Populations of the brown frogs Rana arvalis, R. dalmatina and R. temporaria in 46 ponds in south Zealand during the years 1992-2020

For 29 consecutive years, the populations of three species of brown frogs, Rana arvalis, R. dalmatina and R. temporaria, were monitored in an open area (military training field) in South Zealand, Denmark. Population sizes were recorded by counting egg clumps. Not all egg clumps could be determined to species with full certainty. Some are designated “Likely R. temporaria”, and some are designated “Undetermined”. To obtain the most likely total number of R. temporaria egg clumps, figures for “Certain R. temporaria” and “Likely R. temporaria”  should be added. The tables show the number of egg clumps for each species in each of the waterbodies. Some waterbodies exist every year; others came into existence during the study period, and still others are temporary floodings existing only in a few years. In years when a given waterbody did not exist, the cell in the table is left blank. 
The waterbodies are numbered from 1 to 46 and their positions are shown on the map.

The data allow analyses of changes in population size from year to year and shifts in the location of breeding populations. Analyses have been made of the time course of colonisation after a water body came into existence. 15 initially unoccupied suitable ponds were available for colonisation by R. dalmatina after 1992. Permanent colonisation usually happened in the very first year that the waterbody existed. A total of 19 initially unoccupied suitable waterbodies could potentially be colonised by the two other species. Rana arvalis permanently colonised 17 ponds after an average of 10.5 years. Rana temporaria permanently colonised eight ponds after an average of 13.4 years.  

Methods
The Excel sheets present data on the number of egg clumps of three species of brown frogs, in 46 water bodies, during the period 1992 to 2020 in a 1.8 km² area in Denmark 
The map shows the position of the 46 water bodies in the area Kulsbjerge in south Zealand.