Explaining declines of newt abundance in northern Italy

Abstract

Amphibians are an exemplary case of the current biodiversity crisis, being among the vertebrates suffering the fastest decline. Population dynamics of amphibians can result from processes acting at different scales. Both the local characteristics of breeding wetlands and the features of the surrounding landscape can strongly affect the temporal dynamics of amphibian populations. European newts are particularly threatened by land‐use change and invasive alien species. While it is known that newts are declining across Europe, few studies have performed broad‐scale assessments of their decline, either because abundance dynamics are more complex to analyse than presence/absence data or because they require a high sampling effort and long‐term monitoring. In this study, we show that long‐term distribution data can be combined with demographic models to quantify the decline in abundance of newt species at the regional scale, and to assess the importance of multiple factors in determining abundance dynamics. We performed multiple surveys between 1996 and 2020 and used N‐mixture models in a Bayesian framework. We then calculated abundance changes between the first and the last sampling season, which were performed with an average timespan of 13 years across all wetlands. Both Italian crested newts and smooth newts showed large declines, with an average estimated abundance loss between the first and last sampling season of 57% and 63%, respectively. Local characteristics of the wetlands were the main determinants of abundance dynamics: the abundance of both species showed a positive relationship with the area and the permanence of the wetland and a negative relationship with the presence of fish. Additionally, the abundance of Italian crested newts was negatively related to the presence of invasive crayfish. No relationship was detected between abundance and terrestrial habitat availability or connectivity measures. Despite uncertainties in the absolute values of estimated abundance, the striking regional‐scale decline of newts is evident. Among the major determinants of population dynamics, fish and crayfish presence increased their prevalence in the study area, while other factors remained more stable. Management actions aimed at eradicating or controlling invasive fish and crayfish might halt abundance loss and even revert this declining trend. The application of N‐mixture models to long‐term data from representative sites permits the analysis of temporal trends of species at the regional scale even when data come from complex monitoring schemes. We found large declines in abundance of two newt species, suggesting that European newts may be more threatened than previously thought.

Potential Threat of an Invasive Fish Species for Two Native Newts Inhabiting Wetlands of Europe Vulnerable to Climate Change

“…Two most widely distributed species of newts vulgaris and T. cristatus) protected in the European Union will decrease in abundance and range, whereas the expansion of the invasive predatory fish Chinese sleeper (P. glenii) will intensify within the next decades. The expansion of this invasive predator, due to considerable overlap of suitable combination of bioclimatic factors, is an additional threat to native species of wetlands [61,62]. Therefore, it is necessary to establish management plans for the protection of native herpetofauna species taking adequately into account the heavy influence of invasive species and bringing their further expansion under strict control.…”

Monitoring spatiotemporal impacts of changes in land surface temperature on near eastern fire salamander (Salamandra infraimmaculata) in the Middle East

“…With the increase in temperature in winter and the decrease in precipitation and increase in evaporation and transpiration [ 86 ], the hydroperiod of pools, wetlands and streams will change. Hydroperiod of wetlands and ponds is one of the most important parameters for estimating population growth for organisms with water-developing larvae [ 87 ]. A long hydroperiod affects the survival of larvae [ 88 ].…”

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

“…However, many amphibians can show complex patterns of seasonal migration outside and inside breeding wetlands. In these cases, a correct timing of the surveys is fundamental, and it is often impossible to obtain accurate measures of abundance with a single survey, requiring multiple intra-annual site visits to study population dynamics [ 25 , 26 , 27 , 28 , 29 ]. In the case of brown frog populations, the correct timing of surveys can be achieved through preliminary monitoring of a selected subset of sites in late winter.…”