Science, statistics and surveys: a herpetological perspective

Griffiths, Richard A.; Foster, Jim; Wilkinson, John W.; Sewell, David L.

doi:10.1111/1365-2664.12463

Cited by 28 publications

(25 citation statements)

References 14 publications

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“…Using eDNA to map population trends would therefore be problematical, although a relative abundance estimate between similar ponds, sampled concurrently under the same environmental conditions may be possible. Current traditional count-based population assessments from visual or trapping surveys for amphibians or other aquatic organisms suffer from the same issues, as detection rates may have poorly understood relationships to total population sizes and vary according to environmental conditions51. For stream fish, predictive models incorporating eDNA concentration are developing to identify detection probabilities, abundance, as well as eDNA production and discharge52.…”

Section: Discussionmentioning

confidence: 99%

Seasonal variation in environmental DNA in relation to population size and environmental factors

Buxton

Groombridge

Zakaria

et al. 2017

Sci Rep

Self Cite

143

140

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Analysing DNA that organisms release into the environment (environmental DNA, or eDNA) has enormous potential for assessing rare and cryptic species. At present the method is only reliably used to assess the presence-absence of species in natural environments, as seasonal influences on eDNA in relation to presence, abundance, life stages and seasonal behaviours are poorly understood. A naturally colonised, replicated pond system was used to show how seasonal changes in eDNA were influenced by abundance of adults and larvae of great crested newts (Triturus cristatus). Peaks in eDNA were observed in early June when adult breeding was coming to an end, and between mid-July and mid-August corresponding to a peak in newt larval abundance. Changes in adult body condition associated with reproduction also influenced eDNA concentrations, as did temperature (but not rainfall or UV). eDNA concentration fell rapidly as larvae metamorphosed and left the ponds. eDNA concentration may therefore reflect relative abundance in different ponds, although environmental factors can affect the concentrations observed. Nevertheless, eDNA surveys may still represent an improvement over unadjusted counts which are widely used in population assessments but have unreliable relationships with population size.

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Section: Discussionmentioning

confidence: 99%

Seasonal variation in environmental DNA in relation to population size and environmental factors

Buxton

Groombridge

Zakaria

et al. 2017

Sci Rep

Self Cite

143

140

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“…Obtaining quantitative measures of species trends over broad areas is challenging, as it generally requires repeated surveys of many sites covering significant portions of species’ ranges. Volunteers can provide data at low cost, thus helping the measurement of the trends of widespread species living in easily accessible regions (Kéry et al ., ; Bonardi et al ., ; Sewell et al ., ; Griffiths et al ., ; Petrovan & Schmidt, ). However, there are cases in which volunteer data are not available, particularly for species requiring specific monitoring protocols or living in difficult to access areas.…”

Section: Introductionmentioning

confidence: 99%

Optimizing monitoring schemes to detect trends in abundance over broad scales

Ficetola

Romano

Salvidio

et al. 2017

Animal Conservation

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Measuring population changes and trends is essential to identify threatened species, and is requested by several environmental regulations (e.g. European Habitat Directive). However, obtaining this information for small and cryptic animals is challenging, and requires complex, broad-scale monitoring schemes. How should we allocate the limited resources available for monitoring, to maximize the probability of detecting declines? The analysis of simulated data can help to identify the performance of monitoring scenarios across species with different features. We simulated data of populations with a wide range of abundance, detection probability and rate of decline, and tested under which circumstances open-population N-mixture models can successfully detect the decline of populations. We tested multiple monitoring strategies, to identify the ones having the highest probability of detecting declines. If 30 sites are surveyed, strong declines (≥30%) can be successfully spotted for nearly all the simulated species, except the species with lowest abundance and detection probability. Weaker declines are successfully identified only in species that are easy to detect and have high abundance. Increasing the number of sites quickly increases model power, but hundreds of sites would require monitoring to measure trends of the least detectable species. For most of species, performance of monitoring was improved by: surveying many sites with a few replicates per site; surveying many small sites instead of a few large sites; combining data from sites monitored for multiple species. Our findings show that one single monitoring approach cannot be appropriate for all the species, and that surveying efforts should be modulated across them, according to their detection probabilities and abundances. We provide quantitative values on how the number of surveys and the number of sites to be surveyed can be assigned to different species, and emphasize the need of planning to maximize the performance of monitoring.

