Scale-dependent effects of summer density on autumn mass in reindeer

Abstract: The ongoing dispute about reindeer overabundance in the West Finnmark (Norway) herding region has ac-centuated the need for an in-depth understanding of the density-dependent and-independent processes driving this pastoral system, as well as the spatial and temporal scale(s) they operate on. Using 20 604 records of individual male reindeer yearlings we assessed the spatial and temporal variation in animals ’ performance (measured by their autumn carcass mass), and investigated summer density dependent effects on autumn carcass masses at different scales. We defined three spatial scales; a regional scale represented by the whole summer range of West Finnmark, a sub-regional scale represented by the mainland (14) and the island (11) summer districts, and a fine scale represented by eight individual summer districts. We defined two temporal scales; the whole collection phase (13 years) and a temporal dimension based on the three periods of population growth. We found carcass masses to be higher at island than at mainland and to vary among districts. Effect of period was found at the regional, sub-regional and often at the district scale. The autumn carcass masses were sensitive to density at West Finnmark and mainland scales, but not at island scale, the effect being negative. This suggests intra-specific competition for summer forage due to consistent higher density resulting in reduced range quality at mainland as compared to island. On the finest scale the density effect was highly variable. Response of carcass mass to density appeared to be scale dependent both in space and time at regional and sub-regional scales. These findings underline the importance, for skilful management, of site specific biologica