Status and population dynamics of the Critically Endangered Valcheta frog Pleurodema somuncurense on the Patagonian Somuncura Plateau

Abstract

Amphibian populations are declining globally. In this scenario, detailed information on their ecology is crucial to determine the status and extinction risk of their populations and, therefore, better plan conservation activities. The Valcheta frog Pleurodema somuncurense is a Critically Endangered species, which is endemic to the Valcheta Stream, Patagonia, Argentina. We assessed the status of this species at the metapopulation level, which we consider is a key step in planning management activities. We conducted visual encounter surveys from 2013 to 2019 to determine the distribution range of each local population of the Valcheta frog. During 2015, we also applied a capture-recapture survey to estimate the density and apparent survival of 1 local population. We used POPAN models for density estimation and the classic model of Cormack-Jolly-Seber to estimate apparent survival, using snout-vent length as a covariate. The metapopulation of the Valcheta frog is composed of 9 isolated local populations: 7 extant and 2 extinct. The extant populations have population sizes ranging from 243 to 4516 individuals. The small size of the smaller local populations makes their long-term viability in isolation unlikely. We found a positive correlation between the apparent survival and the snout-vent length of individuals. Our results showed that management strategies should be aimed at ensuring the long-term survival of this species, with a focus on the recovery of extinct populations, the restoration of disturbed habitats and the improvement of connectivity between local populations.

The Critically Endangered El Rincon stream frog: Population viability and management actions in Patagonia, Argentina

“…Conversely, long‐term viability was defined in the models as the probability of extinction of less than 0.01 (PE ≤ 0.01). The initial population size was based on density estimations for this species (Velasco et al, 2019b). Other relevant variables to build the models were: (i) 2 years as the age at first reproduction, based on information from an ex‐situ breeding colony (Kacoliris, personal observation); (ii) 5 years as the maximum reproductive age; (iii) 6 years as the lifespan, based on information from the ex‐situ breeding colony and knowledge of the related species Pleurodema thaul (Iturra‐Cid, Ortiz & Ibargüengoytía, 2010); (iv) 80 juveniles as the maximum number of progeny; (v) a maximum number of three clutches per reproductive female per year, both data obtained from the ex‐situ colony; (vi) the sex ratio at birth set to 1:1; (vii) only individuals fully metamorphosed were considered newborns in the models; (viii) the percentage of adult females in the pool was set at 80%, based on field records where a small proportion of clutches failed owing to drought and predation (Velasco, personal observation); (ix) reproductive males in the pool were set at 100%, following Auffarth et al (2017), assuming that all the males in the area have the same probability of reproducing; and (x) mortality and density for adults and juveniles came from estimations obtained through capture–mark–recapture studies conducted with a wild population of this species between January and March 2015 (Velasco et al, 2019b).…”

“…The initial population size was based on density estimations for this species (Velasco et al, 2019b). Other relevant variables to build the models were: (i) 2 years as the age at first reproduction, based on information from an ex‐situ breeding colony (Kacoliris, personal observation); (ii) 5 years as the maximum reproductive age; (iii) 6 years as the lifespan, based on information from the ex‐situ breeding colony and knowledge of the related species Pleurodema thaul (Iturra‐Cid, Ortiz & Ibargüengoytía, 2010); (iv) 80 juveniles as the maximum number of progeny; (v) a maximum number of three clutches per reproductive female per year, both data obtained from the ex‐situ colony; (vi) the sex ratio at birth set to 1:1; (vii) only individuals fully metamorphosed were considered newborns in the models; (viii) the percentage of adult females in the pool was set at 80%, based on field records where a small proportion of clutches failed owing to drought and predation (Velasco, personal observation); (ix) reproductive males in the pool were set at 100%, following Auffarth et al (2017), assuming that all the males in the area have the same probability of reproducing; and (x) mortality and density for adults and juveniles came from estimations obtained through capture–mark–recapture studies conducted with a wild population of this species between January and March 2015 (Velasco et al, 2019b).…”

“…In the case of reproductive variables, the uncertainty was based on the potential differences between the variables related to the differences between ex-situ and in-situ conditions. In the case of survival, the uncertainty was based on potential differences between the real parameter and the estimated parameter obtained in Velasco et al (2019b). In both cases, sensitivity tests were run to assess the effect of these variables on the probability of extinction.…”

“…The critical conservation status of the El Rincon stream frog requires urgent actions. During the last 10 years, several studies on this frog provided information about its natural history and population ecology (Velasco et al, 2016; Velasco et al, 2017; Velasco et al, 2018; Velasco et al, 2019a; Velasco et al, 2019b). The El Rincon stream frog is restricted at present to eight isolated local populations, including a recently reintroduced one (Martínez Aguirre et al, 2019).…”

“…The El Rincon stream frog is restricted at present to eight isolated local populations, including a recently reintroduced one (Martínez Aguirre et al, 2019). The global population size of this frog is limited to a few thousand individuals (Velasco et al, 2019b). However, information on extinction risk and population dynamics is needed to help lead management actions (Vaira, Akmentins & Lavilla, 2018).…”