The effective size of the German wolf population from molecular and life history data

The effective population size is a critical parameter in evolutionary biology and conservation of populations, yet it can be notoriously difficult to estimate. Many methods are available to estimate Ne with molecular methods, but these methods can be very sensitive to underlying assumptions. In order to detect biases in commonly used molecular methods, we present two types of independent datasets with which the effective population size of the German wolf population can be estimated. The first is a life history dataset that provides per individual the life span, the life-time reproductive effort and life-time reproductive success. The second dataset represents wolf genotypes in Germany across three time periodes, representing three age cohorts.

Methods
The DBBW (Dokumentations- und Beratungsstelle des Bundes zum Thema Wolf) hosts a compilation of wolf data collected in the German federal states and makes it accessible to the general public (https://www.dbb-wolf.de/).The data used here cover the occupation of wolf territories in Germany from 2000 to 2020. Each monitoring year (from the 1st of May until the 30th of April the next year) wolf territories were evaluated and the following data were recorded: the name and location of the territory, whether a territory was occupied by a solitary animal, a pair or a pack, the genetic identification code of each animal, and the number of pups born each year in every territory. Most of these data are based on genetic analyses, accompanied by camera trap data.

Individual wolves are continuously monitored and genotyped on the basis of various DNA sources, such as scat, hairs, or kill swabs at 13 autosomal microsatellite loci and 2 sex-linked markers according to Jarausch et al. (2021). Genotype data are used to establish sibship relations and identify packs. We combined these data with the DBBW data to track life-time reproductive success of individual female and male wolves between 2006 and 2020. A reproduction event was deemed successful if the offspring survived to adulthood and established its own territory. This excluded offspring emigrating to other countries. We assumed that wolves established a territory at the age of 2, and tracked for how many years they held a particular territory. The longevity per individual was calculated as the number of territorial years plus 2.