Monitoring and Assessment of the Distribution of the Dice Snake in Ticino, Southern Switzerland

Based on a two-year monitoring, we analysed the distribution of dice snake populations in the Canton of Ticino (Switzerland). Imperfect detection was taken into account in order to avoid underestimation of the distrubtion range and hence overestimating the species threat status: we therefore used a model based on a mark-recapturelike approach to estimate detection probability, which was 61.2% (± 6.8%; standard error), and site occupancy, which was 78.0% (± 7.9%). Detection probability depended on habitat characteristics (tree cover and naturalness of the streams and lake shores) while occupancy was best predicted by the number of previous dice snake records at a site. We observed local decline or extinction of some small populations located on secondary streams, apparently because of habitat deterioration. However, populations located on lakes (Lugano, Maggiore) and main rivers (Ticino, Brenno, Maggia, Vedeggio and Tresa) showed no signs of decline and rather high densities. Therefore, the status of Natrix tessellata in Ticino should be considered as stable. The endangered status reported by the Swiss Red List for these species is adequate because of the small area occupied at national level (IUCN criteria B2a, B2b (iii, iv)) and vulnerability of freshwater ecosystems. A specific action plan in favour of the conservation of dice snakes populations in Ticino, Switzerland, will now be based on the collected data

Monitoraggio della Biscia tassellata, Natrix tessellata (Laurenti, 1768) nel Cantone Ticino (Svizzera)

ITALIAN: Sulla base dei dati raccolti durante due anni di monitoraggio abbiamo valutato la distribuzione attuale delle popolazioni ticinesi di Biscia tassellata (Natrix tessellata). La valutazione è stata effettuata tenendo conto del fatto che il mancato rilevamento della specie sul campo non indica necessariamente una sua assenza: infatti, grazie ad un modello basato su un approccio di tipo mark-recapture, abbiamo calcolato la probabilità di rilevamento, che risulta pari al 61.2% (± 6.8%), e la proporzione di siti occupati, pari al 78.0% (± 7.9%) dei siti conosciuti. Localmente, alcune piccole popolazioni situate lungo corsi d’acqua secondari appaiono soggette a dinamiche di regressione o estinzione, probabilmente in seguito al deterioramento della qualità degli habitat. Al contrario, le popolazioni che si trovano sulle rive dei laghi (Verbano e Ceresio) e sui corsi d’acqua principali (Ticino, Brenno, Maggia, Vedeggio e Tresa) sono ben distribuite sul territorio e caratterizzate da effettivi localmente abbondanti. La situazione è dunque da considerare sostanzialmente stabile. Lo statuto di specie minacciata secondo la Lista Rossa è tuttavia pienamente giustificato per N. tessellata, soprattutto considerate l’esiguità dell’area occupata a livello svizzero e la fragilità degli ambienti acquatici ai quali essa è strettamente legata. I dati raccolti in questo studio saranno utilizzati per l’allestimento di un piano d’azione specifico per la conservazione delle popolazioni di N. tessellata in Ticino. ENGLISH: Based on two years of field work, we surveyed the distribution of Dice Snakes (Natrix tessellata) populations in the Canton of Ticino (Switzerland). Imperfect detection has been taken into account in order to avoid underestimation of the species range: we therefore used a model based on a mark-recapture-like approach to estimate detection probability, which is 61.2% (± 6.8%), and site occupancy, which is 78.0% (± 7.9%). We observed local declines or extinctions of some small opulations inhabiting secondary streams, apparently because of the habitat deterioration. However, populations located along lakes (Ceresio, Verbano) and main rivers (Ticino, Brenno, Maggia, Vedeggio and Tresa) are widely distributed and show rather high densities. Therefore, the status of N. tessellata in Ticino should be considered as stable. The endangered status reported by the Swiss Red List for these species is adequate because of the small area occupied at national level and vulnerability of freshwater ecosystems. A specific action plan in favour of the conservation of Dice Snakes populations in Ticino, Switzerland, will now be based on the collected data

In Situ Formation of Zwitterionic Ligands: Changing the Passivation Paradigms of CsPbBr3 Nanocrystals

CsPbBr3 nanocrystals (NCs) passivated by conventional lipophilic capping ligands suffer from colloidal and optical instability under ambient conditions, commonly due to the surface rearrangements induced by the polar solvents used for the NC purification steps. To avoid onerous postsynthetic approaches, ascertained as the only viable stability-improvement strategy, the surface passivation paradigms of as-prepared CsPbBr3 NCs should be revisited. In this work, the addition of an extra halide source (8-bromooctanoic acid) to the typical CsPbBr3 synthesis precursors and surfactants leads to the in situ formation of a zwitterionic ligand already before cesium injection. As a result, CsPbBr3 NCs become insoluble in nonpolar hexane, with which they can be washed and purified, and form stable colloidal solutions in a relatively polar medium (dichloromethane), even when longly exposed to ambient conditions. The improved NC stability stems from the effective bidentate adsorption of the zwitterionic ligand on the perovskite surfaces, as supported by theoretical investigations. Furthermore, the bidentate functionalization of the zwitterionic ligand enables the obtainment of blue-emitting perovskite NCs with high PLQYs by UV-irradiation in dichloromethane, functioning as the photoinduced chlorine source