Large-scale habitat variability, delayed density effects and red deer populations in Norway

1. Parallel to the large-scale changes in land-use patterns over the last century in Europe, many deer species have expanded their range and increased in density, but the role of habitat changes for their population ecology remains poorly documented. 2. We tested for effects of variability in agricultural (proportion of meadow and density of sheep) and forestry practices (proportion of coniferous and deciduous forest) in 106 municipalities in Norway on body weight of 10 206 female and 15 499 male adult red deer collected over the period 1965-2000. 3. Long-term temporal changes in body weights may also be due to delayed density effects, either due to that persistent high density of red deer through grazing and browsing may affect vegetation composition (i.e. an effect of cumulative density after present-day density is controlled for), or that individuals born at high density start to penetrate the population (cohort-effects). As these effects may be confounding to variability in forestry or agricultural practice, we also test whether cohort and/or cumulative density may affect body weight of red deer. 4. There was a strong negative effect of cohort density, but no effect of cumulative density in the previous 10 years once the cohort effect was accounted for. 5. There was a clear positive effect of proportion of meadow on red deer body weight, while there was no effect of sheep density once the effect of proportion of meadow was adjusted for. Proportion of meadow increased during the study, but most of the variation was between municipalities (i.e. in space). 6. Neither proportional area of coniferous or deciduous forest consistently affected body weight of red deer in Norway. 7. Our study emphasizes the multitude of factors over time and space that affects body weight, and hence demography and population dynamics, of large herbivores.