Optimization of capture–recapture monitoring of elusive species illustrated with a threatened grasshopper |
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Authors: | Linda Bröder Laurent Tatin Axel Hochkirch Andreas Schuld Lucas Pabst Aurélien Besnard |
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Institution: | 1. Department of Biogeography, Trier University, Universitätsring 15, 54296 Trier, Germany;2. Conservatoire d'espaces naturels de Provence-Alpes-Côte d'Azur, 2 Place Léon Michaud, 13310 Saint Martin de Crau, France;3. EPHE, PSL Research University, CNRS, UM, SupAgro, IRD, INRA, UMR 5175 CEFE, Centre d'Ecologie Fonctionnelle et Evolutive, Campus CNRS - 1919 route de Mende, 34293 Montpellier, France |
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Abstract: | Information on population sizes and trends of threatened species is essential for their conservation, but obtaining reliable estimates can be challenging. We devised a method to improve the precision of estimates of population size obtained from capture–recapture studies for species with low capture and recapture probabilities and short seasonal activity, illustrated with population data of an elusive grasshopper (Prionotropis rhodanica). We used data from 5 capture–recapture studies to identify methodological and environmental factors affecting capture and recapture probabilities and estimates of population size. In a simulation, we used the population size and capture and recapture probability estimates obtained from the field studies to identify the minimum number of sampling occasions needed to obtain unbiased and robust estimates of population size. Based on these results we optimized the capture–recapture design, implemented it in 2 additional studies, and compared their precision with those of the nonoptimized studies. Additionally, we simulated scenarios based on thresholds of population size in criteria C and D of the International Union for Conservation of Nature (IUCN) Red List to investigate whether estimates of population size for elusive species can reliably inform red-list assessments. Identifying parameters that affect capture and recapture probabilities (for the grasshopper time since emergence of first adults) and optimizing field protocols based on this information reduced study effort (?6% to ?27% sampling occasions) and provided more precise estimates of population size (reduced coefficient of variation) compared with nonoptimized studies. Estimates of population size from the scenarios based on the IUCN thresholds were mostly unbiased and robust (only the combination of very small populations and little study effort produced unreliable estimates), suggesting capture–recapture can be considered reliable for informing red-list assessments. Although capture–recapture remains difficult and costly for elusive species, our optimization procedure can help determine efficient protocols to increase data quality and minimize monitoring effort. |
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Keywords: | capture probability IUCN Red List monitoring population size Lista Roja UICN monitoreo probabilidad de captura tamaño poblacional 捕获概率 IUCN 红色名录 监测 种群大小 |
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