The recovery of terrestrial carnivores in Europe is a conservation success story. Initiatives focused on restoring top predators, require information on how resident species may interact with the re-introduced species as their interactions have the potential to alter food webs, yet such data are scarce for Europe.

In this study, we assessed patterns of occupancy and interactions between three carnivore species in the Romanian Carpathians. Romania houses one of the few intact carnivore guilds in Europe, making it an ideal system to assess intraguild interactions, and serve as a guide for reintroductions elsewhere.

We used camera trap data from two seasons in Transylvanian forests to assess occupancy and co-occurrence of carnivores using multispecies occupancy models.

Mean occupancy in the study area was highest for lynx ( Y_winter= 0.76 95% CI: 0.42-0.92; Yautumn= 0.71 CI: 0.38-0.84) and wolf (Y_winter= 0.60 CI: 0.34-0.78;  Y_autumn= 0.81 CI: 0.25-0.95) and lowest for wildcat (Y_winter= 0.40 CI: 0.19-0.63; Y_autumn= 0.52 CI: 0.17-0.78)

We found that marginal occupancy predictors for carnivores varied between seasons. We also found differences in predictors of co-occurrence between seasons for both lynx-wolf and wildcat-wolf co-occurrence. For both seasons, we found that conditional occupancy probabilities of all three species were higher when another species was present.

Our results indicate that while there are seasonal differences in predictors of occupancy and co-occurrence of the three species, co-occurrence in our study area is high, and is dependent on the existence of continuous, relatively undisturbed forests.

Terrestrial carnivore recovery efforts are ongoing worldwide. Insights into interspecific relations between carnivore species are critical when considering the depauperate communities they are introduced in. Our work showcases that apex carnivore coexistence is possible, but dependent on protection afforded to forest habitats and their prey base.

Data was collected in the Southern Carpathians, Romania, covering 1,200 km2 in the eastern part of the Făgăraș Mountains, Piatra Craiului, and parts of Leaota Mountains. We divided the study area into a grid of 2.7 km x 2.7 km cells and removed cells with more than ⅔ of their area exceeding 1800 m altitude and cells more than ½ of their area covered by urban landscape features.  From the remaining cells, we sampled every other cell, when it was not possible to reach a selected cell, we used an adjacent cell. Each sampled cell contained a trap station, randomly located within the cell. We conducted two seasons of monitoring: (1) December 17th, 2018, to March 31st, 2019 (winter) and (2) October 9th, 2019, to January 15th, 2020 (autumn).  We installed 64 camera trap stations during winter, and 76 during autumn, with high spatial overlap between seasons. Each trap station had two opposite cameras installed at a height of 40 to 60 cm positioned towards animal paths. We used two camera models per trap station, a CuddeBack C1 Model 1279 with white flash for high quality color pictures in night conditions, and a Bushnell Trophy infrared camera. Camera traps were installed on animal trails along mountain ridges, mid-slopes, upper valleys, and bottom of slopes to detect carnivores at various altitudes/habitats. Camera traps were installed 1-2 weeks prior to the start of monitoring to account for additional anthropogenic disturbance from the camera installation process. We checked camera trap stations every two weeks to replace batteries and SD cards. At each camera trap location, we recorded the presence or absences of anthropogenic disturbance (i.e., logging or settlements) as a binary variable for species detection and occurrence. We also recorded altitude (m) via GPS and extracted distance to stream (m), distance to settlement (m), and distance to roads (m) from the camera trap location using Geographic Information Systems (ArcGIS 10.7, ESRI, Redlands CA). Within a 500-meter buffer around each camera trap location, we calculated the density of local roads (km/km2), the proportion of forested area and a terrain ruggedness index (TRI). We implemented a multispecies occupancy model of two or more interacting species (Rota et al., 2016) in program R 3.5.1 (R Core Team, 2019) via package unmarked (Fiske & Chandler, 2011) to explore how environmental and anthropogenic variables affect the marginal occupancy (occupancy without accounting for interactions with other species), co-occurrence (overlap in marginal occupancy between species), and conditional occupancy (effects of each species presence on other species detection and occupancy) of lynx, wildcat, and wolf in the Romanian Carpathians.

Code for this analysis is available via GitHub 

We also have data for other carnivores and prey species in the area. If you are interested in using this data for an analysis please email the corresponding author.