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“…The ability to obtain accurate and reasonably precise population estimates of lizards across large regions will be critical for monitoring trends and identifying the effects of stressors including climate change and land use (Gibbons et al, ; Griffiths et al, ). Impacts identified to lizards may provide a good indicator of impacts to the larger ecosystem, because of this taxon's sensitivity to temperature and land use (Thompson et al, ; Waudby & Petit, ; Whitford & Creusere, ).…”

Section: Discussionmentioning

confidence: 99%

“…Indeed, both small and large disparities from our validation correspond closely to our estimates of availability during intermediate temperature conditions that were reflective of the JNTP surveys (25°C; 20% for A. tigris vs. 80% for U. stansburiana). Those surveys occurred during spring (March-June) and the scheduling of site visits was timed to minimize variation in temperature and maximize availability during a single visit (Barrows et al, 2016) The ability to obtain accurate and reasonably precise population estimates of lizards across large regions will be critical for monitoring trends and identifying the effects of stressors including climate change and land use (Gibbons et al, 2000;Griffiths et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

“…For this reason, agencies and organizations are increasingly investing in long‐term, large‐scale, multispecies wildlife monitoring programs (Ahumada, Hurtado, & Lizcano, ; Furnas & Callas, ; Nielsen, Haughland, Bayne, & Schieck, ). Unlike many species of birds, mammals, and amphibians which can be sampled using automated survey equipment including cameras and sound recorders (Blumstein et al., ; Burton et al, ), reptiles are often much more difficult to detect, in part because of their typically cryptic behavior and generally small body sizes (Griffiths, Foster, Wilkinson, & Sewell, ). Therefore, there is a need for improved survey and analytical methods for estimating occupancy, diversity, and abundance of reptiles for inclusion in multispecies monitoring projects (Gibbons et al, ; Griffiths et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Hierarchical distance sampling to estimate population sizes of common lizards across a desert ecoregion

Furnas

Newton

Capehart

et al. 2019

Ecology and Evolution

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Multispecies wildlife monitoring across large geographical regions is important for effective conservation planning in response to expected impacts from climate change and land use. Unlike many species of birds, mammals, and amphibians which can be efficiently sampled using automated sensors including cameras and sound recorders, reptiles are often much more challenging to detect, in part because of their typically cryptic behavior and generally small body sizes. Although many lizard species are more active during the day which makes them easier to detect using visual encounter surveys, they may be unavailable for sampling during certain periods of the day or year due to their sensitivity to temperature. In recognition of these sampling challenges, we demonstrate application of a recent innovation in distance sampling that adjusts for temporary emigration between repeat survey visits. We used transect surveys to survey lizards at 229 sites throughout the Mojave Desert in California, USA, 2016. We estimated a total population size of 82 million (90% CI: 65–99 million) for the three most common species of lizards across this 66,830 km2 ecoregion. We mapped how density at the 1‐km2 scale was predicted to vary with vegetation cover and human development. We validated these results against independent surveys from the southern portion of our study area. Our methods and results demonstrate how multispecies monitoring programs spanning arid ecoregions can better incorporate information about reptiles.

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Science, statistics and surveys: a herpetological perspective

Cited by 28 publications

References 14 publications

Seasonal variation in environmental DNA in relation to population size and environmental factors

Seasonal variation in environmental DNA in relation to population size and environmental factors

Optimizing monitoring schemes to detect trends in abundance over broad scales

Hierarchical distance sampling to estimate population sizes of common lizards across a desert ecoregion

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