Diet and trophic niche overlap of two Hylid species in a subtropical wetland of NE Argentina

Hyla nana and Hyla sanborni, recently recognized as two distinct species, are similar in morphology, and frequently coexist in the same reproductive sites. To determine whether food partitioning occurred during the reproductive phase, both numerical and volumetric analyses of the stomach contents were conducted on syntopic populations inhabiting a wetland system (Ibera Lake) located in the Corrientes Province, NE Argentina. This area is part of a large wetland system (Ramsar site no. 1162). The study was carried out during the wet season (December to February). The climate is subtropical with a high relative humidity. Specimens came from 9 sampling sites, and food items were identified and photographed to measure prey volume approximating their shape to that of a cylinder or a prolate spheroid. The specific trophic strategies were assessed using the Costello-Amundsen graphic techniques; prey niche breadth and niche overlap were also calculated. Factorial Analysis of the Correspondence (FAC) was applied to volumetric data in order to evaluate how the two species exploited the food resources. The average stomach content and food item volume were correlated to the size (SVL) of both species.A total of 123 stomachs were analysed: 47 of H. nana and 76 of H. sanborni. In terms of prey volume, H. nana showed a preference towards larger food items than H. sanborni. There was no difference between the two species in the mean stomach content volume of individuals, however the stomach contents of H. nana were slightly larger. The diets of Hyla nana and H. sanborni were similar in composition. All the analyses showed a marked preference towards Diptera in both species, particularly in H. sanborni. H. nana exhibited higher prey diversity than H. sanborni but, fewer prey items per stomach. The food spectrum composition, evidenced by the FCA, indicated a preference towards preys of large average size (Aranea and Hexapoda assemblage) for H. nana, whereas the distribution of H. sanborni was clearly linked with the Diptera. As predicted by the the Schoener selection strategy model for a two syntopic predator species system, Hyla nana, the larger species, selected prey bigger in size, while H. sanborni ate a larger number of prey specimens. Despite a high degree of trophic niche overlap, Hyla nana and H. sanborni did not segregate spatially, hence the coexistence mechanism, at least during the reproductive period, should not be related to competition processes

Indagine preliminare sulla popolazione di Potamon fluviatile Herbst, 1785, presente ai Mercati Traianei nel Centro Storico di Roma

Il granchio d’acqua dolce, Potamon fluviatile, è una specie subendemica italiana che colonizza diversi ambienti acquatici, purché non eccessivamente disturbati. Di recente la sua presenza è stata riscontrata all’interno dell’area archeologica dei Mercati Traianei, nel centro storico di Roma. Il principale scopo di questo studio è di incrementare le conoscenze sulla biologia di questa specie in ambiente urbano ed osservare eventuali modificazioni sul suo ciclo vitale. La ricerca è stata condotta da giugno a ottobre del 2004. È stato determinato il sesso di tutti gli animali catturati e successivamente sono state rilevate le dimensioni del carapace (mediante analisi di immagine con il programma Image Tool). Queste sono state utilizzate per costruire diagrammi lunghezza-frequenza analizzati con il metodo di Battacharya, che permette di scomporre l’intero campione in classi di d’età; usando i valori medi dimensionali di ogni classe, è possibile descrivere l’accrescimento secondo von Bertallanfy. Prima del rilascio, ogni esemplare è stato marcato sulle coxe utilizzando un ago scaldato, per stimare l’accrescimento reale. Sono stati catturati 80 maschi e 56 femmine, divisi rispettivamente in 3 e 4 classi di età. I due sessi hanno mostrato un tasso di accrescimento simile, sebbene raggiungano Linf diverse (58.56 per i maschi e 47.97 per le femmine) in tempi molto lunghi. L’accrescimento piuttosto lento è testimoniato anche dalle ricatture degli esemplari che hanno compiuto l’ecdisi. Questi risultati sembrano indicare un probabile gigantismo di questa popolazione (possibile conseguenza dell’isolamento e condizione facilitata dalla presenza di rifugi che evitano l’eccessiva predazione di specie animali sinantropiche). Si rendono necessari ulteriori studi per poter approfondire le conoscenze ecologiche essenziali per idonee attività gestionali

Food selection strategy during the reproductive period in three syntopic hylid species from a subtropical wetland of north-east Argentina

Dendropsophus nanus, D. sanborni and Lysapsus limellum are three hylid species, similar in body size and frequently coexisting at the same reproductive sites. To determine whether food partitioning occurred during the reproductive phase, both numerical and volumetric analyses of stomach contents were performed on syntopic populations inhabiting a wetland system in Corrientes Province, north-east Argentina. The analyses showed a marked specialization towards Diptera prey in Dendropsophus species, particularly in D. sanborni, and a more generalist habit in L. limellum. The three study species exhibited different foraging modes, with L. limellum belonging to the sit-and-wait predator type, D. sanborni to the forager predator type, and D. nanus exhibiting a mixed foraging mode. The comparison of the feeding strategies adopted by the various species in different habitat types and condition of syntopy showed a noteworthy plasticity. According to Schoener’s food size selection strategy model for a syntopic predator species system, the larger species (L. limellum) selected prey bigger in size and the smaller (D. sanborni) ate a larger number of prey specimens, whereas D. nanus showed an intermediate trophic strategy. Although the degree of trophic niche overlap was higher than expected, the study species did not show a clear segregation in terms of use of space, hence the coexistence mechanism during the reproductive period should not be related to competition processes for food resources

Thermoregulation comparisons between a threatened native and an invasive lizard species

Lizard thermoregulation is costly and is largely behavioural. Podarcis raffonei, endemic of few islets of the Aeolian archipelago (southern Italy), is one of the most threatened lizards in Europe, its survival being under threat also due to the presence of the congeneric P. siculus, a successful invader characterised by behavioural plasticity and effectiveness and precision at regulating body temperature (Tb). We tested whether thermoregulation behaviour diverges between the two species by analysing (i) the heating rates under a standard thermal condition, and (ii) the temperature at which lizards ended basking (T-final) along a thermal gradient. Overall, we found behavioural differences between the two lizards (i.e. P. siculus exhibited lower T-final), although both species had comparable heating rates and thermoregulated in the same thermal conditions. The invasive P. siculus had lower T-final and, since heating rates were similar between species, it expended less time basking than native P. raffonei. We speculate that the observed thermal ecology differences could provide a selective advantage to P. siculus in the harsh island environment

Effects of pesticides on eggs and hatchlings of the Italian wall lizard (Podarcis siculus) exposed via maternal route

In oviparous species, pesticides may affect embryo survival via maternal transfer or contaminant absorption from the soil, thus representing an important cause of population decline. Maternal transfer is a source of contamination during vitellogenesis and oviductal egg retention. Currently, there is still limited evidence of the potential risk of embryonic exposure routes in reptiles. We investigated whether different agricultural treatments affect embryo, egg, and hatchling development and survival in the Italian wall lizard. We kept gravid females from conventional and control fields in captivity until oviposition and, after eggs being incubated in a pesticide-free environment, offspring morphology and performance (running speed) were assessed. Our results showed that the size of the mother positively influences the number of the eggs and offspring, as well as hatching body condition. Bigger females from conventional treatments tended to lay more eggs. Moreover, at equal female body conditions, eggs and hatchlings from conventional treatments had worse quality (i.e., smaller size and lower body condition) than those from control areas. No effect of treatment was observed on hatchling locomotor performance. In conclusion, our study provided new insights of the direct and indirect effects of field management (i.e., pesticide exposure) on females' reproductive success through the alteration of female's behaviour, which in turn may affect offspring development and health