Assessing Population Trends of Species with Imperfect Detection: Double Count Analyses and Simulations Confirm Reliable Estimates in Brown Frogs

Falaschi, Mattia; Gibertini, Chiara; Parrino, Elia Lo; Muraro, Martina; Barzaghi, Benedetta; Manenti, Raoul; Ficetola, Gentile Francesco

doi:10.3390/ani12162085

Cited by 5 publications

(5 citation statements)

References 29 publications

(45 reference statements)

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“…Therefore, clutches can be easily spotted and recognized and their number corresponds to the number of breeding females in a population in a given season. Detection probability analyses showed that the detection probability of clutches is >95%; therefore, clutch counts enable reliable estimates of population trends [24]. Preferred sites for egg-laying are perennial and slow-flowing waterbodies, where hatching typically occurs within 2 or 3 weeks and is followed by a relatively long tadpole stage which, depending on water conditions, lasts about 2-3 months [22].…”

Section: Study Area and Study Speciesmentioning

confidence: 99%

Decline and Extinction of the Italian Agile Frog Rana latastei from Core Areas of Its Range

Ficetola¹,

Manenti²,

Parrino³

et al. 2023

Preprint

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Detecting the trends of species and populations is fundamental to identify taxa with high conservation priority. Unfortunately, long-term monitoring programs are challenging and often lacking. The Italian agile frog Rana latastei is endemic to Northern Italy and adjacent countries, is considered vulnerable by the IUCN, and is protected at the European level. However, quantitative estimates of its decline are extremely scarce. In this study, we document the trends in abundance and distribution of Rana latastei within the Monza Park, which currently represents the area closer to the type locality of the species. Wetlands within the park were monitored from 2000 to 2023; counts of egg clutches were taken as a measure of reproductive output and of the abundance of breeding females. In 2000, the species occurred over a significant proportion of the park. Total abundance showed strong yearly variation but remained rather constant from 2000 to 2019. However, Rana latastei disappeared from the park around 2021 and was never detected in 2022-23. The decline is probably related to the joint effect of multiple factors, including the conversion of breeding sites for farming, inappropriate water management, invasive alien species, and severe drought. The local extinction of Rana latastei occurred despite legal protection, highlighting the need for more effective and stringent tools for the conservation of European biodiversity.

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Section: Study Area and Study Speciesmentioning

confidence: 99%

Decline and Extinction of the Italian Agile Frog Rana latastei from Core Areas of Its Range

Ficetola¹,

Manenti²,

Parrino³

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

Section: Study Area and Study Speciesmentioning

confidence: 99%

“…This allowed us to optimize time when more observers are available, without influencing detections. As we performed multiple clutch counts in the same year, we reported the highest count for each breeding site, which represents the minimum number of breeding females in each wetland [24]. In rare cases, we detected a few freshly laid egg clutches after the peak of the breeding season.…”

Section: Field Monitoring and Data Analysesmentioning

confidence: 99%

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Decline and Extinction of the Italian Agile Frog Rana latastei from Core Areas of Its Range

Ficetola,

Manenti,

Lo Parrino

et al. 2023

Animals

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Detecting the trends of species and populations is fundamental to identifying taxa with high conservation priority. Unfortunately, long-term monitoring programs are challenging and often lacking. The Italian agile frog Rana latastei is endemic to Northern Italy and adjacent countries, is considered vulnerable by the IUCN, and is protected at the European level. However, quantitative estimates of its decline are extremely scarce. In this study, we document the trends in abundance and distribution of Rana latastei within Monza Park, which currently represents the area closer to the type locality of the species and holds unique genetic features. Wetlands within the park were monitored from 2000 to 2023; counts of egg clutches were taken as a measure of reproductive output and the abundance of breeding females. In 2000, the species occurred over a significant proportion of the park. Total abundance showed strong yearly variation but remained rather constant from 2000 to 2019. However, Rana latastei disappeared from the park around 2021 and was never detected in 2022–2023. The decline is probably related to the joint effect of multiple factors, including the conversion of breeding sites for farming, inappropriate water management, invasive alien species, and severe drought. The local extinction of Rana latastei occurred despite legal protection, highlighting the need for more effective and stringent tools for the conservation of European biodiversity.

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“…As such, trends that rely on changes in relative abundance may be biased because they assume that detection probability remains constant. Additionally, simulations have suggested that accurately identifying population trends becomes difficult when detectability <80% ( Falaschi et al, 2022 ), such as for smaller, more cryptic species. Studies that directly estimate detection probability can greatly minimize this source of bias, resulting in more robust inferences about the population, and leading to more informed conservation actions.…”

Section: Introductionmentioning

confidence: 99%

Evaluating differences in density estimation for central Iowa butterflies using two methodologies

Patterson,

Harris,

Dinsmore

et al. 2023

PeerJ

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The Pollard-Yates transect is a widely used method for sampling butterflies. Data from these traditional transects are analyzed to produce density estimates, which are then used to make inferences about population status or trends. A key assumption of the Pollard-Yates transect is that detection probability is 1.0, or constant but unknown, out to a fixed distance (generally 2.5 m on either side of a transect line). However, species-specific estimates of detection probability would allow for sampling at farther distances, resulting in more detections of individuals. Our objectives were to (1) evaluate butterfly density estimates derived from Pollard-Yates line transects and distance sampling, (2) estimate how detection probabilities for butterflies vary across sampling distances and butterfly wing lengths, and (3) offer advice on future butterfly sampling techniques to estimate population density. We conducted Pollard-Yates transects and distance-sampling transects in central Iowa in 2014. For comparison to densities derived from Pollard-Yates transects, we used Program DISTANCE to model detection probability (p) and estimate density (D) for eight butterfly species representing a range of morphological characteristics. We found that detection probability among species varied beyond 2.5 m, with variation apparent even within 5 m of the line. Such variation correlated with wing size, where species with larger wing size generally had higher detection probabilities. Distance sampling estimated higher densities at the 5-m truncation for five of the eight species tested. At this truncation, detection probability was <0.8 for all species, and ranged from 0.53 to 0.79. With the exception of the little yellow (Pyrisitia lisa), species with median wing length <5.0 mm had the lowest detection probabilities. We recommend that researchers integrate distance sampling into butterfly sampling and monitoring, particularly for studies utilizing survey transects >5 m wide and when smaller species are targeted.

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Assessing Population Trends of Species with Imperfect Detection: Double Count Analyses and Simulations Confirm Reliable Estimates in Brown Frogs

Cited by 5 publications

References 29 publications

Decline and Extinction of the Italian Agile Frog Rana latastei from Core Areas of Its Range

Decline and Extinction of the Italian Agile Frog Rana latastei from Core Areas of Its Range

Decline and Extinction of the Italian Agile Frog Rana latastei from Core Areas of Its Range

Evaluating differences in density estimation for central Iowa butterflies using two methodologies

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