F1,46 = 26.5, P < 0.001), had

Volunteer expertise

In addition to the problem of detection probabilities varying between species (de Solla et al., 2005), misidentification by volunteers can vary between 4% and 18%, with some species consistently confused (Genet and Sargent, 2003, Lotz and Allen, 2007). We do not believe that misidentification is a major issue for amphibian surveys by trained volunteers in Britain, as adults of the five widespread species are relatively easy to identify in the field. The most difficult to distinguish are palmate

Acknowledgements

We thank the Esmée Fairburn Foundation for financial support and the many students, and members of the Brecknock and Radnorshire Amphibian and Reptile Group, who helped with fieldwork. The adjustments to the collection of terrestrial habitat data were first suggested by Lee Brady. Additionally we thank Rachel McCrea, Gurutzeta Guillera-Arroita and Jose Lahoz-Monfort for their help and patience with the statistical analysis, and also Darryl MacKenzie who made a number of helpful suggestions at

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