Aim Understanding which factors determine the variation in population size across space and time is crucial to plan sound conservation interventions. Amphibians are often characterized by large demographic changes, therefore a better understanding of factors driving these changes could help mitigate their global crisis. We investigated drivers of abundance dynamics of two similar frog species to understand why they met different fates in the same study area. Location Northern Italy. Methods In seven different years between 2004 and 2020, we performed repeated counts of egg masses of two similar frog species, the agile frog (Rana dalmatina) and the Italian agile frog (Rana latastei), in 31 wetlands, and used Bayesian models to estimate the relationships between frog abundance and candidate drivers acting at the scale of (i) site: wetland surface, shading percentage and the presence of the invasive red swamp crayfish (Procambarus clarkii); (ii) landscape: forest cover around wetlands; (iii) climate: yearly precipitation and (iv) spatially structured population (SSP): clutch incidence of the focal species and crayfish incidence in the surrounding landscape. Results The two species showed sharp differences in population size and trends: R. dalmatina was abundant and showed a stable trend throughout the entire study period; R. latastei showed low abundance in the first years and then almost disappeared. The abundance of R. dalmatina was positively related to forest cover, shading, wetland area and precipitation, while negatively related to the occurrence of invasive crayfish at both local and SSP level. R. latastei abundance increased with wetland area and precipitation, while models were not able to detect relationships with other factors. Main conclusions The high sensitivity to drought and demographic stochasticity could have contributed to the quasi‐extinction of R. latastei in the study area, highlighting that similar species can meet different fates even under the same environmental conditions.

The evolution of sexual dimorphism (SD) is driven by intricate interplays between sexual and natural selection. When it comes to SD variation within populations, however, environmental factors play a major role. Sexually selected traits are expected to be strongly dependent on individual body condition, which is influenced by the local environment that individuals experience. As a consequence, the degree of SD may also depend on resource availability. Here, we investigated the potential drivers of SD expression at two sexually dimorphic morphometric traits, body size (snout vent length) and head shape (head geometric morphometrics), in the Italian wall lizard (Podarcis siculus). We assessed the existence of condition- and context-dependent SD across ten islands of the Aeolian archipelago (southern Italy), at within- and among-population scales. We observed strong geographical variation of SD among islands, and tested three potential SD predictors related to resource availability (individual body condition, ecosystem productivity, temperature). Body condition and ecosystem productivity were the main drivers of body size SD variation, and body condition was also the main driver for head shape SD. Our results highlight that the expression of SD in the Italian wall lizard is both condition- and context-dependent. These results are congruent at within- and among-populations scales highlighting that spatial multi-scale analysis represents a useful approach to understand patterns of SD expression.

The cover image relates to the Research Article https://doi.org/10.1111/ddi.13483 “Similar species, different fates: Abundance dynamics in spatially structured populations of common and threatened frogs” by Dalpasso et al. An adult agile frog (Rana dalmatina) at the Groane Regional Park, Northern Italy. Image credit: Simone Giachello.