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

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.

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

Most animal species are detected imperfectly and overlooking individuals can result in a biased inference of the abundance patterns and underlying processes. Several techniques can incorporate the imperfect detection process for a more accurate estimation of abundance, but most of them require repeated surveys, i.e., more sampling effort compared to single counts. In this study, we used the dependent double-observer approach to estimate the detection probability of the egg clutches of two brown frog species, Rana dalmatina and R. latastei. We then simulated the data of a declining population at different levels of detection probability in order to assess under which conditions the double counts provided better estimates of population trends compared to naïve egg counts, given the detectability of frog clutches. Both species showed a very high detection probability, with average values of 93% for Rana dalmatina and 97% for R. latastei. Simulations showed that not considering imperfect detection reduces the power of detecting population trends if detection probability is low. However, at high detection probability (>80%), ignoring the imperfect detection does not bias the estimates of population trends. This suggests that, for species laying large and easily identifiable egg clutches, a single count can provide useful estimates if surveys are correctly timed.

Long-term drivers of persistence and colonization dynamics in spatially structured amphibian populations.

Many organisms live in networks of local populations connected by dispersing individuals, called spatially structured populations (SSPs), where the long-term persistence of the entire network is determined by the balance between 2 processes acting at the scale of local populations: extinction and colonization. When multiple threats act on an SSP, a comparison of the different factors determining local extinctions and colonizations is essential to plan sound conservation actions. We assessed the drivers of long-term population dynamics of multiple amphibian species at the regional scale. We used dynamic occupancy models within a Bayesian framework to identify the factors determining persistence and colonization of local populations. Because connectivity among patches is fundamental to SSPs dynamics, we considered 2 measures of connectivity acting on each focal patch: incidence of the focal species and incidence of invasive crayfish. We used meta-analysis to summarize the effect of different drivers at the community level. Persistence and colonization of local populations were jointly determined by factors acting at different scales. Persistence probability was positively related to the area and the permanence of wetlands, whereas it was negatively related to occurrence of fish. Colonization probability was highest in semipermanent wetlands and in sites with a high incidence of the focal species in nearby sites, whereas it showed a negative relationship with the incidence of invasive crayfish in the landscape. By analyzing long-term data on amphibian population dynamics, we found a strong effect of some classic features commonly used in SSP studies, such as patch area and focal species incidence. The presence of an invasive non-native species at the landscape scale emerged as one of the strongest drivers of colonization dynamics, suggesting that studies on SSPs should consider different connectivity measures more frequently, such as the incidence of predators, especially when dealing with biological invasions.

Factores a Largo Plazo de la Persistencia y las Dinámicas Colonizadoras en una Población Anfibia Estructurada Espacialmente Resumen Muchos organismos viven en redes formadas por poblaciones locales conectadas por individuos dispersos, llamadas poblaciones estructuradas espacialmente (PEE), en donde la persistencia a largo plazo de la red completa está determinada por dos procesos que actúan a escala local en las poblaciones: extinción y colonización. Cuando múltiples amenazas actúan sobre una PEE, es esencial una comparación entre los diferentes factores que determinan las extinciones y colonizaciones locales para planear acciones de conservación prudentes. Analizamos los factores a largo plazo de las dinámicas poblaciones de varias especies anfibias a escala regional. Usamos modelos de ocupación dinámica dentro de un marco de trabajo bayesiano para identificar los factores que determinan la persistencia y colonización de las poblaciones locales. Ya que la conectividad entre los fragmentos es fundamental para las dinámicas de las PEE, consideramos dos medidas de conectividad que actúan sobre cada fragmento focal: la incidencia de las especies focales y la incidencia de cangrejos de río invasores. Usamos un meta análisis para resumir el efecto de los diferentes factores a nivel de comunidad. La persistencia y la colonización de las poblaciones locales estuvieron determinadas en conjunto por los factores que actúan a diferentes escalas. La probabilidad de persistencia estuvo relacionada positivamente con el área y la permanencia de los humedales; mientras que estuvo relacionada negativamente con la presencia de peces. La probabilidad de colonización fue más alta en los humedales semipermanentes y en sitios con una alta incidencia de especies focales en sitios cercanos; mientras que mostró una relación negativa con la incidencia de los cangrejos de río invasores en el paisaje. Cuando analizamos los datos a largo plazo de las dinámicas de las poblaciones anfibias, encontramos un efecto firme de algunos rasgos clásicos de uso común en los estudios de las PEE, como el área del fragmento y la incidencia de la especie focal. La presencia de una especie invasora no nativa a escala de paisaje surgió como uno de los factores más fuertes para las dinámicas de colonización, lo que sugiere que los estudios sobre las PEE deberían considerar diferentes medidas de conectividad con mayor frecuencia, como lo es la incidencia de depredadores, especialmente cuando se está trabajando con invasiones biológicas.

N-mixture models reliably estimate the abundance of small vertebrates.

Accurate measures of species abundance are essential to identify conservation strategies. N-mixture models are increasingly used to estimate abundance on the basis of species counts. In this study we tested whether abundance estimates obtained using N-mixture models provide consistent results with more traditional approaches requiring capture (capture-mark recapture and removal sampling). We focused on endemic, threatened species of amphibians and reptiles in Italy, for which accurate abundance data are needed for conservation assessments: the Lanza's Alpine salamander Salamandra lanzai, the Ambrosi's cave salamander Hydromantes ambrosii and the Aeolian wall lizard Podarcis raffonei. In visual counts, detection probability was variable among species, ranging between 0.14 (Alpine salamanders) and 0.60 (cave salamanders). For all the species, abundance estimates obtained using N-mixture models showed limited differences with the ones obtained through capture-mark-recapture or removal sampling. The match was particularly accurate for cave salamanders in sites with limited abundance and for lizards, nevertheless non-incorporating heterogeneity of detection probability increased bias. N-mixture models provide reliable abundance estimates that are comparable with the ones of more traditional approaches, and offer additional advantages such as a smaller sampling effort and no need of manipulating individuals, which in turn reduces the risk of harming animals and spreading diseases.