Quantifying and explaining the decline in the occupancy of fire salamander populations

Sarah Bänziger, University of Zurich

Biodiversity loss is a major issue of the Anthropocene. A crucial part of biodiversity loss is the loss of populations of a species, which is the first step towards extinction. It is therefore essential to know whether extinction rates in- or decrease or remain constant. This can be seen by investigating the distribution repeatedly over many points of time. Next to the quantification and change of the extinction rates, it is crucial to investigate their causes.

The fire salamander (Salamandra salamandra) is one of the amphibians which have recently suffered from a population decline from unknown causes. I collected new distribution data and investigated whether the population decline continued and the strength and causes of the decline. The distribution of the fire salamander has been investigated in 2003 and 2004 by collecting presence/absence data of larvae at 137 streams within Switzerland. In this study, I revisited 115 streams in Northern Switzerland and collected presence/absence data to determine occupancy, extinction and colonization rates.

The results of my analysis show that the number of occupied sites is still declining. However, some larvae were found in previously vacant locations. This could be due to recolonization. Both terrestrial as well as aquatic variables influenced the occurrence of fire salamanders: In the first decline period – until the year 2003 – terrestrial variables of the wider steam environment such as deadwood and small roads explained the occupancy rate best, while in the second period – from 2003/2004 to 2016 – aquatic variables such as stream characteristics, presence of fish and substrate type were determinants for the extinction probability.

In summary, the inclusion of aquatic as well as terrestrial habitat data is essential for the improvement of conservation management programs and that the decline trend of the fire salamander remains more or less constant.