Long-term changes in the diversity of amphibian communities inhabiting small water bodies in the urban area of Olsztyn (NE Poland)

Long-term research has become increasingly important in predicting ecological changes, although only a few studies have reported changes in amphibian communities over long time scales in urban areas. The main aim of the research was to determine the changes in the number and species composition of amphibian communities in small water bodies of two Olsztyn (NE Poland) settlements in the period between 1997 and 2015. The examined settlements are characterized by a high concentration of small water bodies and different degrees of urbanization. A decrease in the diversity index of reproducing amphibian communities was found between the years 1997 and 2015 at both settlements. Over the period of 18 years, one species - the northern crested newt - disappeared from both settlements, and another - the fire-bellied toad - disappeared from one of the two settlements. We demonstrate a significant relationship between the probability of occupancy of a water reservoir by fire-bellied toad, common frog, edible frog, and pool frog and the degree of isolation of these water reservoirs. Moreover, a decrease in the average number of species in a single water body and in the average values of diversity was also observed. The diversity of amphibian communities in water reservoirs depended mainly on the distance to the nearest water reservoir, the nearest building and the area of vegetation in the water reservoir. Available data suggests that the newly created water reservoirs play a positive role in the protection of amphibians in urban spaces, but the restoration of local amphibian communities is related to the degree of urbanization, and mostly applies to generalist species.